/*

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;

}