/*!
 * visibly - v0.7 Page Visibility API Polyfill
 * http://github.com/addyosmani
 * Copyright (c) 2011-2014 Addy Osmani
 * Dual licensed under the MIT and GPL licenses.
 *
 * Methods supported:
 * visibly.onVisible(callback)
 * visibly.onHidden(callback)
 * visibly.hidden()
 * visibly.visibilityState()
 * visibly.visibilitychange(callback(state));
 */
 
// Packaged for AMD by [email protected]
define('core/engagement/vendor/visibly',[], function () {
 
    var exports = {
        q: document,
        p: undefined,
        prefixes: ['webkit', 'ms','o','moz','khtml'],
        props: ['VisibilityState', 'visibilitychange', 'Hidden'],
        m: ['focus', 'blur'],
        visibleCallbacks: [],
        hiddenCallbacks: [],
        genericCallbacks:[],
        _callbacks: [],
        cachedPrefix:"",
        fn:null,
 
        onVisible: function (_callback) {
            if(typeof _callback == 'function' ){
                this.visibleCallbacks.push(_callback);
            }
        },
        onHidden: function (_callback) {
            if(typeof _callback == 'function' ){
                this.hiddenCallbacks.push(_callback);
            }
        },
        getPrefix:function(){
            if(!this.cachedPrefix){
                for(var l=0;b=this.prefixes[l++];){
                    if(b + this.props[2] in this.q){
                        this.cachedPrefix =  b;
                        return this.cachedPrefix;
                    }
                }
             }
        },
 
        visibilityState:function(){
            return  this._getProp(0);
        },
        hidden:function(){
            return this._getProp(2);
        },
        visibilitychange:function(fn){
            if(typeof fn == 'function' ){
                this.genericCallbacks.push(fn);
            }
 
            var n =  this.genericCallbacks.length;
            if(n){
                if(this.cachedPrefix){
                     while(n--){
                        this.genericCallbacks[n].call(this, this.visibilityState());
                    }
                }else{
                    while(n--){
                        this.genericCallbacks[n].call(this, arguments[0]);
                    }
                }
            }
 
        },
        isSupported: function (index) {
            return ((this._getPropName(2)) in this.q);
        },
        _getPropName:function(index) {
            return (this.cachedPrefix == "" ? this.props[index].substring(0, 1).toLowerCase() + this.props[index].substring(1) : this.cachedPrefix + this.props[index]);
        },
        _getProp:function(index){
            return this.q[this._getPropName(index)];
        },
        _execute: function (index) {
            if (index) {
                this._callbacks = (index == 1) ? this.visibleCallbacks : this.hiddenCallbacks;
                var n =  this._callbacks.length;
                while(n--){
                    this._callbacks[n]();
                }
            }
        },
        _visible: function () {
            exports._execute(1);
            exports.visibilitychange.call(exports, 'visible');
        },
        _hidden: function () {
            exports._execute(2);
            exports.visibilitychange.call(exports, 'hidden');
        },
        _nativeSwitch: function () {
            this[this._getProp(2) ? '_hidden' : '_visible']();
        },
        _listen: function () {
            try { /*if no native page visibility support found..*/
                if (!(this.isSupported())) {
                    if (this.q.addEventListener) { /*for browsers without focusin/out support eg. firefox, opera use focus/blur*/
                        window.addEventListener(this.m[0], this._visible, 1);
                        window.addEventListener(this.m[1], this._hidden, 1);
                    } else { /*IE <10s most reliable focus events are onfocusin/onfocusout*/
                        if (this.q.attachEvent) {
                            this.q.attachEvent('onfocusin', this._visible);
                            this.q.attachEvent('onfocusout', this._hidden);
                        }
                    }
                } else { /*switch support based on prefix detected earlier*/
                    this.q.addEventListener(this._getPropName(1), function () {
                        exports._nativeSwitch.apply(exports, arguments);
                    }, 1);
                }
            } catch (e) {}
        },
        init: function () {
            this.getPrefix();
            this._listen();
        }
    };
 
    exports.init();
    return exports;
});
 
// https://c.disquscdn.com/next/next-core/core/engagement/vendor/visibly.js