feat: use java 8 and spigot api

SADLY

build.gradle.kts

@@ -7,16 +7,22 @@ group = "at.helpch.placeholderapi.expansion"
 version = "2.7.2"
 
 repositories {
-    maven("https://papermc.io/repo/repository/maven-public/")
+    mavenCentral()
+    maven("https://hub.spigotmc.org/nexus/content/repositories/snapshots/")
     maven("https://repo.extendedclip.com/content/repositories/placeholderapi/")
 }
 
 dependencies {
-    compileOnly("io.papermc.paper:paper-api:1.17.1-R0.1-SNAPSHOT")
+    compileOnly("org.spigotmc:spigot-api:1.17.1-R0.1-SNAPSHOT")
     compileOnly("me.clip:placeholderapi:2.11.3")
 }
 
 tasks {
+    java {
+        targetCompatibility = JavaVersion.VERSION_1_8
+        sourceCompatibility = JavaVersion.VERSION_1_8
+    }
+
     shadowJar {
         archiveFileName.set("PAPI-Expansion-Server-${project.version}.jar")
     }

src/main/java/at/helpch/placeholderapi/expansion/server/util/ServerUtil.java

@@ -4,19 +4,22 @@ import org.bukkit.Bukkit;
 
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.Map;
 import java.util.TreeMap;
 
 public final class ServerUtil {
 
     private static final Map<String, String> variants = new TreeMap<>();
-    private static final String variant;
-    private static final String build;
 
     // TPS stuff
     private static final Object craftServer;
     private static final Field tpsField;
-    private static boolean hasTpsMethod; // Paper and its forks have Bukkit#getTps
+    private static Method getTpsMethod; // Paper and its forks have Bukkit#getTPS
+    // ----
+
+    private static final String variant;
+    private static final String build;
 
     static {
         variants.put("net.pl3x.purpur.PurpurConfig", "Purpur");
@@ -78,8 +81,7 @@ public final class ServerUtil {
 
     private static Field getTpsHandler() {
         try {
-            Bukkit.class.getMethod("getTPS");
-            hasTpsMethod = true;
+            getTpsMethod = Bukkit.class.getMethod("getTPS");
             return null;
         } catch (NoSuchMethodException ignored) { }
 
@@ -138,8 +140,12 @@ public final class ServerUtil {
     }
 
     public static double[] getTps() {
-        if (hasTpsMethod) {
-            return Bukkit.getTPS();
+        if (getTpsMethod != null) {
+            try {
+                return (double[]) getTpsMethod.invoke(null);
+            } catch (IllegalAccessException | InvocationTargetException ignored) {
+                return new double[]{0, 0, 0};
+            }
         }
 
         if (craftServer == null || tpsField == null) {

src/main/java/at/helpch/placeholderapi/expansion/server/util/VersionHelper.java

@@ -27,6 +27,8 @@ import com.google.common.primitives.Ints;
 import org.bukkit.Bukkit;
 import org.jetbrains.annotations.NotNull;
 
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -39,11 +41,10 @@ public final class VersionHelper {
 
     private static final int V1_17 = 1_17_0;
 
+    private static final boolean IS_PAPER = checkPaper();
     public static final String MINECRAFT_VERSION = getMinecraftVersion();
     private static final int CURRENT_VERSION = getCurrentVersion();
 
-    private static final boolean IS_PAPER = checkPaper();
-
     public static final boolean IS_1_17_OR_HIGHER = CURRENT_VERSION >= V1_17;
 
     /**
@@ -92,13 +93,16 @@ public final class VersionHelper {
     }
 
     private static String getMinecraftVersion() {
-        try {
-            // Paper method from 2020 - returns the version like 1.20.1
-            return Bukkit.getMinecraftVersion();
-        } catch (NoSuchMethodError ignored) {
-            // The version is formatted as 1.20.1-R0.1-SNAPSHOT
-            return Bukkit.getBukkitVersion().split("-")[0];
+        if (IS_PAPER) {
+            try {
+                // Paper method from 2020 - returns the version like 1.20.1
+                final Method method = Bukkit.class.getDeclaredMethod("getMinecraftVersion");
+                return (String) method.invoke(Bukkit.getServer());
+            } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException ignored) { }
         }
+
+        // The version is formatted as 1.20.1-R0.1-SNAPSHOT
+        return Bukkit.getBukkitVersion().split("-")[0];
     }
 
     public static String getNmsVersion() {