From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Nassim Jahnke <jahnke.nassim@gmail.com>
Date: Mon, 31 Jan 2022 11:21:50 +0100
Subject: [PATCH] Implement regenerateChunk

Co-authored-by: Jason Penilla <11360596+jpenilla@users.noreply.github.com>

diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index 17828c924fa20ebc1d72f73adf62f1c0cb078a68..2e9b782e34ae25e982b45011a36c3b08ab298648 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -133,6 +133,7 @@ import org.bukkit.util.Vector;
 public class CraftWorld extends CraftRegionAccessor implements World {
     public static final int CUSTOM_DIMENSION_OFFSET = 10;
     private static final CraftPersistentDataTypeRegistry DATA_TYPE_REGISTRY = new CraftPersistentDataTypeRegistry();
+    private static final ChunkStatus[] REGEN_CHUNK_STATUSES = {ChunkStatus.BIOMES, ChunkStatus.NOISE, ChunkStatus.SURFACE, ChunkStatus.CARVERS, ChunkStatus.LIQUID_CARVERS, ChunkStatus.FEATURES}; // Paper - implement regenerate chunk method
 
     private final ServerLevel world;
     private WorldBorder worldBorder;
@@ -425,27 +426,61 @@ public class CraftWorld extends CraftRegionAccessor implements World {
     @Override
     public boolean regenerateChunk(int x, int z) {
         org.spigotmc.AsyncCatcher.catchOp("chunk regenerate"); // Spigot
-        throw new UnsupportedOperationException("Not supported in this Minecraft version! Unless you can fix it, this is not a bug :)");
-        /*
-        if (!unloadChunk0(x, z, false)) {
-            return false;
-        }
-
-        final long chunkKey = ChunkCoordIntPair.pair(x, z);
-        world.getChunkProvider().unloadQueue.remove(chunkKey);
+        // Paper start - implement regenerateChunk method
+        final ServerLevel serverLevel = this.world;
+        final net.minecraft.server.level.ServerChunkCache serverChunkCache = serverLevel.getChunkSource();
+        final ChunkPos chunkPos = new ChunkPos(x, z);
+        final net.minecraft.world.level.chunk.LevelChunk levelChunk = serverChunkCache.getChunk(chunkPos.x, chunkPos.z, true);
+        for (final BlockPos blockPos : BlockPos.betweenClosed(chunkPos.getMinBlockX(), serverLevel.getMinBuildHeight(), chunkPos.getMinBlockZ(), chunkPos.getMaxBlockX(), serverLevel.getMaxBuildHeight() - 1, chunkPos.getMaxBlockZ())) {
+            levelChunk.removeBlockEntity(blockPos);
+            serverLevel.setBlock(blockPos, net.minecraft.world.level.block.Blocks.AIR.defaultBlockState(), 16);
+        }
+
+        for (final ChunkStatus chunkStatus : REGEN_CHUNK_STATUSES) {
+            final List<ChunkAccess> list = new ArrayList<>();
+            final int range = Math.max(1, chunkStatus.getRange());
+            for (int chunkX = chunkPos.z - range; chunkX <= chunkPos.z + range; chunkX++) {
+                for (int chunkZ = chunkPos.x - range; chunkZ <= chunkPos.x + range; chunkZ++) {
+                    ChunkAccess chunkAccess = serverChunkCache.getChunk(chunkZ, chunkX, chunkStatus.getParent(), true);
+                    if (chunkAccess instanceof ImposterProtoChunk accessProtoChunk) {
+                        chunkAccess = new ImposterProtoChunk(accessProtoChunk.getWrapped(), true);
+                    } else if (chunkAccess instanceof net.minecraft.world.level.chunk.LevelChunk accessLevelChunk) {
+                        chunkAccess = new ImposterProtoChunk(accessLevelChunk, true);
+                    }
+                    list.add(chunkAccess);
+                }
+            }
 
-        net.minecraft.server.Chunk chunk = world.getChunkProvider().generateChunk(x, z);
-        PlayerChunk playerChunk = world.getPlayerChunkMap().getChunk(x, z);
-        if (playerChunk != null) {
-            playerChunk.chunk = chunk;
+            final com.mojang.datafixers.util.Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure> either = chunkStatus.generate(
+                Runnable::run,
+                serverLevel,
+                serverChunkCache.getGenerator(),
+                serverLevel.getStructureManager(),
+                serverChunkCache.getLightEngine(),
+                chunk -> {
+                    throw new UnsupportedOperationException("Not creating full chunks here");
+                },
+                list,
+                true
+            ).join();
+            if (chunkStatus == ChunkStatus.NOISE) {
+                either.left().ifPresent(chunk -> net.minecraft.world.level.levelgen.Heightmap.primeHeightmaps(chunk, ChunkStatus.POST_FEATURES));
+            }
         }
 
-        if (chunk != null) {
-            refreshChunk(x, z);
+        for (final BlockPos blockPos : BlockPos.betweenClosed(chunkPos.getMinBlockX(), serverLevel.getMinBuildHeight(), chunkPos.getMinBlockZ(), chunkPos.getMaxBlockX(), serverLevel.getMaxBuildHeight() - 1, chunkPos.getMaxBlockZ())) {
+            serverChunkCache.blockChanged(blockPos);
         }
 
-        return chunk != null;
-        */
+        final Set<ChunkPos> chunksToRelight = new HashSet<>(9);
+        for (int chunkX = chunkPos.x - 1; chunkX <= chunkPos.x + 1 ; chunkX++) {
+            for (int chunkZ = chunkPos.z - 1; chunkZ <= chunkPos.z + 1 ; chunkZ++) {
+                chunksToRelight.add(new ChunkPos(chunkX, chunkZ));
+            }
+        }
+        serverChunkCache.getLightEngine().relight(chunksToRelight, pos -> {}, relit -> {});
+        return true;
+        // Paper end
     }
 
     @Override