Implement missing last interacted slot property in chiseled bookshelf

src/block/ChiseledBookshelf.php

@@ -48,11 +48,32 @@ class ChiseledBookshelf extends Opaque{
 	 */
 	private array $slots = [];
 
+	private ?ChiseledBookshelfSlot $lastInteractedSlot = null;
+
 	protected function describeBlockOnlyState(RuntimeDataDescriber $w) : void{
 		$w->horizontalFacing($this->facing);
 		$w->enumSet($this->slots, ChiseledBookshelfSlot::cases());
 	}
 
+	public function readStateFromWorld() : Block{
+		$tile = $this->position->getWorld()->getTile($this->position);
+		if($tile instanceof TileChiseledBookshelf){
+			$this->lastInteractedSlot = $tile->getLastInteractedSlot();
+		}else{
+			$this->lastInteractedSlot = null;
+		}
+		return $this;
+	}
+
+	public function writeStateToWorld() : void{
+		parent::writeStateToWorld();
+
+		$tile = $this->position->getWorld()->getTile($this->position);
+		if($tile instanceof TileChiseledBookshelf){
+			$tile->setLastInteractedSlot($this->lastInteractedSlot);
+		}
+	}
+
 	/**
 	 * Returns whether the given slot is displayed as occupied.
 	 * This doesn't guarantee that there is or isn't a book in the bookshelf's inventory.
@@ -92,6 +113,23 @@ public function getSlots() : array{
 		return $this->slots;
 	}
 
+	/**
+	 * Returns the last slot interacted by a player or null if no slot has been interacted with yet.
+	 */
+	public function getLastInteractedSlot() : ?ChiseledBookshelfSlot{
+		return $this->lastInteractedSlot;
+	}
+
+	/**
+	 * Sets the last slot interacted by a player.
+	 *
+	 * @return $this
+	 */
+	public function setLastInteractedSlot(?ChiseledBookshelfSlot $lastInteractedSlot) : self{
+		$this->lastInteractedSlot = $lastInteractedSlot;
+		return $this;
+	}
+
 	public function onInteract(Item $item, int $face, Vector3 $clickVector, ?Player $player = null, array &$returnedItems = []) : bool{
 		if($face !== $this->facing){
 			return false;
@@ -112,10 +150,12 @@ public function onInteract(Item $item, int $face, Vector3 $clickVector, ?Player
 			$returnedItems[] = $inventory->getItem($slot->value);
 			$inventory->clear($slot->value);
 			$this->setSlot($slot, false);
+			$this->lastInteractedSlot = $slot;
 		}elseif($item instanceof WritableBookBase || $item instanceof Book || $item instanceof EnchantedBook){
 			//TODO: type tags like blocks would be better for this
 			$inventory->setItem($slot->value, $item->pop());
 			$this->setSlot($slot, true);
+			$this->lastInteractedSlot = $slot;
 		}else{
 			return true;
 		}

src/block/tile/ChiseledBookshelf.php

@@ -40,8 +40,12 @@
 class ChiseledBookshelf extends Tile implements Container{
 	use ContainerTrait;
 
+	private const TAG_LAST_INTERACTED_SLOT = "LastInteractedSlot"; //TAG_Int
+
 	private SimpleInventory $inventory;
 
+	private ?ChiseledBookshelfSlot $lastInteractedSlot = null;
+
 	public function __construct(World $world, Vector3 $pos){
 		parent::__construct($world, $pos);
 		$this->inventory = new SimpleInventory(count(ChiseledBookshelfSlot::cases()));
@@ -55,12 +59,30 @@ public function getRealInventory() : SimpleInventory{
 		return $this->inventory;
 	}
 
+	public function getLastInteractedSlot() : ?ChiseledBookshelfSlot{
+		return $this->lastInteractedSlot;
+	}
+
+	public function setLastInteractedSlot(?ChiseledBookshelfSlot $lastInteractedSlot) : void{
+		$this->lastInteractedSlot = $lastInteractedSlot;
+	}
+
 	public function readSaveData(CompoundTag $nbt) : void{
 		$this->loadItems($nbt);
+
+		$lastInteractedSlot = $nbt->getInt(self::TAG_LAST_INTERACTED_SLOT, 0);
+		if($lastInteractedSlot !== 0){
+			$this->lastInteractedSlot = ChiseledBookshelfSlot::tryFrom($lastInteractedSlot - 1);
+		}
 	}
 
 	protected function writeSaveData(CompoundTag $nbt) : void{
 		$this->saveItems($nbt);
+
+		$nbt->setInt(self::TAG_LAST_INTERACTED_SLOT, $this->lastInteractedSlot !== null ?
+			$this->lastInteractedSlot->value + 1 :
+			0
+		);
 	}
 
 	protected function loadItems(CompoundTag $tag) : void{