var Spry;
if (!Spry) 
    Spry = {};
if (!Spry.Utils) 
    Spry.Utils = {};

Spry.Utils.ImageLoader = function(){
    this.queue = [];
    this.timerID = 0;
    this.currentEntry = null;
};

Spry.Utils.ImageLoader.prototype.start = function(){
    if (!this.timerID) {
        var self = this;
        this.timerID = setTimeout(function(){
            self.timerID = 0;
            self.processQueue();
        }, 0);
    }
};

Spry.Utils.ImageLoader.prototype.stop = function(){
    if (this.currentEntry) {
        var entry = this.currentEntry;
        entry.loader.onload = null;
        entry.loader.src = "";
        entry.loader = null;
        this.currentEntry = null;
        this.queue.unshift(entry);
    }
    
    if (this.timerID) 
        clearTimeout(this.timerID);
    
    this.timerID = 0;
};

Spry.Utils.ImageLoader.prototype.clearQueue = function(){
    this.stop();
    this.queue.length = 0;
};

Spry.Utils.ImageLoader.prototype.load = function(url, callback, priority){
    if (url) {
        if (typeof priority == "undefined") 
            priority = 0;
        this.queue.push({
            url: url,
            callback: callback,
            priority: priority
        });
        
        // Entries in the queue are sorted by priority. Those entries
        // with a higher priority are at the start of the queue, while
        // those with lower priority are pushed towards the end. If an
        // entry has the same priority as something already in the queue,
        // it gets processed in the order they were received.
        
        this.queue.sort(function(a, b){
            return (a.priority > b.priority) ? -1 : ((a.priority < b.priority) ? 1 : 0);
        });
        this.start();
    }
};

Spry.Utils.ImageLoader.prototype.processQueue = function(){
    if (this.queue.length < 1) 
        return;
    
    var entry = this.currentEntry = this.queue.shift();
    var loader = entry.loader = new Image;
    var self = this;
    
    loader.onload = function(){
        self.currentEntry = null;
        if (entry.callback) 
            entry.callback(entry.url, entry.loader);
        if (self.queue.length > 0) 
            self.start();
    };
    
    loader.onerror = function(){
        // If a load fails, keep the queue going!
        self.currentEntry = null;
        if (self.queue.length > 0) 
            self.start();
    };
    
    this.currentLoader = loader;
    loader.src = entry.url;
};