/**
 * Simple Observer pattern mixin (custom event dispatching & listening)
 * Doesn't requires any 3rd-party JS libs. It's pure JS
 *
 * Usage:
 *
 *     var MyObject = {...}; // your custom object
 *     Observer.apply(MyObject); // you also can apply Observer to a prototype
 *     MyObject.on('inited', function() { console.log("I'm alive!"); });
 *     MyObject.trigger('inited');
 *
 * Author: kottenator
 * License: MIT
 * Date: 2014-04-11
 */
var Observer = {
    apply: function(obj) {
        obj.events = {};
        obj.on = this.on;
        obj.off = this.off;
        obj.trigger = this.trigger;
    },

    /**
     * Add event listener
     * 
     * {String} events - e.g. 'my-event-1 my-event-2'
     * {Function} fn - event listener
     */
    on: function(events, fn) {
        events = events.replace(/^\s+|\s+$/g, '').split(/\s+/);

        for (var i = 0; i < events.length; i++) {
            var event = events[i];

            if (!this.events[event])
                this.events[event] = {};

            this.events[event].push(fn);
        }
    },

    /**
     * Remove event listener
     * 
     * {String} events - e.g. 'my-event-1 my-event-2'
     * {Function} fn - event listener. If not specified (or null, or undefined, 
     *                 or or any bool-casted to 'false' value) - all listeners will be removed.
     */
    off: function(events, fn) {
        events = events.replace(/^\s+|\s+$/g, '').split(/\s+/);

        for (var i = 0; i < events.length; i++) {
            var event = events[i];

            if (!this.events[event])
                continue;

            var fns = this.events[event],
                nfns = [];

            if (fn) {
                for (var j = 0; j < fns.length; j++) {
                    if (fns[j] !== fn)
                        nfns.push(fns[j]);
                }
            }

            this.events[event] = nfns;
        }
    },

    /**
     * Dispatch an event (call all its listeners)
     *
     * All listeners will be called with 2 arguments: fn({String} eventName, {any type} args)
     *
     * {String} events - e.g. 'my-event-1 my-event-2'
     * {any type} args - custom event arguments (you may specify multiple args as Array or Object)
     */
    trigger: function(events, args) {
        events = events.replace(/^\s+|\s+$/g, '').split(/\s+/);

        for (var i = 0; i < events.length; i++) {
            var event = events[i];

            if (!this.events[event])
                continue;

            var fns = this.events[event];

            for (var j = 0; j < fns.length; j++) {
                fns[j].call(this, event, args);
            }
        }
    }
};