Fix dynamic world management on servers with multiple instances (#276)

This fixes the feature on servers like Hypixel, where you change sub-servers when switching lobbies.

Fixes #250

CHANGELOG.md

@@ -1,4 +1,5 @@
 ### 5.2.1-SNAPSHOT
+- Fix "Dynamic World Management" not working when switching server without full reconnect (#250) (thanks to KrisAphalon!)
 
 ### 5.2.0
 - Update to Minecraft 1.20.6

src/main/java/de/johni0702/minecraft/bobby/FakeChunkManager.java

@@ -112,6 +112,7 @@ public FakeChunkManager(ClientWorld world, ClientChunkManager clientChunkManager
 
         if (config.isDynamicMultiWorld()) {
             worlds = Worlds.getFor(storagePath);
+            worlds.startNewWorld();
             storages.add(worlds::loadTag);
 
             storage = null;

src/main/java/de/johni0702/minecraft/bobby/Worlds.java

@@ -154,6 +154,23 @@ private Worlds(Path directory) {
         }
     }
 
+    public void startNewWorld() {
+        // When switching from one server to another, this function can be executed multiple times
+        // Without this early return, that would create multiple empty words,
+        // after which only the last one would be merged and the empty ones would stay in memory
+        if (worlds.get(currentWorldId).knownRegions.isEmpty()) {
+            return;
+        }
+
+        lock.writeLock().lock();
+        try {
+            currentWorldId = nextWorldId++;
+            worlds.put(currentWorldId, new World(currentWorldId, CURRENT_SAVE_VERSION));
+        } finally {
+            lock.writeLock().unlock();
+        }
+    }
+
     public CompletableFuture<Optional<NbtCompound>> loadTag(ChunkPos chunkPos) {
         RegionPos regionPos = RegionPos.from(chunkPos);
         long regionCoord = regionPos.toLong();