// SpryImageLoader.js - version 0.1 - Spry Pre-Release 1.6
//
// Copyright (c) 2007. Adobe Systems Incorporated.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//   * Redistributions of source code must retain the above copyright notice,
//     this list of conditions and the following disclaimer.
//   * Redistributions in binary form must reproduce the above copyright notice,
//     this list of conditions and the following disclaimer in the documentation
//     and/or other materials provided with the distribution.
//   * Neither the name of Adobe Systems Incorporated nor the names of its
//     contributors may be used to endorse or promote products derived from this
//     software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

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 });

                // 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 > b) ? -1 : 1; });
                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;
};