var overlays = new overlayClass;
var overlaySlotSmall = 0;
var overlaySlotLarge = 1;
var overlaySlotActive = overlaySlotSmall;
var overlayTimerSmall;
var overlayTimerLarge;

function overlayClass() {
    
    this.choose = chooseOverlay;
    this.display = displayOverlay;
    this.images = new Array;
    this.slots = new Array;    
    
    index = 0;

    this.slots.push('');
    this.slots.push('');

    this.images.push('diagrams/2003az84.png');
    this.images.push('diagrams/2004gv9.png');
    this.images.push('diagrams/2015rr245.png');
    this.images.push('diagrams/algiebab-thumbnail.png');
    this.images.push('diagrams/borasisi.png');
    this.images.push('diagrams/halley.png');
    this.images.push('diagrams/hd177830b-thumbnail.png');
    this.images.push('diagrams/kepler97b-thumbnail.png');
    this.images.push('diagrams/kepler301c-thumbnail.png');

    this.images.push('illustrations/10ursaemajoris.gif');
    this.images.push('illustrations/2007jj43.png');
    this.images.push('illustrations/2007or10.png');
    this.images.push('illustrations/51pegasi.gif');
    this.images.push('illustrations/70virginisb.gif');
    this.images.push('illustrations/achernar.gif');
    this.images.push('illustrations/achilles.png');
    this.images.push('illustrations/alderamin.gif');
    this.images.push('illustrations/algol.gif');
    this.images.push('illustrations/alhena.png');
    this.images.push('illustrations/alphacentauri.gif');
    this.images.push('illustrations/alphacircini.gif');
    this.images.push('illustrations/andromeda.gif');
    this.images.push('illustrations/autumnalequinox.gif');
    this.images.push('illustrations/barnardsstar.gif');
    this.images.push('illustrations/bellatrix.gif');
    this.images.push('illustrations/betaindi.gif');
    this.images.push('illustrations/betasagittae.png');
    this.images.push('illustrations/betelgeuse.gif');
    this.images.push('illustrations/c78.png');
    this.images.push('illustrations/capella.gif');
    this.images.push('illustrations/comet.gif');
    this.images.push('illustrations/constellation.gif');
    this.images.push('illustrations/crab.gif');
    this.images.push('illustrations/earth.gif');
    this.images.push('illustrations/egeria.png');
    this.images.push('illustrations/etacoronaeborealis.gif');
    this.images.push('illustrations/etaserpentis.gif');
    this.images.push('illustrations/firstpointofaries.gif');
    this.images.push('illustrations/flamingtree.png');
    this.images.push('illustrations/fly.png');
    this.images.push('illustrations/galaxy.gif');
    this.images.push('illustrations/gomeisa.gif');
    this.images.push('illustrations/horsehead.gif');
    this.images.push('illustrations/ic4756.png');
    this.images.push('illustrations/irene.png');
    this.images.push('illustrations/jupiter.gif');
    this.images.push('illustrations/kochab.gif');
    this.images.push('illustrations/ktype.gif');
    this.images.push('illustrations/lightyear.png');
    this.images.push('illustrations/lumen.gif');
    this.images.push('illustrations/m5.png');
    this.images.push('illustrations/m23.gif');
    this.images.push('illustrations/m38.gif');
    this.images.push('illustrations/marehumorum.png');
    this.images.push('illustrations/mareserenitatis.gif');
    this.images.push('illustrations/mars.gif');
    this.images.push('illustrations/mercury.gif');
//    this.images.push('illustrations/milkyway.gif');
    this.images.push('illustrations/moon.gif');
    this.images.push('illustrations/nebula.gif');
    this.images.push('illustrations/neptune.gif');
    this.images.push('illustrations/ngc6193.gif');
    this.images.push('illustrations/ngc6539.png');
    this.images.push('illustrations/northerncelestialpole.gif');
//    this.images.push('illustrations/orionnebula.gif');
    this.images.push('illustrations/pallas.png');
    this.images.push('illustrations/pleiades.gif');
    this.images.push('illustrations/pluto.gif');
    this.images.push('illustrations/polaris.gif');
    this.images.push('illustrations/procyon.gif');
    this.images.push('illustrations/proxima.gif');
    this.images.push('illustrations/redgiant.gif');
    this.images.push('illustrations/rigel.gif');
    this.images.push('illustrations/saturn.gif');
    this.images.push('illustrations/sirius.gif');
    this.images.push('illustrations/solarsystem.gif');
    this.images.push('illustrations/sombrero.gif');
    this.images.push('illustrations/southequatorialbelt.gif');
    this.images.push('illustrations/star_typ_g.gif');
    this.images.push('illustrations/starcluster.gif');
    this.images.push('illustrations/starcluster2.gif');
    this.images.push('illustrations/stars.gif');
    this.images.push('illustrations/sulaphat.gif');
    this.images.push('illustrations/sun.gif');
    this.images.push('illustrations/terrestrial.gif');
    this.images.push('illustrations/thebe.png');
    this.images.push('illustrations/uranus.gif');
    this.images.push('illustrations/venus.gif');
    this.images.push('illustrations/vernalequinox.gif');

    this.images.push('locations/alphaapodis.svg');
    this.images.push('locations/alphacentauri.svg');
    this.images.push('locations/andromeda.svg');
    this.images.push('locations/betelgeuse.svg');
    this.images.push('locations/halley.svg');
    this.images.push('locations/horsehead.svg');
    this.images.push('locations/ngc2281.svg');
    this.images.push('locations/northerneclipticpole.svg');
    this.images.push('locations/orionnebula.svg');
    this.images.push('locations/polaris.svg');
    this.images.push('locations/ring.svg');
    this.images.push('locations/sirius.svg');

    this.images.push('maps/saturn.png');

    this.images.push('size/betelgeuse.png');
    this.images.push('size/iotapiscium.png');
    this.images.push('size/ixion.png');

    this.images.push('thumbnails/2004gv9.png');
    this.images.push('thumbnails/47tucanae.gif');
    this.images.push('thumbnails/achilles.png');
    this.images.push('thumbnails/algol.gif');
    this.images.push('thumbnails/alphacentauri.gif');
    this.images.push('thumbnails/alsciaukat.gif');
    this.images.push('thumbnails/andromeda.gif');
    this.images.push('thumbnails/barnardsstar.gif');
    this.images.push('thumbnails/bellatrix.gif');
    this.images.push('thumbnails/betapiscisaustrini.png');
    this.images.push('thumbnails/betelgeuse.gif');
    this.images.push('thumbnails/brorsen.png');
    this.images.push('thumbnails/capella.gif');
    // this.images.push('thumbnails/crab.gif'); // ALADIN-REP
    this.images.push('thumbnails/earth.gif');
    this.images.push('thumbnails/epsilonarietis.gif');
    this.images.push('thumbnails/epsiloneridani.gif');
    this.images.push('thumbnails/fracastorius.png');
    this.images.push('thumbnails/galaxies.gif');
    this.images.push('thumbnails/geographos.gif');
    this.images.push('thumbnails/hoedusii.gif');
    this.images.push('thumbnails/horsehead.gif');
    this.images.push('thumbnails/iotapiscium.gif');
    this.images.push('thumbnails/iris.png');
    this.images.push('thumbnails/jupiter.gif');
    this.images.push('thumbnails/kochab.gif');
    this.images.push('thumbnails/m107.gif');
    this.images.push('thumbnails/m84.gif');
    this.images.push('thumbnails/m89.gif');
    this.images.push('thumbnails/m9.gif');
    this.images.push('thumbnails/marenectaris.png');
    this.images.push('thumbnails/mareserenitatis.png');
    this.images.push('thumbnails/mars.gif');
    this.images.push('thumbnails/mercury.gif');
    this.images.push('thumbnails/messier.png');
    this.images.push('thumbnails/mneme.png');
    this.images.push('thumbnails/moon.gif');
    this.images.push('thumbnails/moon_concept.gif');
    this.images.push('thumbnails/muandromedae.png');
    this.images.push('thumbnails/ngc3532.png');
    this.images.push('thumbnails/oceanusprocellarum.png');
    this.images.push('thumbnails/orionnebula.gif');
    this.images.push('thumbnails/pluto.gif');
    this.images.push('thumbnails/polaris.gif');
    this.images.push('thumbnails/proxima.gif');
    this.images.push('thumbnails/rigel.gif');
    this.images.push('thumbnails/saturn.gif');
    this.images.push('thumbnails/sirius.gif');
    this.images.push('thumbnails/spica.gif');
    this.images.push('thumbnails/starcluster.gif');
    this.images.push('thumbnails/summersolstice.gif');
    this.images.push('thumbnails/sun.gif');
    this.images.push('thumbnails/thetisregio.png');
    this.images.push('thumbnails/triton.png');
    this.images.push('thumbnails/ukraina.gif');
    this.images.push('thumbnails/venus.gif');
    this.images.push('thumbnails/yildun.gif');

}

function displayOverlay(slot) {

    var src = '_images/'+this.slots[slot];
    var svgSupport = (window.SVGSVGElement) ? true : false;
    if (! svgSupport) {
        src = src.replace('.svg','.gif');
    }
    var id = 'overlaySlot' + ((slot == 0) ? 'Small' : 'Large');
    document.getElementById(id).style.display = 'block';
    document.getElementById(id).src = src;
    
}

function chooseOverlay() {
    
    var slot = overlaySlotActive;
    var otherSlot = 1-slot;
    var selected = this.slots[slot];
    var index;

    while ((selected == this.slots[slot]) || (selected == this.slots[otherSlot])) {
        index = Math.floor(Math.random() * this.images.length);
        selected = this.images[index];
    }
    
    this.slots[slot] = selected;
    
    this.display(slot);
    overlaySlotActive = otherSlot;
    
}

function startOverlays() {
    overlays.choose(overlaySlotSmall);
    overlays.choose(overlaySlotLarge);
    setInterval('overlays.choose()',8000);
}