/*

File: Fortune.js

Abstract: JavaScript logic for Fortune widget plug-in sample

Version: 1.0

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*/

/**************************/
// Fortune-specific code
// This code drives the Fortune widget 
/**************************/

// swap
//
// Swaps out the current fortune for a new one.  Uses the Obj-C/JavaScript widget
// plugin to get the new fortune.
function swap() {
	if (FortunePlugin) {
		var line = FortunePlugin.getFortune();				// get a fortune from the widget plugin
		document.getElementById("quote").innerHTML = line;	// drop in the new fortune
	}  
	else {
		alert("Widget plugin not loaded.");
	}
}

// next
//
// Performs the transition from the current fortune to the next one.
function next()
{
	hideContent();						// fades out the current fortune
	setTimeout("swap();",500);			// swaps in the new fortune
	setTimeout("showContent();",550);	// fades in the new fortune

}


/**************************/
// Animation code
// Handles the fades in and out
/**************************/

var animation = {duration:0, starttime:0, to:1.0, now:1.0, from:0.0, firstElement:null, timer:null};

function showContent()
{

		if (animation.timer != null)			// reset the animation timer value, in case a value was left behind
		{
			clearInterval (animation.timer);
			animation.timer  = null;
		}
		
		var starttime = (new Date).getTime() - 13; 		// set it back one frame
		
		animation.duration = 500;												// animation time, in ms
		animation.starttime = starttime;										// specify the start time
		animation.firstElement = document.getElementById ('quote');				// specify the element to fade
		animation.timer = setInterval ("animate();", 13);						// set the animation function
		animation.from = animation.now;											// beginning opacity (not ness. 0)
		animation.to = 1.0;														// final opacity
		animate();																// begin animation

}


function hideContent()
{

		if (animation.timer != null)
		{
			clearInterval (animation.timer);
			animation.timer  = null;
		}
		
		var starttime = (new Date).getTime() - 13;
		
		animation.duration = 500;
		animation.starttime = starttime;
		animation.firstElement = document.getElementById ('quote');
		animation.timer = setInterval ("animate();", 13);
		animation.from = animation.now;
		animation.to = 0.0;
		animate();

}


function animate()
{
	var T;
	var ease;
	var time = (new Date).getTime();
		
	
	T = limit_3(time-animation.starttime, 0, animation.duration);
	
	if (T >= animation.duration)
	{
		clearInterval (animation.timer);
		animation.timer = null;
		animation.now = animation.to;
	}
	else
	{
		ease = 0.5 - (0.5 * Math.cos(Math.PI * T / animation.duration));
		animation.now = computeNextFloat (animation.from, animation.to, ease);
	}
	
	animation.firstElement.style.opacity = animation.now;
}


// these functions are utilities used by animate()

function limit_3 (a, b, c)
{
    return a < b ? b : (a > c ? c : a);
}

function computeNextFloat (from, to, ease)
{
    return from + (to - from) * ease;
}