Added __on_chunk_unloaded scarpet event (#1451)

* Fixes #1403

* Use concrete type

docs/scarpet/api/Events.md

@@ -103,6 +103,9 @@ this should not happen, but let you be warned.
 Called right after a chunk at a given coordinate is loaded. All newly generated chunks are considered loaded as well.
  `x` and `z` correspond to the lowest x and z coordinates in the chunk.
 
+### `__on_chunk_unloaded(x, z)`
+Called right before a chunk at the given coordinates is unloaded. `x` and `z` correspond to the lowest x and z coordinates in the chunk.
+
 ### `__on_lightning(block, mode)`
 Triggered right after a lightning strikes. Lightning entity as well as potential horseman trap would 
 already be spawned at that point. `mode` is `true` if the lightning did cause a trap to spawn. 

src/main/java/carpet/mixins/ServerLevel_scarpetMixin.java

@@ -26,6 +26,8 @@ import org.spongepowered.asm.mixin.injection.callback.LocalCapture;
 
 import static carpet.script.CarpetEventServer.Event.EXPLOSION;
 import static carpet.script.CarpetEventServer.Event.LIGHTNING;
+import static carpet.script.CarpetEventServer.Event.CHUNK_UNLOADED;
+
 
 @Mixin(ServerLevel.class)
 public class ServerLevel_scarpetMixin implements ServerWorldInterface
@@ -50,6 +52,16 @@ public class ServerLevel_scarpetMixin implements ServerWorldInterface
             EXPLOSION.onExplosion((ServerLevel) (Object)this, entity, null, d, e, f, g, bl, null, null, destructionType);
     }
 
+    @Inject(method = "unload", at = @At("HEAD"))
+    private void handleChunkUnload(LevelChunk levelChunk, CallbackInfo ci)
+    {
+        if (CHUNK_UNLOADED.isNeeded())
+        {
+            ServerLevel level = (ServerLevel)((Object)this);
+            CHUNK_UNLOADED.onChunkEvent(level, levelChunk.getPos(), false);
+        }
+    }
+
     @Final
     @Shadow
     private ServerLevelData serverLevelData;

src/main/java/carpet/script/CarpetEventServer.java

@@ -467,6 +467,18 @@ public class CarpetEventServer
             }
         };
 
+        public static final Event CHUNK_UNLOADED = new Event("chunk_unloaded", 2, true)
+        {
+            @Override
+            public void onChunkEvent(ServerLevel world, ChunkPos chPos, boolean generated)
+            {
+                handler.call(
+                        () -> Arrays.asList(new NumericValue(chPos.x << 4), new NumericValue(chPos.z << 4)),
+                        () -> CarpetServer.minecraft_server.createCommandSourceStack().withLevel(world)
+                );
+            }
+        };
+
         public static final Event PLAYER_JUMPS = new Event("player_jumps", 1, false)
         {
             @Override