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

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

	// Public

	get size() {
		return this._map.size;
	}

	has(key, value) {
		let valueSet = this._map.get(key);
		if (!valueSet)
			return false;
		return arguments.length === 1 || valueSet.has(value);
	}

	get(key) {
		return this._map.get(key) || new Set;
	}

	set(key, value) {
		let valueSet = this._map.get(key);
		if (!valueSet) {
			valueSet = new Set;
			this._map.set(key, valueSet);
		}
		valueSet.add(value);

		return this;
	}

	delete(key, value) {
		if (arguments.length === 1)
			return this._map.delete(key);

		let valueSet = this._map.get(key);
		if (!valueSet)
			return false;

		let deletedValue = valueSet.delete(value);

		if (!valueSet.size) {
			let deletedKey = this._map.delete(key);
			console.assert(deletedKey === deletedValue, this);
		}

		return deletedValue;
	}

	take(key, value) {
		let valueSet = this._map.get(key);
		if (arguments.length === 1) {
			this._map.delete(key);
			return valueSet;
		}

		let deletedValue = valueSet.delete(value);

		if (!valueSet.size) {
			let deletedKey = this._map.delete(key);
			console.assert(deletedKey === deletedValue, this);
		}

		return deletedValue ? value : undefined;
	}

	clear() {
		this._map.clear();
	}

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

	*values() {
		for (let valueSet of this.sets()) {
			for (let value of valueSet)
				yield value;
		}
	}

	*entries() {
		for (let [key, valueSet] of this._map) {
			for (let value of valueSet)
				yield [key, value];
		}
	}

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

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