export default class EventObject {
	constructor() {
		this.listeners = new Map();
		this.forwards = new Set();
	}

	addEventListener(type, callback) {
		const l = this.listeners.get(type);
		if(l) {
			l.push(callback);
		} else {
			this.listeners.set(type, [callback]);
		}
	}

	removeEventListener(type, fn) {
		const l = this.listeners.get(type);
		if(!l) {
			return;
		}
		const i = l.indexOf(fn);
		if(i !== -1) {
			l.splice(i, 1);
		}
	}

	on(type, fn) {
		this.addEventListener(type, fn);
		return this;
	}

	off(type, fn) {
		this.removeEventListener(type, fn);
		return this;
	}

	countEventListeners(type) {
		return (this.listeners.get(type) || []).length;
	}

	removeAllEventListeners(type) {
		if(type) {
			this.listeners.delete(type);
		} else {
			this.listeners.clear();
		}
	}

	addEventForwarding(target) {
		this.forwards.add(target);
	}

	removeEventForwarding(target) {
		this.forwards.delete(target);
	}

	removeAllEventForwardings() {
		this.forwards.clear();
	}

	trigger(type, params = []) {
		(this.listeners.get(type) || []).forEach(
			(listener) => listener(...params)
		);
		this.forwards.forEach((fwd) => fwd.trigger(type, params));
	}
}