export default class WeakValueMap {
	constructor(items = []) {
		this._map = new Map;

		for (let [key, value] of items)
			this.set(key, value);
	}

	// Public

	get size() {
		let size = 0;
		for (let wrapper of this._map.values()) {
			if (wrapper.deref())
				++size;
		}
		return size;
	}

	has(key) {
		let wrapper = this._map.get(key);
		return !!wrapper?.deref();
	}

	get(key) {
		let wrapper = this._map.get(key);
		return wrapper?.deref();
	}

	set(key, value) {
		console.assert(typeof value === "object", value);
		console.assert(value !== null, value);

		this._map.set(key, new WeakRef(value));
		this._finalizationRegistry.register(value, {weakThis: new WeakRef(this), key: new WeakRef(key)}, key);
	}

	delete(key) {
		let result = this._map.delete(key);
		this._finalizationRegistry.unregister(key);
		return result;
	}

	take(key) {
		let wrapper = this._map.get(key);
		this._map.delete(key);
		this._finalizationRegistry.unregister(key);
		return wrapper?.deref();
	}

	clear() {
		for (let key of this._map.keys())
			this._finalizationRegistry.unregister(key);
		this._map.clear();
	}

	*keys() {
		for (let entry of this.entries())
			yield entry[0];
	}

	*values() {
		for (let entry of this.entries())
			yield entry[1];
	}

	*entries() {
		for (let [key, wrapper] of this._map) {
			let value = wrapper.deref();
			if (value)
				yield [key, value];
		}
	}

	[Symbol.iterator]() {
		return this.entries();
	}

	toJSON() {
		return Array.from(this);
	}

	// Private

	get _finalizationRegistry() {
		return WeakValueMap._finalizationRegistry ??= new FinalizationRegistry(function(heldValue) {
			heldValue.weakThis.deref()?._map.delete(heldValue.key.deref());
		});
	}
}