export default class WeakKeyMap {
	constructor(items = []) {
		this._wrapperForKey = new WeakMap;
		this._valueForWrapper = new Map;

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

	// Public

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

	has(key) {
		let result = this._wrapperForKey.has(key);
		console.assert(Array.from(this._valueForWrapper.keys()).some((wrapper) => wrapper.deref() === key) === result, this, key);
		return result;
	}

	get(key) {
		let wrapper = this._wrapperForKey.has(key);
		if (!wrapper)
			return undefined;

		return this._valueForWrapper.get(wrapper);
	}

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

		this.delete(key);

		let wrapper = new WeakRef(key);
		this._wrapperForKey.set(key, wrapper);
		this._valueForWrapper.set(wrapper, value);
		this._finalizationRegistry.register(key, {weakThis: new WeakRef(this), wrapper}, wrapper);
	}

	delete(key) {
		let wrapper = this._wrapperForKey.get(key);
		if (!wrapper)
			return false;

		let keyDeleted = this._wrapperForKey.delete(key);
		console.assert(keyDeleted, this, key);

		let wrapperDeleted = this._valueForWrapper.delete(wrapper);
		console.assert(wrapperDeleted, this, key);

		this._finalizationRegistry.unregister(wrapper);

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

	take(key) {
		let wrapper = this._wrapperForKey.get(key);
		if (!wrapper)
			return undefined;

		let value = this._valueForWrapper.get(value);

		let keyDeleted = this._wrapperForKey.delete(key);
		console.assert(keyDeleted, this, key);

		let wrapperDeleted = this._valueForWrapper.delete(wrapper);
		console.assert(wrapperDeleted, this, key);

		this._finalizationRegistry.unregister(wrapper);

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

	clear() {
		for (let wrapper of this._valueForWrapper.keys()) {
			this._wrapperForKey.delete(wrapper);
			this._finalizationRegistry.unregister(wrapper);
		}
		this._valueForWrapper.clear();
	}

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

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

	*entries() {
		for (let [wrapper, value] of this._valueForWrapper) {
			let key = wrapper.deref();
			console.assert(!key === !this._wrapperForKey.has(key), this, key);
			if (key)
				yield [key, value];
		}
	}

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

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

	// Private

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