/*
* Web Background Change 0.1
* Copyright (c) 2011 Zhaojiping http://lastidea.net/
* Date: 2011-12-22
* Web Background Change 是一个可以动态平滑改变网页背景(背景图片预加载)的插件
*/ 
(function($) { 
	$.extend({	
		lastidea_net_bkg : function(options){
			var defaults = {    
				images_sm: "",   
				images_lg: "",
				timer: 9000
			};  
			var opts = $.extend(defaults, options);    
			
			var _appName = navigator.appName.toLowerCase();
			var _i = 0;
			var _imgStr = "";
			var _imgArr = "";
			
			var _w = $(window).width();
			var _h = $(window).height();
			
			$("body").append("<div id='blackout' style='width:"+ _w +"px; height:" + _h + "px; display:block;z-index:-9999'></div>");
			
			cyc();
			
			function cyc(){
				if( _w > 1440 || _h > 900)
					_imgArr = opts.images_lg.slice(0);
				else
					_imgArr = opts.images_sm.slice(0);

				if( _imgStr.indexOf( _imgArr[_i] ) != -1 )
					 setBkg(_imgArr[_i]);
				else{
					getImage(_imgArr[_i]);
				}
		
				if( _i++ >= _imgArr.length ) _i = 0;
				
				setTimeout(function(){cyc();}, opts.timer);
			}
			
			function setBkg(imgsrc){
				if (_appName.indexOf("netscape") == -1){
					$("#blackout").fadeTo(400,0, function(){
						$("#blackout").css("background", "url("+ imgsrc +")");
						$("#blackout").fadeTo(800,1);
					});
				}else{
					//firefox
					$("#blackout").css("background", "url("+ imgsrc +")").show();
				}
			}
			
			function getImage(imgsrc){
				var img = new Image();
				img.src = imgsrc;
				if (_appName.indexOf("netscape") == -1){
					img.onreadystatechange = function () {
						if (img.readyState == "complete"){
							_imgStr += imgsrc;
							setBkg(imgsrc);
						}
					};
				} else {
					img.onload = function () {
						if (img.complete == true){
							_imgStr += imgsrc;
						   setBkg(imgsrc);
						}
					}
				}
			}
		}
	});

})(jQuery);