Stack rework

scripts/inventory/inventory_slot.gd

@@ -71,19 +71,25 @@ func can_be_merged(item : Item) -> bool:
 	return item == held_item
 
 ## Add provided stack's amount to this amount. Returns null if stack is empty or items arent matching
-func merge_stack(stack: Stack) -> Stack:
-	if stack == null or stack.held_item == null or stack.amount == 0:
-		return stack
+func merge_stack(stack: Stack) -> bool:
+	if stack == null or stack.is_valid() == false:
+		return false
+	
+	if filter and filter.is_equal(stack.held_item) == false:
+		return false
+	
 	if held_item == null:
-		if filter != null and filter.is_equal(stack.held_item) == false:
-			return stack
 		held_item = stack.held_item
 		amount = stack.amount
-		return null
-	if stack.held_item != held_item:
-		return null
-	var return_stack_amount = max(0,stack.amount-amount)
-	amount += stack.amount - return_stack_amount
-	if return_stack_amount == 0:
-		return null
-	return Stack.new(held_item,return_stack_amount)
+		stack.invalidate()
+		return true
+	
+	var delta_amount = stack.amount - (held_item.stack_size - amount)
+	amount += stack.amount
+	
+	if delta_amount <= 0:
+		stack.invalidate()
+		return true
+	
+	stack.amount = delta_amount
+	return true