Bump version to 5.1.1 for release

Looks like Spigot builds 1.21.1 for 1.20. Mildly annoying.

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+  - package-ecosystem: "maven"
+    directory: "/"
+    schedule:
+      interval: "monthly"

.github/workflows/automerge_dependabot.yml

@@ -0,0 +1,55 @@
+name: Auto-merge Dependabot PRs
+
+on:
+  workflow_run:
+    workflows: [ "Pull Request" ]
+    types: [ completed ]
+
+jobs:
+  merge-dependabot:
+    if: "github.actor == 'dependabot[bot]'
+      && github.event.workflow_run.event == 'pull_request'
+      && github.event.workflow_run.conclusion == 'success'"
+    runs-on: ubuntu-latest
+    steps:
+      # Note: this is directly from GitHub's example for using data from a triggering workflow:
+      # https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#using-data-from-the-triggering-workflow
+      - name: 'Download artifact'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            let allArtifacts = await github.rest.actions.listWorkflowRunArtifacts({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               run_id: context.payload.workflow_run.id,
+            });
+            let matchArtifact = allArtifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "pr_number"
+            })[0];
+            let download = await github.rest.actions.downloadArtifact({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               artifact_id: matchArtifact.id,
+               archive_format: 'zip',
+            });
+            let fs = require('fs');
+            fs.writeFileSync(`${process.env.GITHUB_WORKSPACE}/pr_number.zip`, Buffer.from(download.data));
+
+      # This might be a useless use of cat, but I'm not sure what shell Actions is going to be running.
+      - name: Add Pull Number Variable
+        run: |-
+          unzip pr_number.zip
+          echo "PR_NUMBER=$(cat pr_number)" >> "$GITHUB_ENV"
+
+      - name: Approve
+        uses: hmarr/auto-approve-action@v4.0.0
+        with:
+          github-token: "${{ secrets.GITHUB_TOKEN }}"
+          pull-request-number: "${{ env.PR_NUMBER }}"
+      - name: Merge
+        uses: pascalgn/automerge-action@v0.16.3
+        env:
+          GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
+          MERGE_LABELS: "dependencies,java"
+          MERGE_METHOD: "squash"
+          PULL_REQUEST: "${{ env.PR_NUMBER }}"

.github/workflows/ci.yml

@@ -0,0 +1,45 @@
+name: OpenInv CI
+
+on:
+  push:
+    branches:
+      - 'master'
+    tags-ignore:
+      - '**'
+    paths-ignore:
+      - resource-pack/**
+  # Enable running CI via other Actions, i.e. for drafting releases and handling PRs.
+  workflow_call:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: '21'
+          cache: 'maven'
+
+      # Install Spigot dependencies if necessary.
+      - name: Install Spigot Dependencies
+        run: . scripts/install_spigot_dependencies.sh
+
+      - name: Build With Maven
+        run: mvn -e clean package -am -P all
+
+      # Upload artifacts
+      - name: Upload Distributable Jar
+        id: upload-final
+        uses: actions/upload-artifact@v4
+        with:
+          name: dist
+          path: ./target/*.jar
+      - name: Upload API Jar
+        id: upload-api
+        uses: actions/upload-artifact@v4
+        with:
+          name: api
+          path: ./api/target/openinvapi*.jar

.github/workflows/draft_release.yml

@@ -0,0 +1,45 @@
+name: Draft Github Release
+
+on:
+  push:
+    tags:
+      - '**'
+
+jobs:
+  run-ci:
+    uses: Jikoo/OpenInv/.github/workflows/ci.yml@master
+  draft-release:
+    needs: [ run-ci ]
+    runs-on: ubuntu-latest
+    steps:
+      # Fetch all history - used to assemble changelog.
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set Release Variables
+        run: bash ./scripts/set_release_env.sh
+
+      - name: Download build
+        uses: actions/download-artifact@v4
+        with:
+          name: dist
+          path: dist
+
+      - name: Package resource pack
+        run: |-
+          pushd resource-pack
+          zip -r ../dist/openinv-legibility-pack.zip .
+          popd
+
+      - name: Create Release
+        id: create-release
+        uses: softprops/action-gh-release@v2.0.8
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          name: ${{ env.VERSIONED_NAME }}
+          body: ${{ env.GENERATED_CHANGELOG }}
+          draft: true
+          prerelease: false
+          files: ./dist/**

.github/workflows/external_release.yml

@@ -0,0 +1,37 @@
+name: Release to CurseForge
+
+on:
+  release:
+    types: [ released ]
+
+jobs:
+  curseforge_release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Fetch Github Release Asset
+        uses: dsaltares/fetch-gh-release-asset@1.1.2
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          version: ${{ github.event.release.id }}
+          file: OpenInv.jar
+
+      - name: Set CurseForge Variables
+        run: . scripts/set_curseforge_env.sh "${{ github.event.release.body }}"
+
+      - name: Create CurseForge Release
+        uses: itsmeow/curseforge-upload@v3
+        with:
+          token: "${{ secrets.CURSEFORGE_TOKEN }}"
+          project_id: 31432
+          game_endpoint: minecraft
+          file_path: ./OpenInv.jar
+          display_name: "${{ github.event.release.name }}"
+          game_versions: "${{ env.CURSEFORGE_MINECRAFT_VERSIONS }}"
+          release_type: release
+          changelog_type: markdown
+          changelog: "${{ env.CURSEFORGE_CHANGELOG }}"

.github/workflows/pull_request.yml

@@ -0,0 +1,22 @@
+name: Pull Request
+
+on:
+  pull_request:
+
+jobs:
+  run-ci:
+    uses: Jikoo/OpenInv/.github/workflows/ci.yml@master
+  store-dependabot-pr-data:
+    if: "github.actor == 'dependabot[bot]' && github.event_name == 'pull_request'"
+    runs-on: ubuntu-latest
+    steps:
+      # Note: this is directly from GitHub's example for using data from a triggering workflow:
+      # https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#using-data-from-the-triggering-workflow
+      - name: Store Pull Number
+        run: |
+          mkdir -p ./pr
+          echo ${{ github.event.number }} > ./pr/pr_number
+      - uses: actions/upload-artifact@v4
+        with:
+          name: pr_number
+          path: pr/

.github/workflows/resource_pack_ci.yml

@@ -0,0 +1,24 @@
+name: Resource Pack CI
+
+on:
+  push:
+    branches:
+      - 'master'
+    tags-ignore:
+      - '**'
+    paths:
+      - resource-pack/**
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build resource pack
+        id: upload-resource-pack
+        uses: actions/upload-artifact@v4
+        with:
+          name: openinv-legibility-pack
+          path: ./resource-pack/
+          compression-level: 9

.gitignore

@@ -0,0 +1,10 @@
+**/.settings
+**/.project
+**/.classpath
+**/.idea/
+**.iml
+**/target/
+**/bin/
+**/out/
+**/dependency-reduced-pom.xml
+**/pom.xml.versionsBackup

.settings/org.eclipse.ltk.core.refactoring.prefs

@@ -1,3 +0,0 @@
-#Wed Jun 01 17:38:54 EDT 2011
-eclipse.preferences.version=1
-org.eclipse.ltk.core.refactoring.enable.project.refactoring.history=false

README

@@ -1,13 +0,0 @@
-Copyright (C) 2011-2014 lishid.  All rights reserved.
-
-This program is free software: you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation,  version 3.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program. If not, see <http://www.gnu.org/licenses/>.

README.MD

@@ -0,0 +1,57 @@
+## About
+OpenInv is a [Bukkit plugin](https://dev.bukkit.org/projects/openinv) which allows users to open and edit anyone's inventory or ender chest - online or not!
+
+## Features
+- **OpenInv**: Open anyone's inventory, even if they're offline.
+  - Read-only mode! Don't grant edit permission.
+  - Cross-world support! Allow access only from the same world.
+  - No duplicate slots! Only armor is accessible when opening self (if allowed at all)!
+  - Drop items as the player! Place items in the dropper slot in the bottom right. Can be disabled via permission!
+  - Allow any item in armor slots! Configurable via permission.
+- **OpenEnder**: Open anyone's ender chest, even if they're offline.
+  - Allow access only to own ender chest! Don't grant permission to open others.
+  - Read-only mode! Don't grant edit permission.
+  - Cross-world support! Allow access only from the same world.
+- **SilentContainer**: Open containers without displaying an animation or making sound.
+- **AnyContainer**: Open containers, even if blocked by ocelots or blocks.
+
+## Commands
+See [the wiki](https://github.com/Jikoo/OpenInv/wiki/Commands).
+
+## Permissions
+See [the wiki](https://github.com/Jikoo/OpenInv/wiki/Permissions)
+
+## For Developers
+
+### As a Dependency
+The OpenInv API is available via [JitPack](https://jitpack.io/).
+```xml
+  <repositories>
+    <repository>
+      <id>jitpack.io</id>
+      <url>https://jitpack.io</url>
+    </repository>
+  </repositories>
+```
+```xml
+  <dependencies>
+    <dependency>
+      <groupId>com.github.jikoo.OpenInv</groupId>
+      <artifactId>openinvapi</artifactId>
+      <version>${openinv.version}</version>
+    </dependency>
+  </dependencies>
+```
+
+### Compilation
+To compile, the relevant Spigot jars must be installed in the local repository.
+As OpenInv is compiled against Mojang's mappings, you must run BuildTools with the `--remapped` argument:  
+`java -jar BuildTools.jar --remapped --rev $serverVersion`  
+`$serverVersion` is the version of the server, i.e. `1.18.1`
+
+To compile just the API, execute Maven as usual:  
+`mvn clean package`  
+
+To compile the full plugin, use the provided profile with `-P all`:  
+`mvn clean package -am -P all`  
+For more information, check out the [official Maven guide](http://maven.apache.org/guides/introduction/introduction-to-profiles.html).

addon/togglepersist/pom.xml

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <artifactId>openinvparent</artifactId>
+        <groupId>com.lishid</groupId>
+        <relativePath>../../pom.xml</relativePath>
+        <version>5.1.1</version>
+    </parent>
+
+    <artifactId>openinvtogglepersist</artifactId>
+
+    <dependencies>
+        <dependency>
+            <artifactId>annotations</artifactId>
+            <groupId>org.jetbrains</groupId>
+        </dependency>
+        <dependency>
+            <groupId>org.spigotmc</groupId>
+            <artifactId>spigot-api</artifactId>
+        </dependency>
+        <dependency>
+            <artifactId>openinvapi</artifactId>
+            <groupId>com.lishid</groupId>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>OITogglePersist</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+
+        <plugins>
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+            </plugin>
+            <plugin>
+                <artifactId>maven-resources-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>copy-final-jar</id>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>copy-resources</goal>
+                        </goals>
+                        <configuration>
+                            <outputDirectory>${project.parent.build.directory}</outputDirectory>
+                            <resources>
+                                <resource>
+                                    <directory>${project.build.directory}</directory>
+                                    <includes>
+                                        <include>${project.build.finalName}.jar</include>
+                                    </includes>
+                                </resource>
+                            </resources>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+
+    </build>
+
+</project>

addon/togglepersist/src/main/java/com/github/jikoo/openinv/togglepersist/TogglePersist.java

@@ -0,0 +1,143 @@
+package com.github.jikoo.openinv.togglepersist;
+
+import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.event.PlayerToggledEvent;
+import com.lishid.openinv.util.setting.PlayerToggle;
+import com.lishid.openinv.util.setting.PlayerToggles;
+import org.bukkit.configuration.Configuration;
+import org.bukkit.configuration.file.YamlConfiguration;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.plugin.java.JavaPlugin;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+import java.util.logging.Level;
+
+public class TogglePersist extends JavaPlugin implements Listener {
+
+  private final Map<UUID, Set<String>> enabledToggles = new HashMap<>();
+
+  @Override
+  public void onEnable() {
+    getServer().getPluginManager().registerEvents(this, this);
+
+    File file = new File(getDataFolder(), "toggles.yml");
+
+    // If there's no save file, there's nothing to load.
+    if (!file.exists()) {
+      return;
+    }
+
+    Configuration loaded = YamlConfiguration.loadConfiguration(file);
+
+    // For each toggle, enable loaded players.
+    for (String toggleName : loaded.getKeys(false)) {
+      PlayerToggle toggle = PlayerToggles.get(toggleName);
+      // Ensure toggle exists.
+      if (toggle == null) {
+        continue;
+      }
+
+      for (String idString : loaded.getStringList(toggleName)) {
+        // Ensure valid UUID.
+        UUID uuid;
+        try {
+          uuid = UUID.fromString(idString);
+        } catch (IllegalArgumentException e) {
+          continue;
+        }
+
+        // Track that toggle is enabled.
+        set(uuid, toggleName);
+      }
+    }
+  }
+
+  private void set(UUID playerId, String toggleName) {
+    enabledToggles.compute(playerId, (uuid, toggles) -> {
+      if (toggles == null) {
+        toggles = new HashSet<>();
+      }
+      toggles.add(toggleName);
+      return toggles;
+    });
+  }
+
+  @Override
+  public void onDisable() {
+    Map<String, List<String>> converted = getSaveData();
+
+    YamlConfiguration data = new YamlConfiguration();
+    for (Map.Entry<String, List<String>> playerToggle : converted.entrySet()) {
+      data.set(playerToggle.getKey(), playerToggle.getValue());
+    }
+
+    File file = new File(getDataFolder(), "toggles.yml");
+    try {
+      data.save(file);
+    } catch (IOException e) {
+      getLogger().log(Level.SEVERE, "Unable to save player toggle states", e);
+    }
+  }
+
+  private @NotNull Map<String, List<String>> getSaveData() {
+    Map<String, List<String>> converted = new HashMap<>();
+
+    for (Map.Entry<UUID, Set<String>> playerToggles : enabledToggles.entrySet()) {
+      String idString = playerToggles.getKey().toString();
+      for (String toggleName : playerToggles.getValue()) {
+        // Add player ID to listing for each enabled toggle.
+        converted.compute(toggleName, (name, ids) -> {
+          if (ids == null) {
+            ids = new ArrayList<>();
+          }
+          ids.add(idString);
+          return ids;
+        });
+      }
+    }
+    return converted;
+  }
+
+  @Keep
+  @EventHandler
+  private void onPlayerJoin(@NotNull PlayerJoinEvent event) {
+    UUID playerId = event.getPlayer().getUniqueId();
+    Set<String> toggleNames = enabledToggles.get(playerId);
+
+    if (toggleNames == null) {
+      return;
+    }
+
+    for (String toggleName : toggleNames) {
+      PlayerToggle toggle = PlayerToggles.get(toggleName);
+      if (toggle != null) {
+        toggle.set(playerId, true);
+      }
+    }
+  }
+
+  @Keep
+  @EventHandler
+  private void onToggleSet(@NotNull PlayerToggledEvent event) {
+    if (event.isEnabled()) {
+      set(event.getPlayerId(), event.getToggle().getName());
+    } else {
+      enabledToggles.computeIfPresent(event.getPlayerId(), (uuid, toggles) -> {
+        toggles.remove(event.getToggle().getName());
+        return toggles.isEmpty() ? null : toggles;
+      });
+    }
+  }
+
+}

addon/togglepersist/src/main/resources/plugin.yml

@@ -0,0 +1,7 @@
+name: OITogglePersist
+main: com.github.jikoo.openinv.togglepersist.TogglePersist
+version: ${project.version}
+author: Jikoo
+description: An OpenInv addon allowing /anycontainer and /silentcontainer to persist across sessions.
+api-version: "1.20"
+depend: [ OpenInv ]

api/pom.xml

@@ -0,0 +1,49 @@
+<!--
+  ~ Copyright (C) 2011-2022 lishid. All rights reserved.
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by
+  ~ the Free Software Foundation, version 3.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+  ~ GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License
+  ~ along with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <artifactId>openinvparent</artifactId>
+    <groupId>com.lishid</groupId>
+    <version>5.1.1</version>
+  </parent>
+
+  <artifactId>openinvapi</artifactId>
+  <name>OpenInvAPI</name>
+
+  <dependencies>
+    <dependency>
+      <artifactId>annotations</artifactId>
+      <groupId>org.jetbrains</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>spigot-api</artifactId>
+      <groupId>org.spigotmc</groupId>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>

api/src/main/java/com/lishid/openinv/IOpenInv.java

@@ -0,0 +1,185 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv;
+
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.UUID;
+import java.util.logging.Logger;
+
+/**
+ * Interface defining behavior for the OpenInv plugin.
+ */
+public interface IOpenInv {
+
+    /**
+     * Check if the server version is supported by OpenInv.
+     *
+     * @return true if the server version is supported
+     */
+    boolean isSupportedVersion();
+
+    /**
+     * Check the configuration value for whether OpenInv saves player data when unloading players. This is exclusively
+     * for users who do not allow editing of inventories, only viewing, and wish to prevent any possibility of bugs such
+     * as lishid#40. If true, OpenInv will not ever save any edits made to players.
+     *
+     * @return false unless configured otherwise
+     */
+    boolean disableSaving();
+
+    /**
+     * Check the configuration value for whether OpenInv allows offline access. If true, OpenInv will not load or allow
+     * modification of players while they are not online. This does not prevent other plugins from using existing loaded
+     * players who have gone offline.
+     *
+     * @return false unless configured otherwise
+     * @since 4.2.0
+     */
+    boolean disableOfflineAccess();
+
+    /**
+     * Check the configuration value for whether OpenInv uses history for opening commands. If false, OpenInv will use
+     * the previous parameterized search when no parameters are provided.
+     *
+     * @return false unless configured otherwise
+     * @since 4.3.0
+     */
+    boolean noArgsOpensSelf();
+
+    /**
+     * Get the active {@link IAnySilentContainer} implementation.
+     *
+     * @return the active implementation for the server version
+     * @throws IllegalStateException if the server version is unsupported
+     */
+    @NotNull IAnySilentContainer getAnySilentContainer();
+
+    /**
+     * Get whether a user has AnyContainer mode enabled.
+     *
+     * @param offline the user to obtain the state of
+     * @return true if AnyContainer mode is enabled
+     */
+    boolean getAnyContainerStatus(@NotNull OfflinePlayer offline);
+
+    /**
+     * Set whether a user has AnyContainer mode enabled.
+     *
+     * @param offline the user to set the state of
+     * @param status the state of the mode
+     */
+    void setAnyContainerStatus(@NotNull OfflinePlayer offline, boolean status);
+
+    /**
+     * Get whether a user has SilentContainer mode enabled.
+     *
+     * @param offline the user to obtain the state of
+     * @return true if SilentContainer mode is enabled
+     */
+    boolean getSilentContainerStatus(@NotNull OfflinePlayer offline);
+
+    /**
+     * Set whether a user has SilentContainer mode enabled.
+     *
+     * @param offline the user to set the state of
+     * @param status the state of the mode
+     */
+    void setSilentContainerStatus(@NotNull OfflinePlayer offline, boolean status);
+
+    /**
+     * Get an {@link ISpecialEnderChest} for a user.
+     *
+     * @param player the {@link Player} owning the inventory
+     * @param online whether the owner is currently online
+     * @return the created inventory
+     * @throws IllegalStateException if the server version is unsupported
+     * @throws InstantiationException if there was an issue creating the inventory
+     */
+    @NotNull ISpecialEnderChest getSpecialEnderChest(@NotNull Player player, boolean online) throws InstantiationException;
+
+    /**
+     * Get an {@link ISpecialPlayerInventory} for a user.
+     *
+     * @param player the {@link Player} owning the inventory
+     * @param online whether the owner is currently online
+     * @return the created inventory
+     * @throws IllegalStateException if the server version is unsupported
+     * @throws InstantiationException if there was an issue creating the inventory
+     */
+    @NotNull ISpecialPlayerInventory getSpecialInventory(@NotNull Player player, boolean online) throws InstantiationException;
+
+    /**
+     * Open an {@link ISpecialInventory} for a {@link Player}.
+     *
+     * @param player the viewer
+     * @param inventory the inventory to open
+     * @return the resulting {@link InventoryView}
+     */
+    @Nullable InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory);
+
+    /**
+     * Check if a {@link Player} is currently loaded by OpenInv.
+     *
+     * @param playerUuid the {@link UUID} of the {@code Player}
+     * @return whether the {@code Player} is loaded
+     * @since 4.2.0
+     */
+    boolean isPlayerLoaded(@NotNull UUID playerUuid);
+
+    /**
+     * Load a {@link Player} from an {@link OfflinePlayer}. If the user has not played before or the default world for
+     * the server is not loaded, this will return {@code null}.
+     *
+     * @param offline the {@code OfflinePlayer} to load a {@code Player} for
+     * @return the loaded {@code Player}
+     * @throws IllegalStateException if the server version is unsupported
+     */
+    @Nullable Player loadPlayer(@NotNull final OfflinePlayer offline);
+
+    /**
+     * Match an existing {@link OfflinePlayer}. If the name is a {@link UUID#toString() UUID string}, this will only
+     * return the user if they have actually played on the server before, unlike {@link Bukkit#getOfflinePlayer(UUID)}.
+     *
+     * <p>This method is potentially very heavily blocking. It should not ever be called on the
+     * main thread, and if it is, a stack trace will be displayed alerting server owners to the
+     * call.
+     *
+     * @param name the string to match
+     * @return the user with the closest matching name
+     */
+    @Nullable OfflinePlayer matchPlayer(@NotNull String name);
+
+    /**
+     * Forcibly close inventories of and unload any cached data for a user.
+     *
+     * @param offline the {@link OfflinePlayer} to unload
+     */
+    void unload(@NotNull OfflinePlayer offline);
+
+    Logger getLogger();
+
+}

api/src/main/java/com/lishid/openinv/event/OpenPlayerSaveEvent.java

@@ -0,0 +1,56 @@
+package com.lishid.openinv.event;
+
+import com.google.errorprone.annotations.RestrictedApi;
+import com.lishid.openinv.internal.ISpecialInventory;
+import org.bukkit.entity.Player;
+import org.bukkit.event.HandlerList;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Event fired before OpenInv saves a player's data when closing an {@link ISpecialInventory}.
+ */
+public class OpenPlayerSaveEvent extends PlayerSaveEvent {
+
+  private static final HandlerList HANDLERS = new HandlerList();
+
+  private final ISpecialInventory inventory;
+
+  /**
+   * Construct a new {@code OpenPlayerSaveEvent}.
+   *
+   * <p>The constructor is not considered part of the API, and may be subject to change.</p>
+   *
+   * @param player the player to be saved
+   * @param inventory the {@link ISpecialInventory} being closed
+   */
+  @RestrictedApi(
+      explanation = "Constructor is not considered part of the API and may be subject to change.",
+      link = "",
+      allowedOnPath = ".*/com/lishid/openinv/event/OpenEvents.java")
+  @ApiStatus.Internal
+  OpenPlayerSaveEvent(@NotNull Player player, @NotNull ISpecialInventory inventory) {
+    super(player);
+    this.inventory = inventory;
+  }
+
+  /**
+   * Get the {@link ISpecialInventory} that triggered the save by being closed.
+   *
+   * @return the special inventory
+   */
+  public @NotNull ISpecialInventory getInventory() {
+    return inventory;
+  }
+
+  @NotNull
+  @Override
+  public HandlerList getHandlers() {
+    return HANDLERS;
+  }
+
+  public static HandlerList getHandlerList() {
+    return HANDLERS;
+  }
+
+}

api/src/main/java/com/lishid/openinv/event/PlayerSaveEvent.java

@@ -0,0 +1,67 @@
+package com.lishid.openinv.event;
+
+
+import com.google.errorprone.annotations.RestrictedApi;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.player.PlayerEvent;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Event fired before a {@link Player} loaded via OpenInv is saved.
+ */
+public class PlayerSaveEvent extends PlayerEvent implements Cancellable {
+
+  private static final HandlerList HANDLERS = new HandlerList();
+
+  private boolean cancelled = false;
+
+  /**
+   * Construct a new {@code PlayerSaveEvent}.
+   *
+   * <p>The constructor is not considered part of the API, and may be subject to change.</p>
+   *
+   * @param player the player to be saved
+   */
+  @RestrictedApi(
+      explanation = "Constructor is not considered part of the API and may be subject to change.",
+      link = "",
+      allowedOnPath = ".*/com/lishid/openinv/event/(OpenPlayerSaveEvent|OpenEvents).java")
+  @ApiStatus.Internal
+  PlayerSaveEvent(@NotNull Player player) {
+    super(player);
+  }
+
+  /**
+   * Get whether the event is cancelled.
+   *
+   * @return true if the event is cancelled
+   */
+  @Override
+  public boolean isCancelled() {
+    return cancelled;
+  }
+
+  /**
+   * Set whether the event is cancelled.
+   *
+   * @param cancel whether the event is cancelled
+   */
+  @Override
+  public void setCancelled(boolean cancel) {
+    this.cancelled = cancel;
+  }
+
+  @NotNull
+  @Override
+  public HandlerList getHandlers() {
+    return HANDLERS;
+  }
+
+  public static HandlerList getHandlerList() {
+    return HANDLERS;
+  }
+
+}

api/src/main/java/com/lishid/openinv/event/PlayerToggledEvent.java

@@ -0,0 +1,71 @@
+package com.lishid.openinv.event;
+
+import com.google.errorprone.annotations.RestrictedApi;
+import com.lishid.openinv.util.setting.PlayerToggle;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+
+/**
+ * Event fired after OpenInv modifies a toggleable setting for a player.
+ */
+public class PlayerToggledEvent extends Event {
+
+  private static final HandlerList HANDLERS = new HandlerList();
+
+  private final @NotNull PlayerToggle toggle;
+  private final @NotNull UUID uuid;
+  private final boolean enabled;
+
+  @RestrictedApi(
+      explanation = "Constructor is not considered part of the API and may be subject to change.",
+      link = "",
+      allowedOnPath = ".*/com/lishid/openinv/event/OpenEvents.java")
+  @ApiStatus.Internal
+  PlayerToggledEvent(@NotNull PlayerToggle toggle, @NotNull UUID uuid, boolean enabled) {
+    this.toggle = toggle;
+    this.uuid = uuid;
+    this.enabled = enabled;
+  }
+
+  /**
+   * Get the {@link PlayerToggle} affected.
+   *
+   * @return the toggle
+   */
+  public @NotNull PlayerToggle getToggle() {
+    return toggle;
+  }
+
+  /**
+   * Get the {@link UUID} of the player whose setting was changed.
+   *
+   * @return the player ID
+   */
+  public @NotNull UUID getPlayerId() {
+    return uuid;
+  }
+
+  /**
+   * Get whether the toggle is enabled.
+   *
+   * @return true if the toggle is enabled
+   */
+  public boolean isEnabled() {
+    return enabled;
+  }
+
+  @NotNull
+  @Override
+  public HandlerList getHandlers() {
+    return HANDLERS;
+  }
+
+  public static HandlerList getHandlerList() {
+    return HANDLERS;
+  }
+
+}

api/src/main/java/com/lishid/openinv/internal/IAnySilentContainer.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+import org.bukkit.block.Block;
+import org.bukkit.block.BlockFace;
+import org.bukkit.block.BlockState;
+import org.bukkit.block.EnderChest;
+import org.bukkit.block.data.Directional;
+import org.bukkit.entity.Cat;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryHolder;
+import org.bukkit.util.BoundingBox;
+import org.jetbrains.annotations.NotNull;
+
+public interface IAnySilentContainer {
+
+    /**
+     * Forcibly open the container at the given coordinates for the Player. This will open blocked containers! Be sure
+     * to check {@link #isAnyContainerNeeded(Block)} first if that is not desirable.
+     *
+     * @param player the {@link Player} opening the container
+     * @param silent whether the container's noise is to be silenced
+     * @param block  the {@link Block} of the container
+     * @return true if the container can be opened
+     */
+    boolean activateContainer(@NotNull Player player, boolean silent, @NotNull Block block);
+
+    /**
+     * Perform operations required to close the current container silently.
+     *
+     * @param player the {@link Player} closing a container
+     */
+    void deactivateContainer(@NotNull Player player);
+
+    /**
+     * Check if the container at the given coordinates is blocked.
+     *
+     * @param block the {@link Block} of the container
+     * @return true if the container is blocked
+     */
+    boolean isAnyContainerNeeded(@NotNull Block block);
+
+    /**
+     * Check if a shulker box block cannot be opened under ordinary circumstances.
+     *
+     * @param shulkerBox the shulker box block
+     * @return whether the container is blocked
+     */
+    default boolean isShulkerBlocked(@NotNull Block shulkerBox) {
+        Directional directional = (Directional) shulkerBox.getBlockData();
+        BlockFace facing = directional.getFacing();
+        // Construct a new 1-block bounding box at the origin.
+        BoundingBox box = new BoundingBox(0, 0, 0, 1, 1, 1);
+        // Expand the box in the direction the shulker will open.
+        box.expand(facing, 0.5);
+        // Move the box away from the origin by a block so only the expansion intersects with a box around the origin.
+        box.shift(facing.getOppositeFace().getDirection());
+        // Check if the relative block's collision shape (which will be at the origin) intersects with the expanded box.
+        return shulkerBox.getRelative(facing).getCollisionShape().overlaps(box);
+    }
+
+    /**
+     * Check if a chest cannot be opened under ordinary circumstances.
+     *
+     * @param chest the chest block
+     * @return whether the container is blocked
+     */
+    default boolean isChestBlocked(@NotNull Block chest) {
+        org.bukkit.block.Block relative = chest.getRelative(0, 1, 0);
+        return relative.getType().isOccluding()
+                || !chest.getWorld().getNearbyEntities(BoundingBox.of(relative), Cat.class::isInstance).isEmpty();
+    }
+
+    /**
+     * Check if the given {@link Block} is a container which can be unblocked or silenced.
+     *
+     * @param block the potential container
+     * @return true if the type is a supported container
+     */
+    boolean isAnySilentContainer(@NotNull Block block);
+
+    /**
+     * Check if the given {@link BlockState} is a container which can be unblocked or silenced.
+     *
+     * @param blockState the potential container
+     * @return true if the type is a supported container
+     */
+    default boolean isAnySilentContainer(@NotNull BlockState blockState) {
+        return (blockState instanceof InventoryHolder holder && isAnySilentContainer(holder))
+                || blockState instanceof EnderChest;
+    }
+
+    /**
+     * Check if the given {@link InventoryHolder} is a container which can be unblocked or silenced.
+     *
+     * @param holder the potential container
+     * @return true if the type is a supported container
+     */
+    default boolean isAnySilentContainer(@NotNull InventoryHolder holder) {
+        return holder instanceof org.bukkit.block.EnderChest
+                || holder instanceof org.bukkit.block.Chest
+                || holder instanceof org.bukkit.block.DoubleChest
+                || holder instanceof org.bukkit.block.ShulkerBox
+                || holder instanceof org.bukkit.block.Barrel;
+    }
+
+}

api/src/main/java/com/lishid/openinv/internal/ISpecialEnderChest.java

@@ -1,23 +1,24 @@
-/*
- * Copyright (C) 2011-2014 lishid.  All rights reserved.
- * 
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation,  version 3.
- * 
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- * 
- * You should have received a copy of the GNU General Public License
- * along with this program. If not, see <http://www.gnu.org/licenses/>.
- */
-
-package com.lishid.openinv.internal;
-
-import org.bukkit.entity.Player;
-
-public interface IPlayerDataManager {
-    public Player loadPlayer(String name);
-}
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+/**
+ * An {@link ISpecialInventory} representing an ender chest.
+ */
+public interface ISpecialEnderChest extends ISpecialInventory {
+
+}

api/src/main/java/com/lishid/openinv/internal/ISpecialInventory.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Interface defining behavior for special inventories backed by other inventories' content listings.
+ */
+public interface ISpecialInventory {
+
+    /**
+     * Get the {@link Inventory} associated with this {@code ISpecialInventory}.
+     *
+     * @return the Bukkit inventory
+     */
+    @NotNull Inventory getBukkitInventory();
+
+    /**
+     * Set the owning {@link Player} instance to a newly-joined user.
+     *
+     * @param player the user coming online
+     */
+    void setPlayerOnline(@NotNull Player player);
+
+    /**
+     * Mark the owner of the inventory offline.
+     */
+    void setPlayerOffline();
+
+    /**
+     * Get whether the inventory is being viewed by any users.
+     *
+     * @return true if the inventory is being viewed
+     */
+    default boolean isInUse() {
+        return !getBukkitInventory().getViewers().isEmpty();
+    }
+
+    /**
+     * Get the {@link Player} who owns the inventory.
+     *
+     * @return the {@link HumanEntity} who owns the inventory
+     */
+    @NotNull HumanEntity getPlayer();
+
+}

api/src/main/java/com/lishid/openinv/internal/ISpecialPlayerInventory.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+import java.util.List;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.Inventory;
+
+/**
+ * An {@link ISpecialInventory} representing a player inventory.
+ */
+public interface ISpecialPlayerInventory extends ISpecialInventory {
+
+    /*
+     * Player inventory usage varies from all other inventories - as the inventory is technically open at all times,
+     * if the player is online or has been online while the inventory is open, they are in the viewer list.
+     */
+    @Override
+    default boolean isInUse() {
+        Inventory inventory = getBukkitInventory();
+        List<HumanEntity> viewers = inventory.getViewers();
+
+        if (viewers.size() != 1) {
+            return !viewers.isEmpty();
+        }
+
+        HumanEntity viewer = viewers.get(0);
+
+        if (!viewer.getUniqueId().equals(getPlayer().getUniqueId())) {
+            return true;
+        }
+
+        return viewer.getOpenInventory().getTopInventory().equals(inventory);
+    }
+
+}

api/src/main/java/com/lishid/openinv/util/InventoryAccess.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util;
+
+import com.google.errorprone.annotations.RestrictedApi;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.function.BiFunction;
+
+public final class InventoryAccess {
+
+    private static @Nullable BiFunction<Inventory, Class<? extends ISpecialInventory>, ISpecialInventory> provider;
+
+    public static boolean isUsable() {
+        return provider != null;
+    }
+
+    /**
+     * Check if an {@link Inventory} is an {@link ISpecialPlayerInventory} implementation.
+     *
+     * @param inventory the Bukkit inventory
+     * @return true if backed by the correct implementation
+     */
+    public static boolean isPlayerInventory(@NotNull Inventory inventory) {
+        return getPlayerInventory(inventory) != null;
+    }
+
+    /**
+     * Get the {@link ISpecialPlayerInventory} backing an {@link Inventory}. Returns {@code null} if the inventory is
+     * not backed by the correct class.
+     *
+     * @param inventory the Bukkit inventory
+     * @return the backing implementation if available
+     */
+    public static @Nullable ISpecialPlayerInventory getPlayerInventory(@NotNull Inventory inventory) {
+        return provider == null ? null : (ISpecialPlayerInventory) provider.apply(inventory, ISpecialPlayerInventory.class);
+    }
+
+    /**
+     * Check if an {@link Inventory} is an {@link ISpecialEnderChest} implementation.
+     *
+     * @param inventory the Bukkit inventory
+     * @return true if backed by the correct implementation
+     */
+    public static boolean isEnderChest(@NotNull Inventory inventory) {
+        return getEnderChest(inventory) != null;
+    }
+
+    /**
+     * Get the {@link ISpecialEnderChest} backing an {@link Inventory}. Returns {@code null} if the inventory is
+     * not backed by the correct class.
+     *
+     * @param inventory the Bukkit inventory
+     * @return the backing implementation if available
+     */
+    public static @Nullable ISpecialEnderChest getEnderChest(@NotNull Inventory inventory) {
+        return provider == null ? null : (ISpecialEnderChest) provider.apply(inventory, ISpecialEnderChest.class);
+    }
+
+    /**
+     * Get a {@link ISpecialInventory} backing an {@link Inventory}. Returns {@code null} if the inventory is not backed
+     * by the correct class.
+     *
+     * @param inventory the Bukkit inventory
+     * @return the backing implementation if available
+     */
+    public static @Nullable ISpecialInventory getInventory(@NotNull Inventory inventory) {
+        return provider == null ? null : provider.apply(inventory, ISpecialInventory.class);
+    }
+
+    @RestrictedApi(
+        explanation = "Not part of the API.",
+        link = "",
+        allowedOnPath = ".*/com/lishid/openinv/util/InternalAccessor.java")
+    @ApiStatus.Internal
+    static void setProvider(@Nullable BiFunction<Inventory, Class<? extends ISpecialInventory>, ISpecialInventory> provider) {
+        InventoryAccess.provider = provider;
+    }
+
+    private InventoryAccess() {
+        throw new IllegalStateException("Cannot create instance of utility class.");
+    }
+
+}

api/src/main/java/com/lishid/openinv/util/setting/PlayerToggle.java

@@ -0,0 +1,36 @@
+package com.lishid.openinv.util.setting;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+
+/**
+ * A per-player setting that may be enabled or disabled.
+ */
+public interface PlayerToggle {
+
+  /**
+   * Get the name of the setting.
+   *
+   * @return the setting name
+   */
+  @NotNull String getName();
+
+  /**
+   * Get the state of the toggle for a particular player ID.
+   *
+   * @param uuid the player ID
+   * @return true if the setting is enabled
+   */
+  boolean is(@NotNull UUID uuid);
+
+  /**
+   * Set the state of the toggle for a particular player ID.
+   *
+   * @param uuid the player ID
+   * @param enabled whether the setting is enabled
+   * @return true if the setting changed as a result of being set
+   */
+  boolean set(@NotNull UUID uuid, boolean enabled);
+
+}

api/src/main/java/com/lishid/openinv/util/setting/PlayerToggles.java

@@ -0,0 +1,106 @@
+package com.lishid.openinv.util.setting;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.UnmodifiableView;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * Utility class containing all of OpenInv's {@link PlayerToggle PlayerToggles}.
+ */
+public final class PlayerToggles {
+
+  private static final Map<String, PlayerToggle> TOGGLES = new HashMap<>();
+  private static final PlayerToggle ANY = add(new MemoryToggle("AnyContainer"));
+  private static final PlayerToggle SILENT = add(new MemoryToggle("SilentContainer"));
+
+  /**
+   * Get the AnyContainer toggle.
+   *
+   * @return the AnyContainer toggle
+   */
+  public static @NotNull PlayerToggle any() {
+    return ANY;
+  }
+
+  /**
+   * Get the SilentContainer toggle.
+   *
+   * @return the SilentContainer toggle
+   */
+  public static @NotNull PlayerToggle silent() {
+    return SILENT;
+  }
+
+  /**
+   * Get a toggle by name.
+   *
+   * @param toggleName the name of the toggle
+   * @return the toggle, or null if no such toggle exists.
+   */
+  public static @Nullable PlayerToggle get(@NotNull String toggleName) {
+    PlayerToggle toggle = TOGGLES.get(toggleName);
+    if (toggle == null) {
+      toggle = TOGGLES.get(toggleName.toLowerCase(Locale.ENGLISH));
+    }
+    return toggle;
+  }
+
+  /**
+   * Get an unmodifable view of all toggles available.
+   *
+   * @return a view of all toggles available
+   */
+  public static @UnmodifiableView @NotNull Collection<PlayerToggle> get() {
+    return Collections.unmodifiableCollection(TOGGLES.values());
+  }
+
+  private static @NotNull PlayerToggle add(@NotNull PlayerToggle toggle) {
+    TOGGLES.put(toggle.getName().toLowerCase(Locale.ENGLISH), toggle);
+    return toggle;
+  }
+
+  private PlayerToggles() {
+    throw new IllegalStateException("Cannot create instance of utility class.");
+  }
+
+  private static class MemoryToggle implements PlayerToggle {
+
+    private final @NotNull Set<UUID> enabled;
+    private final @NotNull String name;
+
+    private MemoryToggle(@NotNull String name) {
+      enabled = new HashSet<>();
+      this.name = name;
+    }
+
+    @Override
+    public @NotNull String getName() {
+      return this.name;
+    }
+
+    @Override
+    public boolean is(@NotNull UUID uuid) {
+      return enabled.contains(uuid);
+    }
+
+    @Override
+    public boolean set(@NotNull UUID uuid, boolean enabled) {
+      if (enabled) {
+        return this.enabled.add(uuid);
+      } else {
+        return this.enabled.remove(uuid);
+      }
+    }
+
+  }
+
+}

common/pom.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>com.lishid</groupId>
+        <artifactId>openinvparent</artifactId>
+        <version>5.1.1</version>
+    </parent>
+
+    <artifactId>openinvcommon</artifactId>
+
+    <dependencies>
+        <dependency>
+            <artifactId>annotations</artifactId>
+            <groupId>org.jetbrains</groupId>
+        </dependency>
+        <dependency>
+            <groupId>org.spigotmc</groupId>
+            <artifactId>spigot-api</artifactId>
+        </dependency>
+        <dependency>
+            <artifactId>openinvapi</artifactId>
+            <groupId>com.lishid</groupId>
+        </dependency>
+    </dependencies>
+
+</project>

common/src/main/java/com/lishid/openinv/event/OpenEvents.java

@@ -0,0 +1,39 @@
+package com.lishid.openinv.event;
+
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.util.setting.PlayerToggle;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.Event;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+
+/**
+ * Construct and call events.
+ */
+public final class OpenEvents {
+
+  public static boolean saveCancelled(@NotNull Player player) {
+    return call(new PlayerSaveEvent(player));
+  }
+
+  public static boolean saveCancelled(@NotNull ISpecialInventory inventory) {
+    return call(new OpenPlayerSaveEvent((Player) inventory.getPlayer(), inventory));
+  }
+
+  public static void notifyPlayerToggle(@NotNull PlayerToggle toggle, @NotNull UUID uuid, boolean state) {
+    Bukkit.getPluginManager().callEvent(new PlayerToggledEvent(toggle, uuid, state));
+  }
+
+  private static <T extends Event & Cancellable> boolean call(T event) {
+    Bukkit.getPluginManager().callEvent(event);
+    return event.isCancelled();
+  }
+
+  private OpenEvents() {
+    throw new IllegalStateException("Cannot create instance of utility class.");
+  }
+
+}

common/src/main/java/com/lishid/openinv/internal/Accessor.java

@@ -0,0 +1,24 @@
+package com.lishid.openinv.internal;
+
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public interface Accessor {
+
+  @NotNull
+  PlayerManager getPlayerManager();
+
+  @NotNull IAnySilentContainer getAnySilentContainer();
+
+  @NotNull ISpecialPlayerInventory createPlayerInventory(@NotNull Player player);
+
+  @NotNull ISpecialEnderChest createEnderChest(@NotNull Player player);
+
+  <T extends ISpecialInventory> @Nullable T get(@NotNull Inventory bukkitInventory, @NotNull Class<T> clazz);
+
+  void reload(@NotNull ConfigurationSection config);
+
+}

common/src/main/java/com/lishid/openinv/internal/AnySilentContainerBase.java

@@ -0,0 +1,106 @@
+package com.lishid.openinv.internal;
+
+import org.bukkit.block.Barrel;
+import org.bukkit.block.Block;
+import org.bukkit.block.BlockFace;
+import org.bukkit.block.BlockState;
+import org.bukkit.block.EnderChest;
+import org.bukkit.block.ShulkerBox;
+import org.bukkit.block.data.BlockData;
+import org.bukkit.block.data.type.Chest;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Method;
+
+public abstract class AnySilentContainerBase implements IAnySilentContainer {
+
+  private static final @Nullable Method BLOCK_GET_STATE_BOOLEAN;
+
+  static {
+    @Nullable Method getState;
+    try {
+      //noinspection JavaReflectionMemberAccess
+      getState = Block.class.getMethod("getState", boolean.class);
+    } catch (NoSuchMethodException e) {
+      getState = null;
+    }
+    BLOCK_GET_STATE_BOOLEAN = getState;
+  }
+
+  private static BlockState getBlockState(Block block) {
+    // Paper: Get state without snapshotting.
+    if (BLOCK_GET_STATE_BOOLEAN != null) {
+      try {
+        return (BlockState) BLOCK_GET_STATE_BOOLEAN.invoke(block, false);
+      } catch (ReflectiveOperationException ignored) {
+        // If we encounter an issue, fall through to regular snapshotting method.
+      }
+    }
+    return block.getState();
+  }
+
+  @Override
+  public boolean isAnyContainerNeeded(@NotNull Block block) {
+    BlockState blockState = getBlockState(block);
+
+    // Barrels do not require AnyContainer.
+    if (blockState instanceof Barrel) {
+      return false;
+    }
+
+    // Enderchests require a non-occluding block on top to open.
+    if (blockState instanceof EnderChest) {
+      return block.getRelative(0, 1, 0).getType().isOccluding();
+    }
+
+    // Shulker boxes require half a block clear in the direction they open.
+    if (blockState instanceof ShulkerBox) {
+      return isShulkerBlocked(block);
+    }
+
+    if (!(blockState instanceof org.bukkit.block.Chest)) {
+      return false;
+    }
+
+    if (isChestBlocked(block)) {
+      return true;
+    }
+
+    BlockData blockData = block.getBlockData();
+    if (!(blockData instanceof Chest chest) || chest.getType() == Chest.Type.SINGLE) {
+      return false;
+    }
+
+    BlockFace relativeFace = switch (chest.getFacing()) {
+      case NORTH -> chest.getType() == Chest.Type.RIGHT ? BlockFace.WEST : BlockFace.EAST;
+      case EAST -> chest.getType() == Chest.Type.RIGHT ? BlockFace.NORTH : BlockFace.SOUTH;
+      case SOUTH -> chest.getType() == Chest.Type.RIGHT ? BlockFace.EAST : BlockFace.WEST;
+      case WEST -> chest.getType() == Chest.Type.RIGHT ? BlockFace.SOUTH : BlockFace.NORTH;
+      default -> BlockFace.SELF;
+    };
+    Block relative = block.getRelative(relativeFace);
+
+    if (relative.getType() != block.getType()) {
+      return false;
+    }
+
+    BlockData relativeData = relative.getBlockData();
+    if (!(relativeData instanceof Chest relativeChest)) {
+      return false;
+    }
+
+    if (relativeChest.getFacing() != chest.getFacing()
+        || relativeChest.getType() != (chest.getType() == Chest.Type.RIGHT ? Chest.Type.LEFT : Chest.Type.RIGHT)) {
+      return false;
+    }
+
+    return isChestBlocked(relative);
+  }
+
+  @Override
+  public boolean isAnySilentContainer(@NotNull Block block) {
+    return isAnySilentContainer(getBlockState(block));
+  }
+
+}

common/src/main/java/com/lishid/openinv/internal/InternalOwned.java

@@ -0,0 +1,7 @@
+package com.lishid.openinv.internal;
+
+public interface InternalOwned<T> {
+
+  T getOwnerHandle();
+
+}

common/src/main/java/com/lishid/openinv/internal/InventoryViewTitle.java

@@ -0,0 +1,48 @@
+package com.lishid.openinv.internal;
+
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.lang.Replacement;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Objects;
+
+public enum InventoryViewTitle {
+
+  PLAYER_INVENTORY("container.player", "'s Inventory"),
+  ENDER_CHEST("container.enderchest", "'s Ender Chest");
+
+  private final String localizationKey;
+  private final String defaultSuffix;
+
+  InventoryViewTitle(String localizationKey, String defaultSuffix) {
+    this.localizationKey = localizationKey;
+    this.defaultSuffix = defaultSuffix;
+  }
+
+  public @NotNull String getTitle(
+      @NotNull LanguageManager lang,
+      @NotNull Player viewer,
+      @NotNull ISpecialInventory inventory) {
+    HumanEntity owner = inventory.getPlayer();
+
+    String localTitle = lang.getLocalizedMessage(
+            viewer,
+            localizationKey,
+            new Replacement("%player%", owner.getName()));
+    return Objects.requireNonNullElseGet(localTitle, () -> owner.getName() + defaultSuffix);
+  }
+
+  public static @Nullable InventoryViewTitle of(@NotNull ISpecialInventory inventory) {
+    if (inventory instanceof ISpecialPlayerInventory) {
+      return PLAYER_INVENTORY;
+    } else if (inventory instanceof ISpecialEnderChest) {
+      return ENDER_CHEST;
+    } else {
+      return null;
+    }
+  }
+
+}

common/src/main/java/com/lishid/openinv/internal/OpenInventoryView.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+
+public class OpenInventoryView extends InventoryView {
+
+    private final @NotNull Player player;
+    private final @NotNull ISpecialInventory inventory;
+    private final @NotNull String originalTitle;
+    private String title;
+
+    public OpenInventoryView(
+            @NotNull Player player,
+            @NotNull ISpecialInventory inventory,
+            @NotNull String originalTitle) {
+        this.player = player;
+        this.inventory = inventory;
+        this.originalTitle = originalTitle;
+    }
+
+    @Override
+    public @NotNull Inventory getTopInventory() {
+        return inventory.getBukkitInventory();
+    }
+
+    @Override
+    public @NotNull Inventory getBottomInventory() {
+        return getPlayer().getInventory();
+    }
+
+    @Override
+    public @NotNull HumanEntity getPlayer() {
+        return player;
+    }
+
+    @Override
+    public @NotNull InventoryType getType() {
+        return inventory.getBukkitInventory().getType();
+    }
+
+    @Override
+    public @NotNull String getTitle() {
+        return title == null ? originalTitle : title;
+    }
+
+    @Override
+    public @NotNull String getOriginalTitle() {
+        return originalTitle;
+    }
+
+    @Override
+    public void setTitle(@NotNull String title) {
+        this.title = title;
+    }
+
+}

common/src/main/java/com/lishid/openinv/internal/PlayerManager.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal;
+
+import org.bukkit.OfflinePlayer;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public interface PlayerManager {
+
+    /**
+     * Loads a Player for an OfflinePlayer.
+     * </p>
+     * This method is potentially blocking, and should not be called on the main thread.
+     *
+     * @param offline the OfflinePlayer
+     * @return the Player loaded
+     */
+    @Nullable Player loadPlayer(@NotNull OfflinePlayer offline);
+
+    /**
+     * Creates a new Player from an existing one that will function slightly better offline.
+     *
+     * @return the Player
+     */
+    @NotNull Player inject(@NotNull Player player);
+
+    /**
+     * Opens an ISpecialInventory for a Player.
+     *
+     * @param player the Player opening the ISpecialInventory
+     * @param inventory the Inventory
+     *`
+     * @return the InventoryView opened
+     */
+    @Nullable InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory, boolean viewOnly);
+
+}

common/src/main/java/com/lishid/openinv/internal/ViewOnly.java

@@ -0,0 +1,4 @@
+package com.lishid.openinv.internal;
+
+public interface ViewOnly {
+}

common/src/main/java/com/lishid/openinv/util/Permissions.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util;
+
+import org.bukkit.permissions.Permissible;
+import org.jetbrains.annotations.NotNull;
+
+public enum Permissions {
+
+    INVENTORY_OPEN_SELF("inventory.open.self"),
+    INVENTORY_OPEN_OTHER("inventory.open.other"),
+    INVENTORY_EDIT_SELF("inventory.edit.self"),
+    INVENTORY_EDIT_OTHER("inventory.edit.other"),
+    INVENTORY_SLOT_HEAD_ANY("inventory.slot.head.any"),
+    INVENTORY_SLOT_CHEST_ANY("inventory.slot.chest.any"),
+    INVENTORY_SLOT_LEGS_ANY("inventory.slot.legs.any"),
+    INVENTORY_SLOT_FEET_ANY("inventory.slot.feet.any"),
+    INVENTORY_SLOT_DROP("inventory.slot.drop"),
+
+    ENDERCHEST_OPEN_SELF("enderchest.open.self"),
+    ENDERCHEST_OPEN_OTHER("enderchest.open.other"),
+    ENDERCHEST_EDIT_SELF("enderchest.edit.self"),
+    ENDERCHEST_EDIT_OTHER("enderchest.edit.other"),
+
+    ACCESS_CROSSWORLD("access.crossworld"),
+    ACCESS_OFFLINE("access.offline"),
+    ACCESS_ONLINE("access.online"),
+
+    SPECTATE_CLICK("spectate.click"),
+
+    CONTAINER_ANY("container.any"),
+    CONTAINER_SILENT("container.silent"),
+    SEARCH_INVENTORY("search.inventory"),
+    SEARCH_CONTAINER("search.container");
+
+    private final String permission;
+
+    Permissions(String permission) {
+        this.permission = "openinv." + permission;
+    }
+
+    public boolean hasPermission(@NotNull Permissible permissible) {
+        return permissible.hasPermission(permission);
+    }
+
+}

common/src/main/java/com/lishid/openinv/util/ReflectionHelper.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2011-2021 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+
+/**
+ * A utility for making reflection easier.
+ */
+public final class ReflectionHelper {
+
+    /**
+     * Grab an {@link Object} stored in a {@link Field} of another {@code Object}.
+     *
+     * <p>This casts the field to the correct class. Any issues will result in a {@code null} return value.
+     *
+     * @param fieldType the {@link Class} of {@code Object} stored in the {@code Field}
+     * @param holder the containing {@code Object}
+     * @param <T> the type of stored {@code Object}
+     * @return the first matching {@code Object} or {@code null} if none match
+     */
+    public static <T> @Nullable T grabObjectByType(final Object holder, final Class<T> fieldType) {
+        Field field = grabFieldByType(holder.getClass(), fieldType);
+
+        if (field != null) {
+            try {
+                return fieldType.cast(field.get(holder));
+            } catch (IllegalAccessException ignored) {
+                // Ignore issues obtaining field
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Grab a {@link Field} of an {@link Object}
+     *
+     * @param fieldType the {@link Class} of the object
+     * @param holderType the containing {@code Class}
+     * @return the first matching object or {@code null} if none match
+     */
+    public static @Nullable Field grabFieldByType(Class<?> holderType, Class<?> fieldType) {
+        for (Field field : holderType.getDeclaredFields()) {
+            if (fieldType.isAssignableFrom(field.getType())) {
+                field.setAccessible(true);
+                return field;
+            }
+        }
+
+        if (holderType.getSuperclass() != null) {
+            return grabFieldByType(fieldType, holderType.getSuperclass());
+        }
+
+        return null;
+    }
+
+    private ReflectionHelper() {
+        throw new IllegalStateException("Cannot create instance of utility class.");
+    }
+
+}

common/src/main/java/com/lishid/openinv/util/lang/LanguageManager.java

@@ -0,0 +1,319 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util.lang;
+
+import net.md_5.bungee.api.ChatMessageType;
+import net.md_5.bungee.api.chat.TextComponent;
+import org.bukkit.ChatColor;
+import org.bukkit.command.CommandSender;
+import org.bukkit.configuration.Configuration;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.configuration.file.YamlConfiguration;
+import org.bukkit.entity.Player;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.function.Predicate;
+import java.util.logging.Level;
+
+/**
+ * A simple language manager supporting both custom and bundled languages.
+ *
+ * @author Jikoo
+ */
+public class LanguageManager {
+
+    private final Plugin plugin;
+    private final File folder;
+    private final String defaultLocale;
+    private final Map<String, YamlConfiguration> locales;
+
+    public LanguageManager(@NotNull Plugin plugin, @NotNull String defaultLocale) {
+        this.plugin = plugin;
+        this.defaultLocale = defaultLocale;
+        this.locales = new HashMap<>();
+        this.folder = new File(plugin.getDataFolder(), "locale");
+
+        if (!folder.exists() && !folder.mkdirs()) {
+            plugin.getLogger().warning(() -> "Unable to create " + folder.getPath() + "! Languages may not be editable.");
+        }
+
+        reload();
+    }
+
+    public void reload() {
+        this.locales.clear();
+        getOrLoadLocale(defaultLocale);
+    }
+
+    private @NotNull YamlConfiguration getOrLoadLocale(@NotNull String locale) {
+        YamlConfiguration loaded = locales.get(locale);
+        if (loaded != null) {
+            return loaded;
+        }
+
+        LangLocation lang = bestMatch(locale, null);
+
+        // If a parent was a better match, check if it is already loaded.
+        if (!locale.equals(lang.locale)) {
+            loaded = locales.get(lang.locale);
+            if (loaded != null) {
+                locales.put(locale, loaded);
+                return loaded;
+            }
+        }
+
+        // Load locale config from disk and bundled locale defaults.
+        YamlConfiguration localeConfig = loadLocale(lang);
+
+        // If the locale is not the default locale, also handle any missing translations from the default locale.
+        if (!locale.equals(defaultLocale)) {
+            addTranslationFallthrough(lang, localeConfig);
+
+            if (plugin.getConfig().getBoolean("settings.secret.warn-about-guess-section", true)
+                    && localeConfig.isConfigurationSection("guess")) {
+                // Warn that guess section exists. This should run once per language per server restart
+                // when accessed by a user to hint to server owners that they can make UX improvements.
+                plugin.getLogger().info(() -> "[LanguageManager] Missing translations from " + lang.locale + ".yml! Check the guess section!");
+            }
+        }
+
+        locales.put(locale, localeConfig);
+        locales.put(lang.locale, localeConfig);
+
+        return localeConfig;
+    }
+
+    private @NotNull LangLocation bestMatch(@NotNull String locale, @Nullable LangLocation initial) {
+        File file = new File(folder, locale + ".yml");
+        InputStream bundled = plugin.getResource("locale/" + locale + ".yml");
+
+        if (file.exists() || bundled != null) {
+            return new LangLocation(locale, file, bundled);
+        }
+
+        if (initial == null) {
+            initial = new LangLocation(locale, file, null);
+        }
+
+        int lastSeparator = locale.lastIndexOf('_');
+
+        // Must be at least some content before separator.
+        if (lastSeparator < 1) {
+            return initial;
+        }
+
+        return bestMatch(locale.substring(0, lastSeparator), initial);
+    }
+
+    private @NotNull YamlConfiguration loadLocale(@NotNull LangLocation lang) {
+        YamlConfiguration localeConfigDefaults;
+        if (lang.bundled == null) {
+            localeConfigDefaults = new YamlConfiguration();
+        } else {
+            try (BufferedReader reader = new BufferedReader(new InputStreamReader(lang.bundled, StandardCharsets.UTF_8))) {
+                localeConfigDefaults = YamlConfiguration.loadConfiguration(reader);
+            } catch (IOException e) {
+                plugin.getLogger().log(Level.WARNING, e, () -> "[LanguageManager] Unable to load resource " + lang.locale + ".yml");
+                localeConfigDefaults = new YamlConfiguration();
+            }
+        }
+
+        if (!lang.file.exists()) {
+            // If the file does not exist on disk, save bundled defaults.
+            try {
+                localeConfigDefaults.save(lang.file);
+            } catch (IOException e) {
+                plugin.getLogger().log(Level.WARNING, e, () -> "[LanguageManager] Unable to save resource " + lang.locale + ".yml");
+            }
+            // Return loaded bundled locale.
+            return localeConfigDefaults;
+        }
+
+        // If the file does exist on disk, load it.
+        YamlConfiguration localeConfig = YamlConfiguration.loadConfiguration(lang.file);
+        // Check for missing translations from the bundled file.
+        List<String> newKeys = getMissingKeys(localeConfigDefaults, localeConfig::isSet);
+
+        if (newKeys.isEmpty()) {
+            return localeConfig;
+        }
+
+        // Get guess section for missing keys.
+        ConfigurationSection guess = localeConfig.getConfigurationSection("guess");
+
+        for (String newKey : newKeys) {
+            // Set all missing keys to defaults.
+            localeConfig.set(newKey, localeConfigDefaults.get(newKey));
+
+            // Delete relevant guess keys in case this is a new translation.
+            if (guess != null) {
+                guess.set(newKey, null);
+            }
+        }
+
+        // If guess section is empty, delete it.
+        if (guess != null && guess.getKeys(false).isEmpty()) {
+            localeConfig.set("guess", null);
+        }
+
+        plugin.getLogger().info(() -> "[LanguageManager] Added new translation keys to " + lang.locale + ".yml: " + String.join(", ", newKeys));
+
+        // Write new keys to disk.
+        try {
+            localeConfig.save(lang.file);
+        } catch (IOException e) {
+            plugin.getLogger().log(Level.WARNING, e, () -> "[LanguageManager] Unable to save resource " + lang.locale + ".yml");
+        }
+
+        return localeConfig;
+    }
+
+    private void addTranslationFallthrough(@NotNull LangLocation location, @NotNull YamlConfiguration localeConfig) {
+        YamlConfiguration defaultLocaleConfig = locales.get(defaultLocale);
+
+        // Get missing keys. Keys that already have a guess value are not new and don't need to trigger another write.
+        List<String> missingKeys = getMissingKeys(
+                defaultLocaleConfig,
+                key -> localeConfig.isSet(key) || localeConfig.isSet("guess." + key));
+
+        if (!missingKeys.isEmpty()) {
+            // Set up guess section for missing keys.
+            for (String key : missingKeys) {
+                localeConfig.set("guess." + key, defaultLocaleConfig.get(key));
+            }
+
+            // Write modified guess section to disk.
+            try {
+                localeConfig.save(location.file);
+            } catch (IOException e) {
+                plugin.getLogger().log(Level.WARNING, e, () -> "[LanguageManager] Unable to save resource " + location.locale + ".yml");
+            }
+        }
+
+        // Fall through to default locale.
+        localeConfig.setDefaults(defaultLocaleConfig);
+    }
+
+    private @NotNull List<String> getMissingKeys(
+            @NotNull Configuration configurationDefault,
+            @NotNull Predicate<String> nodeSetPredicate) {
+        List<String> missingKeys = new ArrayList<>();
+        for (String key : configurationDefault.getKeys(true)) {
+            if (!configurationDefault.isConfigurationSection(key) && !nodeSetPredicate.test(key)) {
+                // Missing keys are non-section keys that fail the predicate.
+                missingKeys.add(key);
+            }
+        }
+        return missingKeys;
+    }
+
+    public @Nullable String getValue(@NotNull String key, @Nullable String locale) {
+        String value = getOrLoadLocale(locale == null ? defaultLocale : locale.toLowerCase(Locale.ENGLISH)).getString(key);
+        if (value == null || value.isBlank()) {
+            return null;
+        }
+
+        value = ChatColor.translateAlternateColorCodes('&', value);
+
+        return value;
+    }
+
+    public @Nullable String getValue(@NotNull String key, @Nullable String locale, Replacement @NotNull ... replacements) {
+        String value = getValue(key, locale);
+
+        if (value == null) {
+            return null;
+        }
+
+        for (Replacement replacement : replacements) {
+            value = value.replace(replacement.placeholder(), replacement.value());
+        }
+
+        return value;
+    }
+
+    public @Nullable String getLocalizedMessage(@NotNull CommandSender sender, @NotNull String key) {
+        return getValue(key, getLocale(sender));
+    }
+
+    public @Nullable String getLocalizedMessage(
+        @NotNull CommandSender sender,
+        @NotNull String key,
+        Replacement @NotNull ... replacements) {
+        return getValue(key, getLocale(sender), replacements);
+    }
+
+    private @NotNull String getLocale(@NotNull CommandSender sender) {
+        if (sender instanceof Player) {
+            return ((Player) sender).getLocale();
+        } else {
+            return plugin.getConfig().getString("settings.locale", "en");
+        }
+    }
+
+    public void sendMessage(@NotNull CommandSender sender, @NotNull String key) {
+        String message = getLocalizedMessage(sender, key);
+
+        if (message != null && !message.isEmpty()) {
+            sender.sendMessage(message);
+        }
+    }
+
+    public void sendMessage(@NotNull CommandSender sender, @NotNull String key, Replacement @NotNull... replacements) {
+        String message = getLocalizedMessage(sender, key, replacements);
+
+        if (message != null && !message.isEmpty()) {
+            sender.sendMessage(message);
+        }
+    }
+
+    public void sendSystemMessage(@NotNull Player player, @NotNull String key) {
+        String message = getLocalizedMessage(player, key);
+
+        if (message == null) {
+            return;
+        }
+
+        int newline = message.indexOf('\n');
+        if (newline != -1) {
+            // No newlines in action bar chat.
+            message = message.substring(0, newline);
+        }
+
+        if (message.isEmpty()) {
+            return;
+        }
+
+        player.spigot().sendMessage(ChatMessageType.ACTION_BAR, TextComponent.fromLegacy(message));
+    }
+
+    private record LangLocation(@NotNull String locale, @NotNull File file, @Nullable InputStream bundled) {}
+
+}

common/src/main/java/com/lishid/openinv/util/lang/Replacement.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util.lang;
+
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A data holder for string replacement in translations.
+ *
+ * @param placeholder the placeholder to be replaced
+ * @param value the value to insert
+ */
+public record Replacement(@NotNull String placeholder, @NotNull String value) {
+
+}

internal/v1_20_R3/pom.xml

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright (C) 2011-2023 lishid. All rights reserved.
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by
+  ~ the Free Software Foundation, version 3.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+  ~ GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License
+  ~ along with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <artifactId>openinvparent</artifactId>
+    <groupId>com.lishid</groupId>
+    <relativePath>../../pom.xml</relativePath>
+    <version>5.1.1</version>
+  </parent>
+
+  <artifactId>openinvadapter1_20_R3</artifactId>
+  <name>OpenInvAdapter1_20_R3</name>
+
+  <properties>
+    <maven.compiler.system>17</maven.compiler.system>
+    <maven.compiler.release>17</maven.compiler.release>
+    <spigot.version>1.20.4-R0.1-SNAPSHOT</spigot.version>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.spigotmc</groupId>
+      <artifactId>spigot-api</artifactId>
+      <version>${spigot.version}</version>
+    </dependency>
+    <dependency>
+      <artifactId>spigot</artifactId>
+      <groupId>org.spigotmc</groupId>
+      <scope>provided</scope>
+      <version>${spigot.version}</version>
+      <classifier>remapped-mojang</classifier>
+    </dependency>
+    <dependency>
+      <artifactId>openinvapi</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>openinvcommon</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>annotations</artifactId>
+      <groupId>org.jetbrains</groupId>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <groupId>net.md-5</groupId>
+        <artifactId>specialsource-maven-plugin</artifactId>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>

internal/v1_20_R3/src/main/java/com/lishid/openinv/internal/v1_20_R3/AnySilentContainer.java

@@ -0,0 +1,208 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R3;
+
+import com.lishid.openinv.internal.AnySilentContainerBase;
+import com.lishid.openinv.util.ReflectionHelper;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.core.BlockPos;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.level.ServerPlayerGameMode;
+import net.minecraft.world.MenuProvider;
+import net.minecraft.world.SimpleMenuProvider;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.PlayerEnderChestContainer;
+import net.minecraft.world.level.GameType;
+import net.minecraft.world.level.block.BarrelBlock;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.ChestBlock;
+import net.minecraft.world.level.block.ShulkerBoxBlock;
+import net.minecraft.world.level.block.TrappedChestBlock;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.entity.EnderChestBlockEntity;
+import net.minecraft.world.level.block.entity.RandomizableContainerBlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+import org.bukkit.GameMode;
+import org.bukkit.Material;
+import org.bukkit.Statistic;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.logging.Logger;
+
+public class AnySilentContainer extends AnySilentContainerBase {
+
+    private final @NotNull Logger logger;
+    private final @NotNull LanguageManager lang;
+    private @Nullable Field serverPlayerGameModeGameType;
+
+    public AnySilentContainer(@NotNull Logger logger, @NotNull LanguageManager lang) {
+        this.logger = logger;
+        this.lang = lang;
+        try {
+            try {
+                this.serverPlayerGameModeGameType = ServerPlayerGameMode.class.getDeclaredField("b");
+                this.serverPlayerGameModeGameType.setAccessible(true);
+            } catch (NoSuchFieldException e) {
+                logger.warning("ServerPlayerGameMode#gameModeForPlayer's obfuscated name has changed!");
+                logger.warning("Please report this at https://github.com/Jikoo/OpenInv/issues");
+                logger.warning("Attempting to fall through using reflection. Please verify that SilentContainer does not fail.");
+                // N.B. gameModeForPlayer is (for now) declared before previousGameModeForPlayer so silent shouldn't break.
+                this.serverPlayerGameModeGameType = ReflectionHelper.grabFieldByType(ServerPlayerGameMode.class, GameType.class);
+            }
+        } catch (SecurityException e) {
+            logger.warning("Unable to directly write player game mode! SilentContainer will fail.");
+            logger.log(java.util.logging.Level.WARNING, "Error obtaining GameType field", e);
+        }
+    }
+
+    @Override
+    public boolean activateContainer(
+            @NotNull final Player bukkitPlayer,
+            final boolean silentchest,
+            @NotNull final org.bukkit.block.Block bukkitBlock) {
+
+        // Silent ender chest is API-only
+        if (silentchest && bukkitBlock.getType() == Material.ENDER_CHEST) {
+            bukkitPlayer.openInventory(bukkitPlayer.getEnderChest());
+            bukkitPlayer.incrementStatistic(Statistic.ENDERCHEST_OPENED);
+            return true;
+        }
+
+        ServerPlayer player = PlayerManager.getHandle(bukkitPlayer);
+
+        final net.minecraft.world.level.Level level = player.level();
+        final BlockPos blockPos = new BlockPos(bukkitBlock.getX(), bukkitBlock.getY(), bukkitBlock.getZ());
+        final BlockEntity blockEntity = level.getBlockEntity(blockPos);
+
+        if (blockEntity == null) {
+            return false;
+        }
+
+        if (blockEntity instanceof EnderChestBlockEntity enderChestTile) {
+            // Anychest ender chest. See net.minecraft.world.level.block.EnderChestBlock
+            PlayerEnderChestContainer enderChest = player.getEnderChestInventory();
+            enderChest.setActiveChest(enderChestTile);
+            player.openMenu(new SimpleMenuProvider((containerCounter, playerInventory, ignored) -> {
+                MenuType<?> containers = PlayerManager.getContainers(enderChest.getContainerSize());
+                int rows = enderChest.getContainerSize() / 9;
+                return new ChestMenu(containers, containerCounter, playerInventory, enderChest, rows);
+            }, Component.translatable("container.enderchest")));
+            bukkitPlayer.incrementStatistic(Statistic.ENDERCHEST_OPENED);
+            return true;
+        }
+
+        if (!(blockEntity instanceof MenuProvider menuProvider)) {
+            return false;
+        }
+
+        BlockState blockState = level.getBlockState(blockPos);
+        Block block = blockState.getBlock();
+
+        if (block instanceof ChestBlock chestBlock) {
+
+            // boolean flag: do not check if chest is blocked
+            menuProvider = chestBlock.getMenuProvider(blockState, level, blockPos, true);
+
+            if (menuProvider == null) {
+                lang.sendSystemMessage(bukkitPlayer, "messages.error.lootNotGenerated");
+                return false;
+            }
+
+            if (block instanceof TrappedChestBlock) {
+                bukkitPlayer.incrementStatistic(Statistic.TRAPPED_CHEST_TRIGGERED);
+            } else {
+                bukkitPlayer.incrementStatistic(Statistic.CHEST_OPENED);
+            }
+        }
+
+        if (block instanceof ShulkerBoxBlock) {
+            bukkitPlayer.incrementStatistic(Statistic.SHULKER_BOX_OPENED);
+        }
+
+        if (block instanceof BarrelBlock) {
+            bukkitPlayer.incrementStatistic(Statistic.OPEN_BARREL);
+        }
+
+        // AnyChest only - SilentChest not active, container unsupported, or unnecessary.
+        if (!silentchest || player.gameMode.getGameModeForPlayer() == GameType.SPECTATOR) {
+            player.openMenu(menuProvider);
+            return true;
+        }
+
+        // SilentChest requires access to setting players' game mode directly.
+        if (this.serverPlayerGameModeGameType == null) {
+            return false;
+        }
+
+        if (blockEntity instanceof RandomizableContainerBlockEntity lootable) {
+            if (lootable.lootTable != null) {
+                lang.sendSystemMessage(bukkitPlayer, "messages.error.lootNotGenerated");
+                return false;
+            }
+        }
+
+        GameType gameType = player.gameMode.getGameModeForPlayer();
+        this.forceGameType(player, GameType.SPECTATOR);
+        player.openMenu(menuProvider);
+        this.forceGameType(player, gameType);
+        return true;
+    }
+
+    @Override
+    public void deactivateContainer(@NotNull final Player bukkitPlayer) {
+        if (this.serverPlayerGameModeGameType == null || bukkitPlayer.getGameMode() == GameMode.SPECTATOR) {
+            return;
+        }
+
+        ServerPlayer player = PlayerManager.getHandle(bukkitPlayer);
+
+        // Force game mode change without informing plugins or players.
+        // Regular game mode set calls GameModeChangeEvent and is cancellable.
+        GameType gameType = player.gameMode.getGameModeForPlayer();
+        this.forceGameType(player, GameType.SPECTATOR);
+
+        // ServerPlayer#closeContainer cannot be called without entering an
+        // infinite loop because this method is called during inventory close.
+        // From ServerPlayer#closeContainer -> CraftEventFactory#handleInventoryCloseEvent
+        player.containerMenu.transferTo(player.inventoryMenu, player.getBukkitEntity());
+        // From ServerPlayer#closeContainer
+        player.doCloseContainer();
+        // Regular inventory close will handle the rest - packet sending, etc.
+
+        // Revert forced game mode.
+        this.forceGameType(player, gameType);
+    }
+
+    private void forceGameType(final ServerPlayer player, final GameType gameMode) {
+        if (this.serverPlayerGameModeGameType == null) {
+            // No need to warn repeatedly, error on startup and lack of function should be enough.
+            return;
+        }
+        try {
+            this.serverPlayerGameModeGameType.setAccessible(true);
+            this.serverPlayerGameModeGameType.set(player.gameMode, gameMode);
+        } catch (IllegalArgumentException | IllegalAccessException e) {
+            logger.log(java.util.logging.Level.WARNING, "Error bypassing GameModeChangeEvent", e);
+        }
+    }
+
+}

internal/v1_20_R3/src/main/java/com/lishid/openinv/internal/v1_20_R3/InternalAccessor.java

@@ -0,0 +1,64 @@
+package com.lishid.openinv.internal.v1_20_R3;
+
+import com.lishid.openinv.internal.Accessor;
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.world.Container;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.craftbukkit.v1_20_R3.inventory.CraftInventory;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.logging.Logger;
+
+public class InternalAccessor implements Accessor {
+
+  private final @NotNull PlayerManager manager;
+  private final @NotNull AnySilentContainer anySilentContainer;
+
+  public InternalAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
+    manager = new PlayerManager(logger, lang);
+    anySilentContainer = new AnySilentContainer(logger, lang);
+  }
+
+  @Override
+  public @NotNull PlayerManager getPlayerManager() {
+    return manager;
+  }
+
+  @Override
+  public @NotNull IAnySilentContainer getAnySilentContainer() {
+    return anySilentContainer;
+  }
+
+  @Override
+  public @NotNull ISpecialPlayerInventory createPlayerInventory(@NotNull Player player) {
+    return new SpecialPlayerInventory(player, player.isOnline());
+  }
+
+  @Override
+  public @NotNull ISpecialEnderChest createEnderChest(@NotNull Player player) {
+    return new SpecialEnderChest(player, player.isOnline());
+  }
+
+  @Override
+  public <T extends ISpecialInventory> @Nullable T get(@NotNull Inventory bukkitInventory, @NotNull Class<T> clazz) {
+    if (!(bukkitInventory instanceof CraftInventory craftInventory)) {
+      return null;
+    }
+    Container container = craftInventory.getInventory();
+    if (clazz.isInstance(container)) {
+      return clazz.cast(container);
+    }
+    return null;
+  }
+
+  @Override
+  public void reload(@NotNull ConfigurationSection config) {}
+
+}

internal/v1_20_R3/src/main/java/com/lishid/openinv/internal/v1_20_R3/OpenPlayer.java

@@ -0,0 +1,184 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R3;
+
+import com.lishid.openinv.event.OpenEvents;
+import com.mojang.logging.LogUtils;
+import net.minecraft.Util;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.nbt.NumericTag;
+import net.minecraft.nbt.Tag;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.storage.PlayerDataStorage;
+import org.bukkit.craftbukkit.v1_20_R3.CraftServer;
+import org.bukkit.craftbukkit.v1_20_R3.entity.CraftPlayer;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Set;
+
+public class OpenPlayer extends CraftPlayer {
+
+    private static final Set<String> RESET_TAGS = Set.of(
+        // net.minecraft.world.Entity#saveWithoutId(CompoundTag)
+        "CustomName",
+        "CustomNameVisible",
+        "Silent",
+        "NoGravity",
+        "Glowing",
+        "TicksFrozen",
+        "HasVisualFire",
+        "Tags",
+        "Passengers",
+        // net.minecraft.server.level.ServerPlayer#addAdditionalSaveData(CompoundTag)
+        // Intentional omissions to prevent mount loss: Attach, Entity, and RootVehicle
+        "warden_spawn_tracker",
+        "enteredNetherPosition",
+        "SpawnX",
+        "SpawnY",
+        "SpawnZ",
+        "SpawnForced",
+        "SpawnAngle",
+        "SpawnDimension",
+        // net.minecraft.world.entity.player.Player#addAdditionalSaveData(CompoundTag)
+        "ShoulderEntityLeft",
+        "ShoulderEntityRight",
+        "LastDeathLocation",
+        // net.minecraft.world.entity.LivingEntity#addAdditionalSaveData(CompoundTag)
+        "ActiveEffects", // Backwards compat: Renamed from 1.19
+        "active_effects",
+        "SleepingX",
+        "SleepingY",
+        "SleepingZ",
+        "Brain"
+    );
+
+    private final PlayerManager manager;
+
+    OpenPlayer(CraftServer server, ServerPlayer entity, PlayerManager manager) {
+        super(server, entity);
+        this.manager = manager;
+    }
+
+    @Override
+    public void loadData() {
+        manager.loadData(getHandle());
+    }
+
+    @Override
+    public void saveData() {
+        if (OpenEvents.saveCancelled(this)) {
+            return;
+        }
+
+        ServerPlayer player = this.getHandle();
+        // See net.minecraft.world.level.storage.PlayerDataStorage#save(EntityHuman)
+        try {
+            PlayerDataStorage worldNBTStorage = player.server.getPlayerList().playerIo;
+
+            CompoundTag oldData = isOnline() ? null : worldNBTStorage.getPlayerData(player.getStringUUID());
+            CompoundTag playerData = getWritableTag(oldData);
+            playerData = player.saveWithoutId(playerData);
+            setExtraData(playerData);
+
+            if (oldData != null) {
+                // Revert certain special data values when offline.
+                revertSpecialValues(playerData, oldData);
+            }
+
+            Path playerDataDir = worldNBTStorage.getPlayerDir().toPath();
+            Path file = Files.createTempFile(playerDataDir, player.getStringUUID() + "-", ".dat");
+            NbtIo.writeCompressed(playerData, file);
+            Path dataFile = playerDataDir.resolve(player.getStringUUID() + ".dat");
+            Path backupFile = playerDataDir.resolve(player.getStringUUID() + ".dat_old");
+            Util.safeReplaceFile(dataFile, file, backupFile);
+        } catch (Exception e) {
+            LogUtils.getLogger().warn("Failed to save player data for {}: {}", player.getScoreboardName(), e);
+        }
+    }
+
+    @Contract("null -> new")
+    private @NotNull CompoundTag getWritableTag(@Nullable CompoundTag oldData) {
+        if (oldData == null) {
+            return new CompoundTag();
+        }
+
+        // Copy old data. This is a deep clone, so operating on it should be safe.
+        oldData = oldData.copy();
+
+        // Remove vanilla/server data that is not written every time.
+        oldData.getAllKeys()
+            .removeIf(key -> RESET_TAGS.contains(key) || key.startsWith("Bukkit"));
+
+        return oldData;
+    }
+
+    private void revertSpecialValues(@NotNull CompoundTag newData, @NotNull CompoundTag oldData) {
+        // Revert automatic updates to play timestamps.
+        copyValue(oldData, newData, "bukkit", "lastPlayed", NumericTag.class);
+        copyValue(oldData, newData, "Paper", "LastSeen", NumericTag.class);
+        copyValue(oldData, newData, "Paper", "LastLogin", NumericTag.class);
+    }
+
+    private <T extends Tag> void copyValue(
+        @NotNull CompoundTag source,
+        @NotNull CompoundTag target,
+        @NotNull String container,
+        @NotNull String key,
+        @NotNull Class<T> tagType) {
+        CompoundTag oldContainer = getTag(source, container, CompoundTag.class);
+        CompoundTag newContainer = getTag(target, container, CompoundTag.class);
+
+        // New container being null means the server implementation doesn't store this data.
+        if (newContainer == null) {
+            return;
+        }
+
+        // If old tag exists, copy it to new location, removing otherwise.
+        setTag(newContainer, key, getTag(oldContainer, key, tagType));
+    }
+
+    private <T extends Tag> @Nullable T getTag(
+        @Nullable CompoundTag container,
+        @NotNull String key,
+        @NotNull Class<T> dataType) {
+        if (container == null) {
+            return null;
+        }
+        Tag value = container.get(key);
+        if (value == null || !dataType.isAssignableFrom(value.getClass())) {
+            return null;
+        }
+        return dataType.cast(value);
+    }
+
+    private <T extends Tag> void setTag(
+        @NotNull CompoundTag container,
+        @NotNull String key,
+        @Nullable T data) {
+        if (data == null) {
+            container.remove(key);
+        } else {
+            container.put(key, data);
+        }
+    }
+
+}

internal/v1_20_R3/src/main/java/com/lishid/openinv/internal/v1_20_R3/PlayerManager.java

@@ -0,0 +1,292 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R3;
+
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.InventoryViewTitle;
+import com.lishid.openinv.internal.OpenInventoryView;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.mojang.authlib.GameProfile;
+import com.mojang.serialization.Dynamic;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtOps;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.protocol.game.ClientboundOpenScreenPacket;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ClientInformation;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.player.ChatVisiblity;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.dimension.DimensionType;
+import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.Server;
+import org.bukkit.World;
+import org.bukkit.craftbukkit.v1_20_R3.CraftServer;
+import org.bukkit.craftbukkit.v1_20_R3.CraftWorld;
+import org.bukkit.craftbukkit.v1_20_R3.entity.CraftPlayer;
+import org.bukkit.craftbukkit.v1_20_R3.event.CraftEventFactory;
+import org.bukkit.craftbukkit.v1_20_R3.inventory.CraftContainer;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.UUID;
+import java.util.logging.Logger;
+
+public class PlayerManager implements com.lishid.openinv.internal.PlayerManager {
+
+    private static boolean paper;
+
+    static {
+        try {
+            Class.forName("io.papermc.paper.configuration.Configuration");
+            paper = true;
+        } catch (ClassNotFoundException ignored) {
+            paper = false;
+        }
+    }
+
+    private final @NotNull Logger logger;
+    private final @NotNull LanguageManager lang;
+    private @Nullable Field bukkitEntity;
+
+    public PlayerManager(@NotNull Logger logger, @NotNull LanguageManager lang) {
+        this.logger = logger;
+        this.lang = lang;
+        try {
+            bukkitEntity = Entity.class.getDeclaredField("bukkitEntity");
+        } catch (NoSuchFieldException e) {
+            logger.warning("Unable to obtain field to inject custom save process - certain player data may be lost when saving!");
+            logger.log(java.util.logging.Level.WARNING, e.getMessage(), e);
+            bukkitEntity = null;
+        }
+    }
+
+    public static @NotNull ServerPlayer getHandle(final Player player) {
+        if (player instanceof CraftPlayer) {
+            return ((CraftPlayer) player).getHandle();
+        }
+
+        Server server = player.getServer();
+        ServerPlayer nmsPlayer = null;
+
+        if (server instanceof CraftServer) {
+            nmsPlayer = ((CraftServer) server).getHandle().getPlayer(player.getUniqueId());
+        }
+
+        if (nmsPlayer == null) {
+            // Could use reflection to examine fields, but it's honestly not worth the bother.
+            throw new RuntimeException("Unable to fetch EntityPlayer from Player implementation " + player.getClass().getName());
+        }
+
+        return nmsPlayer;
+    }
+
+    @Override
+    public @Nullable Player loadPlayer(@NotNull final OfflinePlayer offline) {
+        MinecraftServer server = ((CraftServer) Bukkit.getServer()).getServer();
+        ServerLevel worldServer = server.getLevel(Level.OVERWORLD);
+
+        if (worldServer == null) {
+            return null;
+        }
+
+        // Create a new ServerPlayer.
+        ServerPlayer entity = createNewPlayer(server, worldServer, offline);
+
+        // Stop listening for advancement progression - if this is not cleaned up, loading causes a memory leak.
+        entity.getAdvancements().stopListening();
+
+        // Try to load the player's data.
+        if (loadData(entity)) {
+            // If data is loaded successfully, return the Bukkit entity.
+            return entity.getBukkitEntity();
+        }
+
+        return null;
+    }
+
+    private @NotNull ServerPlayer createNewPlayer(
+        @NotNull MinecraftServer server,
+        @NotNull ServerLevel worldServer,
+        @NotNull final OfflinePlayer offline) {
+        // See net.minecraft.server.players.PlayerList#canPlayerLogin(ServerLoginPacketListenerImpl, GameProfile)
+        // See net.minecraft.server.network.ServerLoginPacketListenerImpl#handleHello(ServerboundHelloPacket)
+        GameProfile profile = new GameProfile(offline.getUniqueId(),
+            offline.getName() != null ? offline.getName() : offline.getUniqueId().toString());
+
+        ClientInformation dummyInfo = new ClientInformation(
+            "en_us",
+            1, // Reduce distance just in case.
+            ChatVisiblity.HIDDEN, // Don't accept chat.
+            false,
+            ServerPlayer.DEFAULT_MODEL_CUSTOMIZATION,
+            ServerPlayer.DEFAULT_MAIN_HAND,
+            true,
+            false // Don't list in player list (not that this player is in the list anyway).
+        );
+
+        ServerPlayer entity = new ServerPlayer(server, worldServer, profile, dummyInfo);
+
+        try {
+            injectPlayer(entity);
+        } catch (IllegalAccessException e) {
+            logger.log(
+                java.util.logging.Level.WARNING,
+                e,
+                () -> "Unable to inject ServerPlayer, certain player data may be lost when saving!");
+        }
+
+        return entity;
+    }
+
+    boolean loadData(@NotNull ServerPlayer player) {
+        // See CraftPlayer#loadData
+        CompoundTag loadedData = player.server.getPlayerList().playerIo.load(player);
+
+        if (loadedData == null) {
+            // Exceptions with loading are logged by Mojang.
+            return false;
+        }
+
+        // Read basic data into the player.
+        player.load(loadedData);
+        // Also read "extra" data.
+        player.readAdditionalSaveData(loadedData);
+        // Game type settings are also loaded separately.
+        player.loadGameTypes(loadedData);
+
+        if (paper) {
+            // Paper: world is not loaded by ServerPlayer#load(CompoundTag).
+            parseWorld(player, loadedData);
+        }
+
+        return true;
+    }
+
+    private void parseWorld(@NotNull ServerPlayer player, @NotNull CompoundTag loadedData) {
+        // See PlayerList#placeNewPlayer
+        World bukkitWorld;
+        if (loadedData.contains("WorldUUIDMost") && loadedData.contains("WorldUUIDLeast")) {
+            // Modern Bukkit world.
+            bukkitWorld = Bukkit.getServer().getWorld(new UUID(loadedData.getLong("WorldUUIDMost"), loadedData.getLong("WorldUUIDLeast")));
+        } else if (loadedData.contains("world", net.minecraft.nbt.Tag.TAG_STRING)) {
+            // Legacy Bukkit world.
+            bukkitWorld = Bukkit.getServer().getWorld(loadedData.getString("world"));
+        } else {
+            // Vanilla player data.
+            DimensionType.parseLegacy(new Dynamic<>(NbtOps.INSTANCE, loadedData.get("Dimension")))
+                .resultOrPartial(logger::warning)
+                .map(player.server::getLevel)
+                // If ServerLevel exists, set, otherwise move to spawn.
+                .ifPresentOrElse(player::setServerLevel, () -> player.spawnIn(null));
+            return;
+        }
+        if (bukkitWorld == null) {
+            player.spawnIn(null);
+            return;
+        }
+        player.setServerLevel(((CraftWorld) bukkitWorld).getHandle());
+    }
+
+    private void injectPlayer(ServerPlayer player) throws IllegalAccessException {
+        if (bukkitEntity == null) {
+            return;
+        }
+
+        bukkitEntity.setAccessible(true);
+
+        bukkitEntity.set(player, new OpenPlayer(player.server.server, player, this));
+    }
+
+    @Override
+    public @NotNull Player inject(@NotNull Player player) {
+        try {
+            ServerPlayer nmsPlayer = getHandle(player);
+            if (nmsPlayer.getBukkitEntity() instanceof OpenPlayer openPlayer) {
+                return openPlayer;
+            }
+            injectPlayer(nmsPlayer);
+            return nmsPlayer.getBukkitEntity();
+        } catch (IllegalAccessException e) {
+            logger.log(
+                java.util.logging.Level.WARNING,
+                e,
+                () -> "Unable to inject ServerPlayer, certain player data may be lost when saving!");
+            return player;
+        }
+    }
+
+    @Override
+    public @Nullable InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory, boolean viewOnly) {
+
+        ServerPlayer nmsPlayer = getHandle(player);
+
+        if (nmsPlayer.connection == null) {
+            return null;
+        }
+
+        InventoryViewTitle title = InventoryViewTitle.of(inventory);
+
+        if (title == null) {
+            return player.openInventory(inventory.getBukkitInventory());
+        }
+
+        InventoryView view = new OpenInventoryView(player, inventory, title.getTitle(lang, player, inventory));
+        AbstractContainerMenu container = new CraftContainer(view, nmsPlayer, nmsPlayer.nextContainerCounter()) {
+            @Override
+            public MenuType<?> getType() {
+                return getContainers(inventory.getBukkitInventory().getSize());
+            }
+        };
+
+        container.setTitle(Component.literal(view.getOriginalTitle()));
+        container = CraftEventFactory.callInventoryOpenEvent(nmsPlayer, container);
+
+        if (container == null) {
+            return null;
+        }
+
+        nmsPlayer.connection.send(new ClientboundOpenScreenPacket(container.containerId, container.getType(),
+                Component.literal(container.getBukkitView().getTitle())));
+        nmsPlayer.containerMenu = container;
+        nmsPlayer.initMenu(container);
+
+        return container.getBukkitView();
+
+    }
+
+    static @NotNull MenuType<?> getContainers(int inventorySize) {
+
+        return switch (inventorySize) {
+            case 9 -> MenuType.GENERIC_9x1;
+            case 18 -> MenuType.GENERIC_9x2;
+            case 36 -> MenuType.GENERIC_9x4; // PLAYER
+            case 41, 45 -> MenuType.GENERIC_9x5;
+            case 54 -> MenuType.GENERIC_9x6;
+            default -> MenuType.GENERIC_9x3; // Default 27-slot inventory
+        };
+    }
+
+}

internal/v1_20_R3/src/main/java/com/lishid/openinv/internal/v1_20_R3/SpecialEnderChest.java

@@ -0,0 +1,351 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R3;
+
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import net.minecraft.core.NonNullList;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.ContainerListener;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.entity.player.StackedContents;
+import net.minecraft.world.inventory.PlayerEnderChestContainer;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.level.block.entity.EnderChestBlockEntity;
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.v1_20_R3.entity.CraftHumanEntity;
+import org.bukkit.craftbukkit.v1_20_R3.inventory.CraftInventory;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.InventoryHolder;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class SpecialEnderChest extends PlayerEnderChestContainer implements ISpecialEnderChest {
+
+    private final CraftInventory inventory;
+    private ServerPlayer owner;
+    private NonNullList<ItemStack> items;
+    private boolean playerOnline;
+
+    public SpecialEnderChest(final org.bukkit.entity.Player player, final Boolean online) {
+        super(PlayerManager.getHandle(player));
+        this.inventory = new CraftInventory(this);
+        this.owner = PlayerManager.getHandle(player);
+        this.playerOnline = online;
+        this.items = this.owner.getEnderChestInventory().items;
+    }
+
+    @Override
+    public @NotNull CraftInventory getBukkitInventory() {
+        return inventory;
+    }
+
+    @Override
+    public void setPlayerOffline() {
+        this.playerOnline = false;
+    }
+
+    @Override
+    public void setPlayerOnline(@NotNull final org.bukkit.entity.Player player) {
+        if (this.playerOnline) {
+            return;
+        }
+
+        ServerPlayer offlinePlayer = this.owner;
+        ServerPlayer onlinePlayer = PlayerManager.getHandle(player);
+
+        // Set owner to new player.
+        this.owner = onlinePlayer;
+
+        // Set player's ender chest contents to our modified contents.
+        PlayerEnderChestContainer onlineEnderChest = onlinePlayer.getEnderChestInventory();
+        for (int i = 0; i < onlineEnderChest.getContainerSize(); ++i) {
+            onlineEnderChest.setItem(i, this.items.get(i));
+        }
+
+        // Set our item array to the new inventory's array.
+        this.items = onlineEnderChest.items;
+
+        // Add viewers to new inventory.
+        onlineEnderChest.transaction.addAll(offlinePlayer.getEnderChestInventory().transaction);
+
+        this.playerOnline = true;
+    }
+
+    @Override
+    public @NotNull org.bukkit.entity.Player getPlayer() {
+        return owner.getBukkitEntity();
+    }
+
+    @Override
+    public void setChanged() {
+        this.owner.getEnderChestInventory().setChanged();
+    }
+
+    @Override
+    public List<ItemStack> getContents() {
+        return this.items;
+    }
+
+    @Override
+    public void onOpen(CraftHumanEntity who) {
+        this.owner.getEnderChestInventory().onOpen(who);
+    }
+
+    @Override
+    public void onClose(CraftHumanEntity who) {
+        this.owner.getEnderChestInventory().onClose(who);
+    }
+
+    @Override
+    public List<HumanEntity> getViewers() {
+        return this.owner.getEnderChestInventory().getViewers();
+    }
+
+    @Override
+    public boolean stillValid(Player player) {
+        return true;
+    }
+
+    @Override
+    public void setActiveChest(EnderChestBlockEntity enderChest) {
+        this.owner.getEnderChestInventory().setActiveChest(enderChest);
+    }
+
+    @Override
+    public boolean isActiveChest(EnderChestBlockEntity enderChest) {
+        return this.owner.getEnderChestInventory().isActiveChest(enderChest);
+    }
+
+    @Override
+    public int getMaxStackSize() {
+        return this.owner.getEnderChestInventory().getMaxStackSize();
+    }
+
+    @Override
+    public void setMaxStackSize(int i) {
+        this.owner.getEnderChestInventory().setMaxStackSize(i);
+    }
+
+    @Override
+    public InventoryHolder getOwner() {
+        return this.owner.getEnderChestInventory().getOwner();
+    }
+
+    @Override
+    public @Nullable Location getLocation() {
+        return null;
+    }
+
+    @Override
+    public void addListener(ContainerListener listener) {
+        this.owner.getEnderChestInventory().addListener(listener);
+    }
+
+    @Override
+    public void removeListener(ContainerListener listener) {
+        this.owner.getEnderChestInventory().removeListener(listener);
+    }
+
+    @Override
+    public ItemStack getItem(int i) {
+        return i >= 0 && i < this.items.size() ? this.items.get(i) : ItemStack.EMPTY;
+    }
+
+    @Override
+    public ItemStack removeItem(int i, int j) {
+        ItemStack itemstack = ContainerHelper.removeItem(this.items, i, j);
+        if (!itemstack.isEmpty()) {
+            this.setChanged();
+        }
+
+        return itemstack;
+    }
+
+    @Override
+    public ItemStack addItem(ItemStack itemstack) {
+        ItemStack localItem = itemstack.copy();
+        this.moveItemToOccupiedSlotsWithSameType(localItem);
+        if (localItem.isEmpty()) {
+            return ItemStack.EMPTY;
+        } else {
+            this.moveItemToEmptySlots(localItem);
+            return localItem.isEmpty() ? ItemStack.EMPTY : localItem;
+        }
+    }
+
+    @Override
+    public boolean canAddItem(ItemStack itemstack) {
+        for (ItemStack itemstack1 : this.items) {
+            if (itemstack1.isEmpty() || (ItemStack.isSameItemSameTags(itemstack1, itemstack) && itemstack1.getCount() < itemstack1.getMaxStackSize())) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private void moveItemToEmptySlots(ItemStack itemstack) {
+        for(int i = 0; i < this.getContainerSize(); ++i) {
+            ItemStack localItem = this.getItem(i);
+            if (localItem.isEmpty()) {
+                this.setItem(i, itemstack.copy());
+                itemstack.setCount(0);
+                return;
+            }
+        }
+    }
+
+    private void moveItemToOccupiedSlotsWithSameType(ItemStack itemstack) {
+        for(int i = 0; i < this.getContainerSize(); ++i) {
+            ItemStack localItem = this.getItem(i);
+            if (ItemStack.isSameItemSameTags(localItem, itemstack)) {
+                this.moveItemsBetweenStacks(itemstack, localItem);
+                if (itemstack.isEmpty()) {
+                    return;
+                }
+            }
+        }
+    }
+
+    private void moveItemsBetweenStacks(ItemStack itemstack, ItemStack itemstack1) {
+        int i = Math.min(this.getMaxStackSize(), itemstack1.getMaxStackSize());
+        int j = Math.min(itemstack.getCount(), i - itemstack1.getCount());
+        if (j > 0) {
+            itemstack1.grow(j);
+            itemstack.shrink(j);
+            this.setChanged();
+        }
+    }
+
+    @Override
+    public ItemStack removeItemNoUpdate(int i) {
+        ItemStack itemstack = this.items.get(i);
+        if (itemstack.isEmpty()) {
+            return ItemStack.EMPTY;
+        } else {
+            this.items.set(i, ItemStack.EMPTY);
+            return itemstack;
+        }
+    }
+
+    @Override
+    public void setItem(int i, ItemStack itemstack) {
+        this.items.set(i, itemstack);
+        if (!itemstack.isEmpty() && itemstack.getCount() > this.getMaxStackSize()) {
+            itemstack.setCount(this.getMaxStackSize());
+        }
+
+        this.setChanged();
+    }
+
+    @Override
+    public int getContainerSize() {
+        return this.owner.getEnderChestInventory().getContainerSize();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return this.items.stream().allMatch(ItemStack::isEmpty);
+    }
+
+    @Override
+    public void startOpen(Player player) {
+    }
+
+    @Override
+    public void stopOpen(Player player) {
+    }
+
+    @Override
+    public boolean canPlaceItem(int i, ItemStack itemstack) {
+        return true;
+    }
+
+    @Override
+    public void clearContent() {
+        this.items.clear();
+        this.setChanged();
+    }
+
+    @Override
+    public void fillStackedContents(StackedContents stackedContents) {
+        for (ItemStack itemstack : this.items) {
+            stackedContents.accountStack(itemstack);
+        }
+
+    }
+
+    @Override
+    public List<ItemStack> removeAllItems() {
+        List<ItemStack> list = this.items.stream().filter(Predicate.not(ItemStack::isEmpty)).collect(Collectors.toList());
+        this.clearContent();
+        return list;
+    }
+
+    @Override
+    public ItemStack removeItemType(Item item, int i) {
+        ItemStack itemstack = new ItemStack(item, 0);
+
+        for(int j = this.getContainerSize() - 1; j >= 0; --j) {
+            ItemStack localItem = this.getItem(j);
+            if (localItem.getItem().equals(item)) {
+                int k = i - itemstack.getCount();
+                ItemStack splitItem = localItem.split(k);
+                itemstack.grow(splitItem.getCount());
+                if (itemstack.getCount() == i) {
+                    break;
+                }
+            }
+        }
+
+        if (!itemstack.isEmpty()) {
+            this.setChanged();
+        }
+
+        return itemstack;
+    }
+
+    @Override
+    public String toString() {
+        return this.items.stream().filter((itemStack) -> !itemStack.isEmpty()).toList().toString();
+    }
+
+    @Override
+    public void fromTag(ListTag listTag) {
+        for (int i = 0; i < this.getContainerSize(); ++i) {
+            this.setItem(i, ItemStack.EMPTY);
+        }
+
+        for (int i = 0; i < listTag.size(); ++i) {
+            CompoundTag compoundTag = listTag.getCompound(i);
+            int j = compoundTag.getByte("Slot") & 255;
+            if (j < this.getContainerSize()) {
+                this.setItem(j, ItemStack.of(compoundTag));
+            }
+        }
+
+    }
+
+}

internal/v1_20_R3/src/main/java/com/lishid/openinv/internal/v1_20_R3/SpecialPlayerInventory.java

@@ -0,0 +1,807 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R3;
+
+import com.google.common.collect.ImmutableList;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import net.minecraft.CrashReport;
+import net.minecraft.CrashReportCategory;
+import net.minecraft.ReportedException;
+import net.minecraft.core.NonNullList;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.protocol.game.ClientboundContainerSetSlotPacket;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.tags.DamageTypeTags;
+import net.minecraft.tags.TagKey;
+import net.minecraft.world.Container;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.damagesource.DamageSource;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Inventory;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.entity.player.StackedContents;
+import net.minecraft.world.item.ArmorItem;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.level.block.state.BlockState;
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.v1_20_R3.entity.CraftHumanEntity;
+import org.bukkit.craftbukkit.v1_20_R3.inventory.CraftInventory;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.InventoryHolder;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class SpecialPlayerInventory extends Inventory implements ISpecialPlayerInventory {
+
+    private final CraftInventory inventory;
+    private boolean playerOnline;
+    private Player player;
+    private NonNullList<ItemStack> items;
+    private NonNullList<ItemStack> armor;
+    private NonNullList<ItemStack> offhand;
+    private List<NonNullList<ItemStack>> compartments;
+
+    public SpecialPlayerInventory(@NotNull org.bukkit.entity.Player bukkitPlayer, @NotNull Boolean online) {
+        super(PlayerManager.getHandle(bukkitPlayer));
+        this.inventory = new CraftInventory(this);
+        this.playerOnline = online;
+        this.player = super.player;
+        this.selected = player.getInventory().selected;
+        this.items = this.player.getInventory().items;
+        this.armor = this.player.getInventory().armor;
+        this.offhand = this.player.getInventory().offhand;
+        this.compartments = ImmutableList.of(this.items, this.armor, this.offhand);
+    }
+
+    @Override
+    public void setPlayerOnline(@NotNull org.bukkit.entity.Player player) {
+        if (this.playerOnline) {
+            return;
+        }
+
+        Player offlinePlayer = this.player;
+        Player onlinePlayer = PlayerManager.getHandle(player);
+        onlinePlayer.getInventory().transaction.addAll(this.transaction);
+
+        // Set owner to new player.
+        this.player = onlinePlayer;
+
+        // Set player's inventory contents to our modified contents.
+        Inventory onlineInventory = onlinePlayer.getInventory();
+        for (int i = 0; i < getContainerSize(); ++i) {
+            onlineInventory.setItem(i, getRawItem(i));
+        }
+        onlineInventory.selected = this.selected;
+
+        // Set our item arrays to the new inventory's arrays.
+        this.items = onlineInventory.items;
+        this.armor = onlineInventory.armor;
+        this.offhand = onlineInventory.offhand;
+        this.compartments = ImmutableList.of(this.items, this.armor, this.offhand);
+
+        // Add existing viewers to new viewer list.
+        Inventory offlineInventory = offlinePlayer.getInventory();
+        // Remove self from listing - player is always a viewer of their own inventory, prevent duplicates.
+        offlineInventory.transaction.remove(offlinePlayer.getBukkitEntity());
+        onlineInventory.transaction.addAll(offlineInventory.transaction);
+
+        this.playerOnline = true;
+    }
+
+    @Override
+    public @NotNull CraftInventory getBukkitInventory() {
+        return this.inventory;
+    }
+
+    @Override
+    public void setPlayerOffline() {
+        this.playerOnline = false;
+    }
+
+    @Override
+    public @NotNull HumanEntity getPlayer() {
+        return this.player.getBukkitEntity();
+    }
+
+    private @NotNull ItemStack getRawItem(int i) {
+        if (i < 0) {
+            return ItemStack.EMPTY;
+        }
+
+        NonNullList<ItemStack> list;
+        for (Iterator<NonNullList<ItemStack>> iterator = this.compartments.iterator(); iterator.hasNext(); i -= list.size()) {
+            list = iterator.next();
+            if (i < list.size()) {
+                return list.get(i);
+            }
+        }
+
+        return ItemStack.EMPTY;
+    }
+
+    private void setRawItem(int i, @NotNull ItemStack itemStack) {
+        if (i < 0) {
+            return;
+        }
+
+        NonNullList<ItemStack> list;
+        for (Iterator<NonNullList<ItemStack>> iterator = this.compartments.iterator(); iterator.hasNext(); i -= list.size()) {
+            list = iterator.next();
+            if (i < list.size()) {
+                list.set(i, itemStack);
+            }
+        }
+    }
+
+    private record IndexedCompartment(@Nullable NonNullList<ItemStack> compartment, int index) {}
+
+    private @NotNull SpecialPlayerInventory.IndexedCompartment getIndexedContent(int index) {
+        if (index < items.size()) {
+            return new IndexedCompartment(items, getReversedItemSlotNum(index));
+        }
+
+        index -= items.size();
+
+        if (index < armor.size()) {
+            return new IndexedCompartment(armor, getReversedArmorSlotNum(index));
+        }
+
+        index -= armor.size();
+
+        if (index < offhand.size()) {
+            return new IndexedCompartment(offhand, index);
+        }
+
+        index -= offhand.size();
+
+        return new IndexedCompartment(null, index);
+    }
+
+    private int getReversedArmorSlotNum(final int i) {
+        if (i == 0) {
+            return 3;
+        }
+        if (i == 1) {
+            return 2;
+        }
+        if (i == 2) {
+            return 1;
+        }
+        if (i == 3) {
+            return 0;
+        }
+        return i;
+    }
+
+    private int getReversedItemSlotNum(final int i) {
+        if (i >= 27) {
+            return i - 27;
+        }
+        return i + 9;
+    }
+
+    private boolean contains(Predicate<ItemStack> predicate) {
+        return this.compartments.stream().flatMap(NonNullList::stream).anyMatch(predicate);
+    }
+
+    @Override
+    public List<ItemStack> getArmorContents() {
+        return this.armor;
+    }
+
+    @Override
+    public void onOpen(CraftHumanEntity who) {
+        this.player.getInventory().onOpen(who);
+    }
+
+    @Override
+    public void onClose(CraftHumanEntity who) {
+        this.player.getInventory().onClose(who);
+    }
+
+    @Override
+    public List<HumanEntity> getViewers() {
+        return this.player.getInventory().getViewers();
+    }
+
+    @Override
+    public InventoryHolder getOwner() {
+        return this.player.getBukkitEntity();
+    }
+
+    @Override
+    public int getMaxStackSize() {
+        return this.player.getInventory().getMaxStackSize();
+    }
+
+    @Override
+    public void setMaxStackSize(int size) {
+        this.player.getInventory().setMaxStackSize(size);
+    }
+
+    @Override
+    public Location getLocation() {
+        return this.player.getBukkitEntity().getLocation();
+    }
+
+    @Override
+    public boolean hasCustomName() {
+        return false;
+    }
+
+    @Override
+    public List<ItemStack> getContents() {
+        return this.compartments.stream().flatMap(Collection::stream).collect(Collectors.toList());
+    }
+
+    @Override
+    public ItemStack getSelected() {
+        return isHotbarSlot(this.selected) ? this.items.get(this.selected) : ItemStack.EMPTY;
+    }
+
+    private boolean hasRemainingSpaceForItem(ItemStack itemstack, ItemStack itemstack1) {
+        return !itemstack.isEmpty() && ItemStack.isSameItemSameTags(itemstack, itemstack1) && itemstack.isStackable() && itemstack.getCount() < itemstack.getMaxStackSize() && itemstack.getCount() < this.getMaxStackSize();
+    }
+
+    @Override
+    public int canHold(ItemStack itemstack) {
+        int remains = itemstack.getCount();
+
+        for (int i = 0; i < this.items.size(); ++i) {
+            ItemStack itemstack1 = this.getRawItem(i);
+            if (itemstack1.isEmpty()) {
+                return itemstack.getCount();
+            }
+
+            if (this.hasRemainingSpaceForItem(itemstack1, itemstack)) {
+                remains -= (itemstack1.getMaxStackSize() < this.getMaxStackSize() ? itemstack1.getMaxStackSize() : this.getMaxStackSize()) - itemstack1.getCount();
+            }
+
+            if (remains <= 0) {
+                return itemstack.getCount();
+            }
+        }
+
+        ItemStack offhandItemStack = this.getRawItem(this.items.size() + this.armor.size());
+        if (this.hasRemainingSpaceForItem(offhandItemStack, itemstack)) {
+            remains -= (offhandItemStack.getMaxStackSize() < this.getMaxStackSize() ? offhandItemStack.getMaxStackSize() : this.getMaxStackSize()) - offhandItemStack.getCount();
+        }
+
+        return remains <= 0 ? itemstack.getCount() : itemstack.getCount() - remains;
+    }
+
+    @Override
+    public int getFreeSlot() {
+        for(int i = 0; i < this.items.size(); ++i) {
+            if (this.items.get(i).isEmpty()) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    @Override
+    public void setPickedItem(ItemStack itemstack) {
+        int i = this.findSlotMatchingItem(itemstack);
+        if (isHotbarSlot(i)) {
+            this.selected = i;
+        } else if (i == -1) {
+            this.selected = this.getSuitableHotbarSlot();
+            if (!this.items.get(this.selected).isEmpty()) {
+                int j = this.getFreeSlot();
+                if (j != -1) {
+                    this.items.set(j, this.items.get(this.selected));
+                }
+            }
+
+            this.items.set(this.selected, itemstack);
+        } else {
+            this.pickSlot(i);
+        }
+
+    }
+
+    @Override
+    public void pickSlot(int i) {
+        this.selected = this.getSuitableHotbarSlot();
+        ItemStack itemstack = this.items.get(this.selected);
+        this.items.set(this.selected, this.items.get(i));
+        this.items.set(i, itemstack);
+    }
+
+    @Override
+    public int findSlotMatchingItem(ItemStack itemstack) {
+        for(int i = 0; i < this.items.size(); ++i) {
+            if (!this.items.get(i).isEmpty() && ItemStack.isSameItemSameTags(itemstack, this.items.get(i))) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    @Override
+    public int findSlotMatchingUnusedItem(ItemStack itemStack) {
+        for(int i = 0; i < this.items.size(); ++i) {
+            ItemStack localItem = this.items.get(i);
+            if (!this.items.get(i).isEmpty() && ItemStack.isSameItemSameTags(itemStack, this.items.get(i)) && !this.items.get(i).isDamaged() && !localItem.isEnchanted() && !localItem.hasCustomHoverName()) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    @Override
+    public int getSuitableHotbarSlot() {
+        int i;
+        int j;
+        for(j = 0; j < 9; ++j) {
+            i = (this.selected + j) % 9;
+            if (this.items.get(i).isEmpty()) {
+                return i;
+            }
+        }
+
+        for(j = 0; j < 9; ++j) {
+            i = (this.selected + j) % 9;
+            if (!this.items.get(i).isEnchanted()) {
+                return i;
+            }
+        }
+
+        return this.selected;
+    }
+
+    @Override
+    public void swapPaint(double d0) {
+        if (d0 > 0.0D) {
+            d0 = 1.0D;
+        }
+
+        if (d0 < 0.0D) {
+            d0 = -1.0D;
+        }
+
+        this.selected = (int) (this.selected - d0);
+
+        while (this.selected < 0) {
+            this.selected += 9;
+        }
+
+        while(this.selected >= 9) {
+            this.selected -= 9;
+        }
+    }
+
+    @Override
+    public int clearOrCountMatchingItems(Predicate<ItemStack> predicate, int i, Container container) {
+        byte b0 = 0;
+        boolean flag = i == 0;
+        int j = b0 + ContainerHelper.clearOrCountMatchingItems(this, predicate, i - b0, flag);
+        j += ContainerHelper.clearOrCountMatchingItems(container, predicate, i - j, flag);
+        ItemStack itemstack = this.player.containerMenu.getCarried();
+        j += ContainerHelper.clearOrCountMatchingItems(itemstack, predicate, i - j, flag);
+        if (itemstack.isEmpty()) {
+            this.player.containerMenu.setCarried(ItemStack.EMPTY);
+        }
+
+        return j;
+    }
+
+    private int addResource(ItemStack itemstack) {
+        int i = this.getSlotWithRemainingSpace(itemstack);
+        if (i == -1) {
+            i = this.getFreeSlot();
+        }
+
+        return i == -1 ? itemstack.getCount() : this.addResource(i, itemstack);
+    }
+
+    private int addResource(int i, ItemStack itemstack) {
+        Item item = itemstack.getItem();
+        int j = itemstack.getCount();
+        ItemStack localItemStack = this.getRawItem(i);
+        if (localItemStack.isEmpty()) {
+            localItemStack = new ItemStack(item, 0);
+            if (itemstack.hasTag()) {
+                // hasTag ensures tag not null
+                //noinspection ConstantConditions
+                localItemStack.setTag(itemstack.getTag().copy());
+            }
+
+            this.setRawItem(i, localItemStack);
+        }
+
+        int k = Math.min(j, localItemStack.getMaxStackSize() - localItemStack.getCount());
+
+        if (k > this.getMaxStackSize() - localItemStack.getCount()) {
+            k = this.getMaxStackSize() - localItemStack.getCount();
+        }
+
+        if (k != 0) {
+            j -= k;
+            localItemStack.grow(k);
+            localItemStack.setPopTime(5);
+        }
+
+        return j;
+    }
+
+    @Override
+    public int getSlotWithRemainingSpace(ItemStack itemstack) {
+        if (this.hasRemainingSpaceForItem(this.getRawItem(this.selected), itemstack)) {
+            return this.selected;
+        } else if (this.hasRemainingSpaceForItem(this.getRawItem(40), itemstack)) {
+            return 40;
+        } else {
+            for(int i = 0; i < this.items.size(); ++i) {
+                if (this.hasRemainingSpaceForItem(this.items.get(i), itemstack)) {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+    }
+
+    @Override
+    public void tick() {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            for (int i = 0; i < compartment.size(); ++i) {
+                if (!compartment.get(i).isEmpty()) {
+                    compartment.get(i).inventoryTick(this.player.level(), this.player, i, this.selected == i);
+                }
+            }
+        }
+
+    }
+
+    @Override
+    public boolean add(ItemStack itemStack) {
+        return this.add(-1, itemStack);
+    }
+
+    @Override
+    public boolean add(int i, ItemStack itemStack) {
+        if (itemStack.isEmpty()) {
+            return false;
+        } else {
+            try {
+                if (itemStack.isDamaged()) {
+                    if (i == -1) {
+                        i = this.getFreeSlot();
+                    }
+
+                    if (i >= 0) {
+                        this.items.set(i, itemStack.copy());
+                        this.items.get(i).setPopTime(5);
+                        itemStack.setCount(0);
+                        return true;
+                    } else if (this.player.getAbilities().instabuild) {
+                        itemStack.setCount(0);
+                        return true;
+                    } else {
+                        return false;
+                    }
+                } else {
+                    int j;
+                    do {
+                        j = itemStack.getCount();
+                        if (i == -1) {
+                            itemStack.setCount(this.addResource(itemStack));
+                        } else {
+                            itemStack.setCount(this.addResource(i, itemStack));
+                        }
+                    } while(!itemStack.isEmpty() && itemStack.getCount() < j);
+
+                    if (itemStack.getCount() == j && this.player.getAbilities().instabuild) {
+                        itemStack.setCount(0);
+                        return true;
+                    } else {
+                        return itemStack.getCount() < j;
+                    }
+                }
+            } catch (Throwable var6) {
+                CrashReport crashReport = CrashReport.forThrowable(var6, "Adding item to inventory");
+                CrashReportCategory crashReportCategory = crashReport.addCategory("Item being added");
+                crashReportCategory.setDetail("Item ID", Item.getId(itemStack.getItem()));
+                crashReportCategory.setDetail("Item data", itemStack.getDamageValue());
+                crashReportCategory.setDetail("Item name", () -> itemStack.getHoverName().getString());
+                throw new ReportedException(crashReport);
+            }
+        }
+    }
+
+    @Override
+    public void placeItemBackInInventory(ItemStack itemStack) {
+        this.placeItemBackInInventory(itemStack, true);
+    }
+
+    @Override
+    public void placeItemBackInInventory(ItemStack itemStack, boolean flag) {
+        while(true) {
+            if (!itemStack.isEmpty()) {
+                int i = this.getSlotWithRemainingSpace(itemStack);
+                if (i == -1) {
+                    i = this.getFreeSlot();
+                }
+
+                if (i != -1) {
+                    int j = itemStack.getMaxStackSize() - this.getRawItem(i).getCount();
+                    if (this.add(i, itemStack.split(j)) && flag && this.player instanceof ServerPlayer) {
+                        ((ServerPlayer)this.player).connection.send(new ClientboundContainerSetSlotPacket(-2, 0, i, this.getRawItem(i)));
+                    }
+                    continue;
+                }
+
+                this.player.drop(itemStack, false);
+            }
+
+            return;
+        }
+    }
+
+    @Override
+    public ItemStack removeItem(int rawIndex, final int j) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null
+                || indexedCompartment.compartment().get(indexedCompartment.index()).isEmpty()) {
+            return ItemStack.EMPTY;
+        }
+
+        return ContainerHelper.removeItem(indexedCompartment.compartment(), indexedCompartment.index(), j);
+    }
+
+    @Override
+    public void removeItem(ItemStack itemStack) {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            for (int i = 0; i < compartment.size(); ++i) {
+                if (compartment.get(i) == itemStack) {
+                    compartment.set(i, ItemStack.EMPTY);
+                    break;
+                }
+            }
+        }
+    }
+
+    @Override
+    public ItemStack removeItemNoUpdate(int rawIndex) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null) {
+            return ItemStack.EMPTY;
+        }
+
+        ItemStack removed = indexedCompartment.compartment().set(indexedCompartment.index(), ItemStack.EMPTY);
+
+        if (removed.isEmpty()) {
+            return ItemStack.EMPTY;
+        }
+
+        return removed;
+    }
+
+    @Override
+    public void setItem(int rawIndex, final ItemStack itemStack) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null) {
+            this.player.drop(itemStack, true);
+            return;
+        }
+
+        indexedCompartment.compartment().set(indexedCompartment.index(), itemStack);
+    }
+
+    @Override
+    public float getDestroySpeed(BlockState blockState) {
+        return this.items.get(this.selected).getDestroySpeed(blockState);
+    }
+
+    @Override
+    public ListTag save(ListTag listTag) {
+        for (int i = 0; i < this.items.size(); ++i) {
+            if (!this.items.get(i).isEmpty()) {
+                CompoundTag compoundTag = new CompoundTag();
+                compoundTag.putByte("Slot", (byte)i);
+                this.items.get(i).save(compoundTag);
+                listTag.add(compoundTag);
+            }
+        }
+
+        for (int i = 0; i < this.armor.size(); ++i) {
+            if (!this.armor.get(i).isEmpty()) {
+                CompoundTag compoundTag = new CompoundTag();
+                compoundTag.putByte("Slot", (byte)(i + 100));
+                this.armor.get(i).save(compoundTag);
+                listTag.add(compoundTag);
+            }
+        }
+
+        for (int i = 0; i < this.offhand.size(); ++i) {
+            if (!this.offhand.get(i).isEmpty()) {
+                CompoundTag compoundTag = new CompoundTag();
+                compoundTag.putByte("Slot", (byte)(i + 150));
+                this.offhand.get(i).save(compoundTag);
+                listTag.add(compoundTag);
+            }
+        }
+
+        return listTag;
+    }
+
+    @Override
+    public void load(ListTag listTag) {
+        this.items.clear();
+        this.armor.clear();
+        this.offhand.clear();
+
+        for(int i = 0; i < listTag.size(); ++i) {
+            CompoundTag compoundTag = listTag.getCompound(i);
+            int j = compoundTag.getByte("Slot") & 255;
+            ItemStack itemstack = ItemStack.of(compoundTag);
+            if (!itemstack.isEmpty()) {
+                if (j < this.items.size()) {
+                    this.items.set(j, itemstack);
+                } else if (j >= 100 && j < this.armor.size() + 100) {
+                    this.armor.set(j - 100, itemstack);
+                } else if (j >= 150 && j < this.offhand.size() + 150) {
+                    this.offhand.set(j - 150, itemstack);
+                }
+            }
+        }
+
+    }
+
+    @Override
+    public int getContainerSize() {
+        return 45;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return !contains(itemStack -> !itemStack.isEmpty());
+    }
+
+    @Override
+    public ItemStack getItem(int rawIndex) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null) {
+            return ItemStack.EMPTY;
+        }
+
+        return indexedCompartment.compartment().get(indexedCompartment.index());
+    }
+
+    @Override
+    public Component getName() {
+        return this.player.getName();
+    }
+
+    @Override
+    public ItemStack getArmor(int index) {
+        return this.armor.get(index);
+    }
+
+    @Override
+    public void hurtArmor(DamageSource damagesource, float damage, int[] armorIndices) {
+        if (damage > 0.0F) {
+            damage /= 4.0F;
+            if (damage < 1.0F) {
+                damage = 1.0F;
+            }
+
+            for (int index : armorIndices) {
+                ItemStack itemstack = this.armor.get(index);
+                if ((!damagesource.is(DamageTypeTags.IS_FIRE) || !itemstack.getItem().isFireResistant()) && itemstack.getItem() instanceof ArmorItem) {
+                    itemstack.hurtAndBreak((int) damage, this.player, localPlayer -> localPlayer.broadcastBreakEvent(EquipmentSlot.byTypeAndIndex(EquipmentSlot.Type.ARMOR, index)));
+                }
+            }
+        }
+    }
+
+    @Override
+    public void dropAll() {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            for (int i = 0; i < compartment.size(); ++i) {
+                ItemStack itemstack = compartment.get(i);
+                if (!itemstack.isEmpty()) {
+                    this.player.drop(itemstack, true, false);
+                    compartment.set(i, ItemStack.EMPTY);
+                }
+            }
+        }
+    }
+
+    @Override
+    public void setChanged() {
+        super.setChanged();
+    }
+
+    @Override
+    public int getTimesChanged() {
+        return super.getTimesChanged();
+    }
+
+    @Override
+    public boolean stillValid(Player player) {
+        return true;
+    }
+
+    @Override
+    public boolean contains(ItemStack itemstack) {
+        return contains(itemStack -> !itemStack.isEmpty() && itemStack.is(itemstack.getItem()));
+    }
+
+    @Override
+    public boolean contains(TagKey<Item> tagKey) {
+
+        return contains(itemStack -> !itemStack.isEmpty() && itemStack.is(tagKey));
+    }
+
+    @Override
+    public void replaceWith(Inventory inventory) {
+        Function<Integer, ItemStack> getter;
+
+        if (inventory instanceof SpecialPlayerInventory specialPlayerInventory) {
+            getter = specialPlayerInventory::getRawItem;
+        } else {
+            getter = inventory::getItem;
+        }
+
+        for(int i = 0; i < this.getContainerSize(); ++i) {
+            this.setRawItem(i, getter.apply(i));
+        }
+
+        this.selected = inventory.selected;
+    }
+
+    @Override
+    public void clearContent() {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            compartment.clear();
+        }
+    }
+
+    @Override
+    public void fillStackedContents(StackedContents stackedContents) {
+        for (ItemStack itemstack : this.items) {
+            stackedContents.accountSimpleStack(itemstack);
+        }
+    }
+
+    @Override
+    public ItemStack removeFromSelected(boolean dropWholeStack) {
+        ItemStack itemstack = this.getSelected();
+        return itemstack.isEmpty() ? ItemStack.EMPTY : this.removeItem(this.selected, dropWholeStack ? itemstack.getCount() : 1);
+    }
+
+}

internal/v1_20_R4/pom.xml

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright (C) 2011-2023 lishid. All rights reserved.
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by
+  ~ the Free Software Foundation, version 3.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+  ~ GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License
+  ~ along with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <artifactId>openinvparent</artifactId>
+    <groupId>com.lishid</groupId>
+    <relativePath>../../pom.xml</relativePath>
+    <version>5.1.1</version>
+  </parent>
+
+  <artifactId>openinvadapter1_20_R4</artifactId>
+  <name>OpenInvAdapter1_20_R4</name>
+
+  <properties>
+    <maven.compiler.system>21</maven.compiler.system>
+    <maven.compiler.release>21</maven.compiler.release>
+    <spigot.version>1.20.6-R0.1-SNAPSHOT</spigot.version>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.spigotmc</groupId>
+      <artifactId>spigot-api</artifactId>
+      <version>${spigot.version}</version>
+    </dependency>
+    <dependency>
+      <artifactId>spigot</artifactId>
+      <groupId>org.spigotmc</groupId>
+      <scope>provided</scope>
+      <version>${spigot.version}</version>
+      <classifier>remapped-mojang</classifier>
+    </dependency>
+    <dependency>
+      <artifactId>openinvapi</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>openinvcommon</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>annotations</artifactId>
+      <groupId>org.jetbrains</groupId>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <groupId>net.md-5</groupId>
+        <artifactId>specialsource-maven-plugin</artifactId>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>

internal/v1_20_R4/src/main/java/com/lishid/openinv/internal/v1_20_R4/AnySilentContainer.java

@@ -0,0 +1,208 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R4;
+
+import com.lishid.openinv.internal.AnySilentContainerBase;
+import com.lishid.openinv.util.ReflectionHelper;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.core.BlockPos;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.level.ServerPlayerGameMode;
+import net.minecraft.world.MenuProvider;
+import net.minecraft.world.SimpleMenuProvider;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.PlayerEnderChestContainer;
+import net.minecraft.world.level.GameType;
+import net.minecraft.world.level.block.BarrelBlock;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.ChestBlock;
+import net.minecraft.world.level.block.ShulkerBoxBlock;
+import net.minecraft.world.level.block.TrappedChestBlock;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.entity.EnderChestBlockEntity;
+import net.minecraft.world.level.block.entity.RandomizableContainerBlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+import org.bukkit.GameMode;
+import org.bukkit.Material;
+import org.bukkit.Statistic;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.logging.Logger;
+
+public class AnySilentContainer extends AnySilentContainerBase {
+
+    private final @NotNull Logger logger;
+    private final @NotNull LanguageManager lang;
+    private @Nullable Field serverPlayerGameModeGameType;
+
+    public AnySilentContainer(@NotNull Logger logger, @NotNull LanguageManager lang) {
+        this.logger = logger;
+        this.lang = lang;
+        try {
+            try {
+                this.serverPlayerGameModeGameType = ServerPlayerGameMode.class.getDeclaredField("b");
+                this.serverPlayerGameModeGameType.setAccessible(true);
+            } catch (NoSuchFieldException e) {
+                logger.warning("ServerPlayerGameMode#gameModeForPlayer's obfuscated name has changed!");
+                logger.warning("Please report this at https://github.com/Jikoo/OpenInv/issues");
+                logger.warning("Attempting to fall through using reflection. Please verify that SilentContainer does not fail.");
+                // N.B. gameModeForPlayer is (for now) declared before previousGameModeForPlayer so silent shouldn't break.
+                this.serverPlayerGameModeGameType = ReflectionHelper.grabFieldByType(ServerPlayerGameMode.class, GameType.class);
+            }
+        } catch (SecurityException e) {
+            logger.warning("Unable to directly write player game mode! SilentContainer will fail.");
+            logger.log(java.util.logging.Level.WARNING, "Error obtaining GameType field", e);
+        }
+    }
+
+    @Override
+    public boolean activateContainer(
+            @NotNull final Player bukkitPlayer,
+            final boolean silentchest,
+            @NotNull final org.bukkit.block.Block bukkitBlock) {
+
+        // Silent ender chest is API-only
+        if (silentchest && bukkitBlock.getType() == Material.ENDER_CHEST) {
+            bukkitPlayer.openInventory(bukkitPlayer.getEnderChest());
+            bukkitPlayer.incrementStatistic(Statistic.ENDERCHEST_OPENED);
+            return true;
+        }
+
+        ServerPlayer player = PlayerManager.getHandle(bukkitPlayer);
+
+        final net.minecraft.world.level.Level level = player.level();
+        final BlockPos blockPos = new BlockPos(bukkitBlock.getX(), bukkitBlock.getY(), bukkitBlock.getZ());
+        final BlockEntity blockEntity = level.getBlockEntity(blockPos);
+
+        if (blockEntity == null) {
+            return false;
+        }
+
+        if (blockEntity instanceof EnderChestBlockEntity enderChestTile) {
+            // Anychest ender chest. See net.minecraft.world.level.block.EnderChestBlock
+            PlayerEnderChestContainer enderChest = player.getEnderChestInventory();
+            enderChest.setActiveChest(enderChestTile);
+            player.openMenu(new SimpleMenuProvider((containerCounter, playerInventory, ignored) -> {
+                MenuType<?> containers = PlayerManager.getContainers(enderChest.getContainerSize());
+                int rows = enderChest.getContainerSize() / 9;
+                return new ChestMenu(containers, containerCounter, playerInventory, enderChest, rows);
+            }, Component.translatable("container.enderchest")));
+            bukkitPlayer.incrementStatistic(Statistic.ENDERCHEST_OPENED);
+            return true;
+        }
+
+        if (!(blockEntity instanceof MenuProvider menuProvider)) {
+            return false;
+        }
+
+        BlockState blockState = level.getBlockState(blockPos);
+        Block block = blockState.getBlock();
+
+        if (block instanceof ChestBlock chestBlock) {
+
+            // boolean flag: do not check if chest is blocked
+            menuProvider = chestBlock.getMenuProvider(blockState, level, blockPos, true);
+
+            if (menuProvider == null) {
+                lang.sendSystemMessage(bukkitPlayer, "messages.error.lootNotGenerated");
+                return false;
+            }
+
+            if (block instanceof TrappedChestBlock) {
+                bukkitPlayer.incrementStatistic(Statistic.TRAPPED_CHEST_TRIGGERED);
+            } else {
+                bukkitPlayer.incrementStatistic(Statistic.CHEST_OPENED);
+            }
+        }
+
+        if (block instanceof ShulkerBoxBlock) {
+            bukkitPlayer.incrementStatistic(Statistic.SHULKER_BOX_OPENED);
+        }
+
+        if (block instanceof BarrelBlock) {
+            bukkitPlayer.incrementStatistic(Statistic.OPEN_BARREL);
+        }
+
+        // AnyChest only - SilentChest not active, container unsupported, or unnecessary.
+        if (!silentchest || player.gameMode.getGameModeForPlayer() == GameType.SPECTATOR) {
+            player.openMenu(menuProvider);
+            return true;
+        }
+
+        // SilentChest requires access to setting players' game mode directly.
+        if (this.serverPlayerGameModeGameType == null) {
+            return false;
+        }
+
+        if (blockEntity instanceof RandomizableContainerBlockEntity lootable) {
+            if (lootable.lootTable != null) {
+                lang.sendSystemMessage(bukkitPlayer, "messages.error.lootNotGenerated");
+                return false;
+            }
+        }
+
+        GameType gameType = player.gameMode.getGameModeForPlayer();
+        this.forceGameType(player, GameType.SPECTATOR);
+        player.openMenu(menuProvider);
+        this.forceGameType(player, gameType);
+        return true;
+    }
+
+    @Override
+    public void deactivateContainer(@NotNull final Player bukkitPlayer) {
+        if (this.serverPlayerGameModeGameType == null || bukkitPlayer.getGameMode() == GameMode.SPECTATOR) {
+            return;
+        }
+
+        ServerPlayer player = PlayerManager.getHandle(bukkitPlayer);
+
+        // Force game mode change without informing plugins or players.
+        // Regular game mode set calls GameModeChangeEvent and is cancellable.
+        GameType gameType = player.gameMode.getGameModeForPlayer();
+        this.forceGameType(player, GameType.SPECTATOR);
+
+        // ServerPlayer#closeContainer cannot be called without entering an
+        // infinite loop because this method is called during inventory close.
+        // From ServerPlayer#closeContainer -> CraftEventFactory#handleInventoryCloseEvent
+        player.containerMenu.transferTo(player.inventoryMenu, player.getBukkitEntity());
+        // From ServerPlayer#closeContainer
+        player.doCloseContainer();
+        // Regular inventory close will handle the rest - packet sending, etc.
+
+        // Revert forced game mode.
+        this.forceGameType(player, gameType);
+    }
+
+    private void forceGameType(final ServerPlayer player, final GameType gameMode) {
+        if (this.serverPlayerGameModeGameType == null) {
+            // No need to warn repeatedly, error on startup and lack of function should be enough.
+            return;
+        }
+        try {
+            this.serverPlayerGameModeGameType.setAccessible(true);
+            this.serverPlayerGameModeGameType.set(player.gameMode, gameMode);
+        } catch (IllegalArgumentException | IllegalAccessException e) {
+            logger.log(java.util.logging.Level.WARNING, "Error bypassing GameModeChangeEvent", e);
+        }
+    }
+
+}

internal/v1_20_R4/src/main/java/com/lishid/openinv/internal/v1_20_R4/InternalAccessor.java

@@ -0,0 +1,64 @@
+package com.lishid.openinv.internal.v1_20_R4;
+
+import com.lishid.openinv.internal.Accessor;
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.world.Container;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.craftbukkit.v1_20_R4.inventory.CraftInventory;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.logging.Logger;
+
+public class InternalAccessor implements Accessor {
+
+  private final @NotNull PlayerManager manager;
+  private final @NotNull AnySilentContainer anySilentContainer;
+
+  public InternalAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
+    manager = new PlayerManager(logger, lang);
+    anySilentContainer = new AnySilentContainer(logger, lang);
+  }
+
+  @Override
+  public @NotNull PlayerManager getPlayerManager() {
+    return manager;
+  }
+
+  @Override
+  public @NotNull IAnySilentContainer getAnySilentContainer() {
+    return anySilentContainer;
+  }
+
+  @Override
+  public @NotNull ISpecialPlayerInventory createPlayerInventory(@NotNull Player player) {
+    return new SpecialPlayerInventory(player, player.isOnline());
+  }
+
+  @Override
+  public @NotNull ISpecialEnderChest createEnderChest(@NotNull Player player) {
+    return new SpecialEnderChest(player, player.isOnline());
+  }
+
+  @Override
+  public <T extends ISpecialInventory> @Nullable T get(@NotNull Inventory bukkitInventory, @NotNull Class<T> clazz) {
+    if (!(bukkitInventory instanceof CraftInventory craftInventory)) {
+      return null;
+    }
+    Container container = craftInventory.getInventory();
+    if (clazz.isInstance(container)) {
+      return clazz.cast(container);
+    }
+    return null;
+  }
+
+  @Override
+  public void reload(@NotNull ConfigurationSection config) {}
+
+}

internal/v1_20_R4/src/main/java/com/lishid/openinv/internal/v1_20_R4/OpenPlayer.java

@@ -0,0 +1,194 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R4;
+
+import com.lishid.openinv.event.OpenEvents;
+import com.mojang.logging.LogUtils;
+import net.minecraft.Util;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.nbt.NumericTag;
+import net.minecraft.nbt.Tag;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.storage.PlayerDataStorage;
+import org.bukkit.craftbukkit.v1_20_R4.CraftServer;
+import org.bukkit.craftbukkit.v1_20_R4.entity.CraftPlayer;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Set;
+
+public class OpenPlayer extends CraftPlayer {
+
+    /**
+     * List of tags to always reset when saving.
+     *
+     * @see net.minecraft.world.entity.Entity#saveWithoutId(CompoundTag)
+     * @see net.minecraft.server.level.ServerPlayer#addAdditionalSaveData(CompoundTag)
+     * @see net.minecraft.world.entity.player.Player#addAdditionalSaveData(CompoundTag)
+     * @see net.minecraft.world.entity.LivingEntity#addAdditionalSaveData(CompoundTag)
+     */
+    private static final Set<String> RESET_TAGS = Set.of(
+        // Entity#saveWithoutId(CompoundTag)
+        "CustomName",
+        "CustomNameVisible",
+        "Silent",
+        "NoGravity",
+        "Glowing",
+        "TicksFrozen",
+        "HasVisualFire",
+        "Tags",
+        "Passengers",
+        // ServerPlayer#addAdditionalSaveData(CompoundTag)
+        // Intentional omissions to prevent mount loss: Attach, Entity, and RootVehicle
+        "warden_spawn_tracker",
+        "enteredNetherPosition",
+        "SpawnX",
+        "SpawnY",
+        "SpawnZ",
+        "SpawnForced",
+        "SpawnAngle",
+        "SpawnDimension",
+        "raid_omen_position",
+        // Player#addAdditionalSaveData(CompoundTag)
+        "ShoulderEntityLeft",
+        "ShoulderEntityRight",
+        "LastDeathLocation",
+        "current_explosion_impact_pos",
+        // LivingEntity#addAdditionalSaveData(CompoundTag)
+        "ActiveEffects", // Backwards compat: Renamed from 1.19
+        "active_effects",
+        "SleepingX",
+        "SleepingY",
+        "SleepingZ",
+        "Brain"
+    );
+
+    private final PlayerManager manager;
+
+    OpenPlayer(CraftServer server, ServerPlayer entity, PlayerManager manager) {
+        super(server, entity);
+        this.manager = manager;
+    }
+
+    @Override
+    public void loadData() {
+        manager.loadData(getHandle());
+    }
+
+    @Override
+    public void saveData() {
+        if (OpenEvents.saveCancelled(this)) {
+            return;
+        }
+
+        ServerPlayer player = this.getHandle();
+        // See net.minecraft.world.level.storage.PlayerDataStorage#save(EntityHuman)
+        try {
+            PlayerDataStorage worldNBTStorage = player.server.getPlayerList().playerIo;
+
+            CompoundTag oldData = isOnline() ? null : worldNBTStorage.load(player.getName().getString(), player.getStringUUID()).orElse(null);
+            CompoundTag playerData = getWritableTag(oldData);
+            playerData = player.saveWithoutId(playerData);
+            setExtraData(playerData);
+
+            if (oldData != null) {
+                // Revert certain special data values when offline.
+                revertSpecialValues(playerData, oldData);
+            }
+
+            Path playerDataDir = worldNBTStorage.getPlayerDir().toPath();
+            Path tempFile = Files.createTempFile(playerDataDir, player.getStringUUID() + "-", ".dat");
+            NbtIo.writeCompressed(playerData, tempFile);
+            Path dataFile = playerDataDir.resolve(player.getStringUUID() + ".dat");
+            Path backupFile = playerDataDir.resolve(player.getStringUUID() + ".dat_old");
+            Util.safeReplaceFile(dataFile, tempFile, backupFile);
+        } catch (Exception e) {
+            LogUtils.getLogger().warn("Failed to save player data for {}: {}", player.getScoreboardName(), e);
+        }
+    }
+
+    @Contract("null -> new")
+    private @NotNull CompoundTag getWritableTag(@Nullable CompoundTag oldData) {
+        if (oldData == null) {
+            return new CompoundTag();
+        }
+
+        // Copy old data. This is a deep clone, so operating on it should be safe.
+        oldData = oldData.copy();
+
+        // Remove vanilla/server data that is not written every time.
+        oldData.getAllKeys()
+            .removeIf(key -> RESET_TAGS.contains(key) || key.startsWith("Bukkit"));
+
+        return oldData;
+    }
+
+    private void revertSpecialValues(@NotNull CompoundTag newData, @NotNull CompoundTag oldData) {
+        // Revert automatic updates to play timestamps.
+        copyValue(oldData, newData, "bukkit", "lastPlayed", NumericTag.class);
+        copyValue(oldData, newData, "Paper", "LastSeen", NumericTag.class);
+        copyValue(oldData, newData, "Paper", "LastLogin", NumericTag.class);
+    }
+
+    private <T extends Tag> void copyValue(
+        @NotNull CompoundTag source,
+        @NotNull CompoundTag target,
+        @NotNull String container,
+        @NotNull String key,
+        @NotNull Class<T> tagType) {
+        CompoundTag oldContainer = getTag(source, container, CompoundTag.class);
+        CompoundTag newContainer = getTag(target, container, CompoundTag.class);
+
+        // New container being null means the server implementation doesn't store this data.
+        if (newContainer == null) {
+            return;
+        }
+
+        // If old tag exists, copy it to new location, removing otherwise.
+        setTag(newContainer, key, getTag(oldContainer, key, tagType));
+    }
+
+    private <T extends Tag> @Nullable T getTag(
+        @Nullable CompoundTag container,
+        @NotNull String key,
+        @NotNull Class<T> dataType) {
+        if (container == null) {
+            return null;
+        }
+        Tag value = container.get(key);
+        if (value == null || !dataType.isAssignableFrom(value.getClass())) {
+            return null;
+        }
+        return dataType.cast(value);
+    }
+
+    private <T extends Tag> void setTag(
+        @NotNull CompoundTag container,
+        @NotNull String key,
+        @Nullable T data) {
+        if (data == null) {
+            container.remove(key);
+        } else {
+            container.put(key, data);
+        }
+    }
+
+}

internal/v1_20_R4/src/main/java/com/lishid/openinv/internal/v1_20_R4/PlayerManager.java

@@ -0,0 +1,292 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R4;
+
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.InventoryViewTitle;
+import com.lishid.openinv.internal.OpenInventoryView;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.mojang.authlib.GameProfile;
+import com.mojang.serialization.Dynamic;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtOps;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.protocol.game.ClientboundOpenScreenPacket;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ClientInformation;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.player.ChatVisiblity;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.dimension.DimensionType;
+import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.Server;
+import org.bukkit.World;
+import org.bukkit.craftbukkit.v1_20_R4.CraftServer;
+import org.bukkit.craftbukkit.v1_20_R4.CraftWorld;
+import org.bukkit.craftbukkit.v1_20_R4.entity.CraftPlayer;
+import org.bukkit.craftbukkit.v1_20_R4.event.CraftEventFactory;
+import org.bukkit.craftbukkit.v1_20_R4.inventory.CraftContainer;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.UUID;
+import java.util.logging.Logger;
+
+public class PlayerManager implements com.lishid.openinv.internal.PlayerManager {
+
+    private static boolean paper;
+
+    static {
+        try {
+            Class.forName("io.papermc.paper.configuration.Configuration");
+            paper = true;
+        } catch (ClassNotFoundException ignored) {
+            paper = false;
+        }
+    }
+
+    private final @NotNull Logger logger;
+    private final @NotNull LanguageManager lang;
+    private @Nullable Field bukkitEntity;
+
+    public PlayerManager(@NotNull Logger logger, @NotNull LanguageManager lang) {
+        this.logger = logger;
+        this.lang = lang;
+        try {
+            bukkitEntity = Entity.class.getDeclaredField("bukkitEntity");
+        } catch (NoSuchFieldException e) {
+            logger.warning("Unable to obtain field to inject custom save process - certain player data may be lost when saving!");
+            logger.log(java.util.logging.Level.WARNING, e.getMessage(), e);
+            bukkitEntity = null;
+        }
+    }
+
+    public static @NotNull ServerPlayer getHandle(final Player player) {
+        if (player instanceof CraftPlayer) {
+            return ((CraftPlayer) player).getHandle();
+        }
+
+        Server server = player.getServer();
+        ServerPlayer nmsPlayer = null;
+
+        if (server instanceof CraftServer) {
+            nmsPlayer = ((CraftServer) server).getHandle().getPlayer(player.getUniqueId());
+        }
+
+        if (nmsPlayer == null) {
+            // Could use reflection to examine fields, but it's honestly not worth the bother.
+            throw new RuntimeException("Unable to fetch EntityPlayer from Player implementation " + player.getClass().getName());
+        }
+
+        return nmsPlayer;
+    }
+
+    @Override
+    public @Nullable Player loadPlayer(@NotNull final OfflinePlayer offline) {
+        MinecraftServer server = ((CraftServer) Bukkit.getServer()).getServer();
+        ServerLevel worldServer = server.getLevel(Level.OVERWORLD);
+
+        if (worldServer == null) {
+            return null;
+        }
+
+        // Create a new ServerPlayer.
+        ServerPlayer entity = createNewPlayer(server, worldServer, offline);
+
+        // Stop listening for advancement progression - if this is not cleaned up, loading causes a memory leak.
+        entity.getAdvancements().stopListening();
+
+        // Try to load the player's data.
+        if (loadData(entity)) {
+            // If data is loaded successfully, return the Bukkit entity.
+            return entity.getBukkitEntity();
+        }
+
+        return null;
+    }
+
+    private @NotNull ServerPlayer createNewPlayer(
+        @NotNull MinecraftServer server,
+        @NotNull ServerLevel worldServer,
+        @NotNull final OfflinePlayer offline) {
+        // See net.minecraft.server.players.PlayerList#canPlayerLogin(ServerLoginPacketListenerImpl, GameProfile)
+        // See net.minecraft.server.network.ServerLoginPacketListenerImpl#handleHello(ServerboundHelloPacket)
+        GameProfile profile = new GameProfile(offline.getUniqueId(),
+            offline.getName() != null ? offline.getName() : offline.getUniqueId().toString());
+
+        ClientInformation dummyInfo = new ClientInformation(
+            "en_us",
+            1, // Reduce distance just in case.
+            ChatVisiblity.HIDDEN, // Don't accept chat.
+            false,
+            ServerPlayer.DEFAULT_MODEL_CUSTOMIZATION,
+            ServerPlayer.DEFAULT_MAIN_HAND,
+            true,
+            false // Don't list in player list (not that this player is in the list anyway).
+        );
+
+        ServerPlayer entity = new ServerPlayer(server, worldServer, profile, dummyInfo);
+
+        try {
+            injectPlayer(entity);
+        } catch (IllegalAccessException e) {
+            logger.log(
+                java.util.logging.Level.WARNING,
+                e,
+                () -> "Unable to inject ServerPlayer, certain player data may be lost when saving!");
+        }
+
+        return entity;
+    }
+
+    boolean loadData(@NotNull ServerPlayer player) {
+        // See CraftPlayer#loadData
+        CompoundTag loadedData = player.server.getPlayerList().playerIo.load(player).orElse(null);
+
+        if (loadedData == null) {
+            // Exceptions with loading are logged by Mojang.
+            return false;
+        }
+
+        // Read basic data into the player.
+        player.load(loadedData);
+        // Also read "extra" data.
+        player.readAdditionalSaveData(loadedData);
+        // Game type settings are also loaded separately.
+        player.loadGameTypes(loadedData);
+
+        if (paper) {
+            // Paper: world is not loaded by ServerPlayer#load(CompoundTag).
+            parseWorld(player, loadedData);
+        }
+
+        return true;
+    }
+
+    private void parseWorld(@NotNull ServerPlayer player, @NotNull CompoundTag loadedData) {
+        // See PlayerList#placeNewPlayer
+        World bukkitWorld;
+        if (loadedData.contains("WorldUUIDMost") && loadedData.contains("WorldUUIDLeast")) {
+            // Modern Bukkit world.
+            bukkitWorld = Bukkit.getServer().getWorld(new UUID(loadedData.getLong("WorldUUIDMost"), loadedData.getLong("WorldUUIDLeast")));
+        } else if (loadedData.contains("world", net.minecraft.nbt.Tag.TAG_STRING)) {
+            // Legacy Bukkit world.
+            bukkitWorld = Bukkit.getServer().getWorld(loadedData.getString("world"));
+        } else {
+            // Vanilla player data.
+            DimensionType.parseLegacy(new Dynamic<>(NbtOps.INSTANCE, loadedData.get("Dimension")))
+                .resultOrPartial(logger::warning)
+                .map(player.server::getLevel)
+                // If ServerLevel exists, set, otherwise move to spawn.
+                .ifPresentOrElse(player::setServerLevel, () -> player.spawnIn(null));
+            return;
+        }
+        if (bukkitWorld == null) {
+            player.spawnIn(null);
+            return;
+        }
+        player.setServerLevel(((CraftWorld) bukkitWorld).getHandle());
+    }
+
+    private void injectPlayer(ServerPlayer player) throws IllegalAccessException {
+        if (bukkitEntity == null) {
+            return;
+        }
+
+        bukkitEntity.setAccessible(true);
+
+        bukkitEntity.set(player, new OpenPlayer(player.server.server, player, this));
+    }
+
+    @Override
+    public @NotNull Player inject(@NotNull Player player) {
+        try {
+            ServerPlayer nmsPlayer = getHandle(player);
+            if (nmsPlayer.getBukkitEntity() instanceof OpenPlayer openPlayer) {
+                return openPlayer;
+            }
+            injectPlayer(nmsPlayer);
+            return nmsPlayer.getBukkitEntity();
+        } catch (IllegalAccessException e) {
+            logger.log(
+                java.util.logging.Level.WARNING,
+                e,
+                () -> "Unable to inject ServerPlayer, certain player data may be lost when saving!");
+            return player;
+        }
+    }
+
+    @Override
+    public @Nullable InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory, boolean viewOnly) {
+
+        ServerPlayer nmsPlayer = getHandle(player);
+
+        if (nmsPlayer.connection == null) {
+            return null;
+        }
+
+        InventoryViewTitle title = InventoryViewTitle.of(inventory);
+
+        if (title == null) {
+            return player.openInventory(inventory.getBukkitInventory());
+        }
+
+        InventoryView view = new OpenInventoryView(player, inventory, title.getTitle(lang, player, inventory));
+        AbstractContainerMenu container = new CraftContainer(view, nmsPlayer, nmsPlayer.nextContainerCounter()) {
+            @Override
+            public MenuType<?> getType() {
+                return getContainers(inventory.getBukkitInventory().getSize());
+            }
+        };
+
+        container.setTitle(Component.literal(view.getOriginalTitle()));
+        container = CraftEventFactory.callInventoryOpenEvent(nmsPlayer, container);
+
+        if (container == null) {
+            return null;
+        }
+
+        nmsPlayer.connection.send(new ClientboundOpenScreenPacket(container.containerId, container.getType(),
+                Component.literal(container.getBukkitView().getTitle())));
+        nmsPlayer.containerMenu = container;
+        nmsPlayer.initMenu(container);
+
+        return container.getBukkitView();
+
+    }
+
+    static @NotNull MenuType<?> getContainers(int inventorySize) {
+
+        return switch (inventorySize) {
+            case 9 -> MenuType.GENERIC_9x1;
+            case 18 -> MenuType.GENERIC_9x2;
+            case 36 -> MenuType.GENERIC_9x4; // PLAYER
+            case 41, 45 -> MenuType.GENERIC_9x5;
+            case 54 -> MenuType.GENERIC_9x6;
+            default -> MenuType.GENERIC_9x3; // Default 27-slot inventory
+        };
+    }
+
+}

internal/v1_20_R4/src/main/java/com/lishid/openinv/internal/v1_20_R4/SpecialEnderChest.java

@@ -0,0 +1,352 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R4;
+
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import net.minecraft.core.HolderLookup;
+import net.minecraft.core.NonNullList;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.ContainerListener;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.entity.player.StackedContents;
+import net.minecraft.world.inventory.PlayerEnderChestContainer;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.level.block.entity.EnderChestBlockEntity;
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.v1_20_R4.entity.CraftHumanEntity;
+import org.bukkit.craftbukkit.v1_20_R4.inventory.CraftInventory;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.InventoryHolder;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class SpecialEnderChest extends PlayerEnderChestContainer implements ISpecialEnderChest {
+
+    private final CraftInventory inventory;
+    private ServerPlayer owner;
+    private NonNullList<ItemStack> items;
+    private boolean playerOnline;
+
+    public SpecialEnderChest(final org.bukkit.entity.Player player, final Boolean online) {
+        super(PlayerManager.getHandle(player));
+        this.inventory = new CraftInventory(this);
+        this.owner = PlayerManager.getHandle(player);
+        this.playerOnline = online;
+        this.items = this.owner.getEnderChestInventory().items;
+    }
+
+    @Override
+    public @NotNull CraftInventory getBukkitInventory() {
+        return inventory;
+    }
+
+    @Override
+    public void setPlayerOffline() {
+        this.playerOnline = false;
+    }
+
+    @Override
+    public void setPlayerOnline(@NotNull final org.bukkit.entity.Player player) {
+        if (this.playerOnline) {
+            return;
+        }
+
+        ServerPlayer offlinePlayer = this.owner;
+        ServerPlayer onlinePlayer = PlayerManager.getHandle(player);
+
+        // Set owner to new player.
+        this.owner = onlinePlayer;
+
+        // Set player's ender chest contents to our modified contents.
+        PlayerEnderChestContainer onlineEnderChest = onlinePlayer.getEnderChestInventory();
+        for (int i = 0; i < onlineEnderChest.getContainerSize(); ++i) {
+            onlineEnderChest.setItem(i, this.items.get(i));
+        }
+
+        // Set our item array to the new inventory's array.
+        this.items = onlineEnderChest.items;
+
+        // Add viewers to new inventory.
+        onlineEnderChest.transaction.addAll(offlinePlayer.getEnderChestInventory().transaction);
+
+        this.playerOnline = true;
+    }
+
+    @Override
+    public @NotNull org.bukkit.entity.Player getPlayer() {
+        return owner.getBukkitEntity();
+    }
+
+    @Override
+    public void setChanged() {
+        this.owner.getEnderChestInventory().setChanged();
+    }
+
+    @Override
+    public List<ItemStack> getContents() {
+        return this.items;
+    }
+
+    @Override
+    public void onOpen(CraftHumanEntity who) {
+        this.owner.getEnderChestInventory().onOpen(who);
+    }
+
+    @Override
+    public void onClose(CraftHumanEntity who) {
+        this.owner.getEnderChestInventory().onClose(who);
+    }
+
+    @Override
+    public List<HumanEntity> getViewers() {
+        return this.owner.getEnderChestInventory().getViewers();
+    }
+
+    @Override
+    public boolean stillValid(Player player) {
+        return true;
+    }
+
+    @Override
+    public void setActiveChest(EnderChestBlockEntity enderChest) {
+        this.owner.getEnderChestInventory().setActiveChest(enderChest);
+    }
+
+    @Override
+    public boolean isActiveChest(EnderChestBlockEntity enderChest) {
+        return this.owner.getEnderChestInventory().isActiveChest(enderChest);
+    }
+
+    @Override
+    public int getMaxStackSize() {
+        return this.owner.getEnderChestInventory().getMaxStackSize();
+    }
+
+    @Override
+    public void setMaxStackSize(int i) {
+        this.owner.getEnderChestInventory().setMaxStackSize(i);
+    }
+
+    @Override
+    public InventoryHolder getOwner() {
+        return this.owner.getEnderChestInventory().getOwner();
+    }
+
+    @Override
+    public @Nullable Location getLocation() {
+        return null;
+    }
+
+    @Override
+    public void addListener(ContainerListener listener) {
+        this.owner.getEnderChestInventory().addListener(listener);
+    }
+
+    @Override
+    public void removeListener(ContainerListener listener) {
+        this.owner.getEnderChestInventory().removeListener(listener);
+    }
+
+    @Override
+    public ItemStack getItem(int i) {
+        return i >= 0 && i < this.items.size() ? this.items.get(i) : ItemStack.EMPTY;
+    }
+
+    @Override
+    public ItemStack removeItem(int i, int j) {
+        ItemStack itemstack = ContainerHelper.removeItem(this.items, i, j);
+        if (!itemstack.isEmpty()) {
+            this.setChanged();
+        }
+
+        return itemstack;
+    }
+
+    @Override
+    public ItemStack addItem(ItemStack itemstack) {
+        ItemStack localItem = itemstack.copy();
+        this.moveItemToOccupiedSlotsWithSameType(localItem);
+        if (localItem.isEmpty()) {
+            return ItemStack.EMPTY;
+        } else {
+            this.moveItemToEmptySlots(localItem);
+            return localItem.isEmpty() ? ItemStack.EMPTY : localItem;
+        }
+    }
+
+    @Override
+    public boolean canAddItem(ItemStack itemstack) {
+        for (ItemStack itemstack1 : this.items) {
+            if (itemstack1.isEmpty() || (ItemStack.isSameItemSameComponents(itemstack1, itemstack) && itemstack1.getCount() < itemstack1.getMaxStackSize())) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private void moveItemToEmptySlots(ItemStack itemstack) {
+        for(int i = 0; i < this.getContainerSize(); ++i) {
+            ItemStack localItem = this.getItem(i);
+            if (localItem.isEmpty()) {
+                this.setItem(i, itemstack.copy());
+                itemstack.setCount(0);
+                return;
+            }
+        }
+    }
+
+    private void moveItemToOccupiedSlotsWithSameType(ItemStack itemstack) {
+        for(int i = 0; i < this.getContainerSize(); ++i) {
+            ItemStack localItem = this.getItem(i);
+            if (ItemStack.isSameItemSameComponents(localItem, itemstack)) {
+                this.moveItemsBetweenStacks(itemstack, localItem);
+                if (itemstack.isEmpty()) {
+                    return;
+                }
+            }
+        }
+    }
+
+    private void moveItemsBetweenStacks(ItemStack itemstack, ItemStack itemstack1) {
+        int i = Math.min(this.getMaxStackSize(), itemstack1.getMaxStackSize());
+        int j = Math.min(itemstack.getCount(), i - itemstack1.getCount());
+        if (j > 0) {
+            itemstack1.grow(j);
+            itemstack.shrink(j);
+            this.setChanged();
+        }
+    }
+
+    @Override
+    public ItemStack removeItemNoUpdate(int i) {
+        ItemStack itemstack = this.items.get(i);
+        if (itemstack.isEmpty()) {
+            return ItemStack.EMPTY;
+        } else {
+            this.items.set(i, ItemStack.EMPTY);
+            return itemstack;
+        }
+    }
+
+    @Override
+    public void setItem(int i, ItemStack itemstack) {
+        this.items.set(i, itemstack);
+        if (!itemstack.isEmpty() && itemstack.getCount() > this.getMaxStackSize()) {
+            itemstack.setCount(this.getMaxStackSize());
+        }
+
+        this.setChanged();
+    }
+
+    @Override
+    public int getContainerSize() {
+        return this.owner.getEnderChestInventory().getContainerSize();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return this.items.stream().allMatch(ItemStack::isEmpty);
+    }
+
+    @Override
+    public void startOpen(Player player) {
+    }
+
+    @Override
+    public void stopOpen(Player player) {
+    }
+
+    @Override
+    public boolean canPlaceItem(int i, ItemStack itemstack) {
+        return true;
+    }
+
+    @Override
+    public void clearContent() {
+        this.items.clear();
+        this.setChanged();
+    }
+
+    @Override
+    public void fillStackedContents(StackedContents stackedContents) {
+        for (ItemStack itemstack : this.items) {
+            stackedContents.accountStack(itemstack);
+        }
+
+    }
+
+    @Override
+    public List<ItemStack> removeAllItems() {
+        List<ItemStack> list = this.items.stream().filter(Predicate.not(ItemStack::isEmpty)).collect(Collectors.toList());
+        this.clearContent();
+        return list;
+    }
+
+    @Override
+    public ItemStack removeItemType(Item item, int i) {
+        ItemStack itemstack = new ItemStack(item, 0);
+
+        for(int j = this.getContainerSize() - 1; j >= 0; --j) {
+            ItemStack localItem = this.getItem(j);
+            if (localItem.getItem().equals(item)) {
+                int k = i - itemstack.getCount();
+                ItemStack splitItem = localItem.split(k);
+                itemstack.grow(splitItem.getCount());
+                if (itemstack.getCount() == i) {
+                    break;
+                }
+            }
+        }
+
+        if (!itemstack.isEmpty()) {
+            this.setChanged();
+        }
+
+        return itemstack;
+    }
+
+    @Override
+    public String toString() {
+        return this.items.stream().filter((itemStack) -> !itemStack.isEmpty()).toList().toString();
+    }
+
+    @Override
+    public void fromTag(ListTag listTag, HolderLookup.Provider holderLookup) {
+        for (int i = 0; i < this.getContainerSize(); ++i) {
+            this.setItem(i, ItemStack.EMPTY);
+        }
+
+        for (int i = 0; i < listTag.size(); ++i) {
+            CompoundTag compoundTag = listTag.getCompound(i);
+            int j = compoundTag.getByte("Slot") & 255;
+            if (j < this.getContainerSize()) {
+                this.setItem(j, ItemStack.parseOptional(holderLookup, compoundTag));
+            }
+        }
+
+    }
+
+}

internal/v1_20_R4/src/main/java/com/lishid/openinv/internal/v1_20_R4/SpecialPlayerInventory.java

@@ -0,0 +1,768 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_20_R4;
+
+import com.google.common.collect.ImmutableList;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import net.minecraft.CrashReport;
+import net.minecraft.CrashReportCategory;
+import net.minecraft.ReportedException;
+import net.minecraft.core.NonNullList;
+import net.minecraft.core.component.DataComponents;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.protocol.game.ClientboundContainerSetSlotPacket;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.tags.TagKey;
+import net.minecraft.world.Container;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.entity.player.Inventory;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.entity.player.StackedContents;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.level.block.state.BlockState;
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.v1_20_R4.entity.CraftHumanEntity;
+import org.bukkit.craftbukkit.v1_20_R4.inventory.CraftInventory;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.inventory.InventoryHolder;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class SpecialPlayerInventory extends Inventory implements ISpecialPlayerInventory {
+
+    private final CraftInventory inventory;
+    private boolean playerOnline;
+    private Player player;
+    private NonNullList<ItemStack> items;
+    private NonNullList<ItemStack> armor;
+    private NonNullList<ItemStack> offhand;
+    private List<NonNullList<ItemStack>> compartments;
+
+    public SpecialPlayerInventory(@NotNull org.bukkit.entity.Player bukkitPlayer, @NotNull Boolean online) {
+        super(PlayerManager.getHandle(bukkitPlayer));
+        this.inventory = new CraftInventory(this);
+        this.playerOnline = online;
+        this.player = super.player;
+        this.selected = player.getInventory().selected;
+        this.items = this.player.getInventory().items;
+        this.armor = this.player.getInventory().armor;
+        this.offhand = this.player.getInventory().offhand;
+        this.compartments = ImmutableList.of(this.items, this.armor, this.offhand);
+    }
+
+    @Override
+    public void setPlayerOnline(@NotNull org.bukkit.entity.Player player) {
+        if (this.playerOnline) {
+            return;
+        }
+
+        Player offlinePlayer = this.player;
+        Player onlinePlayer = PlayerManager.getHandle(player);
+        onlinePlayer.getInventory().transaction.addAll(this.transaction);
+
+        // Set owner to new player.
+        this.player = onlinePlayer;
+
+        // Set player's inventory contents to our modified contents.
+        Inventory onlineInventory = onlinePlayer.getInventory();
+        for (int i = 0; i < getContainerSize(); ++i) {
+            onlineInventory.setItem(i, getRawItem(i));
+        }
+        onlineInventory.selected = this.selected;
+
+        // Set our item arrays to the new inventory's arrays.
+        this.items = onlineInventory.items;
+        this.armor = onlineInventory.armor;
+        this.offhand = onlineInventory.offhand;
+        this.compartments = ImmutableList.of(this.items, this.armor, this.offhand);
+
+        // Add existing viewers to new viewer list.
+        Inventory offlineInventory = offlinePlayer.getInventory();
+        // Remove self from listing - player is always a viewer of their own inventory, prevent duplicates.
+        offlineInventory.transaction.remove(offlinePlayer.getBukkitEntity());
+        onlineInventory.transaction.addAll(offlineInventory.transaction);
+
+        this.playerOnline = true;
+    }
+
+    @Override
+    public @NotNull CraftInventory getBukkitInventory() {
+        return this.inventory;
+    }
+
+    @Override
+    public void setPlayerOffline() {
+        this.playerOnline = false;
+    }
+
+    @Override
+    public @NotNull HumanEntity getPlayer() {
+        return this.player.getBukkitEntity();
+    }
+
+    private @NotNull ItemStack getRawItem(int i) {
+        if (i < 0) {
+            return ItemStack.EMPTY;
+        }
+
+        NonNullList<ItemStack> list;
+        for (Iterator<NonNullList<ItemStack>> iterator = this.compartments.iterator(); iterator.hasNext(); i -= list.size()) {
+            list = iterator.next();
+            if (i < list.size()) {
+                return list.get(i);
+            }
+        }
+
+        return ItemStack.EMPTY;
+    }
+
+    private void setRawItem(int i, @NotNull ItemStack itemStack) {
+        if (i < 0) {
+            return;
+        }
+
+        NonNullList<ItemStack> list;
+        for (Iterator<NonNullList<ItemStack>> iterator = this.compartments.iterator(); iterator.hasNext(); i -= list.size()) {
+            list = iterator.next();
+            if (i < list.size()) {
+                list.set(i, itemStack);
+            }
+        }
+    }
+
+    private record IndexedCompartment(@Nullable NonNullList<ItemStack> compartment, int index) {}
+
+    private @NotNull SpecialPlayerInventory.IndexedCompartment getIndexedContent(int index) {
+        if (index < items.size()) {
+            return new IndexedCompartment(items, getReversedItemSlotNum(index));
+        }
+
+        index -= items.size();
+
+        if (index < armor.size()) {
+            return new IndexedCompartment(armor, getReversedArmorSlotNum(index));
+        }
+
+        index -= armor.size();
+
+        if (index < offhand.size()) {
+            return new IndexedCompartment(offhand, index);
+        }
+
+        index -= offhand.size();
+
+        return new IndexedCompartment(null, index);
+    }
+
+    private int getReversedArmorSlotNum(final int i) {
+        if (i == 0) {
+            return 3;
+        }
+        if (i == 1) {
+            return 2;
+        }
+        if (i == 2) {
+            return 1;
+        }
+        if (i == 3) {
+            return 0;
+        }
+        return i;
+    }
+
+    private int getReversedItemSlotNum(final int i) {
+        if (i >= 27) {
+            return i - 27;
+        }
+        return i + 9;
+    }
+
+    @Override
+    public boolean contains(Predicate<ItemStack> predicate) {
+        return this.compartments.stream().flatMap(NonNullList::stream).anyMatch(predicate);
+    }
+
+    @Override
+    public List<ItemStack> getArmorContents() {
+        return this.armor;
+    }
+
+    @Override
+    public void onOpen(CraftHumanEntity who) {
+        this.player.getInventory().onOpen(who);
+    }
+
+    @Override
+    public void onClose(CraftHumanEntity who) {
+        this.player.getInventory().onClose(who);
+    }
+
+    @Override
+    public List<HumanEntity> getViewers() {
+        return this.player.getInventory().getViewers();
+    }
+
+    @Override
+    public InventoryHolder getOwner() {
+        return this.player.getBukkitEntity();
+    }
+
+    @Override
+    public int getMaxStackSize() {
+        return this.player.getInventory().getMaxStackSize();
+    }
+
+    @Override
+    public void setMaxStackSize(int size) {
+        this.player.getInventory().setMaxStackSize(size);
+    }
+
+    @Override
+    public Location getLocation() {
+        return this.player.getBukkitEntity().getLocation();
+    }
+
+    @Override
+    public boolean hasCustomName() {
+        return false;
+    }
+
+    @Override
+    public List<ItemStack> getContents() {
+        return this.compartments.stream().flatMap(Collection::stream).collect(Collectors.toList());
+    }
+
+    @Override
+    public ItemStack getSelected() {
+        return isHotbarSlot(this.selected) ? this.items.get(this.selected) : ItemStack.EMPTY;
+    }
+
+    private boolean hasRemainingSpaceForItem(ItemStack itemstack, ItemStack itemstack1) {
+        return !itemstack.isEmpty() && ItemStack.isSameItemSameComponents(itemstack, itemstack1) && itemstack.isStackable() && itemstack.getCount() < itemstack.getMaxStackSize() && itemstack.getCount() < this.getMaxStackSize();
+    }
+
+    @Override
+    public int canHold(ItemStack itemstack) {
+        int remains = itemstack.getCount();
+
+        for (int i = 0; i < this.items.size(); ++i) {
+            ItemStack itemstack1 = this.getRawItem(i);
+            if (itemstack1.isEmpty()) {
+                return itemstack.getCount();
+            }
+
+            if (this.hasRemainingSpaceForItem(itemstack1, itemstack)) {
+                remains -= (itemstack1.getMaxStackSize() < this.getMaxStackSize() ? itemstack1.getMaxStackSize() : this.getMaxStackSize()) - itemstack1.getCount();
+            }
+
+            if (remains <= 0) {
+                return itemstack.getCount();
+            }
+        }
+
+        ItemStack offhandItemStack = this.getRawItem(this.items.size() + this.armor.size());
+        if (this.hasRemainingSpaceForItem(offhandItemStack, itemstack)) {
+            remains -= (offhandItemStack.getMaxStackSize() < this.getMaxStackSize() ? offhandItemStack.getMaxStackSize() : this.getMaxStackSize()) - offhandItemStack.getCount();
+        }
+
+        return remains <= 0 ? itemstack.getCount() : itemstack.getCount() - remains;
+    }
+
+    @Override
+    public int getFreeSlot() {
+        for(int i = 0; i < this.items.size(); ++i) {
+            if (this.items.get(i).isEmpty()) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    @Override
+    public void setPickedItem(ItemStack itemstack) {
+        int i = this.findSlotMatchingItem(itemstack);
+        if (isHotbarSlot(i)) {
+            this.selected = i;
+        } else if (i == -1) {
+            this.selected = this.getSuitableHotbarSlot();
+            if (!this.items.get(this.selected).isEmpty()) {
+                int j = this.getFreeSlot();
+                if (j != -1) {
+                    this.items.set(j, this.items.get(this.selected));
+                }
+            }
+
+            this.items.set(this.selected, itemstack);
+        } else {
+            this.pickSlot(i);
+        }
+
+    }
+
+    @Override
+    public void pickSlot(int i) {
+        this.selected = this.getSuitableHotbarSlot();
+        ItemStack itemstack = this.items.get(this.selected);
+        this.items.set(this.selected, this.items.get(i));
+        this.items.set(i, itemstack);
+    }
+
+    @Override
+    public int findSlotMatchingItem(ItemStack itemstack) {
+        for(int i = 0; i < this.items.size(); ++i) {
+            if (!this.items.get(i).isEmpty() && ItemStack.isSameItemSameComponents(itemstack, this.items.get(i))) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    @Override
+    public int findSlotMatchingUnusedItem(ItemStack itemStack) {
+        for(int i = 0; i < this.items.size(); ++i) {
+            ItemStack localItem = this.items.get(i);
+            if (!this.items.get(i).isEmpty() && ItemStack.isSameItemSameComponents(itemStack, this.items.get(i)) && !this.items.get(i).isDamaged() && !localItem.isEnchanted() && !localItem.has(DataComponents.CUSTOM_NAME)) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    @Override
+    public int getSuitableHotbarSlot() {
+        int i;
+        int j;
+        for(j = 0; j < 9; ++j) {
+            i = (this.selected + j) % 9;
+            if (this.items.get(i).isEmpty()) {
+                return i;
+            }
+        }
+
+        for(j = 0; j < 9; ++j) {
+            i = (this.selected + j) % 9;
+            if (!this.items.get(i).isEnchanted()) {
+                return i;
+            }
+        }
+
+        return this.selected;
+    }
+
+    @Override
+    public void swapPaint(double d0) {
+        int i = (int) Math.signum(d0);
+
+        this.selected -= i;
+
+        while (this.selected < 0) {
+            this.selected += 9;
+        }
+
+        while(this.selected >= 9) {
+            this.selected -= 9;
+        }
+    }
+
+    @Override
+    public int clearOrCountMatchingItems(Predicate<ItemStack> predicate, int i, Container container) {
+        byte b0 = 0;
+        boolean flag = i == 0;
+        int j = b0 + ContainerHelper.clearOrCountMatchingItems(this, predicate, i - b0, flag);
+        j += ContainerHelper.clearOrCountMatchingItems(container, predicate, i - j, flag);
+        ItemStack itemstack = this.player.containerMenu.getCarried();
+        j += ContainerHelper.clearOrCountMatchingItems(itemstack, predicate, i - j, flag);
+        if (itemstack.isEmpty()) {
+            this.player.containerMenu.setCarried(ItemStack.EMPTY);
+        }
+
+        return j;
+    }
+
+    private int addResource(ItemStack itemstack) {
+        int i = this.getSlotWithRemainingSpace(itemstack);
+        if (i == -1) {
+            i = this.getFreeSlot();
+        }
+
+        return i == -1 ? itemstack.getCount() : this.addResource(i, itemstack);
+    }
+
+    private int addResource(int i, ItemStack itemstack) {
+        int j = itemstack.getCount();
+        ItemStack localItemStack = this.getRawItem(i);
+        if (localItemStack.isEmpty()) {
+            localItemStack = itemstack.copyWithCount(0);
+            this.setRawItem(i, localItemStack);
+        }
+
+        int k = Math.min(j, this.getMaxStackSize(localItemStack) - localItemStack.getCount());
+
+        if (k != 0) {
+            j -= k;
+            localItemStack.grow(k);
+            localItemStack.setPopTime(5);
+        }
+
+        return j;
+    }
+
+    @Override
+    public int getSlotWithRemainingSpace(ItemStack itemstack) {
+        if (this.hasRemainingSpaceForItem(this.getRawItem(this.selected), itemstack)) {
+            return this.selected;
+        } else if (this.hasRemainingSpaceForItem(this.getRawItem(40), itemstack)) {
+            return 40;
+        } else {
+            for(int i = 0; i < this.items.size(); ++i) {
+                if (this.hasRemainingSpaceForItem(this.items.get(i), itemstack)) {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+    }
+
+    @Override
+    public void tick() {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            for (int i = 0; i < compartment.size(); ++i) {
+                if (!compartment.get(i).isEmpty()) {
+                    compartment.get(i).inventoryTick(this.player.level(), this.player, i, this.selected == i);
+                }
+            }
+        }
+
+    }
+
+    @Override
+    public boolean add(ItemStack itemStack) {
+        return this.add(-1, itemStack);
+    }
+
+    @Override
+    public boolean add(int i, ItemStack itemStack) {
+        if (itemStack.isEmpty()) {
+            return false;
+        } else {
+            try {
+                if (itemStack.isDamaged()) {
+                    if (i == -1) {
+                        i = this.getFreeSlot();
+                    }
+
+                    if (i >= 0) {
+                        this.items.set(i, itemStack.copy());
+                        this.items.get(i).setPopTime(5);
+                        itemStack.setCount(0);
+                        return true;
+                    } else if (this.player.hasInfiniteMaterials()) {
+                        itemStack.setCount(0);
+                        return true;
+                    } else {
+                        return false;
+                    }
+                } else {
+                    int j;
+                    do {
+                        j = itemStack.getCount();
+                        if (i == -1) {
+                            itemStack.setCount(this.addResource(itemStack));
+                        } else {
+                            itemStack.setCount(this.addResource(i, itemStack));
+                        }
+                    } while(!itemStack.isEmpty() && itemStack.getCount() < j);
+
+                    if (itemStack.getCount() == j && this.player.hasInfiniteMaterials()) {
+                        itemStack.setCount(0);
+                        return true;
+                    } else {
+                        return itemStack.getCount() < j;
+                    }
+                }
+            } catch (Throwable var6) {
+                CrashReport crashReport = CrashReport.forThrowable(var6, "Adding item to inventory");
+                CrashReportCategory crashReportCategory = crashReport.addCategory("Item being added");
+                crashReportCategory.setDetail("Item ID", Item.getId(itemStack.getItem()));
+                crashReportCategory.setDetail("Item data", itemStack.getDamageValue());
+                crashReportCategory.setDetail("Item name", () -> itemStack.getHoverName().getString());
+                throw new ReportedException(crashReport);
+            }
+        }
+    }
+
+    @Override
+    public void placeItemBackInInventory(ItemStack itemStack) {
+        this.placeItemBackInInventory(itemStack, true);
+    }
+
+    @Override
+    public void placeItemBackInInventory(ItemStack itemStack, boolean flag) {
+        while(true) {
+            if (!itemStack.isEmpty()) {
+                int i = this.getSlotWithRemainingSpace(itemStack);
+                if (i == -1) {
+                    i = this.getFreeSlot();
+                }
+
+                if (i != -1) {
+                    int j = itemStack.getMaxStackSize() - this.getRawItem(i).getCount();
+                    if (this.add(i, itemStack.split(j)) && flag && this.player instanceof ServerPlayer) {
+                        ((ServerPlayer)this.player).connection.send(new ClientboundContainerSetSlotPacket(-2, 0, i, this.getRawItem(i)));
+                    }
+                    continue;
+                }
+
+                this.player.drop(itemStack, false);
+            }
+
+            return;
+        }
+    }
+
+    @Override
+    public ItemStack removeItem(int rawIndex, final int j) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null
+                || indexedCompartment.compartment().get(indexedCompartment.index()).isEmpty()) {
+            return ItemStack.EMPTY;
+        }
+
+        return ContainerHelper.removeItem(indexedCompartment.compartment(), indexedCompartment.index(), j);
+    }
+
+    @Override
+    public void removeItem(ItemStack itemStack) {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            for (int i = 0; i < compartment.size(); ++i) {
+                if (compartment.get(i) == itemStack) {
+                    compartment.set(i, ItemStack.EMPTY);
+                    break;
+                }
+            }
+        }
+    }
+
+    @Override
+    public ItemStack removeItemNoUpdate(int rawIndex) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null) {
+            return ItemStack.EMPTY;
+        }
+
+        ItemStack removed = indexedCompartment.compartment().set(indexedCompartment.index(), ItemStack.EMPTY);
+
+        if (removed.isEmpty()) {
+            return ItemStack.EMPTY;
+        }
+
+        return removed;
+    }
+
+    @Override
+    public void setItem(int rawIndex, final ItemStack itemStack) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null) {
+            this.player.drop(itemStack, true);
+            return;
+        }
+
+        indexedCompartment.compartment().set(indexedCompartment.index(), itemStack);
+    }
+
+    @Override
+    public float getDestroySpeed(BlockState blockState) {
+        return this.items.get(this.selected).getDestroySpeed(blockState);
+    }
+
+    @Override
+    public ListTag save(ListTag listTag) {
+        for (int i = 0; i < this.items.size(); ++i) {
+            if (!this.items.get(i).isEmpty()) {
+                CompoundTag compoundTag = new CompoundTag();
+                compoundTag.putByte("Slot", (byte)i);
+                this.items.get(i).save(this.player.registryAccess(), compoundTag);
+                listTag.add(compoundTag);
+            }
+        }
+
+        for (int i = 0; i < this.armor.size(); ++i) {
+            if (!this.armor.get(i).isEmpty()) {
+                CompoundTag compoundTag = new CompoundTag();
+                compoundTag.putByte("Slot", (byte)(i + 100));
+                this.armor.get(i).save(this.player.registryAccess(), compoundTag);
+                listTag.add(compoundTag);
+            }
+        }
+
+        for (int i = 0; i < this.offhand.size(); ++i) {
+            if (!this.offhand.get(i).isEmpty()) {
+                CompoundTag compoundTag = new CompoundTag();
+                compoundTag.putByte("Slot", (byte)(i + 150));
+                this.offhand.get(i).save(this.player.registryAccess(), compoundTag);
+                listTag.add(compoundTag);
+            }
+        }
+
+        return listTag;
+    }
+
+    @Override
+    public void load(ListTag listTag) {
+        this.items.clear();
+        this.armor.clear();
+        this.offhand.clear();
+
+        for(int i = 0; i < listTag.size(); ++i) {
+            CompoundTag compoundTag = listTag.getCompound(i);
+            int j = compoundTag.getByte("Slot") & 255;
+            ItemStack itemstack = ItemStack.parse(this.player.registryAccess(), compoundTag).orElse(ItemStack.EMPTY);
+            if (j < this.items.size()) {
+                this.items.set(j, itemstack);
+            } else if (j >= 100 && j < this.armor.size() + 100) {
+                this.armor.set(j - 100, itemstack);
+            } else if (j >= 150 && j < this.offhand.size() + 150) {
+                this.offhand.set(j - 150, itemstack);
+            }
+        }
+
+    }
+
+    @Override
+    public int getContainerSize() {
+        return 45;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return !contains(itemStack -> !itemStack.isEmpty());
+    }
+
+    @Override
+    public ItemStack getItem(int rawIndex) {
+        IndexedCompartment indexedCompartment = getIndexedContent(rawIndex);
+
+        if (indexedCompartment.compartment() == null) {
+            return ItemStack.EMPTY;
+        }
+
+        return indexedCompartment.compartment().get(indexedCompartment.index());
+    }
+
+    @Override
+    public Component getName() {
+        return this.player.getName();
+    }
+
+    @Override
+    public ItemStack getArmor(int index) {
+        return this.armor.get(index);
+    }
+
+    @Override
+    public void dropAll() {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            for (int i = 0; i < compartment.size(); ++i) {
+                ItemStack itemstack = compartment.get(i);
+                if (!itemstack.isEmpty()) {
+                    this.player.drop(itemstack, true, false);
+                    compartment.set(i, ItemStack.EMPTY);
+                }
+            }
+        }
+    }
+
+    @Override
+    public void setChanged() {
+        super.setChanged();
+    }
+
+    @Override
+    public int getTimesChanged() {
+        return super.getTimesChanged();
+    }
+
+    @Override
+    public boolean stillValid(Player player) {
+        return true;
+    }
+
+    @Override
+    public boolean contains(ItemStack itemstack) {
+        return contains(itemStack -> !itemStack.isEmpty() && ItemStack.isSameItemSameComponents(itemstack, itemStack));
+    }
+
+    @Override
+    public boolean contains(TagKey<Item> tagKey) {
+        return contains(itemStack -> !itemStack.isEmpty() && itemStack.is(tagKey));
+    }
+
+    @Override
+    public void replaceWith(Inventory inventory) {
+        Function<Integer, ItemStack> getter;
+
+        if (inventory instanceof SpecialPlayerInventory specialPlayerInventory) {
+            getter = specialPlayerInventory::getRawItem;
+        } else {
+            getter = inventory::getItem;
+        }
+
+        for(int i = 0; i < this.getContainerSize(); ++i) {
+            this.setRawItem(i, getter.apply(i));
+        }
+
+        this.selected = inventory.selected;
+    }
+
+    @Override
+    public void clearContent() {
+        for (NonNullList<ItemStack> compartment : this.compartments) {
+            compartment.clear();
+        }
+    }
+
+    @Override
+    public void fillStackedContents(StackedContents stackedContents) {
+        for (ItemStack itemstack : this.items) {
+            stackedContents.accountSimpleStack(itemstack);
+        }
+    }
+
+    @Override
+    public ItemStack removeFromSelected(boolean dropWholeStack) {
+        ItemStack itemstack = this.getSelected();
+        return itemstack.isEmpty() ? ItemStack.EMPTY : this.removeItem(this.selected, dropWholeStack ? itemstack.getCount() : 1);
+    }
+
+}

internal/v1_21_R1/pom.xml

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright (C) 2011-2023 lishid. All rights reserved.
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by
+  ~ the Free Software Foundation, version 3.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+  ~ GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License
+  ~ along with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <artifactId>openinvparent</artifactId>
+    <groupId>com.lishid</groupId>
+    <relativePath>../../pom.xml</relativePath>
+    <version>5.1.1</version>
+  </parent>
+
+  <artifactId>openinvadapter1_21_R1</artifactId>
+  <name>OpenInvAdapter1_21_R1</name>
+
+  <properties>
+    <maven.compiler.system>21</maven.compiler.system>
+    <maven.compiler.release>21</maven.compiler.release>
+    <spigot.version>1.21.1-R0.1-SNAPSHOT</spigot.version>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.spigotmc</groupId>
+      <artifactId>spigot-api</artifactId>
+      <version>${spigot.version}</version>
+    </dependency>
+    <dependency>
+      <artifactId>spigot</artifactId>
+      <groupId>org.spigotmc</groupId>
+      <scope>provided</scope>
+      <version>${spigot.version}</version>
+      <classifier>remapped-mojang</classifier>
+    </dependency>
+    <dependency>
+      <artifactId>openinvapi</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>openinvcommon</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>annotations</artifactId>
+      <groupId>org.jetbrains</groupId>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <groupId>net.md-5</groupId>
+        <artifactId>specialsource-maven-plugin</artifactId>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/InternalAccessor.java

@@ -0,0 +1,81 @@
+package com.lishid.openinv.internal.v1_21_R1;
+
+import com.lishid.openinv.internal.Accessor;
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.AnySilentContainer;
+import com.lishid.openinv.internal.v1_21_R1.container.OpenEnderChest;
+import com.lishid.openinv.internal.v1_21_R1.container.OpenInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import com.lishid.openinv.internal.v1_21_R1.player.PlayerManager;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.world.Container;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventory;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class InternalAccessor implements Accessor {
+
+  private final @NotNull Logger logger;
+  private final @NotNull PlayerManager manager;
+  private final @NotNull AnySilentContainer anySilentContainer;
+
+  public InternalAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
+    this.logger = logger;
+    manager = new PlayerManager(logger);
+    anySilentContainer = new AnySilentContainer(logger, lang);
+  }
+
+  @Override
+  public @NotNull PlayerManager getPlayerManager() {
+    return manager;
+  }
+
+  @Override
+  public @NotNull IAnySilentContainer getAnySilentContainer() {
+    return anySilentContainer;
+  }
+
+  @Override
+  public @NotNull ISpecialPlayerInventory createPlayerInventory(@NotNull Player player) {
+    return new OpenInventory(player);
+  }
+
+  @Override
+  public @NotNull ISpecialEnderChest createEnderChest(@NotNull Player player) {
+    return new OpenEnderChest(player);
+  }
+
+  @Override
+  public <T extends ISpecialInventory> @Nullable T get(@NotNull Inventory bukkitInventory, @NotNull Class<T> clazz) {
+    if (!(bukkitInventory instanceof CraftInventory craftInventory)) {
+      return null;
+    }
+    Container container = craftInventory.getInventory();
+    if (clazz.isInstance(container)) {
+      return clazz.cast(container);
+    }
+    return null;
+  }
+
+  @Override
+  public void reload(@NotNull ConfigurationSection config) {
+    ConfigurationSection placeholders = config.getConfigurationSection("placeholders");
+    if (placeholders != null) {
+      try {
+        Placeholders.load(placeholders);
+      } catch (Exception e) {
+        logger.log(Level.WARNING, "Caught exception loading placeholder overrides!", e);
+      }
+    }
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/AnySilentContainer.java

@@ -0,0 +1,210 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.internal.v1_21_R1.container;
+
+import com.lishid.openinv.internal.AnySilentContainerBase;
+import com.lishid.openinv.internal.v1_21_R1.container.menu.OpenChestMenu;
+import com.lishid.openinv.internal.v1_21_R1.player.PlayerManager;
+import com.lishid.openinv.util.ReflectionHelper;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.core.BlockPos;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.level.ServerPlayerGameMode;
+import net.minecraft.world.MenuProvider;
+import net.minecraft.world.SimpleMenuProvider;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.PlayerEnderChestContainer;
+import net.minecraft.world.level.GameType;
+import net.minecraft.world.level.block.BarrelBlock;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.ChestBlock;
+import net.minecraft.world.level.block.ShulkerBoxBlock;
+import net.minecraft.world.level.block.TrappedChestBlock;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.entity.EnderChestBlockEntity;
+import net.minecraft.world.level.block.entity.RandomizableContainerBlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+import org.bukkit.GameMode;
+import org.bukkit.Material;
+import org.bukkit.Statistic;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.logging.Logger;
+
+public class AnySilentContainer extends AnySilentContainerBase {
+
+    private final @NotNull Logger logger;
+    private final @NotNull LanguageManager lang;
+    private @Nullable Field serverPlayerGameModeGameType;
+
+    public AnySilentContainer(@NotNull Logger logger, @NotNull LanguageManager lang) {
+        this.logger = logger;
+        this.lang = lang;
+        try {
+            try {
+                this.serverPlayerGameModeGameType = ServerPlayerGameMode.class.getDeclaredField("b");
+                this.serverPlayerGameModeGameType.setAccessible(true);
+            } catch (NoSuchFieldException e) {
+                logger.warning("ServerPlayerGameMode#gameModeForPlayer's obfuscated name has changed!");
+                logger.warning("Please report this at https://github.com/Jikoo/OpenInv/issues");
+                logger.warning("Attempting to fall through using reflection. Please verify that SilentContainer does not fail.");
+                // N.B. gameModeForPlayer is (for now) declared before previousGameModeForPlayer so silent shouldn't break.
+                this.serverPlayerGameModeGameType = ReflectionHelper.grabFieldByType(ServerPlayerGameMode.class, GameType.class);
+            }
+        } catch (SecurityException e) {
+            logger.warning("Unable to directly write player game mode! SilentContainer will fail.");
+            logger.log(java.util.logging.Level.WARNING, "Error obtaining GameType field", e);
+        }
+    }
+
+    @Override
+    public boolean activateContainer(
+            @NotNull final Player bukkitPlayer,
+            final boolean silentchest,
+            @NotNull final org.bukkit.block.Block bukkitBlock) {
+
+        // Silent ender chest is API-only
+        if (silentchest && bukkitBlock.getType() == Material.ENDER_CHEST) {
+            bukkitPlayer.openInventory(bukkitPlayer.getEnderChest());
+            bukkitPlayer.incrementStatistic(Statistic.ENDERCHEST_OPENED);
+            return true;
+        }
+
+        ServerPlayer player = PlayerManager.getHandle(bukkitPlayer);
+
+        final net.minecraft.world.level.Level level = player.level();
+        final BlockPos blockPos = new BlockPos(bukkitBlock.getX(), bukkitBlock.getY(), bukkitBlock.getZ());
+        final BlockEntity blockEntity = level.getBlockEntity(blockPos);
+
+        if (blockEntity == null) {
+            return false;
+        }
+
+        if (blockEntity instanceof EnderChestBlockEntity enderChestTile) {
+            // Anychest ender chest. See net.minecraft.world.level.block.EnderChestBlock
+            PlayerEnderChestContainer enderChest = player.getEnderChestInventory();
+            enderChest.setActiveChest(enderChestTile);
+            player.openMenu(new SimpleMenuProvider((containerCounter, playerInventory, ignored) -> {
+                MenuType<?> containers = OpenChestMenu.getChestMenuType(enderChest.getContainerSize());
+                int rows = enderChest.getContainerSize() / 9;
+                return new ChestMenu(containers, containerCounter, playerInventory, enderChest, rows);
+            }, Component.translatable("container.enderchest")));
+            bukkitPlayer.incrementStatistic(Statistic.ENDERCHEST_OPENED);
+            return true;
+        }
+
+        if (!(blockEntity instanceof MenuProvider menuProvider)) {
+            return false;
+        }
+
+        BlockState blockState = level.getBlockState(blockPos);
+        Block block = blockState.getBlock();
+
+        if (block instanceof ChestBlock chestBlock) {
+
+            // boolean flag: do not check if chest is blocked
+            menuProvider = chestBlock.getMenuProvider(blockState, level, blockPos, true);
+
+            if (menuProvider == null) {
+                lang.sendSystemMessage(bukkitPlayer, "messages.error.lootNotGenerated");
+                return false;
+            }
+
+            if (block instanceof TrappedChestBlock) {
+                bukkitPlayer.incrementStatistic(Statistic.TRAPPED_CHEST_TRIGGERED);
+            } else {
+                bukkitPlayer.incrementStatistic(Statistic.CHEST_OPENED);
+            }
+        }
+
+        if (block instanceof ShulkerBoxBlock) {
+            bukkitPlayer.incrementStatistic(Statistic.SHULKER_BOX_OPENED);
+        }
+
+        if (block instanceof BarrelBlock) {
+            bukkitPlayer.incrementStatistic(Statistic.OPEN_BARREL);
+        }
+
+        // AnyChest only - SilentChest not active, container unsupported, or unnecessary.
+        if (!silentchest || player.gameMode.getGameModeForPlayer() == GameType.SPECTATOR) {
+            player.openMenu(menuProvider);
+            return true;
+        }
+
+        // SilentChest requires access to setting players' game mode directly.
+        if (this.serverPlayerGameModeGameType == null) {
+            return false;
+        }
+
+        if (blockEntity instanceof RandomizableContainerBlockEntity lootable) {
+            if (lootable.lootTable != null) {
+                lang.sendSystemMessage(bukkitPlayer, "messages.error.lootNotGenerated");
+                return false;
+            }
+        }
+
+        GameType gameType = player.gameMode.getGameModeForPlayer();
+        this.forceGameType(player, GameType.SPECTATOR);
+        player.openMenu(menuProvider);
+        this.forceGameType(player, gameType);
+        return true;
+    }
+
+    @Override
+    public void deactivateContainer(@NotNull final Player bukkitPlayer) {
+        if (this.serverPlayerGameModeGameType == null || bukkitPlayer.getGameMode() == GameMode.SPECTATOR) {
+            return;
+        }
+
+        ServerPlayer player = PlayerManager.getHandle(bukkitPlayer);
+
+        // Force game mode change without informing plugins or players.
+        // Regular game mode set calls GameModeChangeEvent and is cancellable.
+        GameType gameType = player.gameMode.getGameModeForPlayer();
+        this.forceGameType(player, GameType.SPECTATOR);
+
+        // ServerPlayer#closeContainer cannot be called without entering an
+        // infinite loop because this method is called during inventory close.
+        // From ServerPlayer#closeContainer -> CraftEventFactory#handleInventoryCloseEvent
+        player.containerMenu.transferTo(player.inventoryMenu, player.getBukkitEntity());
+        // From ServerPlayer#closeContainer
+        player.doCloseContainer();
+        // Regular inventory close will handle the rest - packet sending, etc.
+
+        // Revert forced game mode.
+        this.forceGameType(player, gameType);
+    }
+
+    private void forceGameType(final ServerPlayer player, final GameType gameMode) {
+        if (this.serverPlayerGameModeGameType == null) {
+            // No need to warn repeatedly, error on startup and lack of function should be enough.
+            return;
+        }
+        try {
+            this.serverPlayerGameModeGameType.setAccessible(true);
+            this.serverPlayerGameModeGameType.set(player.gameMode, gameMode);
+        } catch (IllegalArgumentException | IllegalAccessException e) {
+            logger.log(java.util.logging.Level.WARNING, "Error bypassing GameModeChangeEvent", e);
+        }
+    }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/OpenEnderChest.java

@@ -0,0 +1,196 @@
+package com.lishid.openinv.internal.v1_21_R1.container;
+
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.InternalOwned;
+import com.lishid.openinv.internal.v1_21_R1.container.menu.OpenEnderChestMenu;
+import com.lishid.openinv.internal.v1_21_R1.player.PlayerManager;
+import net.minecraft.core.NonNullList;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.entity.player.StackedContents;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.StackedContentsCompatible;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.v1_21_R1.entity.CraftHumanEntity;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventory;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class OpenEnderChest implements Container, StackedContentsCompatible, InternalOwned<ServerPlayer>,
+    ISpecialEnderChest {
+
+  private CraftInventory inventory;
+  private @NotNull ServerPlayer owner;
+  private NonNullList<ItemStack> items;
+  private int maxStack = 64;
+  private final List<HumanEntity> transaction = new ArrayList<>();
+
+  public OpenEnderChest(@NotNull org.bukkit.entity.Player player) {
+    this.owner = PlayerManager.getHandle(player);
+    this.items = owner.getEnderChestInventory().items;
+  }
+
+  @Override
+  public @NotNull ServerPlayer getOwnerHandle() {
+    return owner;
+  }
+
+  @Override
+  public @NotNull org.bukkit.inventory.Inventory getBukkitInventory() {
+    if (inventory == null) {
+      inventory = new CraftInventory(this) {
+        @Override
+        public @NotNull InventoryType getType() {
+          return InventoryType.ENDER_CHEST;
+        }
+      };
+    }
+    return inventory;
+  }
+
+  @Override
+  public void setPlayerOnline(@NotNull org.bukkit.entity.Player player) {
+    owner = PlayerManager.getHandle(player);
+    NonNullList<ItemStack> activeItems = owner.getEnderChestInventory().items;
+
+    // Guard against size changing. Theoretically on Purpur all row variations still have 6 rows internally.
+    int max = Math.min(items.size(), activeItems.size());
+    for (int index = 0; index < max; ++index) {
+      activeItems.set(index, items.get(index));
+    }
+
+    items = activeItems;
+  }
+
+  @Override
+  public void setPlayerOffline() {}
+
+  @Override
+  public @NotNull org.bukkit.entity.Player getPlayer() {
+    return owner.getBukkitEntity();
+  }
+
+  @Override
+  public int getContainerSize() {
+    return items.size();
+  }
+
+  @Override
+  public boolean isEmpty() {
+    return items.stream().allMatch(ItemStack::isEmpty);
+  }
+
+  @Override
+  public ItemStack getItem(int index) {
+    return index >= 0 && index < items.size() ? items.get(index) : ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack removeItem(int index, int amount) {
+    ItemStack itemstack = ContainerHelper.removeItem(items, index, amount);
+
+    if (!itemstack.isEmpty()) {
+      setChanged();
+    }
+
+    return itemstack;
+  }
+
+  @Override
+  public ItemStack removeItemNoUpdate(int index) {
+    return index >= 0 && index < items.size() ? items.set(index, ItemStack.EMPTY) : ItemStack.EMPTY;
+  }
+
+  @Override
+  public void setItem(int index, ItemStack itemStack) {
+    if (index >= 0 && index < items.size()) {
+      items.set(index, itemStack);
+    }
+  }
+
+  @Override
+  public int getMaxStackSize() {
+    return maxStack;
+  }
+
+  @Override
+  public void setChanged() {
+    this.owner.getEnderChestInventory().setChanged();
+  }
+
+  @Override
+  public boolean stillValid(Player player) {
+    return true;
+  }
+
+  @Override
+  public List<ItemStack> getContents() {
+    return items;
+  }
+
+  @Override
+  public void onOpen(CraftHumanEntity craftHumanEntity) {
+    transaction.add(craftHumanEntity);
+  }
+
+  @Override
+  public void onClose(CraftHumanEntity craftHumanEntity) {
+    transaction.remove(craftHumanEntity);
+  }
+
+  @Override
+  public List<HumanEntity> getViewers() {
+    return transaction;
+  }
+
+  @Override
+  public org.bukkit.entity.Player getOwner() {
+    return getPlayer();
+  }
+
+  @Override
+  public void setMaxStackSize(int size) {
+    maxStack = size;
+  }
+
+  @Override
+  public @Nullable Location getLocation() {
+    return null;
+  }
+
+  @Override
+  public void clearContent() {
+    items.clear();
+    setChanged();
+  }
+
+  @Override
+  public void fillStackedContents(StackedContents stackedContents) {
+    for (ItemStack itemstack : items) {
+      stackedContents.accountStack(itemstack);
+    }
+  }
+
+  public Component getTitle() {
+    return Component.translatableWithFallback("openinv.container.enderchest.prefix", "", owner.getName())
+        .append(Component.translatable("container.enderchest"))
+        .append(Component.translatableWithFallback("openinv.container.enderchest.suffix", " - %s", owner.getName()));
+  }
+
+  public @Nullable AbstractContainerMenu createMenu(Player player, int i, boolean viewOnly) {
+    if (player instanceof ServerPlayer serverPlayer) {
+      return new OpenEnderChestMenu(this, serverPlayer, i, viewOnly);
+    }
+    return null;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/OpenInventory.java

@@ -0,0 +1,364 @@
+package com.lishid.openinv.internal.v1_21_R1.container;
+
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.internal.InternalOwned;
+import com.lishid.openinv.internal.v1_21_R1.container.bukkit.OpenPlayerInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.menu.OpenInventoryMenu;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.Content;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentCrafting;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentCraftingResult;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentCursor;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentDrop;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentEquipment;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentList;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentOffHand;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentViewOnly;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.SlotViewOnly;
+import com.lishid.openinv.internal.v1_21_R1.player.PlayerManager;
+import net.minecraft.ChatFormatting;
+import net.minecraft.core.NonNullList;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.chat.MutableComponent;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Inventory;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.v1_21_R1.entity.CraftHumanEntity;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventory;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class OpenInventory implements Container, InternalOwned<ServerPlayer>, ISpecialPlayerInventory {
+
+  private final List<Content> slots;
+  private final int size;
+  private ServerPlayer owner;
+  private int maxStackSize = 99;
+  private CraftInventory bukkitEntity;
+  public List<HumanEntity> transaction = new ArrayList<>();
+
+  public OpenInventory(@NotNull org.bukkit.entity.Player bukkitPlayer) {
+    owner = PlayerManager.getHandle(bukkitPlayer);
+
+    // Get total size, rounding up to nearest 9 for client compatibility.
+    int rawSize = owner.getInventory().getContainerSize() + owner.inventoryMenu.getCraftSlots().getContainerSize() + 1;
+    size = ((int) Math.ceil(rawSize / 9.0)) * 9;
+
+    slots = NonNullList.withSize(size, new ContentViewOnly(owner));
+    setupSlots();
+  }
+
+  private void setupSlots() {
+    // Top of inventory: Regular contents.
+    int nextIndex = addMainInventory();
+
+    // If inventory is expected size, we can arrange slots to be pretty.
+    Inventory ownerInv = owner.getInventory();
+    if (ownerInv.items.size() == 36
+        && ownerInv.armor.size() == 4
+        && ownerInv.offhand.size() == 1
+        && owner.inventoryMenu.getCraftSlots().getContainerSize() == 4) {
+      // Armor slots: Bottom left.
+      addArmor(36);
+      // Off-hand: Below chestplate.
+      addOffHand(46);
+      // Drop slot: Bottom right.
+      slots.set(53, new ContentDrop(owner));
+      // Cursor slot: Above drop.
+      slots.set(44, new ContentCursor(owner));
+
+      // Crafting is displayed in the bottom right corner.
+      // As we're using the pretty view, this is a 3x2.
+      addCrafting(41, true);
+      return;
+    }
+
+    // Otherwise we'll just add elements linearly.
+    nextIndex = addArmor(nextIndex);
+    nextIndex = addOffHand(nextIndex);
+    nextIndex = addCrafting(nextIndex, false);
+    slots.set(nextIndex, new ContentCursor(owner));
+    // Drop slot last.
+    slots.set(slots.size() - 1, new ContentDrop(owner));
+  }
+
+  private int addMainInventory() {
+    int listSize = owner.getInventory().items.size();
+    // Hotbar slots are 0-8. We want those to appear on the bottom of the inventory like a normal player inventory,
+    // so everything else needs to move up a row.
+    int hotbarDiff = listSize - 9;
+    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
+      InventoryType.SlotType type;
+      int invIndex;
+      if (localIndex < hotbarDiff) {
+        invIndex = localIndex + 9;
+        type = InventoryType.SlotType.CONTAINER;
+      } else {
+        type = InventoryType.SlotType.QUICKBAR;
+        invIndex = localIndex - hotbarDiff;
+      }
+
+      slots.set(localIndex, new ContentList(owner, invIndex, type) {
+        @Override
+        public void setHolder(@NotNull ServerPlayer holder) {
+          items = holder.getInventory().items;
+        }
+      });
+    }
+    return listSize;
+  }
+
+  private int addArmor(int startIndex) {
+    int listSize = owner.getInventory().armor.size();
+
+    for (int i = 0; i < listSize; ++i) {
+      // Armor slots go bottom to top; boots are slot 0, helmet is slot 3.
+      // Since we have to display horizontally due to space restrictions,
+      // making the left side the "top" is more user-friendly.
+      int armorIndex;
+      EquipmentSlot slot;
+      switch (i) {
+        case 3 -> {
+          armorIndex = 0;
+          slot = EquipmentSlot.FEET;
+        }
+        case 2 -> {
+          armorIndex = 1;
+          slot = EquipmentSlot.LEGS;
+        }
+        case 1 -> {
+          armorIndex = 2;
+          slot = EquipmentSlot.CHEST;
+        }
+        case 0 -> {
+          armorIndex = 3;
+          slot = EquipmentSlot.HEAD;
+        }
+        default -> {
+          // In the event that new armor slots are added, they can be placed at the end.
+          armorIndex = i;
+          slot = EquipmentSlot.MAINHAND;
+        }
+      }
+
+      slots.set(startIndex + i, new ContentEquipment(owner, armorIndex, slot));
+    }
+
+    return startIndex + listSize;
+  }
+
+  private int addOffHand(int startIndex) {
+    int listSize = owner.getInventory().offhand.size();
+    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
+      slots.set(startIndex + localIndex, new ContentOffHand(owner, localIndex));
+    }
+    return startIndex + listSize;
+  }
+
+  private int addCrafting(int startIndex, boolean pretty) {
+    int listSize = owner.inventoryMenu.getCraftSlots().getContents().size();
+    pretty &= listSize == 4;
+
+    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
+      // Pretty display is a 2x2 rather than linear.
+      // If index is in top row, grid is not 2x2, or pretty is disabled, just use current index.
+      // Otherwise, subtract 2 and add 9 to start in the same position on the next row.
+      int modIndex = startIndex + (localIndex < 2 || !pretty ? localIndex : localIndex + 7);
+
+      slots.set(modIndex, new ContentCrafting(owner, localIndex));
+    }
+
+    if (pretty) {
+      slots.set(startIndex + 2, new ContentViewOnly(owner) {
+        @Override
+        public Slot asSlot(Container container, int slot, int x, int y) {
+          return new SlotViewOnly(container, slot, x, y) {
+            @Override
+            public ItemStack getOrDefault() {
+              return Placeholders.craftingOutput;
+            }
+          };
+        }
+      });
+      slots.set(startIndex + 11, new ContentCraftingResult(owner));
+    }
+
+    return startIndex + listSize;
+  }
+
+  public Slot getMenuSlot(int index, int x, int y) {
+    return slots.get(index).asSlot(this, index, x, y);
+  }
+
+  public InventoryType.SlotType getSlotType(int index) {
+    return slots.get(index).getSlotType();
+  }
+
+  public @NotNull Component getTitle(@Nullable ServerPlayer viewer) {
+    MutableComponent component = Component.empty();
+    // Prefix for use with custom bitmap image fonts.
+    if (owner.equals(viewer)) {
+      component.append(
+          Component.translatableWithFallback("openinv.container.inventory.self", "")
+              .withStyle(style -> style
+                  .withFont(ResourceLocation.parse("openinv:font/inventory"))
+                  .withColor(ChatFormatting.WHITE)));
+    } else {
+      component.append(
+          Component.translatableWithFallback("openinv.container.inventory.other", "")
+              .withStyle(style -> style
+                  .withFont(ResourceLocation.parse("openinv:font/inventory"))
+                  .withColor(ChatFormatting.WHITE)));
+    }
+    // Normal title: "Inventory - OwnerName"
+    component.append(Component.translatableWithFallback("openinv.container.inventory.prefix", "", owner.getName()))
+        .append(Component.translatable("container.inventory"))
+        .append(Component.translatableWithFallback("openinv.container.inventory.suffix", " - %s", owner.getName()));
+    return component;
+  }
+
+  @Override
+  public ServerPlayer getOwnerHandle() {
+    return owner;
+  }
+
+  @Override
+  public @NotNull org.bukkit.inventory.Inventory getBukkitInventory() {
+    if (bukkitEntity == null) {
+      bukkitEntity = new OpenPlayerInventory(this);
+    }
+    return bukkitEntity;
+  }
+
+  @Override
+  public void setPlayerOnline(@NotNull org.bukkit.entity.Player player) {
+    ServerPlayer newOwner = PlayerManager.getHandle(player);
+    // Only transfer regular inventory - crafting and cursor slots are transient.
+    newOwner.getInventory().replaceWith(owner.getInventory());
+    owner = newOwner;
+    // Update slots to point to new inventory.
+    slots.forEach(slot -> slot.setHolder(newOwner));
+  }
+
+  @Override
+  public void setPlayerOffline() {}
+
+  @Override
+  public boolean isInUse() {
+    return !transaction.isEmpty();
+  }
+
+  @Override
+  public @NotNull org.bukkit.entity.Player getPlayer() {
+    return getOwner();
+  }
+
+  @Override
+  public int getContainerSize() {
+    return size;
+  }
+
+  @Override
+  public boolean isEmpty() {
+    return slots.stream().map(Content::get).allMatch(ItemStack::isEmpty);
+  }
+
+  @Override
+  public ItemStack getItem(int index) {
+    return slots.get(index).get();
+  }
+
+  @Override
+  public ItemStack removeItem(int index, int amount) {
+    return slots.get(index).removePartial(amount);
+  }
+
+  @Override
+  public ItemStack removeItemNoUpdate(int index) {
+    return slots.get(index).remove();
+  }
+
+  @Override
+  public void setItem(int index, ItemStack itemStack) {
+    slots.get(index).set(itemStack);
+  }
+
+  @Override
+  public int getMaxStackSize() {
+    return maxStackSize;
+  }
+
+  @Override
+  public void setMaxStackSize(int maxStackSize) {
+    this.maxStackSize = maxStackSize;
+  }
+
+  @Override
+  public void setChanged() {}
+
+  @Override
+  public boolean stillValid(Player player) {
+    return true;
+  }
+
+  @Override
+  public List<ItemStack> getContents() {
+    NonNullList<ItemStack> contents = NonNullList.withSize(getContainerSize(), ItemStack.EMPTY);
+    for (int i = 0; i < getContainerSize(); ++i) {
+      contents.set(i, getItem(i));
+    }
+    return contents;
+  }
+
+  @Override
+  public void onOpen(CraftHumanEntity viewer) {
+    transaction.add(viewer);
+  }
+
+  @Override
+  public void onClose(CraftHumanEntity viewer) {
+    transaction.remove(viewer);
+  }
+
+  @Override
+  public List<HumanEntity> getViewers() {
+    return transaction;
+  }
+
+  @Override
+  public org.bukkit.entity.Player getOwner() {
+    return owner.getBukkitEntity();
+  }
+
+  @Override
+  public Location getLocation() {
+    return owner.getBukkitEntity().getLocation();
+  }
+
+  @Override
+  public void clearContent() {
+    owner.getInventory().clearContent();
+    owner.inventoryMenu.getCraftSlots().clearContent();
+    owner.inventoryMenu.slotsChanged(owner.inventoryMenu.getCraftSlots());
+    owner.containerMenu.setCarried(ItemStack.EMPTY);
+  }
+
+  public @Nullable AbstractContainerMenu createMenu(Player player, int i, boolean viewOnly) {
+    if (player instanceof ServerPlayer serverPlayer) {
+      return new OpenInventoryMenu(this, serverPlayer, i, viewOnly);
+    }
+    return null;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/Placeholders.java

@@ -0,0 +1,183 @@
+package com.lishid.openinv.internal.v1_21_R1.container;
+
+import net.minecraft.core.Registry;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.component.DataComponents;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.TagParser;
+import net.minecraft.network.chat.Component;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.util.Unit;
+import net.minecraft.world.item.DyeColor;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.item.Items;
+import net.minecraft.world.item.component.CustomModelData;
+import net.minecraft.world.item.component.DyedItemColor;
+import net.minecraft.world.level.GameType;
+import net.minecraft.world.level.ItemLike;
+import net.minecraft.world.level.block.entity.BannerPattern;
+import net.minecraft.world.level.block.entity.BannerPatternLayers;
+import net.minecraft.world.level.block.entity.BannerPatterns;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.craftbukkit.v1_21_R1.CraftRegistry;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Optional;
+
+public final class Placeholders {
+
+  private static final CustomModelData DEFAULT_CUSTOM_MODEL_DATA = new CustomModelData(9999);
+  public static final @NotNull EnumMap<GameType, ItemStack> BLOCKED_GAME_TYPE = new EnumMap<>(GameType.class);
+  public static @NotNull ItemStack craftingOutput = defaultCraftingOutput();
+  public static @NotNull ItemStack cursor = defaultCursor();
+  public static @NotNull ItemStack drop = defaultDrop();
+  public static @NotNull ItemStack emptyHelmet = getEmptyArmor(Items.LEATHER_HELMET);
+  public static @NotNull ItemStack emptyChestplate = getEmptyArmor(Items.LEATHER_CHESTPLATE);
+  public static @NotNull ItemStack emptyLeggings = getEmptyArmor(Items.LEATHER_LEGGINGS);
+  public static @NotNull ItemStack emptyBoots = getEmptyArmor(Items.LEATHER_BOOTS);
+  public static @NotNull ItemStack emptyOffHand = getEmptyShield();
+  public static @NotNull ItemStack notSlot = defaultNotSlot();
+  public static @NotNull ItemStack blockedOffline = defaultBlockedOffline();
+
+  static {
+    for (GameType type : GameType.values()) {
+      // Barrier: "Not available - Creative" etc.
+      ItemStack typeItem = new ItemStack(Items.BARRIER);
+      typeItem.set(
+          DataComponents.ITEM_NAME,
+          Component.translatable("options.narrator.notavailable").append(" - ").append(type.getShortDisplayName()));
+      BLOCKED_GAME_TYPE.put(type, typeItem);
+    }
+  }
+
+  public static void load(@NotNull ConfigurationSection section) throws Exception {
+    craftingOutput = parse(section, "crafting-output", craftingOutput);
+    cursor = parse(section, "cursor", cursor);
+    drop = parse(section, "drop", drop);
+    emptyHelmet = parse(section, "empty-helmet", emptyHelmet);
+    emptyChestplate = parse(section, "empty-chestplate", emptyChestplate);
+    emptyLeggings = parse(section, "empty-leggings", emptyLeggings);
+    emptyBoots = parse(section, "empty-boots", emptyBoots);
+    emptyOffHand = parse(section, "empty-off-hand", emptyOffHand);
+    notSlot = parse(section, "not-a-slot", notSlot);
+    blockedOffline = parse(section, "blocked.offline", blockedOffline);
+    BLOCKED_GAME_TYPE.put(GameType.CREATIVE, parse(section, "blocked.creative", BLOCKED_GAME_TYPE.get(GameType.CREATIVE)));
+    BLOCKED_GAME_TYPE.put(GameType.SPECTATOR, parse(section, "blocked.spectator", BLOCKED_GAME_TYPE.get(GameType.SPECTATOR)));
+  }
+
+  private static @NotNull ItemStack parse(
+      @NotNull ConfigurationSection section,
+      @NotNull String path,
+      @NotNull ItemStack defaultStack) throws Exception {
+    String itemText = section.getString(path);
+
+    if (itemText == null) {
+      return defaultStack;
+    }
+
+    CompoundTag compoundTag = TagParser.parseTag(itemText);
+    Optional<ItemStack> parsed = ItemStack.parse(CraftRegistry.getMinecraftRegistry(), compoundTag);
+    return parsed.filter(itemStack -> !itemStack.isEmpty()).orElse(defaultStack);
+  }
+
+  public static ItemStack survivalOnly(@NotNull ServerPlayer serverPlayer) {
+    if (serverPlayer.connection == null || serverPlayer.connection.isDisconnected()) {
+      return blockedOffline;
+    }
+
+    return BLOCKED_GAME_TYPE.getOrDefault(serverPlayer.gameMode.getGameModeForPlayer(), ItemStack.EMPTY);
+  }
+
+  private static ItemStack defaultCraftingOutput() {
+    // Crafting table: "Crafting"
+    ItemStack itemStack = new ItemStack(Items.CRAFTING_TABLE);
+    itemStack.set(DataComponents.ITEM_NAME, Component.translatable("container.crafting"));
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+    return itemStack;
+  }
+
+  private static ItemStack defaultCursor() {
+    // Cursor-like banner with no tooltip
+    ItemStack itemStack = new ItemStack(Items.WHITE_BANNER);
+    RegistryAccess minecraftRegistry = CraftRegistry.getMinecraftRegistry();
+    Registry<BannerPattern> bannerPatterns = minecraftRegistry.registryOrThrow(Registries.BANNER_PATTERN);
+    BannerPattern halfDiagBottomRight = bannerPatterns.getOrThrow(BannerPatterns.DIAGONAL_RIGHT);
+    BannerPattern downRight = bannerPatterns.getOrThrow(BannerPatterns.STRIPE_DOWNRIGHT);
+    BannerPattern border = bannerPatterns.getOrThrow(BannerPatterns.BORDER);
+    itemStack.set(DataComponents.BANNER_PATTERNS,
+        new BannerPatternLayers(List.of(
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(halfDiagBottomRight), DyeColor.GRAY),
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(downRight), DyeColor.WHITE),
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(border), DyeColor.GRAY))));
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    return itemStack;
+  }
+
+  private static ItemStack defaultDrop() {
+    // Dropper: "Drop Selected Item"
+    ItemStack itemStack = new ItemStack(Items.DROPPER);
+    // Note: translatable component, not keybind component! We want the text identifying the keybind, not the key.
+    itemStack.set(DataComponents.ITEM_NAME, Component.translatable("key.drop"));
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+    return itemStack;
+  }
+
+  private static ItemStack getEmptyArmor(ItemLike item) {
+    // Inventory-background-grey-ish leather armor with no tooltip
+    ItemStack itemStack = new ItemStack(item);
+    DyedItemColor color = new DyedItemColor(0xC8C8C8, false);
+    itemStack.set(DataComponents.DYED_COLOR, color);
+    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+    return itemStack;
+  }
+
+  private static ItemStack getEmptyShield() {
+    ItemStack itemStack = new ItemStack(Items.SHIELD);
+    itemStack.set(DataComponents.BASE_COLOR, DyeColor.MAGENTA);
+    RegistryAccess minecraftRegistry = CraftRegistry.getMinecraftRegistry();
+    Registry<BannerPattern> bannerPatterns = minecraftRegistry.registryOrThrow(Registries.BANNER_PATTERN);
+    BannerPattern halfLeft = bannerPatterns.getOrThrow(BannerPatterns.HALF_VERTICAL);
+    BannerPattern topLeft = bannerPatterns.getOrThrow(BannerPatterns.SQUARE_TOP_LEFT);
+    BannerPattern topRight = bannerPatterns.getOrThrow(BannerPatterns.SQUARE_TOP_RIGHT);
+    BannerPattern bottomLeft = bannerPatterns.getOrThrow(BannerPatterns.SQUARE_BOTTOM_LEFT);
+    BannerPattern bottomRight = bannerPatterns.getOrThrow(BannerPatterns.SQUARE_BOTTOM_RIGHT);
+    itemStack.set(DataComponents.BANNER_PATTERNS,
+        new BannerPatternLayers(List.of(
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(halfLeft), DyeColor.BLACK),
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(topLeft), DyeColor.MAGENTA),
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(bottomLeft), DyeColor.MAGENTA),
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(topRight), DyeColor.BLACK),
+            new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(bottomRight), DyeColor.BLACK))));
+    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+    return itemStack;
+  }
+
+  private static ItemStack defaultNotSlot() {
+    // White pane with no tooltip
+    ItemStack itemStack = new ItemStack(Items.WHITE_STAINED_GLASS_PANE);
+    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+    return itemStack;
+  }
+
+  private static ItemStack defaultBlockedOffline() {
+    // Barrier: "Not available - Offline"
+    ItemStack itemStack = new ItemStack(Items.BARRIER);
+    itemStack.set(DataComponents.ITEM_NAME,
+        Component.translatable("options.narrator.notavailable")
+            .append(Component.literal(" - "))
+            .append(Component.translatable("gui.socialInteractions.status_offline")));
+    return itemStack;
+  }
+
+  private Placeholders() {
+    throw new IllegalStateException("Cannot create instance of utility class.");
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/bukkit/OpenDummyInventory.java

@@ -0,0 +1,163 @@
+package com.lishid.openinv.internal.v1_21_R1.container.bukkit;
+
+import com.lishid.openinv.internal.ViewOnly;
+import net.minecraft.world.Container;
+import org.bukkit.Material;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventory;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.ListIterator;
+
+/**
+ * A locked down "empty" inventory that rejects plugin interaction.
+ */
+public class OpenDummyInventory extends CraftInventory implements ViewOnly {
+
+  public OpenDummyInventory(Container inventory) {
+    super(inventory);
+  }
+
+  @Override
+  public @Nullable ItemStack getItem(int index) {
+    return null;
+  }
+
+  @Override
+  public void setItem(int index, @Nullable ItemStack item) {
+
+  }
+
+  @SuppressWarnings("NonApiType")
+  @Override
+  public @NotNull HashMap<Integer, ItemStack> addItem(@NotNull ItemStack... items) throws IllegalArgumentException {
+    return arrayToHashMap(items);
+  }
+
+  @SuppressWarnings("NonApiType")
+  @Override
+  public @NotNull HashMap<Integer, ItemStack> removeItem(@NotNull ItemStack... items) throws IllegalArgumentException {
+    return arrayToHashMap(items);
+  }
+
+  @SuppressWarnings("NonApiType")
+  private static @NotNull HashMap<Integer, ItemStack> arrayToHashMap(@NotNull ItemStack[] items) {
+    HashMap<Integer, ItemStack> ignored = new HashMap<>();
+    for (int index = 0; index < items.length; ++index) {
+      ignored.put(index, items[index]);
+    }
+    return ignored;
+  }
+
+  @Override
+  public ItemStack[] getContents() {
+    return new ItemStack[getSize()];
+  }
+
+  @Override
+  public void setContents(@NotNull ItemStack[] items) throws IllegalArgumentException {
+
+  }
+
+  @Override
+  public @NotNull ItemStack[] getStorageContents() {
+    return new ItemStack[getSize()];
+  }
+
+  @Override
+  public void setStorageContents(@NotNull ItemStack[] items) throws IllegalArgumentException {
+
+  }
+
+  @Override
+  public boolean contains(@NotNull Material material) throws IllegalArgumentException {
+    return false;
+  }
+
+  @Override
+  public boolean contains(@Nullable ItemStack item) {
+    return false;
+  }
+
+  @Override
+  public boolean contains(@NotNull Material material, int amount) throws IllegalArgumentException {
+    return false;
+  }
+
+  @Override
+  public boolean contains(@Nullable ItemStack item, int amount) {
+    return false;
+  }
+
+  @Override
+  public boolean containsAtLeast(@Nullable ItemStack item, int amount) {
+    return false;
+  }
+
+  @SuppressWarnings("NonApiType")
+  @Override
+  public @NotNull HashMap<Integer, ItemStack> all(
+      @NotNull Material material) throws IllegalArgumentException {
+    return new HashMap<>();
+  }
+
+  @SuppressWarnings("NonApiType")
+  @Override
+  public @NotNull HashMap<Integer, ItemStack> all(@Nullable ItemStack item) {
+    return new HashMap<>();
+  }
+
+  @Override
+  public int first(@NotNull Material material) throws IllegalArgumentException {
+    return -1;
+  }
+
+  @Override
+  public int first(@NotNull ItemStack item) {
+    return -1;
+  }
+
+  @Override
+  public int firstEmpty() {
+    return -1;
+  }
+
+  @Override
+  public boolean isEmpty() {
+    return true;
+  }
+
+  @Override
+  public void remove(@NotNull Material material) throws IllegalArgumentException {
+
+  }
+
+  @Override
+  public void remove(@NotNull ItemStack item) {
+
+  }
+
+  @Override
+  public void clear(int index) {
+
+  }
+
+  @Override
+  public void clear() {
+
+  }
+
+  @Override
+  public @NotNull ListIterator<ItemStack> iterator() {
+    return Collections.emptyListIterator();
+  }
+
+  @Override
+  public @NotNull ListIterator<ItemStack> iterator(int index) {
+    return Collections.emptyListIterator();
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/bukkit/OpenPlayerInventory.java

@@ -0,0 +1,221 @@
+package com.lishid.openinv.internal.v1_21_R1.container.bukkit;
+
+import com.google.common.base.Preconditions;
+import com.lishid.openinv.internal.v1_21_R1.container.OpenInventory;
+import net.minecraft.core.NonNullList;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Inventory;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventory;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftItemStack;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.PlayerInventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenPlayerInventory extends CraftInventory implements PlayerInventory {
+
+  public OpenPlayerInventory(@NotNull OpenInventory inventory) {
+    super(inventory);
+  }
+
+  @Override
+  public @NotNull OpenInventory getInventory() {
+    return (OpenInventory) super.getInventory();
+  }
+
+  @Override
+  public ItemStack[] getContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().getContents());
+  }
+
+  @Override
+  public void setContents(ItemStack[] items) {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    int size = internal.getContainerSize();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+
+    for (int index = 0; index < size; ++index) {
+      if (index < items.length) {
+        internal.setItem(index, CraftItemStack.asNMSCopy(items[index]));
+      } else {
+        internal.setItem(index, net.minecraft.world.item.ItemStack.EMPTY);
+      }
+    }
+  }
+
+  @Override
+  public ItemStack[] getStorageContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().items);
+  }
+
+  @Override
+  public void setStorageContents(ItemStack[] items) throws IllegalArgumentException {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().items;
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @NotNull InventoryType getType() {
+    return InventoryType.PLAYER;
+  }
+
+  @Override
+  public @NotNull Player getHolder() {
+    return getInventory().getOwner();
+  }
+
+  @Override
+  public @NotNull ItemStack[] getArmorContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().armor);
+  }
+
+  @Override
+  public void setArmorContents(@Nullable ItemStack[] items) {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().armor;
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @NotNull ItemStack[] getExtraContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().offhand);
+  }
+
+  @Override
+  public void setExtraContents(@Nullable ItemStack[] items) {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().offhand;
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @Nullable ItemStack getHelmet() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.HEAD.getIndex()));
+  }
+
+  @Override
+  public void setHelmet(@Nullable ItemStack helmet) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.HEAD.getIndex(), CraftItemStack.asNMSCopy(helmet));
+  }
+
+  @Override
+  public @Nullable ItemStack getChestplate() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.HEAD.getIndex()));
+  }
+
+  @Override
+  public void setChestplate(@Nullable ItemStack chestplate) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.CHEST.getIndex(), CraftItemStack.asNMSCopy(chestplate));
+  }
+
+  @Override
+  public @Nullable ItemStack getLeggings() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.LEGS.getIndex()));
+  }
+
+  @Override
+  public void setLeggings(@Nullable ItemStack leggings) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.LEGS.getIndex(), CraftItemStack.asNMSCopy(leggings));
+  }
+
+  @Override
+  public @Nullable ItemStack getBoots() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.FEET.getIndex()));
+  }
+
+  @Override
+  public void setBoots(@Nullable ItemStack boots) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.FEET.getIndex(), CraftItemStack.asNMSCopy(boots));
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInMainHand() {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    return CraftItemStack.asCraftMirror(internal.getItem(internal.selected));
+  }
+
+  @Override
+  public void setItemInMainHand(@Nullable ItemStack item) {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    internal.setItem(internal.selected, CraftItemStack.asNMSCopy(item));
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInOffHand() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().offhand.getFirst());
+  }
+
+  @Override
+  public void setItemInOffHand(@Nullable ItemStack item) {
+    getInventory().getOwnerHandle().getInventory().offhand.set(0, CraftItemStack.asNMSCopy(item));
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInHand() {
+    return getItemInMainHand();
+  }
+
+  @Override
+  public void setItemInHand(@Nullable ItemStack stack) {
+    setItemInMainHand(stack);
+  }
+
+  @Override
+  public int getHeldItemSlot() {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    return internal.items.size() - 9 + internal.selected;
+  }
+
+  @Override
+  public void setHeldItemSlot(int slot) {
+    slot %= 9;
+    getInventory().getOwnerHandle().getInventory().selected = slot;
+  }
+
+  @Override
+  public @Nullable ItemStack getItem(@NotNull org.bukkit.inventory.EquipmentSlot slot) {
+    return switch (slot) {
+      case HAND -> getItemInMainHand();
+      case OFF_HAND -> getItemInOffHand();
+      case FEET -> getBoots();
+      case LEGS -> getLeggings();
+      case CHEST -> getChestplate();
+      case HEAD -> getHelmet();
+      default -> throw new IllegalArgumentException("Unsupported EquipmentSlot " + slot);
+    };
+  }
+
+  @Override
+  public void setItem(@NotNull org.bukkit.inventory.EquipmentSlot slot, @Nullable ItemStack item) {
+    switch (slot) {
+      case HAND -> setItemInMainHand(item);
+      case OFF_HAND -> setItemInOffHand(item);
+      case FEET -> setBoots(item);
+      case LEGS -> setLeggings(item);
+      case CHEST -> setChestplate(item);
+      case HEAD -> setHelmet(item);
+      default -> throw new IllegalArgumentException("Unsupported EquipmentSlot " + slot);
+    }
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/bukkit/OpenPlayerInventorySelf.java

@@ -0,0 +1,26 @@
+package com.lishid.openinv.internal.v1_21_R1.container.bukkit;
+
+import com.lishid.openinv.internal.v1_21_R1.container.OpenInventory;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+public class OpenPlayerInventorySelf extends OpenPlayerInventory {
+
+  private final int offset;
+
+  public OpenPlayerInventorySelf(@NotNull OpenInventory inventory, int offset) {
+    super(inventory);
+    this.offset = offset;
+  }
+
+  @Override
+  public ItemStack getItem(int index) {
+    return super.getItem(offset + index);
+  }
+
+  @Override
+  public void setItem(int index, ItemStack item) {
+    super.setItem(offset + index, item);
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/menu/OpenChestMenu.java

@@ -0,0 +1,478 @@
+package com.lishid.openinv.internal.v1_21_R1.container.menu;
+
+import com.google.common.base.Suppliers;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.InternalOwned;
+import com.lishid.openinv.internal.v1_21_R1.container.bukkit.OpenDummyInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.SlotPlaceholder;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.SlotViewOnly;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
+import it.unimi.dsi.fastutil.ints.IntList;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.ClickType;
+import net.minecraft.world.inventory.ContainerData;
+import net.minecraft.world.inventory.ContainerListener;
+import net.minecraft.world.inventory.ContainerSynchronizer;
+import net.minecraft.world.inventory.DataSlot;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventoryView;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Supplier;
+
+/**
+ * An extension of {@link AbstractContainerMenu} that supports {@link SlotPlaceholder placeholders}.
+ */
+public abstract class OpenChestMenu<T extends Container & ISpecialInventory & InternalOwned<ServerPlayer>>
+    extends AbstractContainerMenu {
+
+  protected static final int BOTTOM_INVENTORY_SIZE = 36;
+
+  protected final T container;
+  protected final ServerPlayer viewer;
+  protected final boolean viewOnly;
+  protected final boolean ownContainer;
+  protected final int topSize;
+  private CraftInventoryView<OpenChestMenu<T>> bukkitEntity;
+  // Syncher fields
+  private @Nullable ContainerSynchronizer synchronizer;
+  private final List<DataSlot> dataSlots = new ArrayList<>();
+  private final IntList remoteDataSlots = new IntArrayList();
+  private final List<ContainerListener> containerListeners = new ArrayList<>();
+  private ItemStack remoteCarried = ItemStack.EMPTY;
+  private boolean suppressRemoteUpdates;
+
+  protected OpenChestMenu(
+      @NotNull MenuType<ChestMenu> type,
+      int containerCounter,
+      @NotNull T container,
+      @NotNull ServerPlayer viewer,
+      boolean viewOnly) {
+    super(type, containerCounter);
+    this.container = container;
+    this.viewer = viewer;
+    this.viewOnly = viewOnly;
+    ownContainer = container.getOwnerHandle().equals(viewer);
+    topSize = getTopSize(viewer);
+
+    preSlotSetup();
+
+    int upperRows = topSize / 9;
+    // View's upper inventory - our container
+    for (int row = 0; row < upperRows; ++row) {
+      for (int col = 0; col < 9; ++col) {
+        // x and y for client purposes, but hey, we're thorough here.
+        // Adapted from net.minecraft.world.inventory.ChestMenu
+        int x = 8 + col * 18;
+        int y = 18 + row * 18;
+        int index = row * 9 + col;
+
+        // Guard against weird inventory sizes.
+        if (index >= container.getContainerSize()) {
+          addSlot(new SlotViewOnly(container, index, x, y));
+          continue;
+        }
+
+        Slot slot = getUpperSlot(index, x, y);
+
+        addSlot(slot);
+      }
+    }
+
+    // View's lower inventory - viewer inventory
+    int playerInvPad = (upperRows - 4) * 18;
+    for (int row = 0; row < 3; ++row) {
+      for (int col = 0; col < 9; ++col) {
+        int x = 8 + col * 18;
+        int y = playerInvPad + row * 18 + 103;
+        addSlot(new Slot(viewer.getInventory(), row * 9 + col + 9, x, y));
+      }
+    }
+    // Hotbar
+    for (int col = 0; col < 9; ++col) {
+      int x = 8 + col * 18;
+      int y = playerInvPad + 161;
+      addSlot(new Slot(viewer.getInventory(), col, x, y));
+    }
+  }
+
+  public static @NotNull MenuType<ChestMenu> getChestMenuType(int inventorySize) {
+    inventorySize = ((int) Math.ceil(inventorySize / 9.0)) * 9;
+    return switch (inventorySize) {
+      case 9 -> MenuType.GENERIC_9x1;
+      case 18 -> MenuType.GENERIC_9x2;
+      case 27 -> MenuType.GENERIC_9x3;
+      case 36 -> MenuType.GENERIC_9x4;
+      case 45 -> MenuType.GENERIC_9x5;
+      case 54 -> MenuType.GENERIC_9x6;
+      default -> throw new IllegalArgumentException("Inventory size unsupported: " + inventorySize);
+    };
+  }
+
+  protected void preSlotSetup() {}
+
+  protected @NotNull Slot getUpperSlot(int index, int x, int y) {
+    if (viewOnly) {
+      return new SlotViewOnly(container, index, x, y);
+    }
+    return new Slot(container, index, x, y);
+  }
+
+
+  @Override
+  public final @NotNull CraftInventoryView<OpenChestMenu<T>> getBukkitView() {
+    if (bukkitEntity == null) {
+      bukkitEntity = createBukkitEntity();
+    }
+
+    return bukkitEntity;
+  }
+
+  protected @NotNull CraftInventoryView<OpenChestMenu<T>> createBukkitEntity() {
+    Inventory top;
+    if (viewOnly) {
+      top = new OpenDummyInventory(container);
+    } else {
+      top = container.getBukkitInventory();
+    }
+    return new CraftInventoryView<>(viewer.getBukkitEntity(), top, this) {
+      @Override
+      public @Nullable Inventory getInventory(int rawSlot) {
+        if (viewOnly) {
+          return null;
+        }
+        return super.getInventory(rawSlot);
+      }
+
+      @Override
+      public int convertSlot(int rawSlot) {
+        if (viewOnly) {
+          return InventoryView.OUTSIDE;
+        }
+        return super.convertSlot(rawSlot);
+      }
+
+      @Override
+      public @NotNull InventoryType.SlotType getSlotType(int slot) {
+        if (viewOnly) {
+          return InventoryType.SlotType.OUTSIDE;
+        }
+        return super.getSlotType(slot);
+      }
+    };
+  }
+
+  private int getTopSize(ServerPlayer viewer) {
+    MenuType<?> menuType = getType();
+    if (menuType == null) {
+      throw new IllegalStateException("MenuType cannot be null!");
+    } else if (menuType == MenuType.GENERIC_9x1) {
+      return 9;
+    } else if (menuType == MenuType.GENERIC_9x2) {
+      return 18;
+    } else if (menuType == MenuType.GENERIC_9x3) {
+      return 27;
+    } else if (menuType == MenuType.GENERIC_9x4) {
+      return 36;
+    } else if (menuType == MenuType.GENERIC_9x5) {
+      return 45;
+    } else if (menuType == MenuType.GENERIC_9x6) {
+      return 54;
+    }
+    // This is a bit gross, but allows us a safe fallthrough.
+    return menuType.create(-1, viewer.getInventory()).slots.size() - BOTTOM_INVENTORY_SIZE;
+  }
+
+  /**
+   * Reimplementation of {@link AbstractContainerMenu#moveItemStackTo(ItemStack, int, int, boolean)} that ignores fake
+   * slots and respects {@link Slot#hasItem()}.
+   *
+   * @param itemStack the stack to quick-move
+   * @param rangeLow the start of the range of slots that can be moved to, inclusive
+   * @param rangeHigh the end of the range of slots that can be moved to, exclusive
+   * @param topDown whether to start at the top of the range or bottom
+   * @return whether the stack was modified as a result of being quick-moved
+   */
+  @Override
+  protected boolean moveItemStackTo(ItemStack itemStack, int rangeLow, int rangeHigh, boolean topDown) {
+    boolean modified = false;
+    boolean stackable = itemStack.isStackable();
+    Slot firstEmpty = null;
+
+    for (int index = topDown ? rangeHigh - 1 : rangeLow;
+         !itemStack.isEmpty() && (topDown ? index >= rangeLow : index < rangeHigh);
+         index += topDown ? -1 : 1
+    ) {
+      Slot slot = slots.get(index);
+      // If the slot cannot be added to, check the next slot.
+      if (slot.isFake() || !slot.mayPlace(itemStack)) {
+        continue;
+      }
+
+      if (slot.hasItem()) {
+        // If the item isn't stackable, check the next slot.
+        if (!stackable) {
+          continue;
+        }
+        // Otherwise, add as many as we can from our stack to the slot.
+        modified |= addToExistingStack(itemStack, slot);
+      } else {
+        // If this is the first empty slot, keep track of it for later use.
+        if (firstEmpty == null) {
+          firstEmpty = slot;
+        }
+        // If the item isn't stackable, we've located the slot we're adding it to, so we're done.
+        if (!stackable) {
+          break;
+        }
+      }
+    }
+
+    // If the item hasn't been fully added yet, add as many as we can to the first open slot.
+    if (!itemStack.isEmpty() && firstEmpty != null) {
+      firstEmpty.setByPlayer(itemStack.split(Math.min(itemStack.getCount(), firstEmpty.getMaxStackSize(itemStack))));
+      firstEmpty.setChanged();
+      modified = true;
+    }
+
+    return modified;
+  }
+
+  private static boolean addToExistingStack(ItemStack itemStack, Slot slot) {
+    ItemStack existing = slot.getItem();
+
+    // If the items aren't the same, we can't add our item.
+    if (!ItemStack.isSameItemSameComponents(itemStack, existing)) {
+      return false;
+    }
+
+    int max = slot.getMaxStackSize(existing);
+    int existingCount = existing.getCount();
+
+    // If the stack is already full, we can't add more.
+    if (existingCount >= max) {
+      return false;
+    }
+
+    int total = existingCount + itemStack.getCount();
+
+    // If the existing item can accept the entirety of our item, we're done!
+    if (total <= max) {
+      itemStack.setCount(0);
+      existing.setCount(total);
+      slot.setChanged();
+      return true;
+    }
+
+    // Otherwise, add as many as we can.
+    itemStack.shrink(max - existingCount);
+    existing.setCount(max);
+    slot.setChanged();
+    return true;
+  }
+
+  @Override
+  public void clicked(int i, int j, ClickType clickType, Player player) {
+    if (viewOnly) {
+      if (clickType == ClickType.QUICK_CRAFT) {
+        sendAllDataToRemote();
+      }
+      return;
+    }
+    super.clicked(i, j, clickType, player);
+  }
+
+  @Override
+  public boolean stillValid(Player player) {
+    return true;
+  }
+
+  // Overrides from here on are purely to modify the sync process to send placeholder items.
+  @Override
+  protected Slot addSlot(Slot slot) {
+    slot.index = this.slots.size();
+    this.slots.add(slot);
+    this.lastSlots.add(ItemStack.EMPTY);
+    this.remoteSlots.add(ItemStack.EMPTY);
+    return slot;
+  }
+
+  @Override
+  protected DataSlot addDataSlot(DataSlot dataSlot) {
+    this.dataSlots.add(dataSlot);
+    this.remoteDataSlots.add(0);
+    return dataSlot;
+  }
+
+  @Override
+  protected void addDataSlots(ContainerData containerData) {
+    for (int i = 0; i < containerData.getCount(); i++) {
+      this.addDataSlot(DataSlot.forContainer(containerData, i));
+    }
+  }
+
+  @Override
+  public void addSlotListener(ContainerListener containerListener) {
+    if (!this.containerListeners.contains(containerListener)) {
+      this.containerListeners.add(containerListener);
+      this.broadcastChanges();
+    }
+  }
+
+  @Override
+  public void setSynchronizer(ContainerSynchronizer containerSynchronizer) {
+    this.synchronizer = containerSynchronizer;
+    this.sendAllDataToRemote();
+  }
+
+  @Override
+  public void sendAllDataToRemote() {
+    for (int index = 0; index < slots.size(); ++index) {
+      Slot slot = slots.get(index);
+      this.remoteSlots.set(index, (slot instanceof SlotPlaceholder placeholder ? placeholder.getOrDefault() : slot.getItem()).copy());
+    }
+
+    remoteCarried = getCarried().copy();
+
+    for (int index = 0; index < this.dataSlots.size(); ++index) {
+      this.remoteDataSlots.set(index, this.dataSlots.get(index).get());
+    }
+
+    if (this.synchronizer != null) {
+      this.synchronizer.sendInitialData(this, this.remoteSlots, this.remoteCarried, this.remoteDataSlots.toIntArray());
+    }
+  }
+
+  @Override
+  public void broadcastCarriedItem() {
+    this.remoteCarried = this.getCarried().copy();
+    if (this.synchronizer != null) {
+      this.synchronizer.sendCarriedChange(this, this.remoteCarried);
+    }
+  }
+
+  @Override
+  public void removeSlotListener(ContainerListener containerListener) {
+    this.containerListeners.remove(containerListener);
+  }
+
+  @Override
+  public void broadcastChanges() {
+    for (int index = 0; index < this.slots.size(); ++index) {
+      Slot slot = this.slots.get(index);
+      ItemStack itemstack = slot instanceof SlotPlaceholder placeholder ? placeholder.getOrDefault() : slot.getItem();
+      Supplier<ItemStack> supplier = Suppliers.memoize(itemstack::copy);
+      this.triggerSlotListeners(index, itemstack, supplier);
+      this.synchronizeSlotToRemote(index, itemstack, supplier);
+    }
+
+    this.synchronizeCarriedToRemote();
+
+    for (int index = 0; index < this.dataSlots.size(); ++index) {
+      DataSlot dataSlot = this.dataSlots.get(index);
+      int j = dataSlot.get();
+      if (dataSlot.checkAndClearUpdateFlag()) {
+        this.updateDataSlotListeners(index, j);
+      }
+
+      this.synchronizeDataSlotToRemote(index, j);
+    }
+  }
+
+  @Override
+  public void broadcastFullState() {
+    for (int index = 0; index < this.slots.size(); ++index) {
+      ItemStack itemstack = this.slots.get(index).getItem();
+      this.triggerSlotListeners(index, itemstack, itemstack::copy);
+    }
+
+    for (int index = 0; index < this.dataSlots.size(); ++index) {
+      DataSlot containerproperty = this.dataSlots.get(index);
+      if (containerproperty.checkAndClearUpdateFlag()) {
+        this.updateDataSlotListeners(index, containerproperty.get());
+      }
+    }
+
+    this.sendAllDataToRemote();
+  }
+
+  private void updateDataSlotListeners(int i, int j) {
+    for (ContainerListener containerListener : this.containerListeners) {
+      containerListener.dataChanged(this, i, j);
+    }
+  }
+
+  private void triggerSlotListeners(int index, ItemStack itemStack, Supplier<ItemStack> supplier) {
+    ItemStack itemStack1 = this.lastSlots.get(index);
+    if (!ItemStack.matches(itemStack1, itemStack)) {
+      ItemStack itemStack2 = supplier.get();
+      this.lastSlots.set(index, itemStack2);
+
+      for (ContainerListener containerListener : this.containerListeners) {
+        containerListener.slotChanged(this, index, itemStack2);
+      }
+    }
+  }
+
+  private void synchronizeSlotToRemote(int i, ItemStack itemStack, Supplier<ItemStack> supplier) {
+    if (!this.suppressRemoteUpdates) {
+      ItemStack itemStack1 = this.remoteSlots.get(i);
+      if (!ItemStack.matches(itemStack1, itemStack)) {
+        ItemStack itemstack2 = supplier.get();
+        this.remoteSlots.set(i, itemstack2);
+        if (this.synchronizer != null) {
+          this.synchronizer.sendSlotChange(this, i, itemstack2);
+        }
+      }
+    }
+  }
+
+  private void synchronizeDataSlotToRemote(int index, int value) {
+    if (!this.suppressRemoteUpdates) {
+      int existing = this.remoteDataSlots.getInt(index);
+      if (existing != value) {
+        this.remoteDataSlots.set(index, value);
+        if (this.synchronizer != null) {
+          this.synchronizer.sendDataChange(this, index, value);
+        }
+      }
+    }
+  }
+
+  private void synchronizeCarriedToRemote() {
+    if (!this.suppressRemoteUpdates && !ItemStack.matches(this.getCarried(), this.remoteCarried)) {
+      this.remoteCarried = this.getCarried().copy();
+      if (this.synchronizer != null) {
+        this.synchronizer.sendCarriedChange(this, this.remoteCarried);
+      }
+    }
+  }
+
+  @Override
+  public void setRemoteCarried(ItemStack itemstack) {
+    this.remoteCarried = itemstack.copy();
+  }
+
+  @Override
+  public void suppressRemoteUpdates() {
+    this.suppressRemoteUpdates = true;
+  }
+
+  @Override
+  public void resumeRemoteUpdates() {
+    this.suppressRemoteUpdates = false;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/menu/OpenEnderChestMenu.java

@@ -0,0 +1,53 @@
+package com.lishid.openinv.internal.v1_21_R1.container.menu;
+
+import com.lishid.openinv.internal.v1_21_R1.container.OpenEnderChest;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+public class OpenEnderChestMenu extends OpenChestMenu<OpenEnderChest> {
+
+  public OpenEnderChestMenu(
+      @NotNull OpenEnderChest enderChest,
+      @NotNull ServerPlayer viewer,
+      int containerId,
+      boolean viewOnly) {
+    super(getChestMenuType(enderChest.getContainerSize()), containerId, enderChest, viewer, viewOnly);
+  }
+
+  @Override
+  public ItemStack quickMoveStack(Player player, int index) {
+    if (viewOnly) {
+      return ItemStack.EMPTY;
+    }
+
+    // See ChestMenu
+    Slot slot = this.slots.get(index);
+
+    if (slot.isFake() || !slot.hasItem()) {
+      return ItemStack.EMPTY;
+    }
+
+    ItemStack itemStack = slot.getItem();
+    ItemStack original = itemStack.copy();
+
+    if (index < topSize) {
+      if (!this.moveItemStackTo(itemStack, topSize, this.slots.size(), true)) {
+        return ItemStack.EMPTY;
+      }
+    } else if (!this.moveItemStackTo(itemStack, 0, topSize, false)) {
+      return ItemStack.EMPTY;
+    }
+
+    if (itemStack.isEmpty()) {
+      slot.setByPlayer(ItemStack.EMPTY);
+    } else {
+      slot.setChanged();
+    }
+
+    return original;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/menu/OpenInventoryMenu.java

@@ -0,0 +1,262 @@
+package com.lishid.openinv.internal.v1_21_R1.container.menu;
+
+import com.google.common.base.Preconditions;
+import com.lishid.openinv.internal.v1_21_R1.container.OpenInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.bukkit.OpenDummyInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.bukkit.OpenPlayerInventorySelf;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentDrop;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.ContentEquipment;
+import com.lishid.openinv.internal.v1_21_R1.container.slot.SlotViewOnly;
+import com.lishid.openinv.util.Permissions;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftInventoryView;
+import org.bukkit.craftbukkit.v1_21_R1.inventory.CraftItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenInventoryMenu extends OpenChestMenu<OpenInventory> {
+
+  private int offset;
+
+  public OpenInventoryMenu(OpenInventory inventory, ServerPlayer viewer, int i, boolean viewOnly) {
+    super(getMenuType(inventory, viewer), i, inventory, viewer, viewOnly);
+  }
+
+  private static MenuType<ChestMenu> getMenuType(OpenInventory inventory, ServerPlayer viewer) {
+    int size = inventory.getContainerSize();
+    // Disallow duplicate access to own main inventory contents.
+    if (inventory.getOwnerHandle().equals(viewer)) {
+      size -= viewer.getInventory().items.size();
+      size = ((int) Math.ceil(size / 9.0)) * 9;
+    }
+
+    return getChestMenuType(size);
+  }
+
+  @Override
+  protected void preSlotSetup() {
+    offset = ownContainer ? viewer.getInventory().items.size() : 0;
+  }
+
+  @Override
+  protected @NotNull Slot getUpperSlot(int index, int x, int y) {
+    index += offset;
+    Slot slot = container.getMenuSlot(index, x, y);
+
+    // If the slot cannot be interacted with there's nothing to configure.
+    if (slot.getClass().equals(SlotViewOnly.class)) {
+      return slot;
+    }
+
+    // Remove drop slot if viewer is not allowed to use it.
+    if (slot instanceof ContentDrop.SlotDrop
+        && (viewOnly || !Permissions.INVENTORY_SLOT_DROP.hasPermission(viewer.getBukkitEntity()))) {
+      return new SlotViewOnly(container, index, x, y);
+    }
+
+    if (slot instanceof ContentEquipment.SlotEquipment equipment) {
+      if (viewOnly) {
+        return SlotViewOnly.wrap(slot);
+      }
+
+      Permissions perm = switch (equipment.getEquipmentSlot()) {
+        case HEAD -> Permissions.INVENTORY_SLOT_HEAD_ANY;
+        case CHEST -> Permissions.INVENTORY_SLOT_CHEST_ANY;
+        case LEGS -> Permissions.INVENTORY_SLOT_LEGS_ANY;
+        case FEET -> Permissions.INVENTORY_SLOT_FEET_ANY;
+        // Off-hand can hold anything, not just equipment.
+        default -> null;
+      };
+
+      // If the viewer doesn't have permission, only allow equipment the viewee can equip in the slot.
+      if (perm != null && !perm.hasPermission(viewer.getBukkitEntity())) {
+        equipment.onlyEquipmentFor(container.getOwnerHandle());
+      }
+
+      // Equipment slots are a core part of the inventory, so they will always be shown.
+      return slot;
+    }
+
+    // When viewing own inventory, only allow access to equipment and drop slots (equipment allowed above).
+    if (ownContainer && !(slot instanceof ContentDrop.SlotDrop)) {
+      return new SlotViewOnly(container, index, x, y);
+    }
+
+    if (viewOnly) {
+      return SlotViewOnly.wrap(slot);
+    }
+
+    return slot;
+  }
+
+  @Override
+  protected @NotNull CraftInventoryView<OpenChestMenu<OpenInventory>> createBukkitEntity() {
+    org.bukkit.inventory.Inventory bukkitInventory;
+    if (viewOnly) {
+      bukkitInventory = new OpenDummyInventory(container);
+    } else if (ownContainer) {
+      bukkitInventory = new OpenPlayerInventorySelf(container, offset);
+    } else {
+      bukkitInventory = container.getBukkitInventory();
+    }
+
+    return new CraftInventoryView<>(viewer.getBukkitEntity(), bukkitInventory, this) {
+      @Override
+      public org.bukkit.inventory.ItemStack getItem(int index) {
+        if (viewOnly || index < 0) {
+          return null;
+        }
+
+        Slot slot = slots.get(index);
+        return CraftItemStack.asCraftMirror(slot.hasItem() ? slot.getItem() : ItemStack.EMPTY);
+      }
+
+      @Override
+      public boolean isInTop(int rawSlot) {
+        return rawSlot < topSize;
+      }
+
+      @Override
+      public @Nullable Inventory getInventory(int rawSlot) {
+        if (viewOnly) {
+          return null;
+        }
+        if (rawSlot == InventoryView.OUTSIDE || rawSlot == -1) {
+          return null;
+        }
+        Preconditions.checkArgument(rawSlot >= 0 && rawSlot < topSize + offset + BOTTOM_INVENTORY_SIZE,
+            "Slot %s outside of inventory", rawSlot);
+        if (rawSlot > topSize) {
+          return getBottomInventory();
+        }
+        Slot slot = slots.get(rawSlot);
+        if (slot.isFake()) {
+          return null;
+        }
+        return getTopInventory();
+      }
+
+      @Override
+      public int convertSlot(int rawSlot) {
+        if (viewOnly) {
+          return InventoryView.OUTSIDE;
+        }
+        if (rawSlot < 0) {
+          return rawSlot;
+        }
+        if (rawSlot < topSize) {
+          Slot slot = slots.get(rawSlot);
+          if (slot.isFake()) {
+            return InventoryView.OUTSIDE;
+          }
+          return rawSlot;
+        }
+
+        int slot = rawSlot - topSize;
+
+        if (slot >= 27) {
+          slot -= 27;
+        } else {
+          slot += 9;
+        }
+
+        return slot;
+      }
+
+      @Override
+      public @NotNull InventoryType.SlotType getSlotType(int slot) {
+        if (viewOnly || slot < 0) {
+          return InventoryType.SlotType.OUTSIDE;
+        }
+        if (slot >= topSize) {
+          slot -= topSize;
+          if (slot >= 27) {
+            return InventoryType.SlotType.QUICKBAR;
+          }
+          return InventoryType.SlotType.CONTAINER;
+        }
+        return OpenInventoryMenu.this.container.getSlotType(offset + slot);
+      }
+
+      @Override
+      public int countSlots() {
+        return topSize + BOTTOM_INVENTORY_SIZE;
+      }
+    };
+  }
+
+  @Override
+  public ItemStack quickMoveStack(Player player, int index) {
+    if (viewOnly) {
+      return ItemStack.EMPTY;
+    }
+
+    // See ChestMenu and InventoryMenu
+    Slot slot = this.slots.get(index);
+
+    if (!slot.hasItem() || slot.isFake()) {
+      return ItemStack.EMPTY;
+    }
+
+    ItemStack itemStack = slot.getItem();
+    ItemStack originalStack = itemStack.copy();
+
+    if (index < topSize) {
+      // If we're moving top to bottom, do a normal transfer.
+      if (!this.moveItemStackTo(itemStack, topSize, this.slots.size(), true)) {
+        return ItemStack.EMPTY;
+      }
+    } else {
+      EquipmentSlot equipmentSlot = player.getEquipmentSlotForItem(itemStack);
+      boolean movedGear = switch (equipmentSlot) {
+        // If this is gear, try to move it to the correct slot first.
+        case OFFHAND, FEET, LEGS, CHEST, HEAD -> {
+          // Locate the correct slot in the contents following the main inventory.
+          for (int extra = container.getOwnerHandle().getInventory().items.size() - offset; extra < topSize; ++extra) {
+            Slot extraSlot = getSlot(extra);
+            if (extraSlot instanceof ContentEquipment.SlotEquipment equipSlot
+                && equipSlot.getEquipmentSlot() == equipmentSlot) {
+              // If we've found a matching slot, try to move to it.
+              // If this succeeds, even partially, we will not attempt to move to other slots.
+              // Otherwise, armor is already occupied, so we'll fall through to main inventory.
+              yield this.moveItemStackTo(itemStack, extra, extra + 1, false);
+            }
+          }
+          yield false;
+        }
+        // Non-gear gets no special treatment.
+        default -> false;
+      };
+
+      // If main inventory is not available, there's nowhere else to move.
+      if (offset != 0) {
+        if (!movedGear) {
+          return ItemStack.EMPTY;
+        }
+      } else {
+        // If we didn't move to a gear slot, try to move to a main inventory slot.
+        if (!movedGear && !this.moveItemStackTo(itemStack, 0, container.getOwnerHandle().getInventory().items.size(), true)) {
+          return ItemStack.EMPTY;
+        }
+      }
+    }
+
+    if (itemStack.isEmpty()) {
+      slot.setByPlayer(ItemStack.EMPTY);
+    } else {
+      slot.setChanged();
+    }
+
+    return originalStack;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/Content.java

@@ -0,0 +1,69 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * An interface defining behaviors for entries in a {@link Container}. Used to reduce duplicate content reordering.
+ */
+public interface Content {
+
+  /**
+   * Update internal holder.
+   *
+   * @param holder the new holder
+   */
+  void setHolder(@NotNull ServerPlayer holder);
+
+  /**
+   * Get the current item.
+   *
+   * @return the current item
+   */
+  ItemStack get();
+
+  /**
+   * Remove the current item.
+   *
+   * @return the current item
+   */
+  ItemStack remove();
+
+  /**
+   * Remove some of the current item.
+   *
+   * @return the current item
+   */
+  ItemStack removePartial(int amount);
+
+  /**
+   * Set the current item. If slot is currently not usable, will drop item instead.
+   *
+   * @param itemStack the item to set
+   */
+  void set(ItemStack itemStack);
+
+  /**
+   * Get a {@link Slot} for use in a {@link net.minecraft.world.inventory.AbstractContainerMenu ContainerMenu}. Will
+   * impose any specific restrictions to insertion or removal.
+   *
+   * @param container the backing container
+   * @param slot the slot of the backing container represented
+   * @param x clientside x dimension from top left of inventory, not used
+   * @param y clientside y dimension from top left of inventory, not used
+   * @return a menu slot
+   */
+  Slot asSlot(Container container, int slot, int x, int y);
+
+  /**
+   * Get a loose Bukkit translation of what this slot stores. For example, any slot that drops items at the owner rather
+   * than insert them will report itself as being {@link org.bukkit.event.inventory.InventoryType.SlotType#OUTSIDE}.
+   *
+   * @return the closes Bukkit slot type
+   */
+  org.bukkit.event.inventory.InventoryType.SlotType getSlotType();
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentCrafting.java

@@ -0,0 +1,131 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.List;
+
+/**
+ * A slot in a survival crafting inventory. Unavailable when not online in a survival mode.
+ */
+public class ContentCrafting implements Content {
+
+  private final int index;
+  private ServerPlayer holder;
+  private List<ItemStack> items;
+
+  public ContentCrafting(@NotNull ServerPlayer holder, int index) {
+    setHolder(holder);
+    this.index = index;
+  }
+
+  private boolean isAvailable() {
+    return isAvailable(holder);
+  }
+
+  static boolean isAvailable(@NotNull ServerPlayer holder) {
+    // Player must be online and not in creative - since the creative client is (semi-)authoritative,
+    // it ignores changes without extra help, and will delete the item as a result.
+    // Spectator mode is technically possible but may cause the item to be dropped if the client opens an inventory.
+    return holder.connection != null && !holder.connection.isDisconnected() && holder.gameMode.isSurvival();
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+    // Note: CraftingContainer#getItems is immutable! Be careful with updates.
+    this.items = holder.inventoryMenu.getCraftSlots().getContents();
+  }
+
+  @Override
+  public ItemStack get() {
+    return isAvailable() ? items.get(index) : ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack remove() {
+    if (!this.isAvailable()) {
+      return ItemStack.EMPTY;
+    }
+    ItemStack removed = items.remove(index);
+    if (removed.isEmpty()) {
+      return ItemStack.EMPTY;
+    }
+    holder.inventoryMenu.slotsChanged(holder.inventoryMenu.getCraftSlots());
+    return removed;
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    if (!this.isAvailable()) {
+      return ItemStack.EMPTY;
+    }
+    ItemStack removed = ContainerHelper.removeItem(items, index, amount);
+    if (removed.isEmpty()) {
+      return ItemStack.EMPTY;
+    }
+    holder.inventoryMenu.slotsChanged(holder.inventoryMenu.getCraftSlots());
+    return removed;
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    if (isAvailable()) {
+      items.set(index, itemStack);
+      holder.inventoryMenu.slotsChanged(holder.inventoryMenu.getCraftSlots());
+    } else {
+      holder.drop(itemStack, false);
+    }
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotCrafting(container, slot, x, y);
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return isAvailable() ? InventoryType.SlotType.CRAFTING : InventoryType.SlotType.OUTSIDE;
+  }
+
+  public class SlotCrafting extends SlotPlaceholder {
+
+    private SlotCrafting(Container container, int index, int x, int y) {
+      super(container, index, x, y);
+    }
+
+    @Override
+    public ItemStack getOrDefault() {
+      return isAvailable() ? items.get(ContentCrafting.this.index) : Placeholders.survivalOnly(holder);
+    }
+
+    @Override
+    public boolean mayPickup(Player player) {
+      return isAvailable();
+    }
+
+    @Override
+    public boolean mayPlace(ItemStack itemStack) {
+      return isAvailable();
+    }
+
+    @Override
+    public boolean hasItem() {
+      return isAvailable() && super.hasItem();
+    }
+
+    @Override
+    public boolean isFake() {
+      return !isAvailable();
+    }
+
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentCraftingResult.java

@@ -0,0 +1,48 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.inventory.InventoryMenu;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A slot allowing viewing of the crafting result.
+ *
+ * <p>Unmodifiable because I said so. Use your own crafting grid.</p>
+ */
+public class ContentCraftingResult extends ContentViewOnly {
+
+  public ContentCraftingResult(@NotNull ServerPlayer holder) {
+    super(holder);
+  }
+
+  @Override
+  public ItemStack get() {
+    InventoryMenu inventoryMenu = holder.inventoryMenu;
+    return inventoryMenu.getSlot(inventoryMenu.getResultSlotIndex()).getItem();
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotViewOnly(container, slot, x, y) {
+      @Override
+      public ItemStack getOrDefault() {
+        if (!ContentCrafting.isAvailable(holder)) {
+          return Placeholders.survivalOnly(holder);
+        }
+        InventoryMenu inventoryMenu = holder.inventoryMenu;
+        return inventoryMenu.getSlot(inventoryMenu.getResultSlotIndex()).getItem();
+      }
+    };
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.RESULT;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentCursor.java

@@ -0,0 +1,117 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A slot wrapping the active menu's cursor. Unavailable when not online in a survival mode.
+ */
+public class ContentCursor implements Content {
+
+  private @NotNull ServerPlayer holder;
+
+  public ContentCursor(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+  }
+
+  @Override
+  public ItemStack get() {
+    return isAvailable() ? holder.containerMenu.getCarried() : ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack remove() {
+    ItemStack carried = holder.containerMenu.getCarried();
+    holder.containerMenu.setCarried(ItemStack.EMPTY);
+    return carried;
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    ItemStack carried = holder.containerMenu.getCarried();
+    if (!carried.isEmpty() && carried.getCount() >= amount) {
+      ItemStack value = carried.split(amount);
+      if (carried.isEmpty()) {
+        holder.containerMenu.setCarried(ItemStack.EMPTY);
+      }
+      return value;
+    }
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    if (isAvailable()) {
+      holder.containerMenu.setCarried(itemStack);
+    } else {
+      holder.drop(itemStack, false);
+    }
+  }
+
+  private boolean isAvailable() {
+    // Player must be online and not in creative - since the creative client is (semi-)authoritative,
+    // it ignores changes without extra help, and will delete the item as a result.
+    // Spectator mode is technically possible but may cause the item to be dropped if the client opens an inventory.
+    return holder.connection != null && !holder.connection.isDisconnected() && holder.gameMode.isSurvival();
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotCursor(container, slot, x, y);
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    // As close as possible to "not real"
+    return InventoryType.SlotType.OUTSIDE;
+  }
+
+  public class SlotCursor extends SlotPlaceholder {
+
+    private SlotCursor(Container container, int index, int x, int y) {
+      super(container, index, x, y);
+    }
+
+    @Override
+    public ItemStack getOrDefault() {
+      if (!isAvailable()) {
+        return Placeholders.survivalOnly(holder);
+      }
+      ItemStack carried = holder.containerMenu.getCarried();
+      return carried.isEmpty() ? Placeholders.cursor : carried;
+    }
+
+    @Override
+    public boolean mayPickup(Player player) {
+      return isAvailable();
+    }
+
+    @Override
+    public boolean mayPlace(ItemStack itemStack) {
+      return isAvailable();
+    }
+
+    @Override
+    public boolean hasItem() {
+      return isAvailable() && super.hasItem();
+    }
+
+    @Override
+    public boolean isFake() {
+      return true;
+    }
+
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentDrop.java

@@ -0,0 +1,88 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A fake slot used to drop items. Unavailable offline.
+ */
+public class ContentDrop implements Content {
+
+  private ServerPlayer holder;
+
+  public ContentDrop(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+  }
+
+  @Override
+  public ItemStack get() {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack remove() {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    holder.drop(itemStack, true);
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotDrop(container, slot, x, y);
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    // Behaves like dropping an item outside the screen, just by the target player.
+    return InventoryType.SlotType.OUTSIDE;
+  }
+
+  public class SlotDrop extends SlotPlaceholder {
+
+    private SlotDrop(Container container, int index, int x, int y) {
+      super(container, index, x, y);
+    }
+
+    @Override
+    public ItemStack getOrDefault() {
+      return holder.connection != null && !holder.connection.isDisconnected()
+          ? Placeholders.drop
+          : Placeholders.blockedOffline;
+    }
+
+    @Override
+    public boolean mayPlace(ItemStack itemStack) {
+      return holder.connection != null && !holder.connection.isDisconnected();
+    }
+
+    @Override
+    public boolean hasItem() {
+      return false;
+    }
+
+    @Override
+    public boolean isFake() {
+      return true;
+    }
+
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentEquipment.java

@@ -0,0 +1,78 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A slot for equipment that displays placeholders if empty.
+ */
+public class ContentEquipment extends ContentList {
+
+  private final ItemStack placeholder;
+  private final EquipmentSlot equipmentSlot;
+
+  public ContentEquipment(ServerPlayer holder, int index, EquipmentSlot equipmentSlot) {
+    super(holder, index, InventoryType.SlotType.ARMOR);
+    placeholder = switch (equipmentSlot) {
+      case HEAD -> Placeholders.emptyHelmet;
+      case CHEST -> Placeholders.emptyChestplate;
+      case LEGS -> Placeholders.emptyLeggings;
+      case FEET -> Placeholders.emptyBoots;
+      default -> Placeholders.emptyOffHand;
+    };
+    this.equipmentSlot = equipmentSlot;
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.items = holder.getInventory().armor;
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotEquipment(container, slot, x, y);
+  }
+
+  public class SlotEquipment extends SlotPlaceholder {
+
+    private ServerPlayer viewer;
+
+    SlotEquipment(Container container, int index, int x, int y) {
+      super(container, index, x, y);
+    }
+
+    @Override
+    public ItemStack getOrDefault() {
+      ItemStack itemStack = getItem();
+      if (!itemStack.isEmpty()) {
+        return itemStack;
+      }
+      return placeholder;
+    }
+
+    public EquipmentSlot getEquipmentSlot() {
+      return equipmentSlot;
+    }
+
+    public void onlyEquipmentFor(ServerPlayer viewer) {
+      this.viewer = viewer;
+    }
+
+    @Override
+    public boolean mayPlace(ItemStack var0) {
+      if (viewer == null) {
+        return true;
+      }
+
+      return equipmentSlot == EquipmentSlot.OFFHAND || viewer.getEquipmentSlotForItem(var0) == equipmentSlot;
+    }
+
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentList.java

@@ -0,0 +1,58 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+
+import java.util.List;
+
+/**
+ * A normal slot backed by an item list.
+ */
+public abstract class ContentList implements Content {
+
+  private final int index;
+  private final InventoryType.SlotType slotType;
+  protected List<ItemStack> items;
+
+  public ContentList(ServerPlayer holder, int index, InventoryType.SlotType slotType) {
+    this.index = index;
+    this.slotType = slotType;
+    setHolder(holder);
+  }
+
+  @Override
+  public ItemStack get() {
+    return items.get(index);
+  }
+
+  @Override
+  public ItemStack remove() {
+    ItemStack removed = items.remove(index);
+    return removed == null || removed.isEmpty() ? ItemStack.EMPTY : removed;
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    return ContainerHelper.removeItem(items, index, amount);
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    items.set(index, itemStack);
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new Slot(container, slot, x, y);
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return slotType;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentOffHand.java

@@ -0,0 +1,46 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.inventory.Slot;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A slot for equipment that updates held items if necessary.
+ */
+public class ContentOffHand extends ContentEquipment {
+
+  private ServerPlayer holder;
+
+  public ContentOffHand(ServerPlayer holder, int localIndex) {
+    super(holder, localIndex, EquipmentSlot.OFFHAND);
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.items = holder.getInventory().offhand;
+    this.holder = holder;
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.QUICKBAR;
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotEquipment(container, slot, x, y) {
+      @Override
+      public void setChanged() {
+        if (holder.connection != null
+            && !holder.connection.isDisconnected()
+            && holder.containerMenu != holder.inventoryMenu) {
+          holder.resendItemInHands();
+        }
+      }
+    };
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/ContentViewOnly.java

@@ -0,0 +1,56 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A view-only slot that can't be interacted with.
+ */
+public class ContentViewOnly implements Content {
+
+  @NotNull ServerPlayer holder;
+
+  public ContentViewOnly(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.holder = holder;
+  }
+
+  @Override
+  public ItemStack get() {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack remove() {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    this.holder.drop(itemStack, false);
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotViewOnly(container, slot, x, y);
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.OUTSIDE;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/SlotPlaceholder.java

@@ -0,0 +1,20 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import net.minecraft.world.Container;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+
+/**
+ * An implementation of a slot as used by a menu that may have fake placeholder items.
+ *
+ * <p>Used to prevent plugins (particularly sorting plugins) from adding placeholders to inventories.</p>
+ */
+public abstract class SlotPlaceholder extends Slot {
+
+  public SlotPlaceholder(Container container, int index, int x, int y) {
+    super(container, index, x, y);
+  }
+
+  public abstract ItemStack getOrDefault();
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/container/slot/SlotViewOnly.java

@@ -0,0 +1,151 @@
+package com.lishid.openinv.internal.v1_21_R1.container.slot;
+
+import com.lishid.openinv.internal.v1_21_R1.container.Placeholders;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Optional;
+
+/**
+ * A view-only {@link Slot}. "Blank" by default, but can wrap another slot to display its content.
+ */
+public class SlotViewOnly extends SlotPlaceholder {
+
+  public static @NotNull SlotViewOnly wrap(@NotNull Slot wrapped) {
+    SlotViewOnly wrapper;
+    if (wrapped instanceof SlotPlaceholder placeholder) {
+      wrapper = new SlotViewOnly(wrapped.container, wrapped.slot, wrapped.x, wrapped.y) {
+        @Override
+        public ItemStack getOrDefault() {
+          return placeholder.getOrDefault();
+        }
+      };
+    } else {
+      wrapper = new SlotViewOnly(wrapped.container, wrapped.slot, wrapped.x, wrapped.y) {
+        @Override
+        public ItemStack getOrDefault() {
+          return wrapped.getItem();
+        }
+      };
+    }
+    wrapper.index = wrapped.index;
+    return wrapper;
+  }
+
+  public SlotViewOnly(Container container, int index, int x, int y) {
+    super(container, index, x, y);
+  }
+
+  @Override
+  public ItemStack getOrDefault() {
+    return Placeholders.notSlot;
+  }
+
+  @Override
+  public void onQuickCraft(ItemStack var0, ItemStack var1) {
+  }
+
+  @Override
+  public void onTake(Player var0, ItemStack var1) {
+  }
+
+  @Override
+  public boolean mayPlace(ItemStack var0) {
+    return false;
+  }
+
+  @Override
+  public ItemStack getItem() {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public boolean hasItem() {
+    return false;
+  }
+
+  @Override
+  public void setByPlayer(ItemStack newStack) {
+  }
+
+  @Override
+  public void setByPlayer(ItemStack newStack, ItemStack oldStack) {
+  }
+
+  @Override
+  public void set(ItemStack var0) {
+  }
+
+  @Override
+  public void setChanged() {
+  }
+
+  @Override
+  public int getMaxStackSize() {
+    return 0;
+  }
+
+  @Override
+  public int getMaxStackSize(ItemStack itemStack) {
+    return 0;
+  }
+
+  @Override
+  public ItemStack remove(int amount) {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public boolean mayPickup(Player var0) {
+    return false;
+  }
+
+  @Override
+  public boolean isActive() {
+    return false;
+  }
+
+  @Override
+  public Optional<ItemStack> tryRemove(int var0, int var1, Player var2) {
+    return Optional.empty();
+  }
+
+  @Override
+  public ItemStack safeTake(int var0, int var1, Player var2) {
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public ItemStack safeInsert(ItemStack itemStack) {
+    return itemStack;
+  }
+
+  @Override
+  public ItemStack safeInsert(ItemStack itemStack, int amount) {
+    return itemStack;
+  }
+
+  @Override
+  public boolean allowModification(Player var0) {
+    return false;
+  }
+
+  @Override
+  public int getContainerSlot() {
+    return this.slot;
+  }
+
+  @Override
+  public boolean isHighlightable() {
+    return false;
+  }
+
+  @Override
+  public boolean isFake() {
+    return true;
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/player/OpenPlayer.java

@@ -0,0 +1,177 @@
+package com.lishid.openinv.internal.v1_21_R1.player;
+
+import com.lishid.openinv.event.OpenEvents;
+import com.mojang.logging.LogUtils;
+import net.minecraft.Util;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.nbt.NumericTag;
+import net.minecraft.nbt.Tag;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.storage.PlayerDataStorage;
+import org.bukkit.craftbukkit.v1_21_R1.CraftServer;
+import org.bukkit.craftbukkit.v1_21_R1.entity.CraftPlayer;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Set;
+
+public class OpenPlayer extends CraftPlayer {
+
+  /**
+   * List of tags to always reset when saving.
+   *
+   * @see net.minecraft.world.entity.Entity#saveWithoutId(CompoundTag)
+   * @see net.minecraft.server.level.ServerPlayer#addAdditionalSaveData(CompoundTag)
+   * @see net.minecraft.world.entity.player.Player#addAdditionalSaveData(CompoundTag)
+   * @see net.minecraft.world.entity.LivingEntity#addAdditionalSaveData(CompoundTag)
+   */
+  private static final Set<String> RESET_TAGS = Set.of(
+      // Entity#saveWithoutId(CompoundTag)
+      "CustomName",
+      "CustomNameVisible",
+      "Silent",
+      "NoGravity",
+      "Glowing",
+      "TicksFrozen",
+      "HasVisualFire",
+      "Tags",
+      "Passengers",
+      // ServerPlayer#addAdditionalSaveData(CompoundTag)
+      // Intentional omissions to prevent mount loss: Attach, Entity, and RootVehicle
+      "warden_spawn_tracker",
+      "enteredNetherPosition",
+      "SpawnX",
+      "SpawnY",
+      "SpawnZ",
+      "SpawnForced",
+      "SpawnAngle",
+      "SpawnDimension",
+      "raid_omen_position",
+      // Player#addAdditionalSaveData(CompoundTag)
+      "ShoulderEntityLeft",
+      "ShoulderEntityRight",
+      "LastDeathLocation",
+      "current_explosion_impact_pos",
+      // LivingEntity#addAdditionalSaveData(CompoundTag)
+      "active_effects",
+      "SleepingX",
+      "SleepingY",
+      "SleepingZ",
+      "Brain"
+  );
+
+  private final PlayerManager manager;
+
+  OpenPlayer(CraftServer server, ServerPlayer entity, PlayerManager manager) {
+    super(server, entity);
+    this.manager = manager;
+  }
+
+  @Override
+  public void loadData() {
+    manager.loadData(getHandle());
+  }
+
+  @Override
+  public void saveData() {
+    if (OpenEvents.saveCancelled(this)) {
+      return;
+    }
+
+    ServerPlayer player = this.getHandle();
+    // See net.minecraft.world.level.storage.PlayerDataStorage#save(EntityHuman)
+    try {
+      PlayerDataStorage worldNBTStorage = player.server.getPlayerList().playerIo;
+
+      CompoundTag oldData = isOnline() ? null : worldNBTStorage.load(player.getName().getString(), player.getStringUUID()).orElse(null);
+      CompoundTag playerData = getWritableTag(oldData);
+      playerData = player.saveWithoutId(playerData);
+      setExtraData(playerData);
+
+      if (oldData != null) {
+        // Revert certain special data values when offline.
+        revertSpecialValues(playerData, oldData);
+      }
+
+      Path playerDataDir = worldNBTStorage.getPlayerDir().toPath();
+      Path tempFile = Files.createTempFile(playerDataDir, player.getStringUUID() + "-", ".dat");
+      NbtIo.writeCompressed(playerData, tempFile);
+      Path dataFile = playerDataDir.resolve(player.getStringUUID() + ".dat");
+      Path backupFile = playerDataDir.resolve(player.getStringUUID() + ".dat_old");
+      Util.safeReplaceFile(dataFile, tempFile, backupFile);
+    } catch (Exception e) {
+      LogUtils.getLogger().warn("Failed to save player data for {}: {}", player.getScoreboardName(), e);
+    }
+  }
+
+  @Contract("null -> new")
+  private @NotNull CompoundTag getWritableTag(@Nullable CompoundTag oldData) {
+    if (oldData == null) {
+      return new CompoundTag();
+    }
+
+    // Copy old data. This is a deep clone, so operating on it should be safe.
+    oldData = oldData.copy();
+
+    // Remove vanilla/server data that is not written every time.
+    oldData.getAllKeys()
+        .removeIf(key -> RESET_TAGS.contains(key) || key.startsWith("Bukkit"));
+
+    return oldData;
+  }
+
+  private void revertSpecialValues(@NotNull CompoundTag newData, @NotNull CompoundTag oldData) {
+    // Revert automatic updates to play timestamps.
+    copyValue(oldData, newData, "bukkit", "lastPlayed", NumericTag.class);
+    copyValue(oldData, newData, "Paper", "LastSeen", NumericTag.class);
+    copyValue(oldData, newData, "Paper", "LastLogin", NumericTag.class);
+  }
+
+  private <T extends Tag> void copyValue(
+      @NotNull CompoundTag source,
+      @NotNull CompoundTag target,
+      @NotNull String container,
+      @NotNull String key,
+      @SuppressWarnings("SameParameterValue") @NotNull Class<T> tagType) {
+    CompoundTag oldContainer = getTag(source, container, CompoundTag.class);
+    CompoundTag newContainer = getTag(target, container, CompoundTag.class);
+
+    // New container being null means the server implementation doesn't store this data.
+    if (newContainer == null) {
+      return;
+    }
+
+    // If old tag exists, copy it to new location, removing otherwise.
+    setTag(newContainer, key, getTag(oldContainer, key, tagType));
+  }
+
+  private <T extends Tag> @Nullable T getTag(
+      @Nullable CompoundTag container,
+      @NotNull String key,
+      @NotNull Class<T> dataType) {
+    if (container == null) {
+      return null;
+    }
+    Tag value = container.get(key);
+    if (value == null || !dataType.isAssignableFrom(value.getClass())) {
+      return null;
+    }
+    return dataType.cast(value);
+  }
+
+  private <T extends Tag> void setTag(
+      @NotNull CompoundTag container,
+      @NotNull String key,
+      @Nullable T data) {
+    if (data == null) {
+      container.remove(key);
+    } else {
+      container.put(key, data);
+    }
+  }
+
+}

internal/v1_21_R1/src/main/java/com/lishid/openinv/internal/v1_21_R1/player/PlayerManager.java

@@ -0,0 +1,265 @@
+package com.lishid.openinv.internal.v1_21_R1.player;
+
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.v1_21_R1.container.OpenEnderChest;
+import com.lishid.openinv.internal.v1_21_R1.container.OpenInventory;
+import com.mojang.authlib.GameProfile;
+import com.mojang.serialization.Dynamic;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtOps;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.protocol.game.ClientboundOpenScreenPacket;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ClientInformation;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.player.ChatVisiblity;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.dimension.DimensionType;
+import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.Server;
+import org.bukkit.World;
+import org.bukkit.craftbukkit.v1_21_R1.CraftServer;
+import org.bukkit.craftbukkit.v1_21_R1.CraftWorld;
+import org.bukkit.craftbukkit.v1_21_R1.entity.CraftPlayer;
+import org.bukkit.craftbukkit.v1_21_R1.event.CraftEventFactory;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.UUID;
+import java.util.logging.Logger;
+
+public class PlayerManager implements com.lishid.openinv.internal.PlayerManager {
+
+  private static boolean paper;
+
+  static {
+    try {
+      Class.forName("io.papermc.paper.configuration.Configuration");
+      paper = true;
+    } catch (ClassNotFoundException ignored) {
+      paper = false;
+    }
+  }
+
+  private final @NotNull Logger logger;
+  private @Nullable Field bukkitEntity;
+
+  public PlayerManager(@NotNull Logger logger) {
+    this.logger = logger;
+    try {
+      bukkitEntity = Entity.class.getDeclaredField("bukkitEntity");
+    } catch (NoSuchFieldException e) {
+      logger.warning("Unable to obtain field to inject custom save process - certain player data may be lost when saving!");
+      logger.log(java.util.logging.Level.WARNING, e.getMessage(), e);
+      bukkitEntity = null;
+    }
+  }
+
+  public static @NotNull ServerPlayer getHandle(final Player player) {
+    if (player instanceof CraftPlayer) {
+      return ((CraftPlayer) player).getHandle();
+    }
+
+    Server server = player.getServer();
+    ServerPlayer nmsPlayer = null;
+
+    if (server instanceof CraftServer) {
+      nmsPlayer = ((CraftServer) server).getHandle().getPlayer(player.getUniqueId());
+    }
+
+    if (nmsPlayer == null) {
+      // Could use reflection to examine fields, but it's honestly not worth the bother.
+      throw new RuntimeException("Unable to fetch EntityPlayer from Player implementation " + player.getClass().getName());
+    }
+
+    return nmsPlayer;
+  }
+
+  @Override
+  public @Nullable Player loadPlayer(@NotNull final OfflinePlayer offline) {
+    MinecraftServer server = ((CraftServer) Bukkit.getServer()).getServer();
+    ServerLevel worldServer = server.getLevel(Level.OVERWORLD);
+
+    if (worldServer == null) {
+      return null;
+    }
+
+    // Create a new ServerPlayer.
+    ServerPlayer entity = createNewPlayer(server, worldServer, offline);
+
+    // Stop listening for advancement progression - if this is not cleaned up, loading causes a memory leak.
+    entity.getAdvancements().stopListening();
+
+    // Try to load the player's data.
+    if (loadData(entity)) {
+      // If data is loaded successfully, return the Bukkit entity.
+      return entity.getBukkitEntity();
+    }
+
+    return null;
+  }
+
+  private @NotNull ServerPlayer createNewPlayer(
+      @NotNull MinecraftServer server,
+      @NotNull ServerLevel worldServer,
+      @NotNull final OfflinePlayer offline) {
+    // See net.minecraft.server.players.PlayerList#canPlayerLogin(ServerLoginPacketListenerImpl, GameProfile)
+    // See net.minecraft.server.network.ServerLoginPacketListenerImpl#handleHello(ServerboundHelloPacket)
+    GameProfile profile = new GameProfile(offline.getUniqueId(),
+        offline.getName() != null ? offline.getName() : offline.getUniqueId().toString());
+
+    ClientInformation dummyInfo = new ClientInformation(
+        "en_us",
+        1, // Reduce distance just in case.
+        ChatVisiblity.HIDDEN, // Don't accept chat.
+        false,
+        ServerPlayer.DEFAULT_MODEL_CUSTOMIZATION,
+        ServerPlayer.DEFAULT_MAIN_HAND,
+        true,
+        false // Don't list in player list (not that this player is in the list anyway).
+    );
+
+    ServerPlayer entity = new ServerPlayer(server, worldServer, profile, dummyInfo);
+
+    try {
+      injectPlayer(entity);
+    } catch (IllegalAccessException e) {
+      logger.log(
+          java.util.logging.Level.WARNING,
+          e,
+          () -> "Unable to inject ServerPlayer, certain player data may be lost when saving!");
+    }
+
+    return entity;
+  }
+
+  boolean loadData(@NotNull ServerPlayer player) {
+    // See CraftPlayer#loadData
+    CompoundTag loadedData = player.server.getPlayerList().playerIo.load(player).orElse(null);
+
+    if (loadedData == null) {
+      // Exceptions with loading are logged by Mojang.
+      return false;
+    }
+
+    // Read basic data into the player.
+    player.load(loadedData);
+    // Also read "extra" data.
+    player.readAdditionalSaveData(loadedData);
+    // Game type settings are also loaded separately.
+    player.loadGameTypes(loadedData);
+
+    if (paper) {
+      // Paper: world is not loaded by ServerPlayer#load(CompoundTag).
+      parseWorld(player, loadedData);
+    }
+
+    return true;
+  }
+
+  private void parseWorld(@NotNull ServerPlayer player, @NotNull CompoundTag loadedData) {
+    // See PlayerList#placeNewPlayer
+    World bukkitWorld;
+    if (loadedData.contains("WorldUUIDMost") && loadedData.contains("WorldUUIDLeast")) {
+      // Modern Bukkit world.
+      bukkitWorld = Bukkit.getServer().getWorld(new UUID(loadedData.getLong("WorldUUIDMost"), loadedData.getLong("WorldUUIDLeast")));
+    } else if (loadedData.contains("world", net.minecraft.nbt.Tag.TAG_STRING)) {
+      // Legacy Bukkit world.
+      bukkitWorld = Bukkit.getServer().getWorld(loadedData.getString("world"));
+    } else {
+      // Vanilla player data.
+      DimensionType.parseLegacy(new Dynamic<>(NbtOps.INSTANCE, loadedData.get("Dimension")))
+          .resultOrPartial(logger::warning)
+          .map(player.server::getLevel)
+          // If ServerLevel exists, set, otherwise move to spawn.
+          .ifPresentOrElse(player::setServerLevel, () -> player.spawnIn(null));
+      return;
+    }
+    if (bukkitWorld == null) {
+      player.spawnIn(null);
+      return;
+    }
+    player.setServerLevel(((CraftWorld) bukkitWorld).getHandle());
+  }
+
+  private void injectPlayer(ServerPlayer player) throws IllegalAccessException {
+    if (bukkitEntity == null) {
+      return;
+    }
+
+    bukkitEntity.setAccessible(true);
+
+    bukkitEntity.set(player, new OpenPlayer(player.server.server, player, this));
+  }
+
+  @Override
+  public @NotNull Player inject(@NotNull Player player) {
+    try {
+      ServerPlayer nmsPlayer = getHandle(player);
+      if (nmsPlayer.getBukkitEntity() instanceof OpenPlayer openPlayer) {
+        return openPlayer;
+      }
+      injectPlayer(nmsPlayer);
+      return nmsPlayer.getBukkitEntity();
+    } catch (IllegalAccessException e) {
+      logger.log(
+          java.util.logging.Level.WARNING,
+          e,
+          () -> "Unable to inject ServerPlayer, certain player data may be lost when saving!");
+      return player;
+    }
+  }
+
+  @Override
+  public @Nullable InventoryView openInventory(@NotNull Player bukkitPlayer, @NotNull ISpecialInventory inventory, boolean viewOnly) {
+    ServerPlayer player = getHandle(bukkitPlayer);
+
+    if (player.connection == null) {
+      return null;
+    }
+
+    // See net.minecraft.server.level.ServerPlayer#openMenu(MenuProvider)
+    AbstractContainerMenu menu;
+    Component title;
+    if (inventory instanceof OpenInventory playerInv) {
+      menu = playerInv.createMenu(player, player.nextContainerCounter(), viewOnly);
+      title = playerInv.getTitle(player);
+    } else if (inventory instanceof OpenEnderChest enderChest) {
+      menu = enderChest.createMenu(player, player.nextContainerCounter(), viewOnly);
+      title = enderChest.getTitle();
+    } else {
+      return null;
+    }
+
+    // Should never happen, player is a ServerPlayer with an active connection.
+    if (menu == null) {
+      return null;
+    }
+
+    // Set up title. Title can only be set once for a menu, and is set during the open process.
+    // Further title changes are a hack where the client is sent a "new" inventory with the same ID,
+    // resulting in a title change but no other state modifications (like cursor position).
+    menu.setTitle(title);
+
+    menu = CraftEventFactory.callInventoryOpenEvent(player, menu, false);
+
+    // Menu is null if event is cancelled.
+    if (menu == null) {
+      return null;
+    }
+
+    player.containerMenu = menu;
+    player.connection.send(new ClientboundOpenScreenPacket(menu.containerId, menu.getType(), menu.getTitle()));
+    player.initMenu(menu);
+
+    return menu.getBukkitView();
+  }
+
+}

plugin/pom.xml

@@ -0,0 +1,146 @@
+<!--
+  ~ Copyright (C) 2011-2022 lishid. All rights reserved.
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by
+  ~ the Free Software Foundation, version 3.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+  ~ GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License
+  ~ along with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <artifactId>openinvparent</artifactId>
+    <groupId>com.lishid</groupId>
+    <version>5.1.1</version>
+  </parent>
+
+  <artifactId>openinvplugin</artifactId>
+  <name>OpenInvPlugin</name>
+
+  <dependencies>
+    <dependency>
+      <artifactId>spigot-api</artifactId>
+      <groupId>org.spigotmc</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>planarwrappers</artifactId>
+      <groupId>com.github.jikoo</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>openinvapi</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <artifactId>openinvcommon</artifactId>
+      <groupId>com.lishid</groupId>
+    </dependency>
+    <dependency>
+      <groupId>com.lishid</groupId>
+      <artifactId>openinvadapter1_21_R1</artifactId>
+      <version>5.1.1</version>
+      <scope>compile</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.lishid</groupId>
+      <artifactId>openinvadapter1_20_R4</artifactId>
+      <version>5.1.1</version>
+      <scope>compile</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.lishid</groupId>
+      <artifactId>openinvadapter1_20_R3</artifactId>
+      <version>5.1.1</version>
+      <scope>compile</scope>
+    </dependency>
+    <dependency>
+      <artifactId>annotations</artifactId>
+      <groupId>org.jetbrains</groupId>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <finalName>OpenInv</finalName>
+    <resources>
+      <resource>
+        <directory>src/main/resources</directory>
+        <filtering>true</filtering>
+      </resource>
+    </resources>
+
+    <plugins>
+      <plugin>
+        <artifactId>maven-shade-plugin</artifactId>
+        <executions>
+          <execution>
+            <phase>package</phase>
+            <goals>
+              <goal>shade</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <filters>
+            <filter>
+              <!-- Always shade entirety of required modules. -->
+              <artifact>com.lishid:openinv*</artifact>
+              <includes>
+                <include>**</include>
+              </includes>
+            </filter>
+            <filter>
+              <artifact>*:*</artifact>
+              <!-- Don't warn about file conflicts that'll be clobbered anyway. -->
+              <excludes>
+                <exclude>META-INF/MANIFEST.MF</exclude>
+              </excludes>
+            </filter>
+          </filters>
+          <relocations>
+            <relocation>
+              <pattern>com.github.jikoo.planarwrappers</pattern>
+              <shadedPattern>com.github.jikoo.openinv.planarwrappers</shadedPattern>
+            </relocation>
+          </relocations>
+          <minimizeJar>true</minimizeJar>
+        </configuration>
+      </plugin>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <artifactId>maven-resources-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>copy-final-jar</id>
+            <phase>package</phase>
+            <goals>
+              <goal>copy-resources</goal>
+            </goals>
+            <configuration>
+              <outputDirectory>${project.parent.build.directory}</outputDirectory>
+              <resources>
+                <resource>
+                  <directory>${project.build.directory}</directory>
+                  <includes>
+                    <include>${project.build.finalName}.jar</include>
+                  </includes>
+                </resource>
+              </resources>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>

plugin/src/main/java/com/lishid/openinv/OpenInv.java

@@ -0,0 +1,314 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv;
+
+import com.github.jikoo.planarwrappers.util.version.BukkitVersions;
+import com.github.jikoo.planarwrappers.util.version.Version;
+import com.lishid.openinv.command.ContainerSettingCommand;
+import com.lishid.openinv.command.OpenInvCommand;
+import com.lishid.openinv.command.SearchContainerCommand;
+import com.lishid.openinv.command.SearchEnchantCommand;
+import com.lishid.openinv.command.SearchInvCommand;
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.listener.ContainerListener;
+import com.lishid.openinv.listener.LegacyInventoryListener;
+import com.lishid.openinv.listener.ToggleListener;
+import com.lishid.openinv.util.AccessEqualMode;
+import com.lishid.openinv.util.InternalAccessor;
+import com.lishid.openinv.util.InventoryManager;
+import com.lishid.openinv.util.Permissions;
+import com.lishid.openinv.util.PlayerLoader;
+import com.lishid.openinv.util.config.Config;
+import com.lishid.openinv.util.config.ConfigUpdater;
+import com.lishid.openinv.util.lang.LangMigrator;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.setting.PlayerToggle;
+import com.lishid.openinv.util.setting.PlayerToggles;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandExecutor;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.PluginCommand;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.bukkit.plugin.PluginManager;
+import org.bukkit.plugin.java.JavaPlugin;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.nio.file.Path;
+import java.util.Locale;
+import java.util.UUID;
+import java.util.function.Consumer;
+
+/**
+ * The main class for OpenInv.
+ */
+public class OpenInv extends JavaPlugin implements IOpenInv {
+
+    private InternalAccessor accessor;
+    private Config config;
+    private InventoryManager inventoryManager;
+    private LanguageManager languageManager;
+    private PlayerLoader playerLoader;
+    private boolean isSpigot = false;
+
+    @Override
+    public void reloadConfig() {
+        super.reloadConfig();
+        config.reload(getConfig());
+        languageManager.reload();
+        if (accessor != null && accessor.isSupported()) {
+            accessor.reload(getConfig());
+        }
+    }
+
+    @Override
+    public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (!isSpigot || !this.accessor.isSupported()) {
+            this.sendVersionError(sender::sendMessage);
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public void onDisable() {
+        inventoryManager.evictAll();
+    }
+
+    @Override
+    public void onEnable() {
+        // Save default configuration if not present.
+        this.saveDefaultConfig();
+
+        // Migrate locale files to a subfolder.
+        Path dataFolder = getDataFolder().toPath();
+        new LangMigrator(dataFolder, dataFolder.resolve("locale"), getLogger()).migrate();
+
+        // Set up configurable features. Note that #reloadConfig is called on the first call to #getConfig!
+        // Configuration values should not be accessed until after all of these have been set up.
+        config = new Config();
+        languageManager = new LanguageManager(this, "en");
+        accessor = new InternalAccessor(getLogger(), languageManager);
+
+        // Perform initial config load.
+        reloadConfig();
+
+        inventoryManager = new InventoryManager(this, config, accessor);
+        playerLoader = new PlayerLoader(this, config, inventoryManager, accessor, getLogger());
+
+        try {
+            Class.forName("org.bukkit.entity.Player$Spigot");
+            isSpigot = true;
+        } catch (ClassNotFoundException e) {
+            isSpigot = false;
+        }
+
+        // Version check
+        if (isSpigot && this.accessor.isSupported()) {
+            reloadConfig();
+
+            // Update existing configuration. May require internal access.
+            new ConfigUpdater(this).checkForUpdates();
+
+            // Register relevant event listeners.
+            registerEvents();
+
+            // Register commands to their executors.
+            registerCommands();
+
+        } else {
+            this.sendVersionError(this.getLogger()::warning);
+        }
+
+    }
+
+    private void registerEvents() {
+        PluginManager pluginManager = this.getServer().getPluginManager();
+        // Legacy: extra listener for permission handling and self-view issue prevention.
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 21))) {
+            pluginManager.registerEvents(new LegacyInventoryListener(this, config), this);
+        }
+        pluginManager.registerEvents(playerLoader, this);
+        pluginManager.registerEvents(inventoryManager, this);
+        pluginManager.registerEvents(new ContainerListener(accessor, languageManager), this);
+        pluginManager.registerEvents(new ToggleListener(), this);
+    }
+
+    private void registerCommands() {
+        this.setCommandExecutor(new OpenInvCommand(this, config, inventoryManager, languageManager, playerLoader), "openinv", "openender");
+        this.setCommandExecutor(new SearchContainerCommand(this, languageManager), "searchcontainer");
+        this.setCommandExecutor(new SearchInvCommand(languageManager), "searchinv", "searchender");
+        this.setCommandExecutor(new SearchEnchantCommand(languageManager), "searchenchant");
+
+        ContainerSettingCommand settingCommand = new ContainerSettingCommand(languageManager);
+        for (PlayerToggle toggle : PlayerToggles.get()) {
+            setCommandExecutor(settingCommand, toggle.getName().toLowerCase(Locale.ENGLISH));
+        }
+    }
+
+    private void setCommandExecutor(@NotNull CommandExecutor executor, String @NotNull ... commands) {
+        for (String commandName : commands) {
+            PluginCommand command = this.getCommand(commandName);
+            if (command != null) {
+                command.setExecutor(executor);
+            }
+        }
+    }
+
+    private void sendVersionError(@NotNull Consumer<String> messageMethod) {
+        if (!accessor.isSupported()) {
+            messageMethod.accept("Your server version (" + accessor.getVersion() + ") is not supported.");
+            messageMethod.accept("Please download the correct version of OpenInv here: " + accessor.getReleasesLink());
+
+            // We check this property late so users can use jars that were remapped by Paper already.
+            if (Boolean.getBoolean("paper.disable-plugin-rewriting")) {
+                messageMethod.accept("OpenInv uses Spigot-mapped internals, but you have disabled plugin rewriting in Paper!");
+                messageMethod.accept("Please set system property 'paper.disable-plugin-rewriting' to false.");
+            }
+        }
+        if (!isSpigot) {
+            messageMethod.accept("OpenInv requires that you use Spigot or a Spigot fork. Per the 1.14 update thread");
+            messageMethod.accept("(https://www.spigotmc.org/threads/369724/ \"A Note on CraftBukkit\"), if you are");
+            messageMethod.accept("encountering an inconsistency with vanilla that prevents you from using Spigot,");
+            messageMethod.accept("that is considered a Spigot bug and should be reported as such.");
+        }
+    }
+
+    @Override
+    public boolean isSupportedVersion() {
+        return this.accessor != null && this.accessor.isSupported();
+    }
+
+    @Override
+    public boolean disableSaving() {
+        return config.isSaveDisabled();
+    }
+
+    @Override
+    public boolean disableOfflineAccess() {
+        return config.isOfflineDisabled();
+    }
+
+    @Override
+    public boolean noArgsOpensSelf() {
+        return config.doesNoArgsOpenSelf();
+    }
+
+    @Override
+    public @NotNull IAnySilentContainer getAnySilentContainer() {
+        return this.accessor.getAnySilentContainer();
+    }
+
+    @Override
+    public boolean getAnyContainerStatus(@NotNull final OfflinePlayer offline) {
+        return PlayerToggles.any().is(offline.getUniqueId());
+    }
+
+    @Override
+    public void setAnyContainerStatus(@NotNull final OfflinePlayer offline, final boolean status) {
+        PlayerToggles.any().set(offline.getUniqueId(), status);
+    }
+
+    @Override
+    public boolean getSilentContainerStatus(@NotNull final OfflinePlayer offline) {
+        return PlayerToggles.silent().is(offline.getUniqueId());
+    }
+
+    @Override
+    public void setSilentContainerStatus(@NotNull final OfflinePlayer offline, final boolean status) {
+        PlayerToggles.silent().set(offline.getUniqueId(), status);
+    }
+
+    @Override
+    public @NotNull ISpecialEnderChest getSpecialEnderChest(@NotNull final Player player, final boolean online) {
+        return inventoryManager.getEnderChest(player);
+    }
+
+    @Override
+    public @NotNull ISpecialPlayerInventory getSpecialInventory(@NotNull final Player player, final boolean online) {
+        return inventoryManager.getInventory(player);
+    }
+
+    @Override
+    public @Nullable InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory) {
+        Permissions edit = null;
+        HumanEntity target = inventory.getPlayer();
+        boolean ownContainer = player.equals(target);
+        if (inventory instanceof ISpecialPlayerInventory) {
+            edit = ownContainer ? Permissions.INVENTORY_EDIT_SELF : Permissions.INVENTORY_EDIT_OTHER;
+        } else if (inventory instanceof ISpecialEnderChest) {
+            edit = ownContainer ? Permissions.ENDERCHEST_EDIT_SELF : Permissions.ENDERCHEST_OPEN_OTHER;
+        }
+
+        boolean viewOnly = edit != null && !edit.hasPermission(player);
+
+        if (!ownContainer && !viewOnly) {
+            for (int level = 4; level > 0; --level) {
+                String permission = "openinv.access.level." + level;
+                // If the target doesn't have this access level...
+                if (!target.hasPermission(permission)) {
+                    // If the viewer does have the access level, all good.
+                    if (player.hasPermission(permission)) {
+                        break;
+                    }
+                    // Otherwise check next access level.
+                    continue;
+                }
+
+                // If the player doesn't have an equal access level or equal access is a denial, deny.
+                if (!player.hasPermission(permission) || config.getAccessEqualMode() == AccessEqualMode.DENY) {
+                    return null;
+                }
+
+                // Since this is a tie, setting decides view state.
+                if (config.getAccessEqualMode() == AccessEqualMode.VIEW) {
+                    viewOnly = true;
+                }
+                break;
+            }
+        }
+
+        return this.accessor.openInventory(player, inventory, viewOnly);
+    }
+
+    @Override
+    public boolean isPlayerLoaded(@NotNull UUID playerUuid) {
+        return inventoryManager.getLoadedPlayer(playerUuid) != null;
+    }
+
+    @Override
+    public @Nullable Player loadPlayer(@NotNull final OfflinePlayer offline) {
+        return playerLoader.load(offline);
+    }
+
+    @Override
+    public @Nullable OfflinePlayer matchPlayer(@NotNull String name) {
+        return playerLoader.match(name);
+    }
+
+    @Override
+    public void unload(@NotNull final OfflinePlayer offline) {
+        inventoryManager.unload(offline.getUniqueId());
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/command/ContainerSettingCommand.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.command;
+
+import com.lishid.openinv.event.OpenEvents;
+import com.lishid.openinv.util.setting.PlayerToggle;
+import com.lishid.openinv.util.TabCompleter;
+import com.lishid.openinv.util.setting.PlayerToggles;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.lang.Replacement;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabExecutor;
+import org.bukkit.entity.Player;
+import org.bukkit.plugin.java.JavaPlugin;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.UUID;
+
+public class ContainerSettingCommand implements TabExecutor {
+
+    private final @NotNull LanguageManager lang;
+
+    public ContainerSettingCommand(@NotNull LanguageManager lang) {
+        this.lang = lang;
+    }
+
+    @Override
+    public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (!(sender instanceof Player player)) {
+            lang.sendMessage(sender, "messages.error.consoleUnsupported");
+            return true;
+        }
+
+        PlayerToggle toggle = PlayerToggles.get(command.getName());
+
+        // Shouldn't be possible.
+        if (toggle == null) {
+            JavaPlugin.getProvidingPlugin(getClass()).getLogger().warning("Command /" + command.getName() + " registered with no corresponding toggle!");
+            return false;
+        }
+
+        UUID playerId = player.getUniqueId();
+
+        if (args.length > 0) {
+            args[0] = args[0].toLowerCase(Locale.ENGLISH);
+
+            if (args[0].equals("on")) {
+                set(toggle, playerId, true);
+            } else if (args[0].equals("off")) {
+                set(toggle, playerId, false);
+            } else if (!args[0].equals("check")) {
+                // Invalid argument, show usage.
+                return false;
+            }
+
+        } else {
+            set(toggle, playerId, !toggle.is(playerId));
+        }
+
+        String onOff = lang.getLocalizedMessage(player, toggle.is(playerId) ? "messages.info.on" : "messages.info.off");
+        if (onOff == null) {
+            onOff = String.valueOf(toggle.is(playerId));
+        }
+
+        lang.sendMessage(
+                sender,
+                "messages.info.settingState",
+                new Replacement("%setting%", toggle.getName()),
+                new Replacement("%state%", onOff));
+
+        return true;
+    }
+
+    private void set(@NotNull PlayerToggle toggle, @NotNull UUID uuid, boolean state) {
+        if (toggle.set(uuid, state)) {
+            OpenEvents.notifyPlayerToggle(toggle, uuid, state);
+        }
+    }
+
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (!command.testPermissionSilent(sender) || args.length != 1) {
+            return Collections.emptyList();
+        }
+
+        return TabCompleter.completeString(args[0], new String[] {"check", "on", "off"});
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/command/OpenInvCommand.java

@@ -0,0 +1,249 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.command;
+
+import com.lishid.openinv.OpenInv;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.util.AccessEqualMode;
+import com.lishid.openinv.util.InventoryManager;
+import com.lishid.openinv.util.Permissions;
+import com.lishid.openinv.util.PlayerLoader;
+import com.lishid.openinv.util.TabCompleter;
+import com.lishid.openinv.util.config.Config;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.lang.Replacement;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.PluginCommand;
+import org.bukkit.command.TabExecutor;
+import org.bukkit.entity.Player;
+import org.bukkit.scheduler.BukkitRunnable;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.StringJoiner;
+import java.util.logging.Level;
+
+public class OpenInvCommand implements TabExecutor {
+
+    private final @NotNull OpenInv plugin;
+    private final @NotNull Config config;
+    private final @NotNull InventoryManager manager;
+    private final @NotNull LanguageManager lang;
+    private final @NotNull PlayerLoader playerLoader;
+    private final HashMap<Player, String> openInvHistory = new HashMap<>();
+    private final HashMap<Player, String> openEnderHistory = new HashMap<>();
+
+    public OpenInvCommand(
+        @NotNull OpenInv plugin,
+        @NotNull Config config,
+        @NotNull InventoryManager manager,
+        @NotNull LanguageManager lang,
+        @NotNull PlayerLoader playerLoader) {
+        this.plugin = plugin;
+        this.config = config;
+        this.manager = manager;
+        this.lang = lang;
+        this.playerLoader = playerLoader;
+    }
+
+    @Override
+    public boolean onCommand(@NotNull final CommandSender sender, @NotNull final Command command, @NotNull final String label, @NotNull final String[] args) {
+        boolean openInv = command.getName().equals("openinv");
+
+        if (openInv && args.length > 0 && (args[0].equalsIgnoreCase("help") || args[0].equals("?"))) {
+            this.showHelp(sender);
+            return true;
+        }
+
+        if (!(sender instanceof Player player)) {
+            lang.sendMessage(sender, "messages.error.consoleUnsupported");
+            return true;
+        }
+
+        String noArgValue;
+        if (config.doesNoArgsOpenSelf()) {
+            noArgValue = player.getUniqueId().toString();
+        } else {
+            // History management
+            noArgValue = (openInv ? this.openInvHistory : this.openEnderHistory).get(player);
+
+            if (noArgValue == null || noArgValue.isEmpty()) {
+                noArgValue = player.getUniqueId().toString();
+                (openInv ? this.openInvHistory : this.openEnderHistory).put(player, noArgValue);
+            }
+        }
+
+        final String name;
+
+        if (args.length < 1) {
+            name = noArgValue;
+        } else {
+            name = args[0];
+        }
+
+        new BukkitRunnable() {
+            @Override
+            public void run() {
+                final OfflinePlayer offlinePlayer = playerLoader.match(name);
+
+                if (offlinePlayer == null || (!offlinePlayer.hasPlayedBefore() && !offlinePlayer.isOnline())) {
+                    lang.sendMessage(player, "messages.error.invalidPlayer");
+                    return;
+                }
+
+                new BukkitRunnable() {
+                    @Override
+                    public void run() {
+                        if (!player.isOnline()) {
+                            return;
+                        }
+                        OpenInvCommand.this.openInventory(player, offlinePlayer, openInv);
+                    }
+                }.runTask(OpenInvCommand.this.plugin);
+
+            }
+        }.runTaskAsynchronously(this.plugin);
+
+        return true;
+    }
+
+    private void showHelp(final CommandSender sender) {
+        // Get registered commands
+        for (String commandName : plugin.getDescription().getCommands().keySet()) {
+            PluginCommand command = plugin.getCommand(commandName);
+
+            // Ensure command is successfully registered and sender can use it
+            if (command == null  || !command.testPermissionSilent(sender)) {
+                continue;
+            }
+
+            // Send usage
+            sender.sendMessage(command.getUsage().replace("<command>", commandName));
+
+            List<String> aliases = command.getAliases();
+            if (!aliases.isEmpty()) {
+                // Assemble alias list
+                StringJoiner aliasJoiner = new StringJoiner(", ", "   (aliases: ", ")");
+                for (String alias : aliases) {
+                    aliasJoiner.add(alias);
+                }
+
+                // Send all aliases
+                sender.sendMessage(aliasJoiner.toString());
+            }
+
+        }
+    }
+
+    private void openInventory(final Player player, final OfflinePlayer target, boolean openinv) {
+        Player onlineTarget;
+        boolean online = target.isOnline();
+
+        if (!online) {
+            if (!config.isOfflineDisabled() && Permissions.ACCESS_OFFLINE.hasPermission(player)) {
+                // Try loading the player's data
+                onlineTarget = playerLoader.load(target);
+            } else {
+                lang.sendMessage(player, "messages.error.permissionPlayerOffline");
+                return;
+            }
+        } else {
+            if (Permissions.ACCESS_ONLINE.hasPermission(player)) {
+                onlineTarget = target.getPlayer();
+            } else {
+                lang.sendMessage(player, "messages.error.permissionPlayerOnline");
+                return;
+            }
+        }
+
+        if (onlineTarget == null) {
+            lang.sendMessage(player, "messages.error.invalidPlayer");
+            return;
+        }
+
+        // Permissions checks
+        if (onlineTarget.equals(player)) {
+            // Permission for opening own inventory.
+            if (!(openinv ? Permissions.INVENTORY_OPEN_SELF : Permissions.ENDERCHEST_OPEN_SELF).hasPermission(player)) {
+                lang.sendMessage(player, "messages.error.permissionOpenSelf");
+                return;
+
+            }
+        } else {
+            // Permission for opening others' inventories.
+            if (!(openinv ? Permissions.INVENTORY_OPEN_OTHER : Permissions.ENDERCHEST_OPEN_OTHER).hasPermission(player)) {
+                lang.sendMessage(player, "messages.error.permissionOpenOther");
+                return;
+            }
+
+            // Protected check
+            for (int level = 4; level > 0; --level) {
+                String permission = "openinv.access.level." + level;
+                if (onlineTarget.hasPermission(permission)
+                        && (!player.hasPermission(permission) || config.getAccessEqualMode() == AccessEqualMode.DENY)) {
+                    lang.sendMessage(
+                        player,
+                        "messages.error.permissionExempt",
+                        new Replacement("%target%", onlineTarget.getDisplayName()));
+                    return;
+                }
+            }
+
+            // Crossworld check
+            if (!Permissions.ACCESS_CROSSWORLD.hasPermission(player)
+                    && !onlineTarget.getWorld().equals(player.getWorld())) {
+                lang.sendMessage(
+                        player,
+                        "messages.error.permissionCrossWorld",
+                        new Replacement("%target%", onlineTarget.getDisplayName()));
+                return;
+            }
+        }
+
+        if (!config.doesNoArgsOpenSelf()) {
+            // Record the target
+            (openinv ? this.openInvHistory : this.openEnderHistory).put(player, target.getUniqueId().toString());
+        }
+
+        // Create the inventory
+        final ISpecialInventory inv;
+        try {
+            inv = openinv ? manager.getInventory(onlineTarget) : manager.getEnderChest(onlineTarget);
+        } catch (Exception e) {
+            lang.sendMessage(player, "messages.error.commandException");
+            plugin.getLogger().log(Level.WARNING, "Unable to create ISpecialInventory", e);
+            return;
+        }
+
+        // Open the inventory
+        plugin.openInventory(player, inv);
+    }
+
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (!command.testPermissionSilent(sender) || args.length != 1) {
+            return Collections.emptyList();
+        }
+
+        return TabCompleter.completeOnlinePlayer(sender, args[0]);
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/command/SearchContainerCommand.java

@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.command;
+
+import com.lishid.openinv.util.TabCompleter;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.lang.Replacement;
+import org.bukkit.Chunk;
+import org.bukkit.Material;
+import org.bukkit.World;
+import org.bukkit.block.BlockState;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabExecutor;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryHolder;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+
+/**
+ * Command for searching containers in a radius of chunks.
+ */
+public class SearchContainerCommand implements TabExecutor {
+
+    private final @NotNull Plugin plugin;
+    private final @NotNull LanguageManager lang;
+
+    public SearchContainerCommand(@NotNull Plugin plugin, @NotNull LanguageManager lang) {
+        this.plugin = plugin;
+        this.lang = lang;
+    }
+
+    @Override
+    public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (!(sender instanceof Player senderPlayer)) {
+            lang.sendMessage(sender, "messages.error.consoleUnsupported");
+            return true;
+        }
+
+        if (args.length < 1) {
+            // Must supply material
+            return false;
+        }
+
+        Material material = Material.matchMaterial(args[0]);
+
+        if (material == null) {
+            lang.sendMessage(
+                    sender,
+                    "messages.error.invalidMaterial",
+                    new Replacement("%target%", args[0]));
+            return false;
+        }
+
+        int radius = 5;
+
+        if (args.length > 1) {
+            try {
+                radius = Integer.parseInt(args[1]);
+            } catch (NumberFormatException e) {
+                // Invalid radius supplied
+                return false;
+            }
+        }
+
+        // Clamp radius.
+        int configMax = plugin.getConfig().getInt("settings.command.searchcontainer.max-radius", 10);
+        radius = Math.max(0, Math.min(radius, configMax));
+
+        World world = senderPlayer.getWorld();
+        Chunk centerChunk = senderPlayer.getLocation().getChunk();
+        StringBuilder locations = new StringBuilder();
+
+        for (int dX = -radius; dX <= radius; ++dX) {
+            for (int dZ = -radius; dZ <= radius; ++dZ) {
+                if (!world.loadChunk(centerChunk.getX() + dX, centerChunk.getZ() + dZ, false)) {
+                    continue;
+                }
+                Chunk chunk = world.getChunkAt(centerChunk.getX() + dX, centerChunk.getZ() + dZ);
+                for (BlockState tileEntity : chunk.getTileEntities()) {
+                    if (!(tileEntity instanceof InventoryHolder holder)) {
+                        continue;
+                    }
+                    if (!holder.getInventory().contains(material)) {
+                        continue;
+                    }
+                    locations.append(holder.getInventory().getType().name().toLowerCase(Locale.ENGLISH)).append(" (")
+                            .append(tileEntity.getX()).append(',').append(tileEntity.getY()).append(',')
+                            .append(tileEntity.getZ()).append("), ");
+                }
+            }
+        }
+
+        // Matches found, delete trailing comma and space
+        if (!locations.isEmpty()) {
+            locations.delete(locations.length() - 2, locations.length());
+        } else {
+            lang.sendMessage(
+                    sender,
+                    "messages.info.container.noMatches",
+                    new Replacement("%target%", material.name()));
+            return true;
+        }
+
+        lang.sendMessage(
+                sender,
+                "messages.info.container.matches",
+                new Replacement("%target%", material.name()),
+                new Replacement("%detail%", locations.toString()));
+        return true;
+    }
+
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, String[] args) {
+        if (args.length < 1 || args.length > 2 || !command.testPermissionSilent(sender)) {
+            return Collections.emptyList();
+        }
+
+        String argument = args[args.length - 1];
+        if (args.length == 1) {
+            return TabCompleter.completeEnum(argument, Material.class);
+        } else {
+            return TabCompleter.completeInteger(argument);
+        }
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/command/SearchEnchantCommand.java

@@ -0,0 +1,172 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.command;
+
+import com.lishid.openinv.util.TabCompleter;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.lang.Replacement;
+import org.bukkit.Bukkit;
+import org.bukkit.Material;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Registry;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabExecutor;
+import org.bukkit.enchantments.Enchantment;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.meta.ItemMeta;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+
+/**
+ * Command adding the ability to search online players' inventories for enchantments of a specific
+ * type at or above the level specified.
+ *
+ * @author Jikoo
+ */
+public class SearchEnchantCommand implements TabExecutor {
+
+    private final @NotNull LanguageManager lang;
+
+    public SearchEnchantCommand(@NotNull LanguageManager lang) {
+        this.lang = lang;
+    }
+
+    @Override
+    public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (args.length == 0) {
+            return false;
+        }
+
+        Enchantment enchant = null;
+        int level = 0;
+
+        for (String argument : args) {
+            try {
+                level = Integer.parseInt(argument);
+                continue;
+            } catch (NumberFormatException ignored) {
+                // Not a level being specified.
+            }
+
+            argument = argument.toLowerCase(Locale.ENGLISH);
+            NamespacedKey key = NamespacedKey.fromString(argument);
+            if (key == null) {
+                continue;
+            }
+
+            Enchantment localEnchant = Registry.ENCHANTMENT.get(key);
+            if (localEnchant != null) {
+                enchant = localEnchant;
+            }
+        }
+
+        // Arguments not set correctly
+        if (level == 0 && enchant == null) {
+            return false;
+        }
+
+        StringBuilder players = new StringBuilder();
+        for (Player player : Bukkit.getServer().getOnlinePlayers()) {
+            boolean flagInventory = containsEnchantment(player.getInventory(), enchant, level);
+            boolean flagEnder = containsEnchantment(player.getEnderChest(), enchant, level);
+
+            // No matches, continue
+            if (!flagInventory && !flagEnder) {
+                continue;
+            }
+
+            // Matches, append details
+            players.append(player.getName()).append(" (");
+            if (flagInventory) {
+                players.append("inv");
+            }
+            if (flagEnder) {
+                if (flagInventory) {
+                    players.append(',');
+                }
+                players.append("ender");
+            }
+            players.append("), ");
+        }
+
+        if (!players.isEmpty()) {
+            // Matches found, delete trailing comma and space
+            players.delete(players.length() - 2, players.length());
+        } else {
+            lang.sendMessage(
+                    sender,
+                    "messages.info.player.noMatches",
+                    new Replacement("%target%", (enchant != null ? enchant.getKey().toString() : "") + " >= " + level));
+            return true;
+        }
+
+        lang.sendMessage(
+                sender,
+                "messages.info.player.matches",
+                new Replacement("%target%", (enchant != null ? enchant.getKey().toString() : "") + " >= " + level),
+                        new Replacement("%detail%", players.toString()));
+        return true;
+    }
+
+    private boolean containsEnchantment(Inventory inventory, @Nullable Enchantment enchant, int minLevel) {
+        for (ItemStack item : inventory.getContents()) {
+            if (item == null || item.getType() == Material.AIR) {
+                continue;
+            }
+            if (enchant != null) {
+                if (item.containsEnchantment(enchant) && item.getEnchantmentLevel(enchant) >= minLevel) {
+                    return true;
+                }
+            } else {
+                if (!item.hasItemMeta()) {
+                    continue;
+                }
+                ItemMeta meta = item.getItemMeta();
+                if (meta == null || !meta.hasEnchants()) {
+                    continue;
+                }
+                for (int enchLevel : meta.getEnchants().values()) {
+                    if (enchLevel >= minLevel) {
+                        return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (!command.testPermissionSilent(sender) || args.length < 1 || args.length > 2) {
+            return Collections.emptyList();
+        }
+
+        if (args.length == 1) {
+            return TabCompleter.completeObject(args[0], enchantment -> enchantment.getKey().toString(), Registry.ENCHANTMENT.stream().toArray(Enchantment[]::new));
+        } else {
+            return TabCompleter.completeInteger(args[1]);
+        }
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/command/SearchInvCommand.java

@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.command;
+
+import com.lishid.openinv.util.TabCompleter;
+import com.lishid.openinv.util.lang.LanguageManager;
+import com.lishid.openinv.util.lang.Replacement;
+import org.bukkit.Bukkit;
+import org.bukkit.Material;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabExecutor;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collections;
+import java.util.List;
+
+public class SearchInvCommand implements TabExecutor {
+
+    private final @NotNull LanguageManager lang;
+
+    public SearchInvCommand(@NotNull LanguageManager lang) {
+        this.lang = lang;
+    }
+
+    @Override
+    public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+
+        Material material = null;
+
+        if (args.length >= 1) {
+            material = Material.matchMaterial(args[0]);
+        }
+
+        if (material == null) {
+            lang.sendMessage(
+                    sender,
+                    "messages.error.invalidMaterial",
+                    new Replacement("%target%", args.length > 0 ? args[0] : "null"));
+            return false;
+        }
+
+        int count = 1;
+
+        if (args.length >= 2) {
+            try {
+                count = Integer.parseInt(args[1]);
+            } catch (NumberFormatException ex) {
+                lang.sendMessage(
+                        sender,
+                        "messages.error.invalidNumber",
+                        new Replacement("%target%", args[1]));
+                return false;
+            }
+        }
+
+        StringBuilder players = new StringBuilder();
+        boolean searchInv = command.getName().equals("searchinv");
+        for (Player player : Bukkit.getServer().getOnlinePlayers()) {
+            Inventory inventory = searchInv ? player.getInventory() : player.getEnderChest();
+            int total = 0;
+            for (ItemStack itemStack : inventory.getContents()) {
+                if (itemStack != null && itemStack.getType() == material) {
+                    total += itemStack.getAmount();
+                    if (total >= count) {
+                        players.append(player.getName()).append(", ");
+                        break;
+                    }
+                }
+            }
+        }
+
+        // Matches found, delete trailing comma and space
+        if (!players.isEmpty()) {
+            players.delete(players.length() - 2, players.length());
+        } else {
+            lang.sendMessage(
+                    sender,
+                    "messages.info.player.noMatches",
+                    new Replacement("%target%", material.name()));
+            return true;
+        }
+
+        lang.sendMessage(
+                sender,
+                "messages.info.player.matches",
+                new Replacement("%target%", material.name()),
+                new Replacement("%detail%", players.toString()));
+        return true;
+    }
+
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
+        if (args.length < 1 || args.length > 2 || !command.testPermissionSilent(sender)) {
+            return Collections.emptyList();
+        }
+
+        String argument = args[args.length - 1];
+        if (args.length == 1) {
+            return TabCompleter.completeEnum(argument, Material.class);
+        } else {
+            return TabCompleter.completeInteger(argument);
+        }
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/listener/ContainerListener.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.listener;
+
+import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.internal.ViewOnly;
+import com.lishid.openinv.util.InternalAccessor;
+import com.lishid.openinv.util.Permissions;
+import com.lishid.openinv.util.setting.PlayerToggles;
+import com.lishid.openinv.util.lang.LanguageManager;
+import org.bukkit.GameMode;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.Event.Result;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.block.Action;
+import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.event.inventory.InventoryCloseEvent;
+import org.bukkit.event.inventory.InventoryDragEvent;
+import org.bukkit.event.inventory.InventoryInteractEvent;
+import org.bukkit.event.player.PlayerInteractEvent;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryHolder;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+
+/**
+ * A listener managing AnyContainer, SilentContainer, and more.
+ */
+public class ContainerListener implements Listener {
+
+  private final @NotNull InternalAccessor accessor;
+  private final @NotNull LanguageManager lang;
+
+  public ContainerListener(@NotNull InternalAccessor accessor, @NotNull LanguageManager lang) {
+    this.accessor = accessor;
+    this.lang = lang;
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
+  private void onPlayerInteract(@NotNull PlayerInteractEvent event) {
+    // Ignore events from other plugins.
+    if (!PlayerInteractEvent.class.equals(event.getClass())) {
+      return;
+    }
+
+    if (event.getAction() != Action.RIGHT_CLICK_BLOCK
+        || event.getPlayer().isSneaking()
+        || event.useInteractedBlock() == Result.DENY
+        || event.getClickedBlock() == null
+        || !accessor.getAnySilentContainer().isAnySilentContainer(event.getClickedBlock())) {
+      return;
+    }
+
+    Player player = event.getPlayer();
+    UUID playerId = player.getUniqueId();
+    boolean any = Permissions.CONTAINER_ANY.hasPermission(player) && PlayerToggles.any().is(playerId);
+    boolean needsAny = accessor.getAnySilentContainer().isAnyContainerNeeded(event.getClickedBlock());
+
+    if (!any && needsAny) {
+      return;
+    }
+
+    boolean silent = Permissions.CONTAINER_SILENT.hasPermission(player) && PlayerToggles.silent().is(playerId);
+
+    // If anycontainer or silentcontainer is active
+    if (any || silent) {
+      if (accessor.getAnySilentContainer().activateContainer(player, silent, event.getClickedBlock())) {
+        if (silent && needsAny) {
+          lang.sendSystemMessage(player, "messages.info.containerBlockedSilent");
+        } else if (needsAny) {
+          lang.sendSystemMessage(player, "messages.info.containerBlocked");
+        } else if (silent) {
+          lang.sendSystemMessage(player, "messages.info.containerSilent");
+        }
+      }
+      event.setCancelled(true);
+    }
+  }
+
+  @Keep
+  @EventHandler
+  private void onInventoryClose(@NotNull final InventoryCloseEvent event) {
+    if (!(event.getPlayer() instanceof Player player)) {
+      return;
+    }
+
+    InventoryHolder holder = event.getInventory().getHolder();
+    if (PlayerToggles.silent().is(player.getUniqueId())
+        && holder != null
+        && this.accessor.getAnySilentContainer().isAnySilentContainer(holder)) {
+      this.accessor.getAnySilentContainer().deactivateContainer(player);
+    }
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.LOWEST)
+  private void onInventoryClick(@NotNull final InventoryClickEvent event) {
+    handleInventoryInteract(event);
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.LOWEST)
+  private void onInventoryDrag(@NotNull final InventoryDragEvent event) {
+    handleInventoryInteract(event);
+  }
+
+  private void handleInventoryInteract(@NotNull final InventoryInteractEvent event) {
+    HumanEntity entity = event.getWhoClicked();
+
+    // Un-cancel spectator interactions.
+    if (entity.getGameMode() == GameMode.SPECTATOR && Permissions.SPECTATE_CLICK.hasPermission(entity)) {
+      event.setCancelled(false);
+    }
+
+    if (event.isCancelled()) {
+      return;
+    }
+
+    Inventory inventory = event.getView().getTopInventory();
+    if (inventory instanceof ViewOnly) {
+      event.setCancelled(true);
+    }
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/listener/LegacyInventoryListener.java

@@ -0,0 +1,234 @@
+package com.lishid.openinv.listener;
+
+import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.util.AccessEqualMode;
+import com.lishid.openinv.util.InventoryAccess;
+import com.lishid.openinv.util.Permissions;
+import com.lishid.openinv.util.config.Config;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.inventory.InventoryAction;
+import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.event.inventory.InventoryDragEvent;
+import org.bukkit.event.inventory.InventoryInteractEvent;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * A listener used to enable functionality and prevent issues on versions < 1.21.
+ */
+public class LegacyInventoryListener implements Listener {
+
+  private final @NotNull Plugin plugin;
+  private final @NotNull Config config;
+
+  public LegacyInventoryListener(@NotNull Plugin plugin, @NotNull Config config) {
+    this.plugin = plugin;
+    this.config = config;
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.LOWEST, ignoreCancelled = true)
+  private void onInventoryClick(@NotNull final InventoryClickEvent event) {
+    if (handleInventoryInteract(event)) {
+      return;
+    }
+
+    // Safe cast - has to be a player to be the holder of a special player inventory.
+    Player player = (Player) event.getWhoClicked();
+
+    if (event.getAction() != InventoryAction.MOVE_TO_OTHER_INVENTORY) {
+      return;
+    }
+
+    // Extra handling for MOVE_TO_OTHER_INVENTORY - apparently Mojang no longer removes the item from the target
+    // inventory prior to adding it to existing stacks.
+    ItemStack currentItem = event.getCurrentItem();
+    if (currentItem == null) {
+      // Other plugin doing some sort of handling (would be NOTHING for null item otherwise), ignore.
+      return;
+    }
+
+    ItemStack clone = currentItem.clone();
+    event.setCurrentItem(null);
+
+    // Complete add action in same tick after event completion.
+    this.plugin.getServer().getScheduler().runTask(this.plugin, () -> player.getInventory().addItem(clone));
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.LOW, ignoreCancelled = true)
+  private void onInventoryDrag(@NotNull final InventoryDragEvent event) {
+    if (handleInventoryInteract(event)) {
+      return;
+    }
+
+    InventoryView view = event.getView();
+
+    if (view.getCursor() == null) {
+      return;
+    }
+
+    int topSize = view.getTopInventory().getSize();
+
+    // Get bottom inventory active slots as player inventory slots.
+    Set<Integer> slots = event.getRawSlots().stream()
+        .filter(slot -> slot >= topSize)
+        .map(slot -> convertToPlayerSlot(view, slot)).collect(Collectors.toSet());
+
+    int overlapLosses = 0;
+
+    // Count overlapping slots.
+    for (Map.Entry<Integer, ItemStack> newItem : event.getNewItems().entrySet()) {
+      int rawSlot = newItem.getKey();
+
+      // Skip bottom inventory slots.
+      if (rawSlot >= topSize) {
+        continue;
+      }
+
+      int convertedSlot = convertToPlayerSlot(view, rawSlot);
+
+      if (slots.contains(convertedSlot)) {
+        overlapLosses += getCountDiff(view.getItem(rawSlot), newItem.getValue());
+      }
+    }
+
+    // Allow no overlap to proceed as usual.
+    if (overlapLosses < 1) {
+      return;
+    }
+
+    final ItemStack lost = view.getCursor().clone();
+    lost.setAmount(overlapLosses);
+
+    // Re-add the lost items in the same tick after the event has completed.
+    plugin.getServer().getScheduler().runTask(plugin, () -> {
+      InventoryView currentOpen = event.getWhoClicked().getOpenInventory();
+
+      if (!currentOpen.equals(view)) {
+        event.getWhoClicked().getWorld().dropItem(event.getWhoClicked().getLocation(), lost).setPickupDelay(0);
+        return;
+      }
+
+      ItemStack cursor = currentOpen.getCursor();
+
+      if (cursor == null) {
+        currentOpen.setCursor(lost);
+      } else if (lost.isSimilar(cursor)) {
+        cursor.setAmount(cursor.getAmount() + lost.getAmount());
+        currentOpen.setCursor(cursor);
+      } else {
+        event.getWhoClicked().getWorld().dropItem(event.getWhoClicked().getLocation(), lost).setPickupDelay(0);
+      }
+    });
+  }
+
+  private int getCountDiff(@Nullable ItemStack original, @NotNull ItemStack result) {
+    if (original == null || original.getType() != result.getType()) {
+      return result.getAmount();
+    }
+
+    return result.getAmount() - original.getAmount();
+  }
+
+  /**
+   * Handle common InventoryInteractEvent functions.
+   *
+   * @param event the InventoryInteractEvent
+   * @return true unless the top inventory is the holder's own inventory
+   */
+  private boolean handleInventoryInteract(@NotNull final InventoryInteractEvent event) {
+    HumanEntity viewer = event.getWhoClicked();
+
+    Inventory inventory = event.getView().getTopInventory();
+    ISpecialInventory backing = InventoryAccess.getInventory(inventory);
+
+    if (backing == null) {
+      return true;
+    }
+
+    Permissions edit;
+    HumanEntity target = backing.getPlayer();
+    boolean ownContainer = viewer.equals(target);
+    if (backing instanceof ISpecialPlayerInventory) {
+      edit = ownContainer ? Permissions.INVENTORY_EDIT_SELF : Permissions.INVENTORY_EDIT_OTHER;
+    } else if (backing instanceof ISpecialEnderChest) {
+      edit = ownContainer ? Permissions.ENDERCHEST_EDIT_SELF : Permissions.ENDERCHEST_OPEN_OTHER;
+    } else {
+      // Unknown implementation.
+      return true;
+    }
+
+    if (!edit.hasPermission(viewer)) {
+      event.setCancelled(true);
+      return true;
+    }
+
+    // If access ties aren't view-only mode, don't bother with permission checks.
+    if (config.getAccessEqualMode() != AccessEqualMode.VIEW) {
+      return !ownContainer || !(backing instanceof ISpecialPlayerInventory);
+    }
+
+    for (int level = 4; level > 0; --level) {
+      String permission = "openinv.access.level." + level;
+      // If the target doesn't have this access level...
+      if (!target.hasPermission(permission)) {
+        // If the viewer does have the access level, all good.
+        if (viewer.hasPermission(permission)) {
+          break;
+        }
+        // Otherwise check next access level.
+        continue;
+      }
+
+      // Either the viewer lacks access (which shouldn't be possible) or this is a tie. View-only.
+      event.setCancelled(true);
+      return true;
+    }
+
+    return !ownContainer || !(backing instanceof ISpecialPlayerInventory);
+  }
+
+  private static int convertToPlayerSlot(InventoryView view, int rawSlot) {
+    int topSize = view.getTopInventory().getSize();
+    if (topSize <= rawSlot) {
+      // Slot is not inside special inventory, use Bukkit logic.
+      return view.convertSlot(rawSlot);
+    }
+
+    // Main inventory, slots 0-26 -> 9-35
+    if (rawSlot < 27) {
+      return rawSlot + 9;
+    }
+    // Hotbar, slots 27-35 -> 0-8
+    if (rawSlot < 36) {
+      return rawSlot - 27;
+    }
+    // Armor, slots 36-39 -> 39-36
+    if (rawSlot < 40) {
+      return 36 + (39 - rawSlot);
+    }
+    // Off-hand
+    if (rawSlot == 40) {
+      return 40;
+    }
+    // Drop slots, "out of inventory"
+    return -1;
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/listener/ToggleListener.java

@@ -0,0 +1,22 @@
+package com.lishid.openinv.listener;
+
+import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.util.setting.PlayerToggles;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerQuitEvent;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+
+public class ToggleListener implements Listener {
+
+  @Keep
+  @EventHandler
+  private void onPlayerQuit(@NotNull PlayerQuitEvent event) {
+    UUID playerId = event.getPlayer().getUniqueId();
+    PlayerToggles.any().set(playerId, false);
+    PlayerToggles.silent().set(playerId, false);
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/util/AccessEqualMode.java

@@ -0,0 +1,23 @@
+package com.lishid.openinv.util;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Locale;
+
+public enum AccessEqualMode {
+
+  DENY, ALLOW, VIEW;
+
+  public static @NotNull AccessEqualMode of(@Nullable String value) {
+    if (value == null) {
+      return VIEW;
+    }
+    return switch (value.toLowerCase(Locale.ENGLISH)) {
+      case "deny", "false" -> DENY;
+      case "allow", "true" -> ALLOW;
+      default -> VIEW;
+    };
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/util/InternalAccessor.java

@@ -0,0 +1,213 @@
+/*
+ * Copyright (C) 2011-2023 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util;
+
+import com.github.jikoo.planarwrappers.util.version.BukkitVersions;
+import com.github.jikoo.planarwrappers.util.version.Version;
+import com.lishid.openinv.internal.Accessor;
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.internal.PlayerManager;
+import com.lishid.openinv.util.lang.LanguageManager;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.logging.Logger;
+
+public class InternalAccessor {
+
+    private @Nullable Accessor internal;
+
+    public InternalAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
+
+        try {
+            if (BukkitVersions.MINECRAFT.equals(Version.of(1, 21, 1))
+                    || BukkitVersions.MINECRAFT.equals(Version.of(1, 21))) {
+                internal = new com.lishid.openinv.internal.v1_21_R1.InternalAccessor(logger, lang);
+            } else if (BukkitVersions.MINECRAFT.equals(Version.of(1, 20, 4))) {
+                internal = new com.lishid.openinv.internal.v1_20_R3.InternalAccessor(logger, lang);
+            } else if (BukkitVersions.MINECRAFT.equals(Version.of(1, 20, 6))) {
+                internal = new com.lishid.openinv.internal.v1_20_R4.InternalAccessor(logger, lang);
+            }
+            if (internal != null) {
+                InventoryAccess.setProvider(internal::get);
+            }
+        } catch (NoClassDefFoundError | Exception e) {
+            internal = null;
+            InventoryAccess.setProvider(null);
+        }
+    }
+
+    public String getReleasesLink() {
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 4, 4))) { // Good luck.
+            return "https://dev.bukkit.org/projects/openinv/files?&sort=datecreated";
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 8, 8))) { // 1.8.8
+            return "https://github.com/lishid/OpenInv/releases/tag/4.1.5";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 13))) { // 1.4.4+ had versioned packages.
+            return "https://github.com/lishid/OpenInv/releases/tag/4.0.0 (OpenInv-legacy)";
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 13))) { // 1.13
+            return "https://github.com/lishid/OpenInv/releases/tag/4.0.0";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 14))) { // 1.13.1, 1.13.2
+            return "https://github.com/lishid/OpenInv/releases/tag/4.0.7";
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 14))) { // 1.14 to 1.14.1 had no revision bump.
+            return "https://github.com/lishid/OpenInv/releases/tag/4.0.0";
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 14, 1))) { // 1.14.1 to 1.14.2 had no revision bump.
+            return "https://github.com/lishid/OpenInv/releases/tag/4.0.1";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 15))) { // 1.14.2
+            return "https://github.com/lishid/OpenInv/releases/tag/4.1.1";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 15, 1))) { // 1.15, 1.15.1
+            return "https://github.com/lishid/OpenInv/releases/tag/4.1.5";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 16))) { // 1.15.2
+            return "https://github.com/Jikoo/OpenInv/commit/502f661be39ee85d300851dd571f3da226f12345 (never released)";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 16, 1))) { // 1.16, 1.16.1
+            return "https://github.com/lishid/OpenInv/releases/tag/4.1.4";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 16, 3))) { // 1.16.2, 1.16.3
+            return "https://github.com/lishid/OpenInv/releases/tag/4.1.5";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 17))) { // 1.16.4, 1.16.5
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.1.8";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 18, 1))) { // 1.17, 1.18, 1.18.1
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.1.10";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 19))) { // 1.18.2
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.3.0";
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 19))) { // 1.19
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.2.0";
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 19, 1))) { // 1.19.1
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.2.2";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 19, 3))) { // 1.19.2, 1.19.3
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.3.0";
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 20))) { // 1.19.4
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.4.3";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 20, 1))) { // 1.20, 1.20.1
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.4.1";
+        }
+        if (BukkitVersions.MINECRAFT.lessThanOrEqual(Version.of(1, 20, 3))) { // 1.20.2, 1.20.3
+            return "https://github.com/Jikoo/OpenInv/releases/tag/4.4.3";
+        }
+        return "https://github.com/Jikoo/OpenInv/releases";
+    }
+
+    /**
+     * Reload internal features.
+     */
+    public void reload(ConfigurationSection config) {
+        if (internal != null) {
+            internal.reload(config);
+        }
+    }
+
+    /**
+     * Gets the server implementation version.
+     *
+     * @return the version
+     */
+    public @NotNull String getVersion() {
+        return BukkitVersions.MINECRAFT.toString();
+    }
+
+    /**
+     * Checks if the server implementation is supported.
+     *
+     * @return true if initialized for a supported server version
+     */
+    public boolean isSupported() {
+        return internal != null;
+    }
+
+    /**
+     * Get the instance of the IAnySilentContainer implementation for the current server version.
+     *
+     * @return the IAnySilentContainer
+     * @throws IllegalStateException if server version is unsupported
+     */
+    public @NotNull IAnySilentContainer getAnySilentContainer() {
+        if (internal == null) {
+            throw new IllegalStateException(String.format("Unsupported server version %s!", BukkitVersions.MINECRAFT));
+        }
+        return internal.getAnySilentContainer();
+    }
+
+    public @Nullable InventoryView openInventory(@NotNull Player player, @NotNull ISpecialInventory inventory, boolean viewOnly) {
+        if (internal == null) {
+            throw new IllegalStateException(String.format("Unsupported server version %s!", BukkitVersions.MINECRAFT));
+        }
+        return internal.getPlayerManager().openInventory(player, inventory, viewOnly);
+    }
+
+    /**
+     * Get the instance of the IPlayerDataManager implementation for the current server version.
+     *
+     * @return the IPlayerDataManager
+     * @throws IllegalStateException if server version is unsupported
+     */
+    @NotNull PlayerManager getPlayerDataManager() {
+        if (internal == null) {
+            throw new IllegalStateException(String.format("Unsupported server version %s!", BukkitVersions.MINECRAFT));
+        }
+        return internal.getPlayerManager();
+    }
+
+    /**
+     * Creates an instance of the ISpecialEnderChest implementation for the given Player.
+     *
+     * @param player the Player
+     * @return the ISpecialEnderChest created
+     */
+    ISpecialEnderChest createEnderChest(final Player player) {
+        if (internal == null) {
+            throw new IllegalStateException(String.format("Unsupported server version %s!", BukkitVersions.MINECRAFT));
+        }
+        return internal.createEnderChest(player);
+    }
+
+    /**
+     * Creates an instance of the ISpecialPlayerInventory implementation for the given Player.
+     *
+     * @param player the Player
+     * @return the ISpecialPlayerInventory created
+     */
+    ISpecialPlayerInventory createInventory(final Player player) {
+        if (internal == null) {
+            throw new IllegalStateException(String.format("Unsupported server version %s!", BukkitVersions.MINECRAFT));
+        }
+        return internal.createPlayerInventory(player);
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/util/InventoryManager.java

@@ -0,0 +1,274 @@
+package com.lishid.openinv.util;
+
+import com.github.jikoo.planarwrappers.util.version.BukkitVersions;
+import com.github.jikoo.planarwrappers.util.version.Version;
+import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.event.OpenEvents;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.util.config.Config;
+import org.bukkit.entity.HumanEntity;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.inventory.InventoryCloseEvent;
+import org.bukkit.event.inventory.InventoryOpenEvent;
+import org.bukkit.event.player.PlayerChangedWorldEvent;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.event.player.PlayerQuitEvent;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Consumer;
+import java.util.logging.Level;
+import java.util.stream.Stream;
+
+/**
+ * A manager for special inventories. Delegates creation and tracks copies in use.
+ */
+public class InventoryManager implements Listener {
+
+  private final Map<UUID, ISpecialPlayerInventory> inventories = new ConcurrentHashMap<>();
+  private final Map<UUID, ISpecialEnderChest> enderChests = new ConcurrentHashMap<>();
+  private final Set<UUID> expectedCloses = new HashSet<>();
+  private final @NotNull Plugin plugin;
+  private final @NotNull Config config;
+  private final @NotNull InternalAccessor accessor;
+
+  public InventoryManager(@NotNull Plugin plugin, @NotNull Config config, @NotNull InternalAccessor accessor) {
+    this.plugin = plugin;
+    this.config = config;
+    this.accessor = accessor;
+  }
+
+  public void evictAll() {
+    Stream.concat(inventories.values().stream(), enderChests.values().stream())
+        .map(inventory -> {
+          // Rather than iterate twice, evict all viewers during remapping.
+          for (HumanEntity viewer : List.copyOf(inventory.getBukkitInventory().getViewers())) {
+            expectedCloses.add(viewer.getUniqueId());
+            viewer.closeInventory();
+          }
+          // If saving is prevented, return a null value for the player to save.
+          if (config.isSaveDisabled() || OpenEvents.saveCancelled(inventory)) {
+            return null;
+          }
+          if (inventory.getPlayer() instanceof Player player) {
+            return player;
+          }
+          return null;
+        })
+        .filter(Objects::nonNull)
+        .distinct()
+        .forEach(player -> {
+          if (!player.isOnline()) {
+            accessor.getPlayerDataManager().inject(player).saveData();
+          }
+        });
+    inventories.clear();
+    enderChests.clear();
+    expectedCloses.clear();
+  }
+
+  public @NotNull ISpecialPlayerInventory getInventory(@NotNull Player player) {
+    return inventories.computeIfAbsent(player.getUniqueId(), uuid -> accessor.createInventory(player));
+  }
+
+  public @NotNull ISpecialEnderChest getEnderChest(@NotNull Player player) {
+    return enderChests.computeIfAbsent(player.getUniqueId(), uuid -> accessor.createEnderChest(player));
+  }
+
+  public @Nullable Player getLoadedPlayer(@NotNull UUID uuid) {
+    ISpecialInventory inUse = inventories.get(uuid);
+    if (inUse != null) {
+      return (Player) inUse.getPlayer();
+    }
+    inUse = enderChests.get(uuid);
+    if (inUse != null) {
+      return (Player) inUse.getPlayer();
+    }
+    return null;
+  }
+
+  public void unload(@NotNull UUID uuid) {
+    inventories.computeIfPresent(uuid, this::remove);
+    enderChests.computeIfPresent(uuid, this::remove);
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.LOWEST)
+  private void onPlayerJoin(@NotNull PlayerJoinEvent event) {
+    consumeLoaded(event.getPlayer().getUniqueId(), inventory -> checkViewerAccess(inventory, true));
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.MONITOR)
+  private void onPlayerQuit(@NotNull PlayerQuitEvent event) {
+    consumeLoaded(event.getPlayer().getUniqueId(), inventory -> checkViewerAccess(inventory, false));
+  }
+
+  @Keep
+  @EventHandler
+  private void onWorldChanged(@NotNull PlayerChangedWorldEvent event) {
+    Player player = event.getPlayer();
+    consumeLoaded(player.getUniqueId(), inventory -> checkViewerAccess(inventory, player.isOnline()));
+  }
+
+  @Keep
+  @EventHandler
+  private void onInventoryClose(@NotNull InventoryCloseEvent event) {
+    ISpecialInventory inventory = InventoryAccess.getInventory(event.getInventory());
+
+    // If this is not an ISpecialInventory or the inventory was closed elsewhere internally, don't handle.
+    if (inventory == null || expectedCloses.remove(event.getPlayer().getUniqueId())) {
+      return;
+    }
+
+    // Fetch the active ISpecialInventory of this type.
+    Map<UUID, ? extends ISpecialInventory> map = inventory instanceof ISpecialPlayerInventory ? inventories : enderChests;
+    UUID key = inventory.getPlayer().getUniqueId();
+    ISpecialInventory loaded = map.get(key);
+
+    // If there is no loaded inventory, it has already been removed and saved.
+    if (loaded == null) {
+      return;
+    }
+
+    // This should only be possible if a plugin is going to extreme lengths to mess with our inventories.
+    if (loaded != inventory) {
+      // Immediately remove affected inventory, then dump all viewers. We don't want to risk duplication bugs.
+      map.remove(key);
+      remove(key, loaded);
+      remove(key, inventory);
+      // The loaded one is "correct" as far as we're concerned, so save that.
+      save(loaded);
+    }
+
+    // Schedule task to check in use status later this tick. Closing user is still in viewer list.
+    plugin.getServer().getScheduler().runTask(plugin, () -> {
+      if (loaded.isInUse()) {
+        return;
+      }
+
+      // Re-fetch from map to reduce odds of a duplicate save.
+      ISpecialInventory current = map.remove(key);
+
+      if (current != null) {
+        save(current);
+      }
+    });
+  }
+
+  @Keep
+  @EventHandler(priority = EventPriority.HIGHEST)
+  private void onInventoryOpen(@NotNull InventoryOpenEvent event) {
+    ISpecialInventory inventory = InventoryAccess.getInventory(event.getInventory());
+    if (inventory == null) {
+      return;
+    }
+
+    Map<UUID, ? extends ISpecialInventory> map = inventory instanceof ISpecialPlayerInventory ? inventories : enderChests;
+    UUID key = inventory.getPlayer().getUniqueId();
+    ISpecialInventory loaded = map.get(key);
+
+    if (!inventory.equals(loaded)) {
+      event.setCancelled(true);
+      plugin.getLogger().log(
+          Level.WARNING,
+          "Prevented a plugin from opening an untracked ISpecialInventory!",
+          new Throwable("Untracked ISpecialInventory"));
+    }
+  }
+
+  private <T extends ISpecialInventory> void checkViewerAccess(@NotNull T inventory, boolean online) {
+
+    Player owner = (Player) inventory.getPlayer();
+    Permissions connectedState = online ? Permissions.ACCESS_ONLINE : Permissions.ACCESS_OFFLINE;
+    boolean alwaysDenied = !online && config.isOfflineDisabled();
+
+    // Copy viewers so we don't modify the list we're iterating over when closing inventories.
+    List<HumanEntity> viewers = new ArrayList<>(inventory.getBukkitInventory().getViewers());
+    // Legacy: Owner is always a viewer of own inventory.
+    if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 21))) {
+      if (inventory instanceof ISpecialPlayerInventory) {
+        Inventory active = owner.getOpenInventory().getTopInventory();
+        if (!active.equals(inventory.getBukkitInventory())) {
+          viewers.remove(owner);
+        }
+      }
+    }
+
+    for (HumanEntity viewer : viewers) {
+      if (alwaysDenied
+          || !connectedState.hasPermission(viewer)
+          || (!Objects.equals(owner.getWorld(), viewer.getWorld()) && !Permissions.ACCESS_CROSSWORLD.hasPermission(viewer))) {
+        expectedCloses.add(viewer.getUniqueId());
+        viewer.closeInventory();
+      }
+    }
+  }
+
+  private void consumeLoaded(@NotNull UUID key, @NotNull Consumer<@NotNull ISpecialInventory> consumer) {
+    boolean saved = consumeLoaded(inventories, key, false, consumer);
+    consumeLoaded(enderChests, key, saved, consumer);
+  }
+
+  private <T extends ISpecialInventory> boolean consumeLoaded(
+      @NotNull Map<UUID, T> map,
+      @NotNull UUID key,
+      boolean saved,
+      @NotNull Consumer<@NotNull ISpecialInventory> consumer) {
+    T inventory = map.get(key);
+
+    if (inventory == null) {
+      return saved;
+    }
+
+    consumer.accept(inventory);
+    if (!inventory.isInUse()) {
+      map.remove(key);
+
+      if (!saved) {
+        save(inventory);
+        return true;
+      }
+    }
+
+    return saved;
+  }
+
+  private void save(@NotNull ISpecialInventory inventory) {
+    if (config.isSaveDisabled()) {
+      return;
+    }
+
+    Player player = (Player) inventory.getPlayer();
+
+    if (!player.isOnline() && !OpenEvents.saveCancelled(inventory)) {
+      accessor.getPlayerDataManager().inject(player).saveData();
+    }
+  }
+
+  @Contract("_, _ -> null")
+  private <T extends ISpecialInventory> @Nullable T remove(@NotNull UUID key, @NotNull T inventory) {
+    for (HumanEntity viewer : List.copyOf(inventory.getBukkitInventory().getViewers())) {
+      expectedCloses.add(viewer.getUniqueId());
+      viewer.closeInventory();
+    }
+    return null;
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/util/PlayerLoader.java

@@ -0,0 +1,222 @@
+package com.lishid.openinv.util;
+
+import com.google.common.cache.Cache;
+import com.google.common.cache.CacheBuilder;
+import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.util.config.Config;
+import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
+import org.bukkit.plugin.Plugin;
+import org.bukkit.profile.PlayerProfile;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Iterator;
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * A utility for looking up and loading players.
+ */
+public class PlayerLoader implements Listener {
+
+  private final @NotNull Plugin plugin;
+  private final @NotNull Config config;
+  private final @NotNull InventoryManager inventoryManager;
+  private final @NotNull InternalAccessor internalAccessor;
+  private final @NotNull Logger logger;
+  private final @NotNull Cache<String, PlayerProfile> lookupCache;
+
+  public PlayerLoader(
+      @NotNull Plugin plugin,
+      @NotNull Config config,
+      @NotNull InventoryManager inventoryManager,
+      @NotNull InternalAccessor internalAccessor,
+      @NotNull Logger logger) {
+    this.plugin = plugin;
+    this.config = config;
+    this.inventoryManager = inventoryManager;
+    this.internalAccessor = internalAccessor;
+    this.logger = logger;
+    this.lookupCache = CacheBuilder.newBuilder().maximumSize(20).build();
+  }
+
+  /**
+   * Load a {@link Player} from an {@link OfflinePlayer}. If the user has not played before or the default world for
+   * the server is not loaded, this will return {@code null}.
+   *
+   * @param offline the {@code OfflinePlayer} to load a {@code Player} for
+   * @return the loaded {@code Player}
+   * @throws IllegalStateException if the server version is unsupported
+   */
+  public @Nullable Player load(@NotNull OfflinePlayer offline) {
+    UUID key = offline.getUniqueId();
+
+    Player player = offline.getPlayer();
+    if (player != null) {
+      return player;
+    }
+
+    player = inventoryManager.getLoadedPlayer(key);
+    if (player != null) {
+      return player;
+    }
+
+    if (config.isOfflineDisabled() || !internalAccessor.isSupported()) {
+      return null;
+    }
+
+    if (Bukkit.isPrimaryThread()) {
+      return internalAccessor.getPlayerDataManager().loadPlayer(offline);
+    }
+
+    Future<Player> future = Bukkit.getScheduler().callSyncMethod(plugin,
+        () -> internalAccessor.getPlayerDataManager().loadPlayer(offline));
+
+    try {
+      player = future.get();
+    } catch (InterruptedException | ExecutionException e) {
+      logger.log(Level.WARNING, e.getMessage(), e);
+      return null;
+    }
+
+    return player;
+  }
+
+  public @Nullable OfflinePlayer match(@NotNull String name) {
+    // Warn if called on the main thread - if we resort to searching offline players, this may take several seconds.
+    if (Bukkit.getServer().isPrimaryThread()) {
+      logger.warning("Call to PlayerSearchCache#matchPlayer made on the main thread!");
+      logger.warning("This can cause the server to hang, potentially severely.");
+      logger.log(Level.WARNING, "Current stack trace", new Throwable("Current stack trace"));
+    }
+
+    OfflinePlayer player;
+
+    try {
+      UUID uuid = UUID.fromString(name);
+      player = Bukkit.getOfflinePlayer(uuid);
+      // Ensure player is an existing player.
+      if (player.hasPlayedBefore() || player.isOnline()) {
+        return player;
+      }
+      // Return null otherwise.
+      return null;
+    } catch (IllegalArgumentException ignored) {
+      // Not a UUID
+    }
+
+    // Exact online match first.
+    player = Bukkit.getServer().getPlayerExact(name);
+
+    if (player != null) {
+      return player;
+    }
+
+    // Cached offline match.
+    PlayerProfile cachedResult = lookupCache.getIfPresent(name);
+    if (cachedResult != null && cachedResult.getUniqueId() != null) {
+      player = Bukkit.getOfflinePlayer(cachedResult.getUniqueId());
+      // Ensure player is an existing player.
+      if (player.hasPlayedBefore() || player.isOnline()) {
+        return player;
+      }
+      // Return null otherwise.
+      return null;
+    }
+
+    // Exact offline match second - ensure offline access works when matchable users are online.
+    player = Bukkit.getServer().getOfflinePlayer(name);
+
+    if (player.hasPlayedBefore()) {
+      lookupCache.put(name, player.getPlayerProfile());
+      return player;
+    }
+
+    // Inexact online match.
+    player = Bukkit.getServer().getPlayer(name);
+
+    if (player != null) {
+      return player;
+    }
+
+    // Finally, inexact offline match.
+    float bestMatch = 0;
+    for (OfflinePlayer offline : Bukkit.getServer().getOfflinePlayers()) {
+      if (offline.getName() == null) {
+        // Loaded by UUID only, name has never been looked up.
+        continue;
+      }
+
+      float currentMatch = StringMetric.compareJaroWinkler(name, offline.getName());
+
+      if (currentMatch == 1.0F) {
+        return offline;
+      }
+
+      if (currentMatch > bestMatch) {
+        bestMatch = currentMatch;
+        player = offline;
+      }
+    }
+
+    if (player != null) {
+      // If a match was found, store it.
+      lookupCache.put(name, player.getPlayerProfile());
+      return player;
+    }
+
+    // No players have ever joined the server.
+    return null;
+  }
+
+  @Keep
+  @EventHandler
+  private void updateMatches(@NotNull PlayerJoinEvent event) {
+    // If player is not new, any cached values are valid.
+    if (event.getPlayer().hasPlayedBefore()) {
+      return;
+    }
+
+    // New player may have a name that already points to someone else in lookup cache.
+    String name = event.getPlayer().getName();
+    lookupCache.invalidate(name);
+
+    // If the cache is empty, nothing to do. Don't hit scheduler.
+    if (lookupCache.size() == 0) {
+      return;
+    }
+
+    plugin.getServer().getScheduler().runTaskLaterAsynchronously(plugin, () -> {
+      Iterator<Map.Entry<String, PlayerProfile>> iterator = lookupCache.asMap().entrySet().iterator();
+      while (iterator.hasNext()) {
+        Map.Entry<String, PlayerProfile> entry = iterator.next();
+        String oldMatch = entry.getValue().getName();
+
+        // Shouldn't be possible - all profiles should be complete.
+        if (oldMatch == null) {
+          iterator.remove();
+          continue;
+        }
+
+        String lookup = entry.getKey();
+        float oldMatchScore = StringMetric.compareJaroWinkler(lookup, oldMatch);
+        float newMatchScore = StringMetric.compareJaroWinkler(lookup, name);
+
+        // If new match exceeds old match, delete old match.
+        if (newMatchScore > oldMatchScore) {
+          iterator.remove();
+        }
+      }
+    }, 7L);
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/util/StringMetric.java

@@ -0,0 +1,150 @@
+/*
+ * Copyright (C) 2011-2021 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util;
+
+public class StringMetric {
+
+    public static float compareJaroWinkler(String a, String b) {
+        final float jaroScore = compareJaro(a, b);
+
+        if (jaroScore < (float) 0.7) {
+            return jaroScore;
+        }
+
+        String prefix = commonPrefix(a, b);
+        int prefixLength = Math.min(prefix.codePointCount(0, prefix.length()), 4);
+
+        return jaroScore + (prefixLength * (float) 0.1 * (1.0f - jaroScore));
+
+    }
+
+    private static float compareJaro(String a, String b) {
+        if (a.isEmpty() && b.isEmpty()) {
+            return 1.0f;
+        }
+
+        if (a.isEmpty() || b.isEmpty()) {
+            return 0.0f;
+        }
+
+        final int[] charsA = a.codePoints().toArray();
+        final int[] charsB = b.codePoints().toArray();
+
+        // Intentional integer division to round down.
+        final int halfLength = Math.max(0, Math.max(charsA.length, charsB.length) / 2 - 1);
+
+        final int[] commonA = getCommonCodePoints(charsA, charsB, halfLength);
+        final int[] commonB = getCommonCodePoints(charsB, charsA, halfLength);
+
+        // commonA and commonB will always contain the same multi-set of
+        // characters. Because getCommonCharacters has been optimized, commonA
+        // and commonB are -1-padded. So in this loop we count transposition
+        // and use commonCharacters to determine the length of the multi-set.
+        float transpositions = 0;
+        int commonCharacters = 0;
+        for (int length = commonA.length; commonCharacters < length
+                && commonA[commonCharacters] > -1; commonCharacters++) {
+            if (commonA[commonCharacters] != commonB[commonCharacters]) {
+                transpositions++;
+            }
+        }
+
+        if (commonCharacters == 0) {
+            return 0.0f;
+        }
+
+        float aCommonRatio = commonCharacters / (float) charsA.length;
+        float bCommonRatio = commonCharacters / (float) charsB.length;
+        float transpositionRatio = (commonCharacters - transpositions / 2.0f) / commonCharacters;
+
+        return (aCommonRatio + bCommonRatio + transpositionRatio) / 3.0f;
+    }
+
+    /*
+     * Returns an array of code points from a within b. A character in b is
+     * counted as common when it is within separation distance from the position
+     * in a.
+     */
+    private static int[] getCommonCodePoints(final int[] charsA, final int[] charsB, final int separation) {
+        final int[] common = new int[Math.min(charsA.length, charsB.length)];
+        final boolean[] matched = new boolean[charsB.length];
+
+        // Iterate of string a and find all characters that occur in b within
+        // the separation distance. Mark any matches found to avoid
+        // duplicate matchings.
+        int commonIndex = 0;
+        for (int i = 0, length = charsA.length; i < length; i++) {
+            final int character = charsA[i];
+            final int index = indexOf(character, charsB, i - separation, i
+                    + separation + 1, matched);
+            if (index > -1) {
+                common[commonIndex++] = character;
+                matched[index] = true;
+            }
+        }
+
+        if (commonIndex < common.length) {
+            common[commonIndex] = -1;
+        }
+
+        // Both invocations will yield the same multi-set terminated by -1, so
+        // they can be compared for transposition without making a copy.
+        return common;
+    }
+
+    /*
+     * Search for code point in buffer starting at fromIndex to toIndex - 1.
+     *
+     * Returns -1 when not found.
+     */
+    private static int indexOf(int character, int[] buffer, int fromIndex, int toIndex, boolean[] matched) {
+
+        // compare char with range of characters to either side
+        for (int j = Math.max(0, fromIndex), length = Math.min(toIndex, buffer.length); j < length; j++) {
+            // check if found
+            if (buffer[j] == character && !matched[j]) {
+                return j;
+            }
+        }
+
+        return -1;
+    }
+
+    private static String commonPrefix(CharSequence a, CharSequence b) {
+        int maxPrefixLength = Math.min(a.length(), b.length());
+
+        int p;
+
+        p = 0;
+        while (p < maxPrefixLength && a.charAt(p) == b.charAt(p)) {
+            ++p;
+        }
+
+        if (validSurrogatePairAt(a, p - 1) || validSurrogatePairAt(b, p - 1)) {
+            --p;
+        }
+
+        return a.subSequence(0, p).toString();
+    }
+
+    private static boolean validSurrogatePairAt(CharSequence string, int index) {
+        return index >= 0 && index <= string.length() - 2 && Character.isHighSurrogate(string.charAt(index)) && Character.isLowSurrogate(string.charAt(index + 1));
+    }
+
+    private StringMetric(){}
+
+}

plugin/src/main/java/com/lishid/openinv/util/TabCompleter.java

@@ -0,0 +1,150 @@
+/*
+ * Copyright (C) 2011-2021 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util;
+
+import org.bukkit.Bukkit;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+import org.bukkit.util.StringUtil;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.function.Function;
+
+/**
+ * Utility class for common tab completions.
+ */
+public final class TabCompleter {
+
+    /**
+     * Offer tab completions for whole numbers.
+     *
+     * @param argument the argument to complete
+     * @return integer options
+     */
+    public static List<String> completeInteger(String argument) {
+        // Ensure existing argument is actually a number
+        if (!argument.isEmpty()) {
+            try {
+                Integer.parseInt(argument);
+            } catch (NumberFormatException e) {
+                return Collections.emptyList();
+            }
+        }
+
+        List<String> completions = new ArrayList<>(10);
+        for (int i = 0; i < 10; ++i) {
+            completions.add(argument + i);
+        }
+
+        return completions;
+    }
+
+    /**
+     * Offer tab completions for a given Enum.
+     *
+     * @param argument the argument to complete
+     * @param enumClazz the Enum to complete for
+     * @return the matching Enum values
+     */
+    public static List<String> completeEnum(String argument, Class<? extends Enum<?>> enumClazz) {
+        argument = argument.toLowerCase(Locale.ENGLISH);
+        List<String> completions = new ArrayList<>();
+
+        for (Enum<?> enumConstant : enumClazz.getEnumConstants()) {
+            String name = enumConstant.name().toLowerCase(Locale.ENGLISH);
+            if (name.startsWith(argument)) {
+                completions.add(name);
+            }
+        }
+
+        return completions;
+    }
+
+    /**
+     * Offer tab completions for a given array of Strings.
+     *
+     * @param argument the argument to complete
+     * @param options the Strings which may be completed
+     * @return the matching Strings
+     */
+    public static List<String> completeString(String argument, String[] options) {
+        argument = argument.toLowerCase(Locale.ENGLISH);
+        List<String> completions = new ArrayList<>();
+
+        for (String option : options) {
+            if (option.startsWith(argument)) {
+                completions.add(option);
+            }
+        }
+
+        return completions;
+    }
+
+    /**
+     * Offer tab completions for visible online Players' names.
+     *
+     * @param sender the command's sender
+     * @param argument the argument to complete
+     * @return the matching Players' names
+     */
+    public static List<String> completeOnlinePlayer(CommandSender sender, String argument) {
+        List<String> completions = new ArrayList<>();
+        Player senderPlayer = sender instanceof Player ? (Player) sender : null;
+
+        for (Player player : Bukkit.getOnlinePlayers()) {
+            if (senderPlayer != null && !senderPlayer.canSee(player)) {
+                continue;
+            }
+
+            if (StringUtil.startsWithIgnoreCase(player.getName(), argument)) {
+                completions.add(player.getName());
+            }
+        }
+
+        return completions;
+    }
+
+    /**
+     * Offer tab completions for a given array of Objects.
+     *
+     * @param argument the argument to complete
+     * @param converter the Function for converting the Object into a comparable String
+     * @param options the Objects which may be completed
+     * @return the matching Strings
+     */
+    public static <T> List<String> completeObject(String argument, Function<T, String> converter, T[] options) {
+        argument = argument.toLowerCase(Locale.ENGLISH);
+        List<String> completions = new ArrayList<>();
+
+        for (T option : options) {
+            String optionString = converter.apply(option).toLowerCase(Locale.ENGLISH);
+            if (optionString.startsWith(argument)) {
+                completions.add(optionString);
+            }
+        }
+
+        return completions;
+    }
+
+    private TabCompleter() {
+        throw new IllegalStateException("Cannot create instance of utility class.");
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/util/config/Config.java

@@ -0,0 +1,43 @@
+package com.lishid.openinv.util.config;
+
+import com.lishid.openinv.util.AccessEqualMode;
+import org.bukkit.configuration.Configuration;
+import org.bukkit.configuration.MemoryConfiguration;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class Config {
+
+  private @NotNull Configuration root;
+  private @Nullable AccessEqualMode accessEqualMode;
+
+  public Config() {
+    root = new MemoryConfiguration();
+  }
+
+  public void reload(@NotNull Configuration configuration) {
+    root = configuration;
+    accessEqualMode = null;
+  }
+
+  public boolean isSaveDisabled() {
+    return root.getBoolean("settings.disable-saving", false);
+  }
+
+  public boolean isOfflineDisabled() {
+    return root.getBoolean("settings.disable-offline-access", false);
+  }
+
+  public boolean doesNoArgsOpenSelf() {
+    return root.getBoolean("settings.command.open.no-args-opens-self", false);
+  }
+
+  public @NotNull AccessEqualMode getAccessEqualMode() {
+    if (accessEqualMode == null) {
+      accessEqualMode = AccessEqualMode.of(root.getString("settings.equal-access"));
+    }
+
+    return accessEqualMode;
+  }
+
+}

plugin/src/main/java/com/lishid/openinv/util/config/ConfigUpdater.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2011-2022 lishid. All rights reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.lishid.openinv.util.config;
+
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.configuration.file.FileConfiguration;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.File;
+import java.io.IOException;
+
+public record ConfigUpdater(@NotNull Plugin plugin) {
+
+    public void checkForUpdates() {
+        final int version = plugin.getConfig().getInt("config-version", 1);
+        ConfigurationSection defaults = plugin.getConfig().getDefaults();
+        if (defaults == null || version >= defaults.getInt("config-version")) {
+            return;
+        }
+
+        plugin.getLogger().info("Configuration update found! Performing update...");
+
+        // Backup the old config file
+        try {
+            plugin.getConfig().save(new File(plugin.getDataFolder(), "config_old.yml"));
+            plugin.getLogger().info("Backed up config.yml to config_old.yml before updating.");
+        } catch (IOException e) {
+            plugin.getLogger().warning("Could not back up config.yml before updating!");
+        }
+
+        if (version < 2) {
+            updateConfig1To2();
+        }
+        if (version < 3) {
+            updateConfig2To3();
+        }
+        if (version < 4) {
+            updateConfig3To4();
+        }
+        if (version < 5) {
+            updateConfig4To5();
+        }
+        if (version < 6) {
+            updateConfig5To6();
+        }
+        if (version < 7) {
+            updateConfig6To7();
+        }
+        if (version < 8) {
+            updateConfig7To8();
+        }
+
+        plugin.saveConfig();
+        plugin.getLogger().info("Configuration update complete!");
+    }
+
+    private void updateConfig7To8() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("settings.equal-access", "view");
+        config.set("config-version", 8);
+    }
+
+    private void updateConfig6To7() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("toggles", null);
+        String consoleLocale = config.getString("settings.locale", "en");
+        if (consoleLocale.isBlank() || consoleLocale.equalsIgnoreCase("en_us")) {
+            consoleLocale = "en";
+        }
+        config.set("settings.console-locale", consoleLocale);
+        config.set("settings.locale", null);
+        config.set("config-version", 7);
+    }
+
+    private void updateConfig5To6() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("settings.command.open.no-args-opens-self", false);
+        config.set("settings.command.searchcontainer.max-radius", 10);
+        config.set("config-version", 6);
+    }
+
+    private void updateConfig4To5() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("settings.disable-offline-access", false);
+        config.set("config-version", 5);
+    }
+
+    private void updateConfig3To4() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("notify", null);
+        config.set("config-version", 4);
+    }
+
+    private void updateConfig2To3() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("items", null);
+        config.set("ItemOpenInv", null);
+        config.set("toggles", null);
+        config.set("settings.disable-saving", config.getBoolean("DisableSaving", false));
+        config.set("DisableSaving", null);
+        config.set("config-version", 3);
+    }
+
+    private void updateConfig1To2() {
+        FileConfiguration config = plugin.getConfig();
+        config.set("ItemOpenInvItemID", null);
+        config.set("NotifySilentChest", null);
+        config.set("NotifyAnyChest", null);
+        config.set("AnyChest", null);
+        config.set("SilentChest", null);
+        config.set("config-version", 2);
+    }
+
+}

plugin/src/main/java/com/lishid/openinv/util/lang/LangMigrator.java

@@ -0,0 +1,87 @@
+package com.lishid.openinv.util.lang;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.DirectoryStream;
+import java.nio.file.FileAlreadyExistsException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class LangMigrator {
+
+  private final @NotNull Path oldFolder;
+  private final @NotNull Path newFolder;
+  private final @NotNull Logger logger;
+
+  public LangMigrator(@NotNull Path oldFolder, @NotNull Path newFolder, @NotNull Logger logger) {
+    this.oldFolder = oldFolder;
+    this.newFolder = newFolder;
+    this.logger = logger;
+  }
+
+  public void migrate() {
+    if (!Files.exists(oldFolder.resolve("en_us.yml"))) {
+      // Probably already migrated.
+      return;
+    }
+
+    logger.info(() -> String.format("[LanguageManager] Migrating language files to %s", newFolder));
+
+    if (!Files.exists(newFolder)) {
+      try {
+        Files.createDirectories(newFolder);
+      } catch (IOException e) {
+        logger.log(Level.WARNING, "Unable to create language subdirectory!", e);
+      }
+    }
+
+    try (DirectoryStream<Path> files = Files.newDirectoryStream(oldFolder)) {
+      files.forEach(path -> {
+        if (path == null) {
+          return;
+        }
+
+        String fileName = path.getFileName().toString();
+
+        if (fileName.startsWith("config") || !fileName.endsWith(".yml")) {
+          return;
+        }
+
+        // Migrate certain files to be parent languages.
+        fileName = switch (fileName) {
+          case "en_us.yml" -> "en.yml";
+          case "de_de.yml" -> "de.yml";
+          case "es_es.yml" -> "es.yml";
+          case "pt_br.yml" -> "pt.yml";
+          default -> fileName;
+        };
+
+        try {
+          Files.copy(path, newFolder.resolve(fileName));
+          Files.delete(path);
+        } catch (FileAlreadyExistsException e1) {
+          // File already migrated?
+          try {
+            Files.copy(path, newFolder.resolve("old_" + fileName));
+            Files.delete(path);
+          } catch (IOException e2) {
+            // If it fails again, just re-throw.
+            throw new UncheckedIOException(e2);
+          }
+        } catch (IOException e) {
+          throw new UncheckedIOException(e);
+        }
+      });
+    } catch (UncheckedIOException e) {
+      logger.log(Level.WARNING, "Unable to migrate languages to subdirectory!", e.getCause());
+    } catch (IOException e) {
+      logger.log(Level.WARNING, "Unable to migrate languages to subdirectory!", e);
+    }
+
+  }
+
+}

plugin/src/main/resources/config.yml

@@ -0,0 +1,11 @@
+config-version: 8
+settings:
+  equal-access: view
+  command:
+    open:
+      no-args-opens-self: false
+    searchcontainer:
+      max-radius: 10
+  disable-offline-access: false
+  disable-saving: false
+  console-locale: 'en'

plugin/src/main/resources/locale/de.yml

@@ -0,0 +1,30 @@
+messages:
+  error:
+    consoleUnsupported: 'Du kannst diesen Befehl nicht von der Konsole ausführen.'
+    lootNotGenerated: '&cBeute noch nicht erstellt! Bitte schalte &b/silentcontainer&c aus.'
+    invalidMaterial: '&cUngültiges Material: "%target%"'
+    invalidNumber: '&cUngültige Nummer: "%target%"'
+    invalidPlayer: '&cSpieler nicht gefunden.'
+    permissionOpenSelf: '&cDu darfst dein eigenes Inventar nicht öffnen.'
+    permissionEnderAll: '&cDu darfst die Endertruhen von anderen Spielern nicht öffnen.'
+    permissionExempt: '&c%target%''s Inventar ist geschützt.'
+    permissionCrossWorld: '&c%target% ist nicht in der selben Welt wie du.'
+    permissionPlayerOnline: '&cDu darfst keine Inventare von Spielern öffnen, die online sind.'
+    permissionPlayerOffline: '&cDu darfst keine Inventare von Spielern öffnen, die offline sind.'
+    commandException: '&cAn error occurred. Please check console for details.'
+  info:
+    containerBlocked: 'Du öffnest einen gesperrten Container.'
+    containerBlockedSilent: 'Du öffnest einen gesperrten Container lautlos.'
+    containerSilent: 'Du öffnest einen Container lautlos.'
+    settingState: '%setting%: %state%'
+    player:
+      noMatches: 'Keine Spieler mit %target% gefunden.'
+      matches: 'Spieler hält %target%: %detail%'
+    container:
+      noMatches: 'Keine Container mit %target% gefunden.'
+      matches: 'Container hat %target%: %detail%'
+    'on': 'an'
+    'off': 'aus'
+container:
+  player: '%player%''s Inventar'
+  enderchest: '%player%''s Endertruhe'