function change_buttons(par, class, enable)
{
  var li = par.getElementsByTagName("li");
  for (var i = 0; i < li.length; i++)
  {
    if (li[i].getAttribute("class") == class)
    {
      var a = li[i].getElementsByTagName("a");
      for (var j = 0; j < a.length; j++)
      {
        a[j].style.display = enable ? "inline" : "none";
      }
      var span = li[i].getElementsByTagName("span");
      for (var j = 0; j < span.length; j++)
      {
        span[j].style.display = enable ? "none" : "inline";
      }
    }
  }
}

function photoshow_prev(id)
{
  var ps = document.getElementById(id);
  if (ps != null)
  {
    var prev = null;
    var i = 0;
//    var d = ps.getElementsByTagName("div");
//    for (var j = 0; j < d.length; j++)
    for (var img = ps.firstChild; img != null; img = img.nextSibling)
    {
      if (img.nodeName.toLowerCase() == "div" &&
          img.getAttribute("class") == "img")
      {
        if (img.style.display != "none" &&
            prev != null)
        {
          img.style.display = "none";
          prev.style.display = "block";
          break;
        }
        prev = img;
        i++;
      }
    }
    if (i == 1)
      change_buttons(ps, "prev", false);
    change_buttons(ps, "next", true);
  }
}

function photoshow_next(id)
{
  var ps = document.getElementById(id);
  if (ps != null)
  {
    var next = null;
    var i = 0;
    for (var img = ps.lastChild; img != null; img = img.previousSibling)
    {
      if (img.nodeName.toLowerCase() == "div" &&
          img.getAttribute("class") == "img")
      {
        if (img.style.display != "none" &&
            next != null)
        {
          img.style.display = "none";
          next.style.display = "block";
          break;
        }
        next = img;
        i++;
      }
    }
    if (i == 1)
      change_buttons(ps, "next", false);
    change_buttons(ps, "prev", true);
  }
}