/**
 * Created by rockyl on 2018-11-25.
 */

'use strict';

var has = Object.prototype.hasOwnProperty
	, prefix = '~';

/**
 * Constructor to create a storage for our `EE` objects.
 * An `Events` instance is a plain object whose properties are event names.
 *
 * @constructor
 * @private
 */
function Events() {}

//
// We try to not inherit from `Object.prototype`. In some engines creating an
// instance in this way is faster than calling `Object.create(null)` directly.
// If `Object.create(null)` is not supported we prefix the event names with a
// character to make sure that the built-in object properties are not
// overridden or used as an attack vector.
//
if (Object.create) {
	Events.prototype = Object.create(null);

	//
	// This hack is needed because the `__proto__` property is still inherited in
	// some old browsers like Android 4, iPhone 5.1, Opera 11 and Safari 5.
	//
	if (!new Events().__proto__) prefix = '';
}

/**
 * Representation of a single event listener.
 *
 * @param {Function} fn The listener function.
 * @param {*} context The context to invoke the listener with.
 * @param {Boolean} [once=false] Specify if the listener is a one-time listener.
 * @constructor
 * @private
 */
function EE(fn, context, once) {
	this.fn = fn;
	this.context = context;
	this.once = once || false;
}

/**
 * Add a listener for a given event.
 *
 * @param {EventEmitter} emitter Reference to the `EventEmitter` instance.
 * @param {(String|Symbol)} event The event name.
 * @param {Function} fn The listener function.
 * @param {*} context The context to invoke the listener with.
 * @param {Boolean} once Specify if the listener is a one-time listener.
 * @returns {EventEmitter}
 * @private
 */
function addListener(emitter, event, fn, context, once) {
	if (typeof fn !== 'function') {
		throw new TypeError('The listener must be a function');
	}

	var listener = new EE(fn, context || emitter, once)
		, evt = prefix ? prefix + event : event;

	if (!emitter._events[evt]) emitter._events[evt] = listener, emitter._eventsCount++;
	else if (!emitter._events[evt].fn) emitter._events[evt].push(listener);
	else emitter._events[evt] = [emitter._events[evt], listener];

	return emitter;
}

/**
 * Clear event by name.
 *
 * @param {EventEmitter} emitter Reference to the `EventEmitter` instance.
 * @param {(String|Symbol)} evt The Event name.
 * @private
 */
function clearEvent(emitter, evt) {
	if (--emitter._eventsCount === 0) emitter._events = new Events();
	else delete emitter._events[evt];
}

/**
 * Minimal `EventEmitter` interface that is molded against the Node.js
 * `EventEmitter` interface.
 *
 * @constructor
 * @public
 */
export default class EventEmitter{
	_events;
	_eventsCount;

	off;
	addListener;

	static get prefixed(){
		return prefix;
	}

	constructor() {
		this._events = new Events();
		this._eventsCount = 0;

		this.off = this.removeListener;
		this.addListener = this.on;
	}

	/**
	 * Return an array listing the events for which the emitter has registered
	 * listeners.
	 *
	 * @returns {Array}
	 * @public
	 */
	eventNames() {
		var names = []
			, events
			, name;

		if (this._eventsCount === 0) return names;

		for (name in (events = this._events)) {
			if (has.call(events, name)) names.push(prefix ? name.slice(1) : name);
		}

		//if (Object.getOwnPropertySymbols) {
		//	return names.concat(Object.getOwnPropertySymbols(events));
		//}

		return names;
	}



	/**
	 * Return the listeners registered for a given event.
	 *
	 * @param {(String|Symbol)} event The event name.
	 * @returns {Array} The registered listeners.
	 * @public
	 */
	listeners(event) {
		var evt = prefix ? prefix + event : event
			, handlers = this._events[evt];

		if (!handlers) return [];
		if (handlers.fn) return [handlers.fn];

		for (var i = 0, l = handlers.length, ee = new Array(l); i < l; i++) {
			ee[i] = handlers[i].fn;
		}

		return ee;
	}

	/**
	 * Return the number of listeners listening to a given event.
	 *
	 * @param {(String|Symbol)} event The event name.
	 * @returns {Number} The number of listeners.
	 * @public
	 */
	listenerCount(event) {
		var evt = prefix ? prefix + event : event
			, listeners = this._events[evt];

		if (!listeners) return 0;
		if (listeners.fn) return 1;
		return listeners.length;
	}

	/**
	 * Calls each of the listeners registered for a given event.
	 *
	 * @param {(String|Symbol)} event The event name.
	 * @returns {Boolean} `true` if the event had listeners, else `false`.
	 * @public
	 */
	emit(event, a1?, a2?, a3?, a4?, a5?) {
		var evt = prefix ? prefix + event : event;

		if (!this._events[evt]) return false;

		var listeners = this._events[evt]
			, len = arguments.length
			, args
			, i;

		if (listeners.fn) {
			if (listeners.once) this.removeListener(event, listeners.fn, undefined, true);

			switch (len) {
				case 1: return listeners.fn.call(listeners.context), true;
				case 2: return listeners.fn.call(listeners.context, a1), true;
				case 3: return listeners.fn.call(listeners.context, a1, a2), true;
				case 4: return listeners.fn.call(listeners.context, a1, a2, a3), true;
				case 5: return listeners.fn.call(listeners.context, a1, a2, a3, a4), true;
				case 6: return listeners.fn.call(listeners.context, a1, a2, a3, a4, a5), true;
			}

			for (i = 1, args = new Array(len -1); i < len; i++) {
				args[i - 1] = arguments[i];
			}

			listeners.fn.apply(listeners.context, args);
		} else {
			var length = listeners.length
				, j;

			for (i = 0; i < length; i++) {
				if (listeners[i].once) this.removeListener(event, listeners[i].fn, undefined, true);

				switch (len) {
					case 1: listeners[i].fn.call(listeners[i].context); break;
					case 2: listeners[i].fn.call(listeners[i].context, a1); break;
					case 3: listeners[i].fn.call(listeners[i].context, a1, a2); break;
					case 4: listeners[i].fn.call(listeners[i].context, a1, a2, a3); break;
					default:
						if (!args) for (j = 1, args = new Array(len -1); j < len; j++) {
							args[j - 1] = arguments[j];
						}

						listeners[i].fn.apply(listeners[i].context, args);
				}
			}
		}

		return true;
	}

	/**
	 * Add a listener for a given event.
	 *
	 * @param {(String|Symbol)} event The event name.
	 * @param {Function} fn The listener function.
	 * @param {*} [context=this] The context to invoke the listener with.
	 * @returns {EventEmitter} `this`.
	 * @public
	 */
	on(event, fn, context) {
		return addListener(this, event, fn, context, false);
	};

	/**
	 * Add a one-time listener for a given event.
	 *
	 * @param {(String|Symbol)} event The event name.
	 * @param {Function} fn The listener function.
	 * @param {*} [context=this] The context to invoke the listener with.
	 * @returns {EventEmitter} `this`.
	 * @public
	 */
	once(event, fn, context) {
		return addListener(this, event, fn, context, true);
	}

	/**
	 * Remove the listeners of a given event.
	 *
	 * @param {(String|Symbol)} event The event name.
	 * @param {Function} fn Only remove the listeners that match this function.
	 * @param {*} context Only remove the listeners that have this context.
	 * @param {Boolean} once Only remove one-time listeners.
	 * @returns {EventEmitter} `this`.
	 * @public
	 */
	removeListener(event, fn, context, once) {
		var evt = prefix ? prefix + event : event;

		if (!this._events[evt]) return this;
		if (!fn) {
			clearEvent(this, evt);
			return this;
		}

		var listeners = this._events[evt];

		if (listeners.fn) {
			if (
				listeners.fn === fn &&
				(!once || listeners.once) &&
				(!context || listeners.context === context)
			) {
				clearEvent(this, evt);
			}
		} else {
			for (var i = 0, events = [], length = listeners.length; i < length; i++) {
				if (
					listeners[i].fn !== fn ||
					(once && !listeners[i].once) ||
					(context && listeners[i].context !== context)
				) {
					events.push(listeners[i]);
				}
			}

			//
			// Reset the array, or remove it completely if we have no more listeners.
			//
			if (events.length) this._events[evt] = events.length === 1 ? events[0] : events;
			else clearEvent(this, evt);
		}

		return this;
	}

	/**
	 * Remove all listeners, or those of the specified event.
	 *
	 * @param {(String|Symbol)} [event] The event name.
	 * @returns {EventEmitter} `this`.
	 * @public
	 */
	removeAllListeners(event) {
		var evt;

		if (event) {
			evt = prefix ? prefix + event : event;
			if (this._events[evt]) clearEvent(this, evt);
		} else {
			this._events = new Events();
			this._eventsCount = 0;
		}

		return this;
	}
}