// addEvent && removeEvent from quirksmode.org
function addEvent(obj,evt,fn) {
    if (obj.addEventListener)
        obj.addEventListener(evt,fn,false);
    else if (obj.attachEvent)
        obj.attachEvent('on'+evt,fn);
}

function removeEvent(obj,evt,fn) {
    if (obj.removeEventListener)
        obj.removeEventListener(evt,fn,false);
    else if (obj.detachEvent)
        obj.detachEvent('on'+evt,fn);
}

function addClass(el, klass)
{
    if(!hasClass(el, klass))
    {
        var classes = el.className.split(' ');
        classes.push(klass);
        el.className = classes.join(' ');
    }
}
function removeClass(el, klass)
{
    var classes = el.className.split(' ');
    for(var i = 0; i < classes.length; i++)
    {
        if(classes == klass)
        {
            classes.splice(i, 1);
            break;
        }
    }
    el.className = classes.join(' ');
}
function hasClass(el, klass)
{
    var classes = el.className.split(' ');
    for(var i = 0; i < classes.length; i++)
    {
        if(classes == klass)
        {
            return true;
        }
    }
    return false;
}


function Draggable(el, events, handler)
{
    this.element = el;
    this.handler = handler || el;
    addClass(this.handler, 'draggable');
    this.handler.dragger = this;
    this.handler.onmousedown = this.dragStart;
    this.events = events;
    this.start, this.mouseStart, this.current;
}
Draggable.current;
Draggable.prototype = {
    'getMousePos': function(e)
    {
        if(!e) e = window.event;
        var x = e.clientX;
        var y = e.clientY;
        return {'x': x, 'y': y};
    },
    'getOffsets': function(el)
    {
        el = el || this.element;
        return {'x': el.offsetLeft, 'y': el.offsetTop};
    },
    'getAbsOffsets': function(el)
    {
        el = el || this.element;
        var offs = this.getOffsets(el);
        if(el.offsetParent)
        {
            var par = this.getAbsOffsets(el.offsetParent);
            offs.x += par.x;
            offs.y += par.y;
        }
        return offs;
    },
    'setPosition': function(x, y)
    {
        this.current = {'x': x, 'y': y};
        this.element.style.left = x + this.start.x + 'px';
        this.element.style.top = y + this.start.y + 'px';
    },
    'setStart': function(x, y)
    {
        x = (x)? x : 0;
        y = (y)? y : 0;
        this.start = {'x': x, 'y': y};
    },
    'dragStart': function(e)
    {
        var drg = this.dragger;
        
        drg.trigger('preDragStart');
        
        Draggable.current = drg;
        drg.mouseStart = drg.getMousePos(e);
        var abs = drg.getAbsOffsets();
        drg.setStart(abs.x - drg.mouseStart.x, abs.y - drg.mouseStart.y);
        document.body.appendChild(drg.element.parentNode.removeChild(drg.element));
        drg.setPosition(drg.mouseStart.x, drg.mouseStart.y);
        drg.element.style.position = 'absolute';
        
        addEvent(document.body, 'mousemove', drg.dragMove);
        addEvent(document.body, 'mouseup', drg.dragEnd);
        
        drg.trigger('postDragStart');
        return false;
    },
    'dragMove': function(e)
    {
        var drg = Draggable.current;
        drg.trigger('preDragMove');
        
        var curMouse = drg.getMousePos(e);
        drg.setPosition(curMouse.x, curMouse.y)
        
        drg.trigger('postDragMove');
    },
    'dragEnd': function(e)
    {
        var drg = Draggable.current;
        drg.trigger('preDragEnd');
        
        removeEvent(document.body, 'mousemove', drg.dragMove);
        removeEvent(document.body, 'mouseup', drg.dragEnd);
        
        Draggable.current = null;
        
        drg.trigger('postDragEnd');
    },
    'trigger': function(event)
    {
        if(this.events[event])
        {
            if(this.events[event].constructor == Array)
            {
                for(var i = 0; i < this.events[event].length; i++)
                {
                    this.events[event].call(this);
                }
            }
            else
            {
                this.events[event].call(this);
            }
        }
    }
};