// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in {Chromium's} LICENSE file.

'use strict';

/**
 * @fileoverview This contains an implementation of the EventTarget interface
 * as defined by DOM Level 2 Events.
 */


/**
 * Creates a new EventTarget. This class implements the DOM level 2
 * EventTarget interface and can be used wherever those are used.
 * @constructor
 * @implements {EventTarget}
 *
 * BSD-licensed, taken from Chromium: src/ui/webui/resources/js/cr/event_target.js
 */
export class BTSEventTarget {
	listeners_: any;

	/**
	 * Adds an event listener to the target.
	 * @param {string} type The name of the event.
	 * @param {EventListenerType} handler The handler for the event. This is
	 *     called when the event is dispatched.
	 */
	addEventListener(type: string, handler: Function): void {
		if (!this.listeners_)
			this.listeners_ = Object.create(null);
		if (!(type in this.listeners_)) {
			this.listeners_[type] = [handler];
		} else {
			let handlers = this.listeners_[type];
			if (handlers.indexOf(handler) < 0)
				handlers.push(handler);
		}
	}

	/**
	 * Removes an event listener from the target.
	 * @param {string} type The name of the event.
	 * @param {EventListenerType} handler The handler for the event.
	 */
	removeEventListener(type: string, handler: Function): void {
		if (!this.listeners_)
			return;
		if (type in this.listeners_) {
			let handlers = this.listeners_[type];
			let index = handlers.indexOf(handler);
			if (index >= 0) {
				// Clean up if this was the last listener.
				if (handlers.length === 1)
					delete this.listeners_[type];
				else
					handlers.splice(index, 1);
			}
		}
	}

	/**
	 * Dispatches an event and calls all the listeners that are listening to
	 * the type of the event.
	 * @param {!Event} event The event to dispatch.
	 * @return {boolean} Whether the default action was prevented. If someone
	 *     calls preventDefault on the event object then this returns false.
	 */
	dispatchEvent(event: any): boolean {
		if (!this.listeners_)
			return true;

		// Since we are using DOM Event objects we need to override some of the
		// properties and methods so that we can emulate this correctly.
		let self = this;
		event.__defineGetter__('target', function(): any {
			return self;
		});

		let type = event.type;
		let prevented = 0;
		if (type in this.listeners_) {
			// Clone to prevent removal during dispatch
			let handlers = this.listeners_[type].concat();
			for (let i = 0, handler: any; (handler = handlers[i]); i++) {
				if (handler.handleEvent)
					prevented |= <any>(handler.handleEvent.call(handler, event) === false);
				else
					prevented |= <any>(handler.call(this, event) === false);
			}
		}

		return !prevented && !event.defaultPrevented;
	}
}