function hookEvent(element, eventName, callback) {
    if (typeof (element) == "string")
        element = document.getElementById(element);
    if (element == null)
        return;
    if (element.addEventListener)
        element.addEventListener(eventName, callback, false);
    else if (element.attachEvent)
        element.attachEvent("on" + eventName, callback);
}

function unhookEvent(element, eventName, callback) {
    if (typeof (element) == "string")
        element = document.getElementById(element);
    if (element == null)
        return;
    if (element.removeEventListener)
        element.removeEventListener(eventName, callback, false);
    else if (element.detachEvent)
        element.detachEvent("on" + eventName, callback);
}

function cancelEvent(e) {
    e = e ? e : window.event;
    if (e.stopPropagation)
        e.stopPropagation();
    if (e.preventDefault)
        e.preventDefault();
    e.cancelBubble = true;
    e.cancel = true;
    e.returnValue = false;
    return false;
}

function Position(x, y) {
    this.X = x;
    this.Y = y;

    this.Add = function (val) {
        var newPos = new Position(this.X, this.Y);
        if (val != null) {
            if (!isNaN(val.X))
                newPos.X += val.X;
            if (!isNaN(val.Y))
                newPos.Y += val.Y
        }
        return newPos;
    }

    this.Subtract = function (val) {
        var newPos = new Position(this.X, this.Y);
        if (val != null) {
            if (!isNaN(val.X))
                newPos.X -= val.X;
            if (!isNaN(val.Y))
                newPos.Y -= val.Y
        }
        return newPos;
    }

    this.Min = function (val) {
        var newPos = new Position(this.X, this.Y)
        if (val == null)
            return newPos;

        if (!isNaN(val.X) && this.X > val.X)
            newPos.X = val.X;
        if (!isNaN(val.Y) && this.Y > val.Y)
            newPos.Y = val.Y;

        return newPos;
    }

    this.Max = function (val) {
        var newPos = new Position(this.X, this.Y)
        if (val == null)
            return newPos;

        if (!isNaN(val.X) && this.X < val.X)
            newPos.X = val.X;
        if (!isNaN(val.Y) && this.Y < val.Y)
            newPos.Y = val.Y;

        return newPos;
    }

    this.Bound = function (lower, upper) {
        var newPos = this.Max(lower);
        return newPos.Min(upper);
    }

    this.Check = function () {
        var newPos = new Position(this.X, this.Y);
        if (isNaN(newPos.X))
            newPos.X = 0;
        if (isNaN(newPos.Y))
            newPos.Y = 0;
        return newPos;
    }

    this.Apply = function (element) {
        if (typeof (element) == "string")
            element = document.getElementById(element);
        if (element == null)
            return;
        if (!isNaN(this.X))
            element.style.left = this.X + 'px';
        if (!isNaN(this.Y))
            element.style.top = this.Y + 'px';
    }
}

function absoluteCursorPostion(eventObj) {
    eventObj = eventObj ? eventObj : window.event;

    if (isNaN(window.scrollX))
        return new Position(eventObj.clientX + document.documentElement.scrollLeft
                         + document.body.scrollLeft,
                         eventObj.clientY + document.documentElement.scrollTop
                         + document.body.scrollTop);
    else
        return new Position(eventObj.clientX + window.scrollX,
                         eventObj.clientY + window.scrollY);
}

function dragObject(element, attachElement, lowerBound, upperBound,
                     startCallback, moveCallback, endCallback, attachLater) {
    if (typeof (element) == "string")
        element = document.getElementById(element);

    if (element == null)
        return;

    if (lowerBound != null && upperBound != null) {
        var temp = lowerBound.Min(upperBound);
        upperBound = lowerBound.Max(upperBound);
        lowerBound = temp;
    }

    var cursorStartPos = null;
    var elementStartPos = null;
    var dragging = false;
    var listening = false;
    var disposed = false;

    function dragStart(eventObj) {
        if (dragging || !listening || disposed)
            return;

        dragging = true;

        if (startCallback != null)
            startCallback(eventObj, element);

        cursorStartPos = absoluteCursorPostion(eventObj);

        elementStartPos = new Position(parseInt(element.style.left),
                                    parseInt(element.style.top));

        elementStartPos = elementStartPos.Check();

        hookEvent(document, "mousemove", dragGo);
        hookEvent(document, "mouseup", dragStopHook);

        return cancelEvent(eventObj);
    }

    function dragGo(eventObj) {
        if (!dragging || disposed)
            return;

        var newPos = absoluteCursorPostion(eventObj);
        newPos = newPos.Add(elementStartPos).Subtract(cursorStartPos);
        newPos = newPos.Bound(lowerBound, upperBound)
        newPos.Apply(element);
        if (moveCallback != null)
            moveCallback(newPos, element);

        return cancelEvent(eventObj);
    }

    function dragStopHook(eventObj) {
        dragStop();
        return cancelEvent(eventObj);
    }

    function dragStop() {
        if (!dragging || disposed)
            return;

        unhookEvent(document, "mousemove", dragGo);
        unhookEvent(document, "mouseup", dragStopHook);
        cursorStartPos = null;
        elementStartPos = null;
        if (endCallback != null)
            endCallback(element);
        dragging = false;
    }

    this.Dispose = function () {
        if (disposed)
            return;

        this.StopListening(true);
        element = null;
        attachElement = null
        lowerBound = null;
        upperBound = null;
        startCallback = null;
        moveCallback = null
        endCallback = null;
        disposed = true;
    }

    this.StartListening = function () {
        if (listening || disposed)
            return;

        listening = true;
        hookEvent(attachElement, "mousedown", dragStart);
    }

    this.StopListening = function (stopCurrentDragging) {
        if (!listening || disposed)
            return;

        unhookEvent(attachElement, "mousedown", dragStart);
        listening = false;

        if (stopCurrentDragging && dragging)
            dragStop();
    }

    this.IsDragging = function () { return dragging; }
    this.IsListening = function () { return listening; }
    this.IsDisposed = function () { return disposed; }

    if (typeof (attachElement) == "string")
        attachElement = document.getElementById(attachElement);
    if (attachElement == null)
        attachElement = element;

    if (!attachLater)
        this.StartListening();
}