Detect default world and, if found, only send its ID

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/CompanionSpigot.java

@@ -1,23 +1,39 @@
 package com.turikhay.mc.mapmodcompanion.spigot;
 
+import org.bukkit.World;
 import org.bukkit.event.Listener;
 import org.bukkit.plugin.java.JavaPlugin;
 
-import java.util.Arrays;
-import java.util.List;
+import java.util.*;
 
 public class CompanionSpigot extends JavaPlugin implements Listener {
     public static final boolean ENABLE_LOGGING = Boolean.parseBoolean(
             System.getProperty(CompanionSpigot.class.getPackage().getName() + ".debug", "false")
     );
 
+    public static final boolean DISABLE_DEFAULT_WORLD_ID = Boolean.parseBoolean(
+            System.getProperty(CompanionSpigot.class.getPackage().getName() + ".defaultId", "false")
+    );
+
     List<Handler<?>> handlers = Arrays.asList(
             new XaerosHandler(this),
             new WorldIdHandler(this)
     );
 
+    DefaultWorld defaultWorld;
+
     @Override
     public void onEnable() {
+        if (DISABLE_DEFAULT_WORLD_ID) {
+            getLogger().info("Plugin will not use default world ID for every world");
+            defaultWorld = DefaultWorld.empty();
+        } else {
+            defaultWorld = DefaultWorld.detectDefaultWorld(this);
+        }
         handlers.forEach(Handler::init);
     }
+
+    Optional<World> getDefaultWorld() {
+        return defaultWorld.optional();
+    }
 }

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/DefaultWorld.java

@@ -0,0 +1,67 @@
+package com.turikhay.mc.mapmodcompanion.spigot;
+
+import org.bukkit.World;
+
+import java.util.*;
+
+interface DefaultWorld {
+    Optional<World> optional();
+
+    static Empty empty() {
+        return new Empty();
+    }
+
+    static DefaultWorld detectDefaultWorld(CompanionSpigot plugin) {
+        List<World> worlds = plugin.getServer().getWorlds();
+        if (worlds.isEmpty()) {
+            throw new RuntimeException("world list is empty");
+        }
+        Set<World.Environment> expectedEnv = new HashSet<>(Arrays.asList(
+                World.Environment.NORMAL,
+                World.Environment.NETHER,
+                World.Environment.THE_END
+        ));
+        for (World world : worlds) {
+            World.Environment env = world.getEnvironment();
+            boolean isExpected = expectedEnv.remove(env);
+            if (!isExpected) {
+                // Non-default server configuration
+                plugin.getLogger().severe("Unexpected world: " + world);
+                plugin.getLogger().severe("For every world plugin will now send their unique IDs");
+                return new Empty();
+            }
+        }
+        World defaultWorld = worlds.get(0);
+        if (CompanionSpigot.ENABLE_LOGGING) {
+            plugin.getLogger().info("Selected default world: " + defaultWorld + " (" + defaultWorld.getUID() + ")");
+        }
+        return new ByUUID(plugin, defaultWorld.getUID());
+    }
+
+    class ByUUID implements DefaultWorld {
+        private final CompanionSpigot plugin;
+        private final UUID uuid;
+
+        public ByUUID(CompanionSpigot plugin, UUID uuid) {
+            this.plugin = plugin;
+            this.uuid = uuid;
+        }
+
+        @Override
+        public Optional<World> optional() {
+            World world = plugin.getServer().getWorld(uuid);
+            if (world == null) {
+                plugin.getLogger().warning("Couldn't find world " + uuid);
+                return Optional.empty();
+            }
+            return Optional.of(world);
+        }
+    }
+
+    class Empty implements DefaultWorld {
+        @Override
+        public Optional<World> optional() {
+            return Optional.empty();
+        }
+    }
+}

spigot/src/main/java/com/turikhay/mc/mapmodcompanion/spigot/Handler.java

@@ -16,6 +16,8 @@ public abstract class Handler<Id extends IdMessagePacket<?>> implements Listener
     private final String channelName;
     protected final CompanionSpigot plugin;
 
+    private IdRef<Id> defaultId;
+
     public Handler(String channelName, CompanionSpigot plugin) {
         this.channelName = channelName;
         this.plugin = plugin;
@@ -24,6 +26,7 @@ public Handler(String channelName, CompanionSpigot plugin) {
     public void init() {
         plugin.getServer().getMessenger().registerOutgoingPluginChannel(plugin, channelName);
         plugin.getServer().getPluginManager().registerEvents(this, plugin);
+        defaultId = plugin.getDefaultWorld().map(world -> IdRef.of(getId(world))).orElse(null);
     }
 
     @EventHandler(priority = EventPriority.MONITOR)
@@ -39,15 +42,20 @@ public void onWorldChanged(PlayerChangedWorldEvent event) {
     public void sendLevelId(Player player, EventSource source) {
         scheduleLevelIdPacket(
                 () -> {
-                    Id id = getId(player.getWorld());
-                    byte[] data = IdMessagePacket.bytesPacket(id);
+                    IdRef<Id> idRef;
+                    if (defaultId == null) {
+                        idRef = IdRef.of(getId(player.getWorld()));
+                    } else {
+                        idRef = defaultId;
+                    }
                     if (CompanionSpigot.ENABLE_LOGGING) {
                         plugin.getLogger().info(String.format(Locale.ROOT,
                                 "Sending world id to %s (channel: %s): %s. Data: %s",
-                                player.getName(), channelName, id, Arrays.toString(data)
+                                player.getName(), channelName, idRef.id,
+                                Arrays.toString(idRef.data)
                         ));
                     }
-                    player.sendPluginMessage(plugin, channelName, data);
+                    player.sendPluginMessage(plugin, channelName, idRef.data);
                 },
                 source
         );
@@ -61,4 +69,26 @@ public enum EventSource {
         WORLD_CHANGE,
         PLUGIN_MESSAGE
     }
+
+    private static class IdRef<Id extends IdMessagePacket<?>> {
+        private final Id id;
+        private final byte[] data;
+
+        private IdRef(Id id, byte[] data) {
+            this.id = id;
+            this.data = data;
+        }
+
+        @Override
+        public String toString() {
+            return "DefaultId{" +
+                    "id=" + id +
+                    ", data=" + Arrays.toString(data) +
+                    '}';
+        }
+
+        private static <Id extends IdMessagePacket<?>> IdRef<Id> of(Id id) {
+            return new IdRef<>(id, IdMessagePacket.bytesPacket(id));
+        }
+    }
 }