/* popup show/hide functions */
function hide_popup() {
  document.getElementById('popup').style.display = 'none';
}
function show_popup() {
  var visits = isNaN(getCookie('visits')) ? 
               1 : getCookie('visits')-0 + 1;
  var expiry = new Date();
  expiry.setYear(expiry.getFullYear() + 10);
  setCookie('visits', visits, expiry, '/');
  if (visits == 1 || visits % 5 == 0) {
    document.getElementById('popup').style.display = 'block';
  }
}

/* cookie functions adapted from
   http://www.netspade.com/articles/javascript/cookies.xml */
function setCookie(name, value, expires, path, domain, secure)
{
    document.cookie= name + "=" + escape(value) +
        ((expires) ? "; expires=" + expires : "") +
        ((path) ? "; path=" + path : "") +
        ((domain) ? "; domain=" + domain : "") +
        ((secure) ? "; secure" : "");
}

function getCookie(name)
{
    var dc = document.cookie;
    var prefix = name + "=";
    var begin = dc.indexOf("; " + prefix);
    if (begin == -1)
    {
        begin = dc.indexOf(prefix);
        if (begin != 0) return null;
    }
    else
    {
        begin += 2;
    }
    var end = document.cookie.indexOf(";", begin);
    if (end == -1)
    {
        end = dc.length;
    }
    return unescape(dc.substring(begin + prefix.length, end));
}

function deleteCookie(name, path, domain)
{
    if (getCookie(name))
    {
        document.cookie = name + "=" + 
            ((path) ? "; path=" + path : "") +
            ((domain) ? "; domain=" + domain : "") +
            "; expires=Thu, 01-Jan-70 00:00:01 GMT";
    }
}

/* addEvent from 
   http://www.scottandrew.com/weblog/articles/cbs-events */
function addEvent(obj, evType, fn, useCapture){
  if (obj.addEventListener){
    obj.addEventListener(evType, fn, useCapture);
    return true;
  } else if (obj.attachEvent){
    var r = obj.attachEvent("on"+evType, fn);
    return r;
  }
}

/* call show_popup() when the page loads */
addEvent(window, 'load', show_popup);