function send_xmlhttprequest(obsluha, method, url, content, headers) {
  if (window.XMLHttpRequest) {xmlhttp = new XMLHttpRequest;}
  else if (window.ActiveXObject) {xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");}
  else return false;
  
  xmlhttp.open(method, url);
  xmlhttp.onreadystatechange = function() {
    obsluha(xmlhttp);
  };

  if (headers) {
    for (var key in headers) {
      xmlhttp.setRequestHeader(key, headers[key]);
    }
  }

  xmlhttp.send(content);
  return true;
}

function ukazMeUls(me) {
  var submenu = me.getElementsByTagName('UL');
  var items = submenu[0].getElementsByTagName('LI');
  if (items.length > 0) submenu[0].style.visibility = 'visible';
}

function schovejMeUls(me) {
  var submenu = me.getElementsByTagName('UL');
  submenu[0].style.visibility = 'hidden';
}

function hideElement(element) {
  if (!element.style) element = document.getElementById(element);
  if (element) element.style.visibility = 'hidden';
}

function photoOpen(url, width, height) {
  return window.open(url, '_blank', 'width='+width+',height='+height+',resizable=yes,menubar=no,toolbar=no,location=no,status=no');
}

function initCounter() {
  var interval = setInterval('setCounter()', 1000);
  return true;
}

function setCounter() {
  var hour, min, sec;
  var element = document.getElementById('counter');
  if (!element) return false;
  
  var time = new Date();
  var counter = element.title - (Math.round(time.getTime()/1000) - window.time_diff);

  if (counter < 0) counter = 0;
  
  hour = Math.floor(counter / 3600);
  min = Math.floor((counter - hour * 3600) / 60);
  sec = counter - hour * 3600 - min * 60;

  if (min < 10) min = '0' + min;
  if (sec < 10) sec = '0' + sec;

  element.innerHTML = hour + ':' + min + ':' + sec;
  
  return true;
}

function getTimeDiff() {
  send_xmlhttprequest(setTimeDiff, 'GET', 'services/time.php', null, '');
  return 0;
}

function setTimeDiff(xmlhttp) {
  if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
    var time = new Date();
    window.time_diff = Math.round(time.getTime()/1000) - xmlhttp.responseText;
  }
}