@tool
class_name LRU extends RefCounted

# LRU 算法
var cache_size = 1
# keys. 新的在后面，旧的在前面
var lru_list = []
# key -> value
var cache = {}
var cache_mutex = Mutex.new()


func _init(size := 8) -> void:
	cache_size = size


func _get(key: Variant) -> Variant:
	var v = null
	cache_mutex.lock()
	if cache.has(key):
		lru_list.erase(key)
		lru_list.append(key)
		v = cache[key]
	cache_mutex.unlock()
	return v


func _set(key: StringName, value: Variant) -> bool:
	cache_mutex.lock()
	if cache.has(key):
		lru_list.erase(key)
		if cache[key] != value:
			_release_value(cache[key])
	cache[key] = value
	lru_list.append(key)
	if lru_list.size() > cache_size:
		var k = lru_list.pop_front()
		_release_value(cache[k])
		cache.erase(k)
	cache_mutex.unlock()
	return true


func _release_value(v: Variant) -> void:
	if v is Node:
		if not v.is_inside_tree() and is_instance_valid(v):
			v.queue_free()
	elif not v is RefCounted:
		v.free()