//转自：http://www.cnblogs.com/cloudgamer/
//拖放程序
var Drag = Class.create();
Drag.prototype = {
  //拖放对象
  initialize: function(drag, options) {
	this.Drag = $$(drag);//拖放对象
	this._x = this._y = 0;//记录鼠标相对拖放对象的位置
	this._marginLeft = this._marginTop = 0;//记录margin
	//事件对象(用于绑定移除事件)
	this._fM = BindAsEventListener(this, this.Move);
	this._fS = Bind(this, this.Stop);
	
	this.SetOptions(options);
	
	this.Limit = !!this.options.Limit;
	this.mxLeft = parseInt(this.options.mxLeft);
	this.mxRight = parseInt(this.options.mxRight);
	this.mxTop = parseInt(this.options.mxTop);
	this.mxBottom = parseInt(this.options.mxBottom);
	
	this.LockX = !!this.options.LockX;
	this.LockY = !!this.options.LockY;
	this.Lock = !!this.options.Lock;
	
	this.onStart = this.options.onStart;
	this.onMove = this.options.onMove;
	this.onStop = this.options.onStop;
	
	this._Handle = $$(this.options.Handle) || this.Drag;
	this._mxContainer = $$(this.options.mxContainer) || null;
	
	this.Drag.style.position = "absolute";
	//透明
	if(isIE && !!this.options.Transparent){
		//填充拖放对象
		with(this._Handle.appendChild(document.createElement("div")).style){
			width = height = "100%"; backgroundColor = "#fff"; filter = "alpha(opacity:0)"; fontSize = 0;
		}
	}
	//修正范围
	this.Repair();
	addEventHandler(this._Handle, "mousedown", BindAsEventListener(this, this.Start));
  },
  //设置默认属性
  SetOptions: function(options) {
	this.options = {//默认值
		Handle:			"",//设置触发对象（不设置则使用拖放对象）
		Limit:			false,//是否设置范围限制(为true时下面参数有用,可以是负数)
		mxLeft:			0,//左边限制
		mxRight:		9999,//右边限制
		mxTop:			0,//上边限制
		mxBottom:		9999,//下边限制
		mxContainer:	"",//指定限制在容器内
		LockX:			false,//是否锁定水平方向拖放
		LockY:			false,//是否锁定垂直方向拖放
		Lock:			false,//是否锁定
		Transparent:	false,//是否透明
		onStart:		function(){},//开始移动时执行
		onMove:			function(){},//移动时执行
		onStop:			function(){}//结束移动时执行
	};
	Extend(this.options, options || {});
  },
  //准备拖动
  Start: function(oEvent) {
	if(this.Lock){ return; }
	this.Repair();
	//记录鼠标相对拖放对象的位置
	this._x = oEvent.clientX - this.Drag.offsetLeft;
	this._y = oEvent.clientY - this.Drag.offsetTop;
	//记录margin
	this._marginLeft = parseInt(CurrentStyle(this.Drag).marginLeft) || 0;
	this._marginTop = parseInt(CurrentStyle(this.Drag).marginTop) || 0;
	//mousemove时移动 mouseup时停止
	addEventHandler(document, "mousemove", this._fM);
	addEventHandler(document, "mouseup", this._fS);
	if(isIE){
		//焦点丢失
		addEventHandler(this._Handle, "losecapture", this._fS);
		//设置鼠标捕获
		this._Handle.setCapture();
	}else{
		//焦点丢失
		addEventHandler(window, "blur", this._fS);
		//阻止默认动作
		oEvent.preventDefault();
	};
	//附加程序
	this.onStart();
  },
  //修正范围
  Repair: function() {
	if(this.Limit){
		//修正错误范围参数
		this.mxRight = Math.max(this.mxRight, this.mxLeft + this.Drag.offsetWidth);
		this.mxBottom = Math.max(this.mxBottom, this.mxTop + this.Drag.offsetHeight);
		//如果有容器必须设置position为relative或absolute来相对或绝对定位，并在获取offset之前设置
		!this._mxContainer || CurrentStyle(this._mxContainer).position == "relative" || CurrentStyle(this._mxContainer).position == "absolute" || (this._mxContainer.style.position = "relative");
	}
  },
  //拖动
  Move: function(oEvent) {
	//判断是否锁定
	if(this.Lock){ this.Stop(); return; };
	//清除选择
	window.getSelection ? window.getSelection().removeAllRanges() : document.selection.empty();
	//设置移动参数
	var iLeft = oEvent.clientX - this._x, iTop = oEvent.clientY - this._y;
	//设置范围限制
	if(this.Limit){
		//设置范围参数
		var mxLeft = this.mxLeft, mxRight = this.mxRight, mxTop = this.mxTop, mxBottom = this.mxBottom;
		//如果设置了容器，再修正范围参数
		if(!!this._mxContainer){
			mxLeft = Math.max(mxLeft, 0);
			mxTop = Math.max(mxTop, 0);
			mxRight = Math.min(mxRight, this._mxContainer.clientWidth);
			mxBottom = Math.min(mxBottom, this._mxContainer.clientHeight);
		};
		//修正移动参数
		iLeft = Math.max(Math.min(iLeft, mxRight - this.Drag.offsetWidth), mxLeft);
		iTop = Math.max(Math.min(iTop, mxBottom - this.Drag.offsetHeight), mxTop);
	}
	//设置位置，并修正margin
	if(!this.LockX){ this.Drag.style.left = iLeft - this._marginLeft + "px"; }
	if(!this.LockY){ this.Drag.style.top = iTop - this._marginTop + "px"; }
	//附加程序
	this.onMove();
  },
  //停止拖动
  Stop: function() {
	//移除事件
	removeEventHandler(document, "mousemove", this._fM);
	removeEventHandler(document, "mouseup", this._fS);
	if(isIE){
		removeEventHandler(this._Handle, "losecapture", this._fS);
		this._Handle.releaseCapture();
	}else{
		removeEventHandler(window, "blur", this._fS);
	};
	//附加程序
	this.onStop();
  }
};