var Dom = YAHOO.util.Dom,
oAnim;  // Animation instance


/*
     "beforeshow" event handler for each submenu of the MenuBar
     instance, used to setup certain style properties before
     the menu is animated.
*/

function onSubmenuBeforeShow(p_sType, p_sArgs) {

    var oBody,
        oShadow,
        oUL;


    if (this.parent) {

        /*
             Get a reference to the Menu's shadow element and 
             set its "height" property to "0px" to syncronize 
             it with the height of the Menu instance.
        */

        oShadow = this.element.lastChild;
        oShadow.style.height = "0px";

        
        /*
            Stop the Animation instance if it is currently 
            animating a Menu.
        */ 
    
        if (oAnim && oAnim.isAnimated()) {
        
            oAnim.stop();
            oAnim = null;
        
        }


        /*
            Set the body element's "overflow" property to 
            "hidden" to clip the display of its negatively 
            positioned <ul> element.
        */ 

        oBody = this.body;


        /*
            There is a bug in gecko-based browsers where 
            an element whose "position" property is set to 
            "absolute" and "overflow" property is set to 
            "hidden" will not render at the correct width when
            its offsetParent's "position" property is also 
            set to "absolute."  It is possible to work around 
            this bug by specifying a value for the width 
            property in addition to overflow.
        */

        if (this.parent && 
            !(this.parent instanceof YAHOO.widget.MenuBarItem) && 
            YAHOO.env.ua.gecko) {

            Dom.setStyle(oBody, "width", (oBody.clientWidth + "px"));
        
        }


        Dom.setStyle(oBody, "overflow", "hidden");


        /*
            Set the <ul> element's "marginTop" property 
            to a negative value so that the Menu's height
            collapses.
        */ 

        oUL = oBody.getElementsByTagName("ul")[0];

        Dom.setStyle(oUL, "marginTop", ("-" + oUL.offsetHeight + "px"));
    
    }

}


/*
    "tween" event handler for the Anim instance, used to 
    syncronize the size and position of the Menu instance's 
    shadow and iframe shim (if it exists) with its 
    changing height.
*/

function onTween(p_sType, p_aArgs, p_oShadow) {

    if (this.cfg.getProperty("iframe")) {
    
        this.syncIframe();

    }

    if (p_oShadow) {

        p_oShadow.style.height = this.element.offsetHeight + "px";
    
    }

}


/*
    "complete" event handler for the Anim instance, used to 
    remove style properties that were animated so that the 
    Menu instance can be displayed at its final height.
*/

function onAnimationComplete(p_sType, p_aArgs, p_oShadow) {

    var oBody = this.body,
        oUL = oBody.getElementsByTagName("ul")[0];

    if (p_oShadow) {
    
        p_oShadow.style.height = this.element.offsetHeight + "px";
    
    }

    Dom.setStyle(oUL, "marginTop", "");
    Dom.setStyle(oBody, "overflow", "");
    

    if (this.parent && 
        !(this.parent instanceof YAHOO.widget.MenuBarItem) && 
        YAHOO.env.ua.gecko) {
    
        Dom.setStyle(oBody, "width", "");
    
    }
    
}


/*
     "show" event handler for each submenu of the MenuBar 
     instance - used to kick off the animation of the 
     <ul> element.
*/

function onSubmenuShow(p_sType, p_sArgs) {

    var oElement,
        oShadow,
        oUL;

    if (this.parent) {

        oElement = this.element;
        oShadow = oElement.lastChild;
        oUL = this.body.getElementsByTagName("ul")[0];
    

        /*
             Animate the <ul> element's "marginTop" style 
             property to a value of 0.
        */

        oAnim = new YAHOO.util.Anim(oUL, 
            { marginTop: { to: 0 } },
            .5, YAHOO.util.Easing.easeOut);


        oAnim.onStart.subscribe(function () {

            oShadow.style.height = "100%";
        
        });


        oAnim.animate();


        /*
            Subscribe to the Anim instance's "tween" event for 
            IE to syncronize the size and position of a 
            submenu's shadow and iframe shim (if it exists)  
            with its changing height.
        */

        if (YAHOO.env.ua.ie) {
            
            oShadow.style.height = oElement.offsetHeight + "px";


            /*
                Subscribe to the Anim instance's "tween"
                event, passing a reference Menu's shadow 
                element and making the scope of the event 
                listener the Menu instance.
            */

            oAnim.onTween.subscribe(onTween, oShadow, this);

        }


        /*
            Subscribe to the Anim instance's "complete" event,
            passing a reference Menu's shadow element and making 
            the scope of the event listener the Menu instance.
        */

        oAnim.onComplete.subscribe(onAnimationComplete, oShadow, this);
    
    }

}


/*
     Subscribe to the "beforeShow" and "show" events for 
     each submenu of the MenuBar instance.
*/
function addAnimation(oMenuBar)
{
    oMenuBar.subscribe("beforeShow", onSubmenuBeforeShow);
    oMenuBar.subscribe("show", onSubmenuShow);
}