/*
 * jQuery Backstretch
 * Version 1.1
 * http://srobbin.com/jquery-plugins/jquery-backstretch/
 *
 * Add a dynamically-resized background image to the page
 *
 * Copyright (c) 2010 Scott Robbin (srobbin.com)
 * Dual licensed under the MIT and GPL licenses.
*/

(function($) {
	$.backstretch = function(src, options, callback) {
		var settings = {
			centeredX: true,         // Should we center the image on the X axis?
			centeredY: true,         // Should we center the image on the Y axis?
			speed: 500               // fadeIn speed for background after image loads (e.g. "fast" or 500)
		},
		rootElement = ("onorientationchange" in window) ? $(document) : $(window), // hack to acccount for iOS position:fixed shortcomings
		imgRatio, bgImg, bgWidth, bgHeight, bgOffset,
		bgCSS = {left: 0, top: 0};

		// Extend the settings with those the user has provided
		if(options && typeof options == "object") $.extend(settings, options);

		// Initialize
		$(document).ready(_init);

		// For chaining
		return this;

		function _init() {
			// Prepend image, wrapped in a DIV, with some positioning and zIndex voodoo
			if(src) {
				var container = $("<div />").attr("id", "backstretch")
											.css({left: 0, top: 0, position: "fixed", overflow: "hidden", zindex: -10}),
					img = $("<img />").css({position: "relative", display: "none"})
									.bind("load", function(e) {
										var self = $(this);
										imgRatio = $(e.target).width() / $(e.target).height();
										_adjustBG(function() {
											self.fadeIn(settings.speed, function(){
												if(typeof callback == "function") callback();
											});
										});
									})
									.appendTo(container);

				$("body").prepend(container);
				img.attr("src", src); // Hack for IE img onload event

				// Adjust the background size when the window is resized or orientation has changed (iOS)
				$(window).resize(_adjustBG);
			}
		}

		function _adjustBG(fn) {
			bgWidth = rootElement.width();
			bgHeight = bgWidth / imgRatio;

			// Make adjustments based on image ratio
			// Note: Offset code provided by Peter Baker (http://ptrbkr.com/). Thanks, Peter!
			if(bgHeight >= rootElement.height()) {
				bgOffset = (bgHeight - rootElement.height()) /2;
				if(settings.centeredY) $.extend(bgCSS, {top: "-" + bgOffset + "px"});
			} else {
				bgHeight = rootElement.height();
				bgWidth = bgHeight * imgRatio;
				bgOffset = (bgWidth - rootElement.width()) / 2;
				if(settings.centeredX) $.extend(bgCSS, {left: "-" + bgOffset + "px"});
			}

			$("#backstretch img").width( bgWidth ).height( bgHeight ).css(bgCSS);

			// Executed the passed in function, if necessary
			if (typeof fn == "function") fn();
		}
	};
})(jQuery);