// introduce some variables we need in the global scope for all functions
// For now specifically made for /projecten/lucht/startband.html

var dia;
var diaBaseSrc = '/projecten/lucht/_img/startBanden';
var diaNumber = 0;
var diaLoad;
var diaHeader;
var nextLink;
var prevLink;

if (document.createElement && document.getElementsByTagName && document.getElementById) {
    function addEventSimple(obj,evt,fn) {
        if (obj.addEventListener)
            obj.addEventListener(evt,fn,false);
        else if (obj.attachEvent)
            obj.attachEvent('on'+evt,fn);
    }
    addEventSimple(window,'load',initDiaShow);
}

function initDiaShow() {
    function loadImage(source) {
        img = new Image();
        img.src = source;
    }
    // as soon the window is loaded start loading all other images
    for (diaLoad = 1;diaLoad <= 23;diaLoad++) {
        loadSrc = diaBaseSrc + diaLoad + '.jpg';
        loadImage(loadSrc);
    }
    
    dia = document.getElementById('dia');
    // diaBaseSrc = dia.src.slice(0,33); see comment line 2
    nextLink = document.getElementById('nextDia');
    prevLink = document.getElementById('prevDia');
    addEventSimple(nextLink,'click',showNext);
    addEventSimple(prevLink,'click',showPrev);
    
    // make heding and controls visible
    diaHeader = document.getElementById('diaHdr');
    diaHeader.style.display = 'block';
    nextLink.style.display = 'block';
    prevLink.style.display = 'block';
}

function showNext(e) {
    if (e && e.preventDefault) {
        // W3C standard
        e.preventDefault();
    }
    else {
        e = window.event;
        //  Microsoft’s way
        e.returnValue = false;
    }
    diaNumber++;
    diaNumber = diaNumber%24;
    dia.src = diaBaseSrc + diaNumber + '.jpg';
}

function showPrev(e) {
    if (e && e.preventDefault) {
        // W3C standard
        e.preventDefault();
    }
    else {
        e = window.event;
        //  Microsoft’s way
        e.returnValue = false;
    }
    // alert(diaNumber);
    diaNumber += 23;
    diaNumber = (diaNumber%24);
    dia.src = diaBaseSrc + diaNumber + '.jpg';
}