export default class IterableWeakSet {
	constructor(items = []) {
		this._wrapperForItem = new WeakMap;
		this._wrappers = new Set;

		for (let item of items)
			this.add(item);
	}

	// Public

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

	has(item) {
		let result = this._wrapperForItem.has(item);
		console.assert(Array.from(this._wrappers).some((wrapper) => wrapper.deref() === item) === result, this, item);
		return result;
	}

	add(item) {
		console.assert(typeof item === "object", item);
		console.assert(item !== null, item);

		this.delete(item);

		let wrapper = new WeakRef(item);
		this._wrapperForItem.set(item, wrapper);
		this._wrappers.add(wrapper);
		this._finalizationRegistry.register(item, {weakThis: new WeakRef(this), wrapper}, wrapper);
	}

	delete(item) {
		let wrapper = this._wrapperForItem.get(item);
		if (!wrapper)
			return false;

		let itemDeleted = this._wrapperForItem.delete(item);
		console.assert(itemDeleted, this, item);

		let wrapperDeleted = this._wrappers.delete(wrapper);
		console.assert(wrapperDeleted, this, item);

		this._finalizationRegistry.unregister(wrapper);

		console.assert(wrapper.deref() === item, this, item);
		return true;
	}

	take(item) {
		let wrapper = this._wrapperForItem.get(item);
		if (!wrapper)
			return undefined;

		let itemDeleted = this._wrapperForItem.delete(item);
		console.assert(itemDeleted, this, item);

		let wrapperDeleted = this._wrappers.delete(wrapper);
		console.assert(wrapperDeleted, this, item);

		this._finalizationRegistry.unregister(wrapper);

		console.assert(wrapper.deref() === item, this, item);
		return item;
	}

	clear() {
		for (let wrapper of this._wrappers) {
			this._wrapperForItem.delete(wrapper);
			this._finalizationRegistry.unregister(wrapper);
		}
		this._wrappers.clear();
	}

	keys() {
		return this.values();
	}

	*values() {
		for (let wrapper of this._wrappers) {
			let item = wrapper.deref();
			console.assert(!item === !this._wrapperForItem.has(item), this, item);
			if (item)
				yield item;
		}
	}

	*entries() {
		for (let wrapper of this._wrappers) {
			let item = wrapper.deref();
			console.assert(!item === !this._wrapperForItem.has(item), this, item);
			if (item)
				yield [item, item];
		}
	}

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

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

	// Private

	get _finalizationRegistry() {
		return IterableWeakSet._finalizationRegistry ??= new FinalizationRegistry(function(heldValue) {
			heldValue.weakThis.deref()?._wrappers.delete(heldValue.wrapper);
		});
	}
}