Chunk: added modification counter

this is independent from the terrain dirty flags (which are specifically used to track state of chunks needing to be saved).

src/world/format/Chunk.php

@@ -42,6 +42,8 @@ class Chunk{
 	public const COORD_BIT_SIZE = SubChunk::COORD_BIT_SIZE;
 	public const COORD_MASK = SubChunk::COORD_MASK;
 
+	private int $modificationCount;
+
 	/** @var int */
 	private $terrainDirtyFlags = 0;
 
@@ -68,7 +70,7 @@ class Chunk{
 	/**
 	 * @param SubChunk[] $subChunks
 	 */
-	public function __construct(array $subChunks, BiomeArray $biomeIds, bool $terrainPopulated){
+	public function __construct(array $subChunks, BiomeArray $biomeIds, bool $terrainPopulated, int $modificationCount = 0){
 		$this->subChunks = new \SplFixedArray(Chunk::MAX_SUBCHUNKS);
 
 		foreach($this->subChunks as $y => $null){
@@ -80,6 +82,7 @@ class Chunk{
 		$this->biomeIds = $biomeIds;
 
 		$this->terrainPopulated = $terrainPopulated;
+		$this->modificationCount = $modificationCount;
 	}
 
 	/**
@@ -108,6 +111,7 @@ class Chunk{
 	public function setFullBlock(int $x, int $y, int $z, int $block) : void{
 		$this->getSubChunk($y >> SubChunk::COORD_BIT_SIZE)->setFullBlock($x, $y & SubChunk::COORD_MASK, $z, $block);
 		$this->terrainDirtyFlags |= self::DIRTY_FLAG_TERRAIN;
+		$this->modificationCount++;
 	}
 
 	/**
@@ -171,6 +175,7 @@ class Chunk{
 	public function setBiomeId(int $x, int $z, int $biomeId) : void{
 		$this->biomeIds->set($x, $z, $biomeId);
 		$this->terrainDirtyFlags |= self::DIRTY_FLAG_BIOMES;
+		$this->modificationCount++;
 	}
 
 	public function isLightPopulated() : ?bool{
@@ -188,6 +193,7 @@ class Chunk{
 	public function setPopulated(bool $value = true) : void{
 		$this->terrainPopulated = $value;
 		$this->terrainDirtyFlags |= self::DIRTY_FLAG_TERRAIN;
+		$this->modificationCount++;
 	}
 
 	public function addTile(Tile $tile) : void{
@@ -270,16 +276,24 @@ class Chunk{
 		}else{
 			$this->terrainDirtyFlags &= ~$flag;
 		}
+		$this->modificationCount++;
 	}
 
 	public function setTerrainDirty() : void{
 		$this->terrainDirtyFlags = ~0;
+		$this->modificationCount++;
 	}
 
 	public function clearTerrainDirtyFlags() : void{
 		$this->terrainDirtyFlags = 0;
 	}
 
+	/**
+	 * Returns the modcount for this chunk. Any saveable change to the chunk will cause this number to be incremented,
+	 * so you can use this to detect when the chunk has been modified.
+	 */
+	public function getModificationCount() : int{ return $this->modificationCount; }
+
 	public function getSubChunk(int $y) : SubChunk{
 		if($y < 0 || $y >= $this->subChunks->getSize()){
 			throw new \InvalidArgumentException("Invalid subchunk Y coordinate $y");

src/world/format/io/FastChunkSerializer.php

@@ -51,6 +51,8 @@ final class FastChunkSerializer{
 	 */
 	public static function serializeTerrain(Chunk $chunk) : string{
 		$stream = new BinaryStream();
+		$stream->putLong($chunk->getModificationCount());
+
 		$stream->putByte(
 			($chunk->isPopulated() ? self::FLAG_POPULATED : 0)
 		);
@@ -88,6 +90,7 @@ final class FastChunkSerializer{
 	 */
 	public static function deserializeTerrain(string $data) : Chunk{
 		$stream = new BinaryStream($data);
+		$modificationCounter = $stream->getLong();
 
 		$flags = $stream->getByte();
 		$terrainPopulated = (bool) ($flags & self::FLAG_POPULATED);
@@ -115,6 +118,6 @@ final class FastChunkSerializer{
 
 		$biomeIds = new BiomeArray($stream->get(256));
 
-		return new Chunk($subChunks, $biomeIds, $terrainPopulated);
+		return new Chunk($subChunks, $biomeIds, $terrainPopulated, $modificationCounter);
 	}
 }