var photoOffset=0;

//
// Functions concerning scrolling of images
//
function increaseOffset() {
    photoOffset++;
    updateImages();
}
function decreaseOffset() {
    photoOffset--;
    if (photoOffset < 0)
        photoOffset = 0;
    updateImages();
}
function updateImages() {
    makeGETRequest("ajax/photo/index.php?offset=" + photoOffset, handleUpdateImages);
}
function handleUpdateImages(xmlhttp) {
    if (xmlhttp.readyState == 4) {
        document.getElementById("photo-scroll").innerHTML = xmlhttp.responseText;
    }
}

//
// Basic AJAX functions
//
function getXMLHttpRequestObject() {
    var http_request = false;
    if (window.XMLHttpRequest) { // Mozilla, Safari,...
     http_request = new XMLHttpRequest();
     if (http_request.overrideMimeType) {
        // set type accordingly to anticipated content type
        //http_request.overrideMimeType('text/xml');
        http_request.overrideMimeType('text/html');
     }
    } else if (window.ActiveXObject) { // IE
     try {
        http_request = new ActiveXObject("Msxml2.XMLHTTP");
     } catch (e) {
        try {
           http_request = new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e) {}
     }
    }
    return http_request;
}  
function makeGETRequest(url, callback) {
    var http_request = getXMLHttpRequestObject();

    http_request.onreadystatechange = function() { callback(http_request) };
    http_request.open('GET', url, true);
    http_request.send(null);
}

//
// Init function
//

function init() {
   // quit if this function has already been called
   if (arguments.callee.done) return;
   // flag this function so we don't do the same thing twice
   arguments.callee.done = true;
   
   updateImages();
}

if (document.addEventListener) {
   document.addEventListener("DOMContentLoaded", init, false);
}
window.onload = init;