Remove ability to unload default worlds.

Small WorldManager updates

src/main/java/com/onarandombox/MultiverseCore/MultiverseCore.java

@@ -68,7 +68,6 @@ import com.onarandombox.MultiverseCore.commands.TeleportCommand;
 import com.onarandombox.MultiverseCore.commands.UnloadCommand;
 import com.onarandombox.MultiverseCore.commands.VersionCommand;
 import com.onarandombox.MultiverseCore.commands.WhoCommand;
-import com.onarandombox.MultiverseCore.commandtools.queue.CommandQueueManager;
 import com.onarandombox.MultiverseCore.destination.AnchorDestination;
 import com.onarandombox.MultiverseCore.destination.BedDestination;
 import com.onarandombox.MultiverseCore.destination.CannonDestination;
@@ -205,7 +204,6 @@ public class MultiverseCore extends JavaPlugin implements MVPlugin, Core {
 
     // Setup our Map for our Commands using the CommandHandler.
     private CommandHandler commandHandler;
-    private CommandQueueManager commandQueueManager;
 
     private static final String LOG_TAG = "[Multiverse-Core]";
 
@@ -290,7 +288,6 @@ public class MultiverseCore extends JavaPlugin implements MVPlugin, Core {
 
         // Setup the command manager
         this.commandHandler = new CommandHandler(this, this.ph);
-        this.commandQueueManager = new CommandQueueManager(this);
         // Call the Function to assign all the Commands to their Class.
         this.registerCommands();
 
@@ -920,15 +917,6 @@ public class MultiverseCore extends JavaPlugin implements MVPlugin, Core {
         return this.commandHandler;
     }
 
-    /**
-     * {@inheritDoc}
-     */
-    @Override
-    @Deprecated
-    public CommandQueueManager getCommandQueueManager() {
-        return commandQueueManager;
-    }
-
     /**
      * Gets the log-tag.
      *

src/main/java/com/onarandombox/MultiverseCore/api/Core.java

@@ -8,7 +8,6 @@
 package com.onarandombox.MultiverseCore.api;
 
 import buscript.Buscript;
-import com.onarandombox.MultiverseCore.commandtools.queue.CommandQueueManager;
 import com.onarandombox.MultiverseCore.destination.DestinationFactory;
 import com.onarandombox.MultiverseCore.utils.AnchorManager;
 import com.onarandombox.MultiverseCore.utils.MVEconomist;
@@ -87,15 +86,6 @@ public interface Core {
      */
     CommandHandler getCommandHandler();
 
-    /**
-     * Manager for command that requires /mv confirm before execution.
-     *
-     * @return A non-null {@link CommandQueueManager}.
-     * @deprecated To be moved to new command manager in 5.0.0
-     */
-    @Deprecated
-    CommandQueueManager getCommandQueueManager();
-
     /**
      * Gets the factory class responsible for loading many different destinations
      * on demand.

src/main/java/com/onarandombox/MultiverseCore/api/MVWorldManager.java

@@ -174,6 +174,16 @@ public interface MVWorldManager {
      */
     MultiverseWorld getMVWorld(String name);
 
+    /**
+     * Returns a {@link MultiverseWorld} if the world with name given exists, and null if it does not.
+     * This will search optionally for alias names.
+     *
+     * @param name          The name or optionally the alias of the world to get.
+     * @param checkAliases  Indicates whether to check for world alias name.
+     * @return A {@link MultiverseWorld} or null.
+     */
+    MultiverseWorld getMVWorld(String name, boolean checkAliases);
+
     /**
      * Returns a {@link MultiverseWorld} if it exists, and null if it does not.
      *
@@ -183,13 +193,24 @@ public interface MVWorldManager {
     MultiverseWorld getMVWorld(World world);
 
     /**
-     * Checks to see if the given name is a valid {@link MultiverseWorld}.
+     * Checks to see if the given name is a valid {@link MultiverseWorld}
+     * Searches based on world name AND alias.
      *
      * @param name The name or alias of the world to check.
      * @return True if the world exists, false if not.
      */
     boolean isMVWorld(String name);
 
+    /**
+     * Checks to see if the given name is a valid {@link MultiverseWorld}.
+     * Optionally searches by alias is specified.
+     *
+     * @param name          The name or alias of the world to check.
+     * @param checkAliases  Indicates whether to check for world alias name.
+     * @return True if the world exists, false if not.
+     */
+    boolean isMVWorld(String name, boolean checkAliases);
+
     /**
      * Checks to see if the given world is a valid {@link MultiverseWorld}.
      *
@@ -198,6 +219,38 @@ public interface MVWorldManager {
      */
     boolean isMVWorld(World world);
 
+    /**
+     * Checks if a world name is the servers default world.
+     *
+     * Generally, default world is defined in level-name of server properties file along with
+     * it's 2 dimensions: [world]_nether, [world]_the_end.
+     *
+     * @param world The world to check.
+     * @return True if world name is a default world, else false.
+     */
+    boolean isDefaultWorld(MultiverseWorld world);
+
+    /**
+     * Checks if a world name is the servers default world.
+     *
+     * Generally, default world is defined in level-name of server properties file along with
+     * it's 2 dimensions: [world]_nether, [world]_the_end.
+     *
+     * @param worldName The name of the world to check.
+     * @return True if world name is a default world, else false.
+     */
+    boolean isDefaultWorld(String worldName);
+
+    /**
+     * Gets all the default world names of the server.
+     *
+     * Generally, default world is defined in level-name of server properties file along with
+     * it's 2 dimensions: [world]_nether, [world]_the_end.
+     *
+     * @return Collection of default world names.
+     */
+    Collection<String> getDefaultWorldNames();
+
     /**
      * Load the Worlds &amp; Settings from the configuration file.
      *
@@ -314,4 +367,11 @@ public interface MVWorldManager {
      * does not exist. {@code includeLoaded} if the world exists and is loaded.
      */
     boolean hasUnloadedWorld(String name, boolean includeLoaded);
+
+    /**
+     * Get all the possible worlds that Multiverse has detected to be importable.
+     *
+     * @return A collection of world names that are deemed importable.
+     */
+    Collection<String> getPotentialWorlds();
 }

src/main/java/com/onarandombox/MultiverseCore/commands/CheckCommand.java

@@ -11,6 +11,7 @@ import com.onarandombox.MultiverseCore.MultiverseCore;
 import com.onarandombox.MultiverseCore.api.MVDestination;
 import com.onarandombox.MultiverseCore.destination.InvalidDestination;
 import com.onarandombox.MultiverseCore.utils.MVPermissions;
+import com.onarandombox.MultiverseCore.utils.PlayerFinder;
 import org.bukkit.ChatColor;
 import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Player;
@@ -37,7 +38,7 @@ public class CheckCommand extends MultiverseCommand {
 
     @Override
     public void runCommand(CommandSender sender, List<String> args) {
-        Player p = this.plugin.getServer().getPlayerExact(args.get(0));
+        Player p = PlayerFinder.get(args.get(0), sender);
         if (p == null) {
             sender.sendMessage("Could not find player " + ChatColor.GREEN + args.get(0));
             sender.sendMessage("Are they online?");

src/main/java/com/onarandombox/MultiverseCore/commands/ConfirmCommand.java

@@ -33,7 +33,7 @@ public class ConfirmCommand extends MultiverseCommand {
 
     @Override
     public void runCommand(CommandSender sender, List<String> args) {
-        this.plugin.getCommandQueueManager().runQueuedCommand(sender);
+        this.plugin.getCommandHandler().confirmQueuedCommand(sender);
     }
 
 }

src/main/java/com/onarandombox/MultiverseCore/commands/DeleteCommand.java

@@ -8,11 +8,9 @@
 package com.onarandombox.MultiverseCore.commands;
 
 import com.onarandombox.MultiverseCore.MultiverseCore;
-import com.onarandombox.MultiverseCore.commandtools.queue.QueuedCommand;
 import org.bukkit.ChatColor;
 import org.bukkit.command.CommandSender;
 import org.bukkit.permissions.PermissionDefault;
-import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -37,24 +35,11 @@ public class DeleteCommand extends MultiverseCommand {
     public void runCommand(CommandSender sender, List<String> args) {
         String worldName = args.get(0);
 
-        this.plugin.getCommandQueueManager().addToQueue(new QueuedCommand(
-                sender,
-                deleteRunnable(sender, worldName),
-                String.format("Are you sure you want to delete world '%s'? You cannot undo this action.", worldName)
-        ));
-    }
-
-    private Runnable deleteRunnable(@NotNull CommandSender sender,
-                                    @NotNull String worldName) {
-
-        return () -> {
-            sender.sendMessage(String.format("Deleting world '%s'...", worldName));
-            if (this.plugin.getMVWorldManager().deleteWorld(worldName)) {
-                sender.sendMessage(String.format("%sWorld %s was deleted!", ChatColor.GREEN, worldName));
-                return;
-            }
-            sender.sendMessage(String.format("%sThere was an issue deleting '%s'! Please check console for errors.",
-                    ChatColor.RED, worldName));
-        };
+        Class<?>[] paramTypes = {String.class};
+        List<Object> objectArgs = new ArrayList<Object>(args);
+        this.plugin.getCommandHandler()
+                   .queueCommand(sender, "mvdelete", "deleteWorld", objectArgs,
+                                 paramTypes, ChatColor.GREEN + "World '" + worldName + "' Deleted!",
+                                 ChatColor.RED + "World '" + worldName + "' could NOT be deleted!");
     }
 }

src/main/java/com/onarandombox/MultiverseCore/commands/ImportCommand.java

@@ -9,7 +9,7 @@ package com.onarandombox.MultiverseCore.commands;
 
 import com.onarandombox.MultiverseCore.MultiverseCore;
 import com.onarandombox.MultiverseCore.api.MVWorldManager;
-import com.onarandombox.MultiverseCore.api.MultiverseWorld;
+import com.onarandombox.MultiverseCore.utils.WorldNameChecker;
 import com.pneumaticraft.commandhandler.CommandHandler;
 import org.bukkit.ChatColor;
 import org.bukkit.World.Environment;
@@ -18,8 +18,6 @@ import org.bukkit.command.CommandSender;
 import org.bukkit.permissions.PermissionDefault;
 
 import java.io.File;
-import java.io.FilenameFilter;
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 
@@ -45,55 +43,17 @@ public class ImportCommand extends MultiverseCommand {
         this.worldManager = this.plugin.getMVWorldManager();
     }
 
-    /**
-     * A very basic check to see if a folder has a level.dat file.
-     * If it does, we can safely assume it's a world folder.
-     *
-     * @param worldFolder The File that may be a world.
-     * @return True if it looks like a world, false if not.
-     */
-    private static boolean checkIfIsWorld(File worldFolder) {
-        if (worldFolder.isDirectory()) {
-            File[] files = worldFolder.listFiles(new FilenameFilter() {
-                @Override
-                public boolean accept(File file, String name) {
-                    return name.toLowerCase().endsWith(".dat");
-                }
-            });
-            if (files != null && files.length > 0) {
-                return true;
-            }
-        }
-        return false;
-    }
-
-    private String getPotentialWorlds() {
-        File worldFolder = this.plugin.getServer().getWorldContainer();
-        if (worldFolder == null) {
-            return "";
-        }
-        File[] files = worldFolder.listFiles();
-        String worldList = "";
-        Collection<MultiverseWorld> worlds = this.worldManager.getMVWorlds();
-        List<String> worldStrings = new ArrayList<String>();
-        for (MultiverseWorld world : worlds) {
-            worldStrings.add(world.getName());
-        }
-        for (String world : this.worldManager.getUnloadedWorlds()) {
-            worldStrings.add(world);
-        }
+    private String getPotentialWorldStrings() {
+        final Collection<String> potentialWorlds = this.worldManager.getPotentialWorlds();
+        StringBuilder worldList = new StringBuilder();
         ChatColor currColor = ChatColor.WHITE;
-        for (File file : files) {
-            if (file.isDirectory() && checkIfIsWorld(file) && !worldStrings.contains(file.getName())) {
-                worldList += currColor + file.getName() + " ";
-                if (currColor == ChatColor.WHITE) {
-                    currColor = ChatColor.YELLOW;
-                } else {
-                    currColor = ChatColor.WHITE;
-                }
-            }
+
+        for (String world : potentialWorlds) {
+            worldList.append(currColor).append(world).append(' ');
+            currColor = currColor == ChatColor.WHITE ? ChatColor.YELLOW : ChatColor.WHITE;
         }
-        return worldList;
+
+        return worldList.toString();
     }
     
     private String trimWorldName(String userInput) {
@@ -106,7 +66,7 @@ public class ImportCommand extends MultiverseCommand {
         String worldName = trimWorldName(args.get(0));
 
         if (worldName.toLowerCase().equals("--list") || worldName.toLowerCase().equals("-l")) {
-            String worldList = this.getPotentialWorlds();
+            String worldList = this.getPotentialWorldStrings();
             if (worldList.length() > 2) {
                 sender.sendMessage(ChatColor.AQUA + "====[ These look like worlds ]====");
                 sender.sendMessage(worldList);
@@ -149,10 +109,10 @@ public class ImportCommand extends MultiverseCommand {
 
         if (!worldFile.exists()) {
             sender.sendMessage(ChatColor.RED + "FAILED.");
-            String worldList = this.getPotentialWorlds();
+            String worldList = this.getPotentialWorldStrings();
             sender.sendMessage("That world folder does not exist. These look like worlds to me:");
             sender.sendMessage(worldList);
-        } else if (!checkIfIsWorld(worldFile)) {
+        } else if (!WorldNameChecker.isValidWorldFolder(worldFile)) {
             sender.sendMessage(ChatColor.RED + "FAILED.");
             sender.sendMessage(String.format("'%s' does not appear to be a world. It is lacking a .dat file.",
                                              worldName));

src/main/java/com/onarandombox/MultiverseCore/commands/RegenCommand.java

@@ -8,11 +8,9 @@
 package com.onarandombox.MultiverseCore.commands;
 
 import com.onarandombox.MultiverseCore.MultiverseCore;
-import com.onarandombox.MultiverseCore.commandtools.queue.QueuedCommand;
 import org.bukkit.ChatColor;
 import org.bukkit.command.CommandSender;
 import org.bukkit.permissions.PermissionDefault;
-import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -39,30 +37,17 @@ public class RegenCommand extends MultiverseCommand {
 
     @Override
     public void runCommand(CommandSender sender, List<String> args) {
-        String worldName = args.get(0);
-        boolean useseed = (!(args.size() == 1));
-        boolean randomseed = (args.size() == 2 && args.get(1).equalsIgnoreCase("-s"));
+        Boolean useseed = (!(args.size() == 1));
+        Boolean randomseed = (args.size() == 2 && args.get(1).equalsIgnoreCase("-s"));
         String seed = (args.size() == 3) ? args.get(2) : "";
 
-        this.plugin.getCommandQueueManager().addToQueue(new QueuedCommand(
-                sender,
-                doWorldRegen(sender, worldName, useseed, randomseed, seed),
-                String.format("Are you sure you want to regen '%s'? You cannot undo this action.", worldName)
-        ));
-    }
-
-    private Runnable doWorldRegen(@NotNull CommandSender sender,
-                                  @NotNull String worldName,
-                                  boolean useSeed,
-                                  boolean randomSeed,
-                                  @NotNull String seed) {
-
-        return () -> {
-            if (this.plugin.getMVWorldManager().regenWorld(worldName, useSeed, randomSeed, seed)) {
-                sender.sendMessage(ChatColor.GREEN + "World Regenerated!");
-                return;
-            }
-            sender.sendMessage(ChatColor.RED + "World could NOT be regenerated!");
-        };
+        Class<?>[] paramTypes = {String.class, Boolean.class, Boolean.class, String.class};
+        List<Object> objectArgs = new ArrayList<Object>();
+        objectArgs.add(args.get(0));
+        objectArgs.add(useseed);
+        objectArgs.add(randomseed);
+        objectArgs.add(seed);
+        this.plugin.getCommandHandler().queueCommand(sender, "mvregen", "regenWorld", objectArgs,
+                paramTypes, ChatColor.GREEN + "World Regenerated!", ChatColor.RED + "World could NOT be regenerated!");
     }
 }

src/main/java/com/onarandombox/MultiverseCore/commands/SpawnCommand.java

@@ -9,6 +9,7 @@ package com.onarandombox.MultiverseCore.commands;
 
 import com.onarandombox.MultiverseCore.MultiverseCore;
 import com.onarandombox.MultiverseCore.api.MultiverseWorld;
+import com.onarandombox.MultiverseCore.utils.PlayerFinder;
 import org.bukkit.ChatColor;
 import org.bukkit.Location;
 import org.bukkit.command.CommandSender;
@@ -50,7 +51,7 @@ public class SpawnCommand extends MultiverseCommand {
                 sender.sendMessage("You don't have permission to teleport another player to spawn. (multiverse.core.spawn.other)");
                 return;
             }
-            Player target = this.plugin.getServer().getPlayerExact(args.get(0));
+            Player target = PlayerFinder.get(args.get(0), sender);
             if (target != null) {
                 target.sendMessage("Teleporting to this world's spawn...");
                 spawnAccurately(target);

src/main/java/com/onarandombox/MultiverseCore/commands/TeleportCommand.java

@@ -11,7 +11,6 @@ import com.dumptruckman.minecraft.util.Logging;
 import com.onarandombox.MultiverseCore.MultiverseCore;
 import com.onarandombox.MultiverseCore.api.Teleporter;
 import com.onarandombox.MultiverseCore.api.MVDestination;
-import com.onarandombox.MultiverseCore.commandtools.queue.QueuedCommand;
 import com.onarandombox.MultiverseCore.destination.CustomTeleporterDestination;
 import com.onarandombox.MultiverseCore.destination.DestinationFactory;
 import com.onarandombox.MultiverseCore.destination.InvalidDestination;
@@ -19,6 +18,7 @@ import com.onarandombox.MultiverseCore.destination.WorldDestination;
 import com.onarandombox.MultiverseCore.enums.TeleportResult;
 import com.onarandombox.MultiverseCore.event.MVTeleportEvent;
 import com.onarandombox.MultiverseCore.api.SafeTTeleporter;
+import com.onarandombox.MultiverseCore.utils.PlayerFinder;
 import org.bukkit.ChatColor;
 import org.bukkit.Location;
 import org.bukkit.World;
@@ -29,7 +29,6 @@ import org.bukkit.permissions.PermissionDefault;
 
 import java.util.ArrayList;
 import java.util.List;
-import java.util.logging.Level;
 
 /**
  * Used to teleport players.
@@ -60,7 +59,7 @@ public class TeleportCommand extends MultiverseCommand {
         String destinationName;
 
         if (args.size() == 2) {
-            teleportee = this.plugin.getServer().getPlayerExact(args.get(0));
+            teleportee = PlayerFinder.get(args.get(0), sender);
             if (teleportee == null) {
                 this.messaging.sendMessage(sender, String.format("Sorry, I couldn't find player: %s%s",
                         ChatColor.GOLD, args.get(0)), false);
@@ -76,22 +75,9 @@ public class TeleportCommand extends MultiverseCommand {
             }
             teleportee = (Player) sender;
         }
-        // Special case for cannons:
-        if (destinationName.matches("(?i)cannon-[\\d]+(\\.[\\d]+)?")) {
-            String[] cannonSpeed = destinationName.split("-");
-            try {
-                double speed = Double.parseDouble(cannonSpeed[1]);
-                destinationName = "ca:" + teleportee.getWorld().getName() + ":" + teleportee.getLocation().getX()
-                        + "," + teleportee.getLocation().getY() + "," + teleportee.getLocation().getZ() + ":"
-                        + teleportee.getLocation().getPitch() + ":" + teleportee.getLocation().getYaw() + ":" + speed;
-            } catch (Exception e) {
-                destinationName = "i:invalid";
-            }
 
-        }
         DestinationFactory df = this.plugin.getDestFactory();
-        MVDestination d = df.getDestination(destinationName);
-
+        MVDestination d = df.getPlayerAwareDestination(teleportee, destinationName);
 
         MVTeleportEvent teleportEvent = new MVTeleportEvent(d, teleportee, teleporter, true);
         this.plugin.getServer().getPluginManager().callEvent(teleportEvent);
@@ -166,27 +152,24 @@ public class TeleportCommand extends MultiverseCommand {
         if (result == TeleportResult.FAIL_UNSAFE) {
             Logging.fine("Could not teleport " + teleportee.getName()
                     + " to " + plugin.getLocationManipulation().strCoordsRaw(d.getLocation(teleportee)));
-
+            Logging.fine("Queueing Command");
+            Class<?>[] paramTypes = { CommandSender.class, Player.class, Location.class };
+            List<Object> items = new ArrayList<Object>();
+            items.add(teleporter);
+            items.add(teleportee);
+            items.add(d.getLocation(teleportee));
             String player = "you";
             if (!teleportee.equals(teleporter)) {
                 player = teleportee.getName();
             }
-
-            this.plugin.getCommandQueueManager().addToQueue(new QueuedCommand(
-                    sender,
-                    doUnsafeTeleport(teleporter, teleportee, d.getLocation(teleportee)),
-                    String.format("%sMultiverse %sdid not teleport %s%s %sto %s%s %sbecause it was unsafe. Would you like to try anyway?",
-                            ChatColor.GREEN, ChatColor.WHITE, ChatColor.AQUA, player, ChatColor.WHITE, ChatColor.DARK_AQUA, d.getName(), ChatColor.WHITE),
-                    UNSAFE_TELEPORT_EXPIRE_DELAY
-            ));
+            String message = String.format("%sMultiverse %sdid not teleport %s%s %sto %s%s %sbecause it was unsafe.",
+                    ChatColor.GREEN, ChatColor.WHITE, ChatColor.AQUA, player, ChatColor.WHITE, ChatColor.DARK_AQUA, d.getName(), ChatColor.WHITE);
+            this.plugin.getCommandHandler().queueCommand(sender, "mvteleport", "teleportPlayer", items,
+                    paramTypes, message, "Would you like to try anyway?", "", "", UNSAFE_TELEPORT_EXPIRE_DELAY);
         }
         // else: Player was teleported successfully (or the tp event was fired I should say)
     }
 
-    private Runnable doUnsafeTeleport(CommandSender teleporter, Player player, Location location) {
-        return () -> this.plugin.getSafeTTeleporter().safelyTeleport(teleporter, player, location, false);
-    }
-
     private boolean checkSendPermissions(CommandSender teleporter, Player teleportee, MVDestination destination) {
         if (teleporter.equals(teleportee)) {
             if (!this.plugin.getMVPerms().hasPermission(teleporter, "multiverse.teleport.self." + destination.getIdentifier(), true)) {

src/main/java/com/onarandombox/MultiverseCore/commandtools/queue/CommandQueueManager.java

@@ -1,158 +0,0 @@
-/******************************************************************************
- * Multiverse 2 Copyright (c) the Multiverse Team 2020.                       *
- * Multiverse 2 is licensed under the BSD License.                            *
- * For more information please check the README.md file included              *
- * with this project.                                                         *
- ******************************************************************************/
-
-package com.onarandombox.MultiverseCore.commandtools.queue;
-
-import com.dumptruckman.minecraft.util.Logging;
-import com.onarandombox.MultiverseCore.MultiverseCore;
-import org.bukkit.Bukkit;
-import org.bukkit.ChatColor;
-import org.bukkit.block.data.type.CommandBlock;
-import org.bukkit.command.BlockCommandSender;
-import org.bukkit.command.CommandSender;
-import org.bukkit.scheduler.BukkitTask;
-import org.jetbrains.annotations.NotNull;
-
-import java.util.Map;
-import java.util.WeakHashMap;
-
-/**
- * Managers the queuing of dangerous commands that needs to use '/mv confirm' before executing.
- */
-public class CommandQueueManager {
-
-    private static final long TICKS_PER_SECOND = 20;
-    private static final DummyCommandBlockSender COMMAND_BLOCK = new DummyCommandBlockSender();
-
-    private final MultiverseCore plugin;
-    private final Map<CommandSender, QueuedCommand> queuedCommandMap;
-
-    public CommandQueueManager(@NotNull MultiverseCore plugin) {
-        this.plugin = plugin;
-        this.queuedCommandMap = new WeakHashMap<>();
-    }
-
-    /**
-     * Adds a queue command into queue.
-     *
-     * @param queuedCommand The queue command to add.
-     */
-    public void addToQueue(QueuedCommand queuedCommand) {
-        CommandSender targetSender = parseSender(queuedCommand.getSender());
-
-        // Since only one command is stored in queue per sender, we remove the old one.
-        this.removeFromQueue(targetSender);
-
-        Logging.finer("Add new command to queue for sender %s.", targetSender);
-        this.queuedCommandMap.put(targetSender, queuedCommand);
-        queuedCommand.setExpireTask(runExpireLater(queuedCommand));
-
-        queuedCommand.getSender().sendMessage(queuedCommand.getPrompt());
-        queuedCommand.getSender().sendMessage(String.format("Run %s/mv confirm %sto continue. This will expire in %s seconds.",
-                ChatColor.GREEN, ChatColor.WHITE, queuedCommand.getValidDuration()));
-    }
-
-    /**
-     * Expire task that remove {@link QueuedCommand} from queue after valid duration defined.
-     *
-     * @param queuedCommand Command to run the expire task on.
-     * @return The expire {@link BukkitTask}.
-     */
-    @NotNull
-    private BukkitTask runExpireLater(@NotNull QueuedCommand queuedCommand) {
-        return Bukkit.getScheduler().runTaskLater(
-                this.plugin,
-                expireRunnable(queuedCommand),
-                queuedCommand.getValidDuration() * TICKS_PER_SECOND
-        );
-    }
-
-    /**
-     * Runnable responsible for expiring the queued command.
-     *
-     * @param queuedCommand Command to create the expire task on.
-     * @return The expire runnable.
-     */
-    @NotNull
-    private Runnable expireRunnable(@NotNull QueuedCommand queuedCommand) {
-        return () -> {
-            CommandSender targetSender = parseSender(queuedCommand.getSender());
-            QueuedCommand matchingQueuedCommand = this.queuedCommandMap.get(targetSender);
-            if (!queuedCommand.equals(matchingQueuedCommand) || queuedCommand.getExpireTask().isCancelled()) {
-                // To be safe, but this shouldn't happen since we cancel old commands before add new once.
-                Logging.finer("This is an old queue command already.");
-                return;
-            }
-            queuedCommand.getSender().sendMessage("Your queued command has expired.");
-            this.queuedCommandMap.remove(queuedCommand.getSender());
-        };
-    }
-
-    /**
-     * Runs the command in queue for the given sender, if any.
-     *
-     * @param sender    {@link CommandSender} that confirmed the command.
-     * @return True if queued command ran successfully, else false.
-     */
-    public boolean runQueuedCommand(@NotNull CommandSender sender) {
-        CommandSender targetSender = parseSender(sender);
-        QueuedCommand queuedCommand = this.queuedCommandMap.get(targetSender);
-        if (queuedCommand == null) {
-            sender.sendMessage(ChatColor.RED + "You do not have any commands in queue.");
-            return false;
-        }
-        Logging.finer("Running queued command...");
-        queuedCommand.getAction().run();
-        return removeFromQueue(targetSender);
-    }
-
-    /**
-     * Since only one command is stored in queue per sender, we remove the old one.
-     *
-     * @param sender    The {@link CommandSender} that executed the command.
-     * @return True if queue command is removed from sender successfully, else false.
-     */
-    public boolean removeFromQueue(@NotNull CommandSender sender) {
-        CommandSender targetSender = parseSender(sender);
-        QueuedCommand previousCommand = this.queuedCommandMap.remove(targetSender);
-        if (previousCommand == null) {
-            Logging.finer("No queue command to remove for sender %s.", targetSender.getName());
-            return false;
-        }
-        previousCommand.getExpireTask().cancel();
-        Logging.finer("Removed queue command for sender %s.", targetSender.getName());
-        return true;
-    }
-
-    /**
-     * To allow all CommandBlocks to be a common sender with use of {@link DummyCommandBlockSender}.
-     * So confirm command can be used for a queue command on another command block.
-     *
-     * @param sender    The sender to parse.
-     * @return The sender, or if its a command block, a {@link DummyCommandBlockSender}.
-     */
-    @NotNull
-    private CommandSender parseSender(@NotNull CommandSender sender) {
-        Logging.fine(sender.getClass().getName());
-        if (isCommandBlock(sender)) {
-            Logging.finer("Is command block.");
-            return COMMAND_BLOCK;
-        }
-        return sender;
-    }
-
-    /**
-     * Check if sender is a command block.
-     *
-     * @param sender    The sender to check on.
-     * @return True if sender is a command block, else false.
-     */
-    private boolean isCommandBlock(@NotNull CommandSender sender) {
-        return sender instanceof BlockCommandSender
-                && ((BlockCommandSender) sender).getBlock().getBlockData() instanceof CommandBlock;
-    }
-}

src/main/java/com/onarandombox/MultiverseCore/commandtools/queue/DummyCommandBlockSender.java

@@ -1,104 +0,0 @@
-package com.onarandombox.MultiverseCore.commandtools.queue;
-
-import org.bukkit.Bukkit;
-import org.bukkit.Server;
-import org.bukkit.command.CommandSender;
-import org.bukkit.permissions.Permission;
-import org.bukkit.permissions.PermissionAttachment;
-import org.bukkit.permissions.PermissionAttachmentInfo;
-import org.bukkit.plugin.Plugin;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-
-import java.util.Set;
-
-/**
- * Used by {@link CommandQueueManager}, so different commands block can be recognised as one.
- */
-class DummyCommandBlockSender implements CommandSender {
-
-    @Override
-    public void sendMessage(@NotNull String message) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public void sendMessage(@NotNull String[] messages) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public @NotNull Server getServer() {
-        return Bukkit.getServer();
-    }
-
-    @Override
-    public @NotNull String getName() {
-        return "DummyCommandBlockSender";
-    }
-
-    @Override
-    public boolean isPermissionSet(@NotNull String name) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public boolean isPermissionSet(@NotNull Permission perm) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public boolean hasPermission(@NotNull String name) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public boolean hasPermission(@NotNull Permission perm) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public @NotNull PermissionAttachment addAttachment(@NotNull Plugin plugin, @NotNull String name, boolean value) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public @NotNull PermissionAttachment addAttachment(@NotNull Plugin plugin) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public @Nullable PermissionAttachment addAttachment(@NotNull Plugin plugin, @NotNull String name, boolean value, int ticks) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public @Nullable PermissionAttachment addAttachment(@NotNull Plugin plugin, int ticks) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public void removeAttachment(@NotNull PermissionAttachment attachment) {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public void recalculatePermissions() {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public @NotNull Set<PermissionAttachmentInfo> getEffectivePermissions() {
-        throw new UnsupportedOperationException();
-    }
-
-    @Override
-    public boolean isOp() {
-        return true;
-    }
-
-    @Override
-    public void setOp(boolean value) {
-        throw new UnsupportedOperationException();
-    }
-}

src/main/java/com/onarandombox/MultiverseCore/commandtools/queue/QueuedCommand.java

@@ -1,86 +0,0 @@
-/******************************************************************************
- * Multiverse 2 Copyright (c) the Multiverse Team 2020.                       *
- * Multiverse 2 is licensed under the BSD License.                            *
- * For more information please check the README.md file included              *
- * with this project.                                                         *
- ******************************************************************************/
-
-package com.onarandombox.MultiverseCore.commandtools.queue;
-
-import org.bukkit.command.CommandSender;
-import org.bukkit.scheduler.BukkitTask;
-import org.jetbrains.annotations.NotNull;
-
-/**
- * Represents a single command used in {@link CommandQueueManager} for confirming before running potentially
- * dangerous action.
- */
-public class QueuedCommand {
-
-    private static final String DEFAULT_PROMPT_MESSAGE = "The command you are trying to run is deemed dangerous.";
-    private static final int DEFAULT_VALID_TIME = 10;
-
-    private final CommandSender sender;
-    private final Runnable action;
-    private final String prompt;
-    private final int validDuration;
-    private BukkitTask expireTask;
-
-    public QueuedCommand(CommandSender sender, Runnable action) {
-        this(sender, action, DEFAULT_PROMPT_MESSAGE, DEFAULT_VALID_TIME);
-    }
-
-    public QueuedCommand(CommandSender sender, Runnable action, String prompt) {
-        this(sender, action, prompt, DEFAULT_VALID_TIME);
-    }
-
-    public QueuedCommand(CommandSender sender, Runnable action, int validDuration) {
-        this(sender, action, DEFAULT_PROMPT_MESSAGE, validDuration);
-    }
-
-    /**
-     * Creates a new queue command, to be registered at {@link CommandQueueManager#addToQueue(QueuedCommand)}.
-     *
-     * @param sender        The sender that ran the command needed for confirmation.
-     * @param action        The logic to execute upon confirming.
-     * @param prompt        Question to ask sender to confirm.
-     * @param validDuration Duration in which the command is valid for confirm in seconds.
-     */
-    public QueuedCommand(CommandSender sender, Runnable action, String prompt, int validDuration) {
-        this.sender = sender;
-        this.action = action;
-        this.prompt = prompt;
-        this.validDuration = validDuration;
-    }
-
-    @NotNull
-    CommandSender getSender() {
-        return sender;
-    }
-
-    @NotNull
-    String getPrompt() {
-        return prompt;
-    }
-
-    int getValidDuration() {
-        return validDuration;
-    }
-
-    @NotNull
-    Runnable getAction() {
-        return action;
-    }
-
-    @NotNull
-    BukkitTask getExpireTask() {
-        return expireTask;
-    }
-
-    void setExpireTask(@NotNull BukkitTask expireTask) {
-        if (this.expireTask != null) {
-            throw new IllegalStateException("This queue command already has an expire task. You can't register twice!");
-        }
-        this.expireTask = expireTask;
-    }
-}

src/main/java/com/onarandombox/MultiverseCore/commandtools/queue/package-info.java

@@ -1,4 +0,0 @@
-/**
- * Manager queuing of dangerous commands in need of confirmation.
- */
-package com.onarandombox.MultiverseCore.commandtools.queue;

src/main/java/com/onarandombox/MultiverseCore/destination/DestinationFactory.java

@@ -11,16 +11,27 @@ import com.onarandombox.MultiverseCore.MultiverseCore;
 import com.onarandombox.MultiverseCore.api.MVDestination;
 import com.onarandombox.MultiverseCore.commands.TeleportCommand;
 import com.onarandombox.MultiverseCore.utils.PermissionTools;
+import com.onarandombox.MultiverseCore.utils.PlayerFinder;
 import com.pneumaticraft.commandhandler.Command;
+import org.bukkit.Bukkit;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
 import org.bukkit.permissions.Permission;
 import org.bukkit.permissions.PermissionDefault;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.regex.Pattern;
 
 /** A factory class that will create destinations from specific strings. */
 public class DestinationFactory {
+
+    private static final Pattern CANNON_PATTERN = Pattern.compile("(?i)cannon-[\\d]+(\\.[\\d]+)?");
+
     private MultiverseCore plugin;
     private Map<String, Class<? extends MVDestination>> destList;
     private Command teleportCommand;
@@ -36,6 +47,59 @@ public class DestinationFactory {
         }
     }
 
+    /**
+     * Parse a destination that has relation to sender, such as a cannon or player destination.
+     *
+     * @param teleportee        The player that is going to be teleported.
+     * @param destinationName   The destination to parse.
+     * @return A non-null MVDestination
+     */
+    @NotNull
+    public MVDestination getPlayerAwareDestination(@NotNull Player teleportee,
+                                                   @NotNull String destinationName) {
+
+        // Prioritise world, in the event that a world is named after a player online.
+        if (Bukkit.getWorld(destinationName) != null) {
+            return getDestination(destinationName);
+        }
+
+        Player targetPlayer = PlayerFinder.get(destinationName, teleportee);
+        if (targetPlayer != null) {
+            return getDestination("pl:" + targetPlayer.getName());
+        }
+
+        if (CANNON_PATTERN.matcher(destinationName).matches()) {
+            return getDestination(parseCannonDest(teleportee, destinationName));
+        }
+
+        return getDestination(destinationName);
+    }
+
+    /**
+     * Parses a cannon destination.
+     *
+     * @param teleportee        The player that is going to be teleported.
+     * @param destinationName   The destination to parse.
+     * @return A destination string.
+     */
+    @NotNull
+    private String parseCannonDest(@NotNull Player teleportee,
+                                   @NotNull String destinationName) {
+
+        String[] cannonSpeed = destinationName.split("-");
+        try {
+            double speed = Double.parseDouble(cannonSpeed[1]);
+            destinationName = "ca:" + teleportee.getWorld().getName() + ":" + teleportee.getLocation().getX()
+                    + "," + teleportee.getLocation().getY() + "," + teleportee.getLocation().getZ() + ":"
+                    + teleportee.getLocation().getPitch() + ":" + teleportee.getLocation().getYaw() + ":" + speed;
+        }
+        catch (Exception e) {
+            destinationName = "i:invalid";
+        }
+
+        return destinationName;
+    }
+
     /**
      * Gets a new destination from a string.
      * Returns a new InvalidDestination if the string could not be parsed.
@@ -101,4 +165,8 @@ public class DestinationFactory {
         this.teleportCommand.addAdditonalPermission(other);
         return true;
     }
+    
+    public Collection<String> getRegisteredIdentifiers() {
+        return this.destList.keySet();
+    }
 }

src/main/java/com/onarandombox/MultiverseCore/utils/PlayerFinder.java

@@ -0,0 +1,176 @@
+package com.onarandombox.MultiverseCore.utils;
+
+import com.dumptruckman.minecraft.util.Logging;
+import org.bukkit.Bukkit;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+
+/**
+ * Helper class to get {@link Player} from name, UUID or Selectors.
+ */
+public class PlayerFinder {
+
+    private static final Pattern UUID_REGEX = Pattern.compile("[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}");
+    private static final Pattern COMMA_SPLIT = Pattern.compile(",");
+
+    /**
+     * Get a {@link Player} based on an identifier of name UUID or selector.
+     *
+     * @param playerIdentifier  An identifier of name UUID or selector.
+     * @param sender            Target sender for selector.
+     * @return The player if found, else null.
+     */
+    @Nullable
+    public static Player get(@NotNull String playerIdentifier,
+                             @NotNull CommandSender sender) {
+
+        Player targetPlayer = getByName(playerIdentifier);
+        if (targetPlayer != null) {
+            return targetPlayer;
+        }
+        targetPlayer = getByUuid(playerIdentifier);
+        if (targetPlayer != null) {
+            return targetPlayer;
+        }
+        return getBySelector(playerIdentifier, sender);
+    }
+
+    /**
+     * Get multiple {@link Player} based on many identifiers of name UUID or selector.
+     *
+     * @param playerIdentifiers An identifier of multiple names, UUIDs or selectors, separated by comma.
+     * @param sender            Target sender for selector.
+     * @return A list of all the {@link Player} found.
+     */
+    @Nullable
+    public static List<Player> getMulti(@NotNull String playerIdentifiers,
+                                        @NotNull CommandSender sender) {
+
+        String[] playerIdentifierArray = COMMA_SPLIT.split(playerIdentifiers);
+        if (playerIdentifierArray == null || playerIdentifierArray.length == 0) {
+            return null;
+        }
+
+        List<Player> playerResults = new ArrayList<>();
+        for (String playerIdentifier : playerIdentifierArray) {
+            Player targetPlayer = getByName(playerIdentifier);
+            if (targetPlayer != null) {
+                playerResults.add(targetPlayer);
+                continue;
+            }
+            targetPlayer = getByUuid(playerIdentifier);
+            if (targetPlayer != null) {
+                playerResults.add(targetPlayer);
+                continue;
+            }
+            List<Player> targetPlayers = getMultiBySelector(playerIdentifier, sender);
+            if (targetPlayers != null) {
+                playerResults.addAll(targetPlayers);
+            }
+        }
+        return playerResults;
+    }
+
+    /**
+     * Get a {@link Player} based on player name.
+     *
+     * @param playerName    Name of a {@link Player}.
+     * @return The player if found, else null.
+     */
+    @Nullable
+    public static Player getByName(@NotNull String playerName) {
+        return Bukkit.getPlayerExact(playerName);
+    }
+
+    /**
+     * Get a {@link Player} based on player UUID.
+     *
+     * @param playerUuid    UUID of a player.
+     * @return The player if found, else null.
+     */
+    @Nullable
+    public static Player getByUuid(@NotNull String playerUuid) {
+        if (!UUID_REGEX.matcher(playerUuid).matches()) {
+            return null;
+        }
+        UUID uuid;
+        try {
+            uuid = UUID.fromString(playerUuid);
+        } catch (Exception e) {
+            return null;
+        }
+        return getByUuid(uuid);
+    }
+
+    /**
+     * Get a {@link Player} based on playerUUID.
+     *
+     * @param playerUuid    UUID of a player.
+     * @return The player if found, else null.
+     */
+    @Nullable
+    public static Player getByUuid(@NotNull UUID playerUuid) {
+        return Bukkit.getPlayer(playerUuid);
+    }
+
+    /**
+     * Get a {@link Player} based on vanilla selectors.
+     * https://minecraft.gamepedia.com/Commands#Target_selectors
+     *
+     * @param playerSelector    A target selector, usually starts with an '@'.
+     * @param sender            Target sender for selector.
+     * @return The player if only one found, else null.
+     */
+    @Nullable
+    public static Player getBySelector(@NotNull String playerSelector,
+                                       @NotNull CommandSender sender) {
+
+        List<Player> matchedPlayers = getMultiBySelector(playerSelector, sender);
+        if (matchedPlayers == null || matchedPlayers.isEmpty()) {
+            Logging.warning("No player found with selector '%s' for %s.", playerSelector, sender.getName());
+            return null;
+        }
+        if (matchedPlayers.size() > 1) {
+            Logging.warning("Ambiguous selector result '%s' for %s (more than one player matched) - %s",
+                    playerSelector, sender.getName(), matchedPlayers.toString());
+            return null;
+        }
+        return matchedPlayers.get(0);
+    }
+
+    /**
+     * Get multiple {@link Player} based on selector.
+     * https://minecraft.gamepedia.com/Commands#Target_selectors
+     *
+     * @param playerSelector    A target selector, usually starts with an '@'.
+     * @param sender            Target sender for selector.
+     * @return A list of all the {@link Player} found.
+     */
+    @Nullable
+    public static List<Player> getMultiBySelector(@NotNull String playerSelector,
+                                                  @NotNull CommandSender sender) {
+
+        if (playerSelector.charAt(0) != '@') {
+            return null;
+        }
+        try {
+            return Bukkit.selectEntities(sender, playerSelector).stream()
+                    .filter(e -> e instanceof Player)
+                    .map(e -> ((Player) e))
+                    .collect(Collectors.toList());
+        } catch (IllegalArgumentException e) {
+            Logging.warning("An error occurred while parsing selector '%s' for %s. Is it is the correct format?",
+                    playerSelector, sender.getName());
+            e.printStackTrace();
+            return null;
+        }
+    }
+}

src/main/java/com/onarandombox/MultiverseCore/utils/ReflectHelper.java

@@ -0,0 +1,140 @@
+package com.onarandombox.MultiverseCore.utils;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+
+/**
+ * Utility class used to help in doing various reflection actions.
+ */
+public class ReflectHelper {
+
+    /**
+     * Try to get the {@link Class} based on its classpath.
+     *
+     * @param classPath The target classpath.
+     * @return A {@link Class} if found, else null.
+     */
+    @Nullable
+    public static Class<?> getClass(String classPath) {
+        try {
+            return Class.forName(classPath);
+        } catch (ClassNotFoundException e) {
+            return null;
+        }
+    }
+
+    /**
+     * Check if the {@link Class} for a give classpath is present/valid.
+     *
+     * @param classPath Target classpath.
+     * @return True if class path is a valid class, else false.
+     */
+    public static boolean hasClass(String classPath) {
+        return getClass(classPath) != null;
+    }
+
+    /**
+     * Try to get a {@link Method} from a given class.
+     *
+     * @param clazz             The class to search the method on.
+     * @param methodName        Name of the method to get.
+     * @param parameterTypes    Parameters present for that method.
+     * @param <C>               The class type.
+     * @return A {@link Method} if found, else null.
+     */
+    @Nullable
+    public static <C> Method getMethod(Class<C> clazz, String methodName, Class<?>... parameterTypes) {
+        try {
+            Method method = clazz.getDeclaredMethod(methodName, parameterTypes);
+            method.setAccessible(true);
+            return method;
+        } catch (NoSuchMethodException e) {
+            return null;
+        }
+    }
+
+    /**
+     * Try to get a {@link Method} from a given class.
+     *
+     * @param classInstance     Instance of the class to search the method on.
+     * @param methodName        Name of the method to get.
+     * @param parameterTypes    Parameters present for that method.
+     * @param <C>               The class type.
+     * @return A {@link Method} if found, else null.
+     */
+    @Nullable
+    public static <C> Method getMethod(C classInstance, String methodName, Class<?>... parameterTypes) {
+        return getMethod(classInstance.getClass(), methodName, parameterTypes);
+    }
+
+    /**
+     * Calls a {@link Method}.
+     *
+     * @param classInstance Instance of the class responsible for the method.
+     * @param method        The method to call.
+     * @param parameters    Parameters needed when calling the method.
+     * @param <C>           The class type.
+     * @param <R>           The return type.
+     * @return Return value of the method call if any, else null.
+     */
+    @Nullable
+    public static <C, R> R invokeMethod(C classInstance, Method method, Object...parameters) {
+        try {
+            return (R) method.invoke(classInstance, parameters);
+        } catch (Exception e) {
+            return null;
+        }
+    }
+
+    /**
+     * Try to get a {@link Field} from a given class.
+     *
+     * @param clazz     The class to search the field on.
+     * @param fieldName Name of the field to get.
+     * @param <C>       The class type.
+     * @return A {@link Field} if found, else null.
+     */
+    @Nullable
+    public static <C> Field getField(Class<C> clazz, String fieldName) {
+        try {
+            Field field = clazz.getDeclaredField(fieldName);
+            field.setAccessible(true);
+            return field;
+        } catch (NoSuchFieldException e) {
+            return null;
+        }
+    }
+
+    /**
+     * Try to get a {@link Field} from a given class.
+     *
+     * @param classInstance Instance of the class to search the field on.
+     * @param fieldName     Name of the field to get.
+     * @param <C>           The class type.
+     * @return A {@link Field} if found, else null.
+     */
+    @Nullable
+    public static <C> Field getField(C classInstance, String fieldName) {
+        return getField(classInstance.getClass(), fieldName);
+    }
+
+    /**
+     * Gets the value of an {@link Field} from an instance of the class responsible.
+     *
+     * @param classInstance Instance of the class to get the field value from.
+     * @param field         The field to get value from.
+     * @param <C>           The class type.
+     * @param <V>           The field value type.
+     * @return The field value if any, else null.
+     */
+    @Nullable
+    public static <C, V> V getFieldValue(C classInstance, Field field)  {
+        try {
+            return (V) field.get(classInstance);
+        } catch (IllegalAccessException e) {
+            return null;
+        }
+    }
+}

src/main/java/com/onarandombox/MultiverseCore/utils/WorldManager.java

@@ -36,19 +36,20 @@ import java.io.File;
 import java.io.FilenameFilter;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Random;
 import java.util.Set;
 import java.util.Stack;
-import java.util.Arrays;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.logging.Level;
-import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.stream.Collectors;
 
 /**
  * Public facing API to add/remove Multiverse worlds.
@@ -59,6 +60,7 @@ public class WorldManager implements MVWorldManager {
     private final WorldPurger worldPurger;
     private final Map<String, MultiverseWorld> worlds;
     private Map<String, WorldProperties> worldsFromTheConfig;
+    private Set<String> defaultWorldNames;
     private FileConfiguration configWorlds = null;
     private Map<String, String> defaultGens;
     private String firstSpawn;
@@ -130,7 +132,7 @@ public class WorldManager implements MVWorldManager {
         }
 
         // Check for valid world name
-        if (!(isValidWorldName(oldName) && isValidWorldName(newName))) {
+        if (!(WorldNameChecker.isValidWorldName(oldName) && WorldNameChecker.isValidWorldName(oldName))) {
             return false;
         }
 
@@ -238,7 +240,9 @@ public class WorldManager implements MVWorldManager {
             return false;
         }
 
-        if (!isValidWorldName(name)) {
+        if (!WorldNameChecker.isValidWorldName(name)) {
+            Logging.warning("Invalid world name '" + name + "'");
+            Logging.warning("World name should not contain spaces or special characters!");
             return false;
         }
 
@@ -381,6 +385,11 @@ public class WorldManager implements MVWorldManager {
      */
     @Override
     public boolean unloadWorld(String name, boolean unloadBukkit) {
+        if (this.isDefaultWorld(name)) {
+            Logging.warning("You cannot unload the default worlds.");
+            Logging.warning("Default worlds on your server are: %s", this.defaultWorldNames);
+            return false;
+        }
         if (this.worlds.containsKey(name)) {
             this.worldsFromTheConfig.get(name).cacheVirtualProperties();
             if (unloadBukkit && this.unloadWorldFromBukkit(name, true)) {
@@ -424,21 +433,6 @@ public class WorldManager implements MVWorldManager {
         }
     }
 
-    /**
-     * Check if the world name is allowed
-     *
-     * @param name   Name of the world
-     * @return True if the world world name is valid based on regex
-     */
-    private boolean isValidWorldName(String name) {
-        if (!worldNamePattern.matcher(name).matches()) {
-            Logging.warning("Invalid world name '" + name + "'");
-            Logging.warning("World name should not contain spaces or special characters!");
-            return false;
-        }
-        return true;
-    }
-
     private void brokenWorld(String name) {
         Logging.severe("The world '" + name + "' could NOT be loaded because it contains errors and is probably corrupt!");
         Logging.severe("Try using Minecraft Region Fixer to repair your world! '" + name + "'");
@@ -630,6 +624,14 @@ public class WorldManager implements MVWorldManager {
      */
     @Override
     public MultiverseWorld getMVWorld(String name) {
+        return this.getMVWorld(name, true);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public MultiverseWorld getMVWorld(String name, boolean checkAliases) {
         if (name == null) {
             return null;
         }
@@ -637,7 +639,7 @@ public class WorldManager implements MVWorldManager {
         if (world != null) {
             return world;
         }
-        return this.getMVWorldByAlias(name);
+        return (checkAliases) ? this.getMVWorldByAlias(name) : null;
     }
 
     /**
@@ -646,7 +648,7 @@ public class WorldManager implements MVWorldManager {
     @Override
     public MultiverseWorld getMVWorld(World world) {
         if (world != null) {
-            return this.getMVWorld(world.getName());
+            return this.getMVWorld(world.getName(), false);
         }
         return null;
     }
@@ -671,7 +673,15 @@ public class WorldManager implements MVWorldManager {
      */
     @Override
     public boolean isMVWorld(final String name) {
-        return (this.worlds.containsKey(name) || isMVWorldAlias(name));
+        return this.isMVWorld(name, true);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public boolean isMVWorld(final String name, boolean checkAliases) {
+        return this.worlds.containsKey(name) || (checkAliases && this.isMVWorldAlias(name));
     }
 
     /**
@@ -704,6 +714,7 @@ public class WorldManager implements MVWorldManager {
     public void loadDefaultWorlds() {
         this.ensureConfigIsPrepared();
         List<World> myWorlds = this.plugin.getServer().getWorlds();
+        this.defaultWorldNames = new HashSet<>(myWorlds.size());
         for (World w : myWorlds) {
             String name = w.getName();
             if (!worldsFromTheConfig.containsKey(name)) {
@@ -711,9 +722,15 @@ public class WorldManager implements MVWorldManager {
                 if (this.defaultGens.containsKey(name)) {
                     generator = this.defaultGens.get(name);
                 }
-                this.addWorld(name, w.getEnvironment(), String.valueOf(w.getSeed()), w.getWorldType(), w.canGenerateStructures(), generator);
+                if (!this.addWorld(name, w.getEnvironment(), String.valueOf(w.getSeed()), w.getWorldType(), w.canGenerateStructures(), generator)) {
+                    Logging.warning("Error loading default world '%s'!", w.getName());
+                    continue;
+                }
             }
+            this.defaultWorldNames.add(name);
         }
+        this.defaultWorldNames = Collections.unmodifiableSet(this.defaultWorldNames);
+        Logging.fine("Loaded default worlds: %s", this.defaultWorldNames);
     }
 
     private void ensureConfigIsPrepared() {
@@ -723,6 +740,21 @@ public class WorldManager implements MVWorldManager {
         }
     }
 
+    @Override
+    public boolean isDefaultWorld(MultiverseWorld world) {
+        return world != null && this.isDefaultWorld(world.getName());
+    }
+
+    @Override
+    public boolean isDefaultWorld(String worldName) {
+        return this.defaultWorldNames != null && this.defaultWorldNames.contains(worldName);
+    }
+
+    @Override
+    public Collection<String> getDefaultWorldNames() {
+        return this.defaultWorldNames;
+    }
+
     /**
      * {@inheritDoc}
      */
@@ -953,4 +985,21 @@ public class WorldManager implements MVWorldManager {
 		}
 		return false;
 	}
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+	public Collection<String> getPotentialWorlds() {
+        File worldContainer = this.plugin.getServer().getWorldContainer();
+        if (worldContainer == null) {
+            return Collections.emptyList();
+        }
+        return Arrays.stream(worldContainer.listFiles())
+                .filter(File::isDirectory)
+                .filter(folder -> !this.isMVWorld(folder.getName(), false))
+                .filter(WorldNameChecker::isValidWorldFolder)
+                .map(File::getName)
+                .collect(Collectors.toList());
+    }
 }

src/main/java/com/onarandombox/MultiverseCore/utils/WorldNameChecker.java

@@ -0,0 +1,159 @@
+package com.onarandombox.MultiverseCore.utils;
+
+import org.bukkit.Bukkit;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.io.File;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.regex.Pattern;
+
+/**
+ * <p>Utility class in helping to check the status of a world name and it's associated world folder.</p>
+ *
+ * <p>Note this is for preliminary checks and better command output. A valid result will suggest but not
+ * 100% determine that a world name can be created, loaded or imported.</p>
+ */
+public class WorldNameChecker {
+
+    private static final Pattern WORLD_NAME_PATTERN = Pattern.compile("[a-zA-Z0-9/._-]+");
+    private static final Set<String> BLACKLIST_NAMES = Collections.unmodifiableSet(new HashSet<String>() {{
+        add("plugins");
+        add("logs");
+        add("cache");
+        add("crash-reports");
+    }});
+
+    /**
+     * Checks if a world name is valid.
+     *
+     * @param worldName The world name to check on.
+     * @return True if check result is valid, else false.
+     */
+    public static boolean isValidWorldName(@Nullable String worldName) {
+        return checkName(worldName) == NameStatus.VALID;
+    }
+
+    /**
+     * Checks the current validity status of a world name.
+     *
+     * @param worldName The world name to check on.
+     * @return The resulting name status.
+     */
+    @NotNull
+    public static NameStatus checkName(@Nullable String worldName) {
+        if (BLACKLIST_NAMES.contains(worldName)) {
+            return NameStatus.BLACKLISTED;
+        }
+        if (worldName == null || !WORLD_NAME_PATTERN.matcher(worldName).matches()) {
+            return NameStatus.INVALID_CHARS;
+        }
+        return NameStatus.VALID;
+    }
+
+    /**
+     * Checks if a world name has a valid world folder.
+     *
+     * @param worldName The world name to check on.
+     * @return True if check result is valid, else false.
+     */
+    public static boolean isValidWorldFolder(@Nullable String worldName) {
+        return checkFolder(worldName) == FolderStatus.VALID;
+    }
+
+    /**
+     * Checks if a world folder is valid.
+     *
+     * @param worldFolder   The world folder to check on.
+     * @return True if check result is valid, else false.
+     */
+    public static boolean isValidWorldFolder(@Nullable File worldFolder) {
+        return checkFolder(worldFolder) == FolderStatus.VALID;
+    }
+
+    /**
+     * Checks the current folder status for a world name.
+     *
+     * @param worldName The world name to check on.
+     * @return The resulting folder status.
+     */
+    @NotNull
+    public static FolderStatus checkFolder(@Nullable String worldName) {
+        if (worldName == null) {
+            return FolderStatus.DOES_NOT_EXIST;
+        }
+        File worldFolder = new File(Bukkit.getWorldContainer(), worldName);
+        return checkFolder(worldFolder);
+    }
+
+    /**
+     * Checks the current folder status.
+     *
+     * @param worldFolder   The world folder to check on.
+     * @return The resulting folder status.
+     */
+    @NotNull
+    public static FolderStatus checkFolder(@Nullable File worldFolder) {
+        if (worldFolder == null || !worldFolder.exists() || !worldFolder.isDirectory()) {
+            return FolderStatus.DOES_NOT_EXIST;
+        }
+        if (!folderHasDat(worldFolder)) {
+            return FolderStatus.NOT_A_WORLD;
+        }
+        return FolderStatus.VALID;
+    }
+
+    /**
+     * A very basic check to see if a folder has a level.dat file. If it does, we can safely assume
+     * it's a world folder.
+     *
+     * @param worldFolder   The File that may be a world.
+     * @return True if it looks like a world, else false.
+     */
+    private static boolean folderHasDat(@NotNull File worldFolder) {
+        File[] files = worldFolder.listFiles((file, name) -> name.toLowerCase().endsWith(".dat"));
+        return files != null && files.length > 0;
+    }
+
+    /**
+     * Result after checking validity of world name.
+     */
+    public enum NameStatus {
+        /**
+         * Name is valid.
+         */
+        VALID,
+
+        /**
+         * Name not valid as it contains invalid characters.
+         */
+        INVALID_CHARS,
+
+        /**
+         * Name not valid as it is deemed blacklisted.
+         */
+        BLACKLISTED
+    }
+
+    /**
+     * Result after checking validity of world folder.
+     */
+    public enum FolderStatus {
+        /**
+         * Folder is valid.
+         */
+        VALID,
+
+        /**
+         * Folder exist, but contents in it doesnt look like a world.
+         */
+        NOT_A_WORLD,
+
+        /**
+         * Folder does not exist.
+         */
+        DOES_NOT_EXIST
+    }
+}