/*
File: flexi-background.js

Author:
Michael Bester <http://kimili.com>

About: Version
2.0

Description:
Javascript to set up full-screen flexible backgrounds in all widely used browsers.

License:
Copyright 2010, Michael Bester.
Released under the MIT license <http://opensource.org/licenses/mit-license.php>
*/

(function(){

/**
CONFIGURATION:
Define the size of our background image
*/
var bgImageSize = {
width : 960,
height : 600
};

/* END CONFIGURATION */

/**
Detect support for CSS background-size. No need for any more javascript if background-size is supported.
Property detection adapted from the most excellent Modernizr <http://modernizr.com>
*/
if ((function(){
var el = document.createElement('div'),
bs = 'backgroundSize',
ubs = bs.charAt(0).toUpperCase() + bs.substr(1),
props = [bs, 'Webkit' + ubs, 'Moz' + ubs, 'O' + ubs];

for ( var i in props ) {
if ( el.style[props[i]] !== undefined ) {
return true;
}
}
return false;
}())) {
return;
};

/**
We also want to leave IE6 and below out in the cold with this
*/
if ( false /*@cc_on || @_jscript_version < 5.7 @*/ ) {
return;
}

/**
If we've gotten here, we don't have background-size support,
so we'll have to mimic it with Javascript.
Let's set up some variables
*/
var elBody,
imageID = 'expando',
tallClass = 'tall',
wideClass = 'wide',
elBgImage, elWrapper, img, url, imgAR,

/**
Since we're not relying on a library, we'll need some utility functions
First, basic cross browser event adders
*/
addEvent = function(el, evnt, func) {
if (el.addEventListener) {
el.addEventListener(evnt, func, false);
} else if (el.attachEvent) {
return el.attachEvent("on" + evnt, func);
} else {
el['on' + evnt] = func;
}
},

domLoaded = function(callback) {
/* Internet Explorer */
/*@cc_on
@if (@_win32 || @_win64)
document.write('<script id="ieScriptLoad" defer src="//:"><\/script>');
document.getElementById('ieScriptLoad').onreadystatechange = function() {
if (this.readyState == 'complete') {
callback();
}
};
@end @*/
/* Mozilla, Chrome, Opera */
if (document.addEventListener) {
document.addEventListener('DOMContentLoaded', callback, false);
}
/* Safari, iCab, Konqueror */
if (/KHTML|WebKit|iCab/i.test(navigator.userAgent)) {
var DOMLoadTimer = setInterval(function () {
if (/loaded|complete/i.test(document.readyState)) {
callback();
clearInterval(DOMLoadTimer);
}
}, 10);
}
},

/**
Next, a way to properly get the computed style of an element
Courtesy of Robert Nyman - http://robertnyman.com/2006/04/24/get-the-rendered-style-of-an-element/
*/
getStyle = function(el, css){
var strValue = "";
if (document.defaultView && document.defaultView.getComputedStyle){
strValue = document.defaultView.getComputedStyle(el, "").getPropertyValue(css);
}
else if (el.currentStyle){
css = css.replace(/\-(\w)/g, function (strMatch, p1){
return p1.toUpperCase();
});
strValue = el.currentStyle[css];
}
return strValue;
},

/**
Finally, some element class manipulation functions
*/
classRegex = function(cls) {
return new RegExp('(\\s|^)'+cls+'(\\s|$)');
},

hasClass = function(el, cls) {
return el.className.match(classRegex(cls));
},

addClass = function(el, cls) {
if ( ! hasClass(el, cls)) {
el.className += ' ' + cls;
}
},

removeClass = function(el, cls) {
if (hasClass(el, cls)) {
el.className = el.className.replace(classRegex(cls), '');
}
},

/*
Now we can move on with the core functionality of Flexibackground
*/
initialize = function() {

// No need for any of this if the screen isn't bigger than the background image
if (screen.availWidth <= bgImageSize.width && screen.availHeight <= bgImageSize.height) {
return;
}

// Grab elements we'll reference throughout
elBody = document.getElementsByTagName('body')[0];

// Parse out the URL of the background image and drop out if we don't have one
url = getStyle(elBody, 'backgroundImage').replace(/^url\(("|')?|("|')?\);?$/g, '') || false;
if (!url || url === "none" || url === "") {
return;
}

// Get the aspect ratio of the image
imgAR = bgImageSize.width / bgImageSize.height;

// Create a new image element
elBgImage = document.createElement('img');
elBgImage.src = url;
elBgImage.id = imageID;

// Create a wrapper and append the image to it.
// The wrapper ensures we don't get scrollbars.
elWrapper = document.createElement('div');
elWrapper.style.overflow = 'hidden';
elWrapper.style.width = '100%';
elWrapper.style.height = '100%';
elWrapper.style.zIndex = '-1';

elWrapper.appendChild(elBgImage);
elBody.appendChild(elWrapper);

// Fix the wrapper into position
elWrapper.style.position = 'fixed';
elWrapper.style.top = 0;
elWrapper.style.left = 0;

// Set up a resize listener to add/remove classes from the body
addEvent(window, 'resize', resizeAction);

// Set it up by triggering a resize
resizeAction();

},

/**
Set up the action that happens on resize
*/
resizeAction = function() {
var win = {
height : window.innerHeight || document.documentElement.clientHeight,
width : window.innerWidth || document.documentElement.clientWidth
},

// The current aspect ratio of the window
winAR = win.width / win.height;

// Determine if we need to show the image and whether it needs to stretch tall or wide
if (win.width < bgImageSize.width && win.height < bgImageSize.height) {
removeClass(elBody, wideClass);
removeClass(elBody, tallClass);
} else if (winAR < imgAR) {
removeClass(elBody, wideClass);
addClass(elBody, tallClass);
// Center the image
elBgImage.style.left = Math.min(((win.width - bgImageSize.width) / 2), 0);
} else if (winAR > imgAR) {
addClass(elBody, wideClass);
removeClass(elBody, tallClass);
elBgImage.style.left = 0;
}
};

// When the document is ready, run this thing.
domLoaded(initialize);

})();