// esj-menu.js
//	simple dynamic menu
//
// by Eric S. Johnsen http://www.ericsjohnsen.com
// Copyright (c) 2010 Eric S. Johnsen
//
// version 1.0.0
//

//configuration variables
var timeout   = 250; //milliseconds
var fadeSpeed = 500; //milliseconds
var useFade   = true;

// timers array
var timers = new Array();

// state array -- by id, value - active, false - inactive
var state = new Array();

// lastOpacity: used to prevent multiple timers from making the fade flicker
var lastOpacity = new Array();

// MSIE check (MSIE has its own way of setting opacity)
var msie = false;
if (navigator.appName == "Microsoft Internet Explorer") msie = true;

// entry point: set element to zero and clear its timers
function setMenu( id )
{
	var e = document.getElementById(id);
	e.style.visibility = "visible";
	state[id] = true;
	setOpacity( id, 1 );
	if(timers[id]) {
		clearTimeout(timers[id]);
		timers[id] = undefined;
	}
}

// set element to hidden and reset its opacity
// typically called by a timer
// may be used as an entry point to bypass timers and fades
function hideMenu( id )
{
	var e = document.getElementById(id);
	e.style.visibility = "hidden";
	if(useFade) setOpacity( id, 1 );
}

// entry point: hide the menu using fade (if enabled)
function clearMenu( id )
{
	if(useFade) timers[id] = setTimeout( 'fadeMenu( "' + id + '" )', timeout );
	else timers[id] = setTimeout( 'hideMenu( "' + id + '" )', timeout );
}

// set the opacity
// special support for MSIE
function setOpacity( id, value )
{
	var e = document.getElementById(id);
	
	if(state[id]) value = 1; // fade was interrupted
	else if(lastOpacity[id] && (lastOpacity[id] < value)) value = lastOpacity[id]; // prevents flicker if multiple timers are making the fade
	
	if(msie) e.style.filter = 'alpha(opacity-' + value * 100 + ')'; // MS Internet Explorer
	else e.style.opacity = (value);
	
	if (value == 0) hideMenu( id ); // when it is faded, reset the menu state
	lastOpacity[id] = value;
}

// fade a menu
// typically called by a timer
function fadeMenu( id )
{
	var start = 0;
	var end = 0;
	var s = Math.round( fadeSpeed / 25 );
	var timer = 0;
	var i;
	
	state[id] = false; 
	
	for( i = s; i >= 0; i--) {
		setTimeout( "setOpacity('" + id + "'," + ( i / s ) + ")", timer++ * fadeSpeed / s )
	}
}