//  บรรทัด <script type="text/javascript"> นี้สำคัญนะ ถ้าไปใช้ <script type="javascript"> คือไม่มี text ตัว script ข้างล่างของ page จะอ้างอิง DragHandle ไม่ได้เลยนะ
var DragHandler = {


	// private property.
	_oElem : null,


	// public method. Attach drag handler to an element.
	attach : function(oElem) {
		oElem.onmousedown = DragHandler._dragBegin;

		// callbacks
		oElem.dragBegin = new Function();
		oElem.drag = new Function();
		oElem.dragEnd = new Function();

		return oElem;
	},


	// private method. Begin drag process.
	_dragBegin : function(e) {
		var oElem = DragHandler._oElem = this;
		
		if (isNaN(parseInt(oElem.style.left))) {oElem.style.left =  '0px'; }
		if (isNaN(parseInt(oElem.style.top))) {  oElem.style.top ='0px';  }

		
		var x = parseInt(oElem.style.left);
		var y = parseInt(oElem.style.top);

		e = e ? e : window.event;
		oElem.mouseX = e.clientX;  // ค่า e.clientX คือตำแหน่งที่เมาส์คลิ๊ก X
		oElem.mouseY = e.clientY; // ค่า e.clientX คือตำแหน่งที่เมาส์คลิ๊ก Y
		
		oElem.dragBegin(oElem, x, y);

		document.onmousemove = DragHandler._drag;
		document.onmouseup = DragHandler._dragEnd;
		return false;
	},


	// private method. Drag (move) element.
	_drag : function(e) {
		var oElem = DragHandler._oElem;
			
		var x = parseInt(oElem.style.left);
		var y = parseInt(oElem.style.top);


		e = e ? e : window.event;
	 	
		oElem.style.left = x + (e.clientX - oElem.mouseX) + 'px';
		oElem.style.top = y + (e.clientY - oElem.mouseY) + 'px';

		oElem.mouseX = e.clientX;
		oElem.mouseY = e.clientY;
		
		oElem.drag(oElem, x, y);

		return false;
	},


	// private method. Stop drag process.
	_dragEnd : function() {
		var oElem = DragHandler._oElem;

		var x = parseInt(oElem.style.left);
		var y = parseInt(oElem.style.top);

		oElem.dragEnd(oElem, x, y);

		document.onmousemove = null;
		document.onmouseup = null;
		DragHandler._oElem = null;

	}

};