var tht_loadAt;   // time of onload
var tht_unLoadAt; // time of unonload

// define the function that adds an event listener
function tht_addEvent(elm, listener, fn){
  try{
    elm.addEventListener(listener, fn, false);
  }
  catch(e){
    // for IE
    elm.attachEvent("on" + listener, fn);
  }
}

// generate a JSON string
function toJSON(hash){
  var data = [];
  for(var i in hash){
    switch(typeof hash[i]){
      case 'string':
        data[data.length] = '"' + i.replace(/"/g, '\\"') + '"' + ':"' + hash[i].replace(/"/g, '\\"') + '"';
        break;
      case 'number':
        data[data.length] = '"' + i.replace(/"/g, '\\"') + '"' + ":" + hash[i];
        break;
    }
  }
  return '{' + data.join(',') + '}';
}

// define the onLoad event
function tht_load(){
  tht_loadAt = new Date();
}

// define the onUnLoad event
function tht_unload(){
  tht_unLoadAt = new Date();
  var stayTime = Math.round(Math.min((tht_unLoadAt - tht_loadAt) / 1000, 60));
  var d = document;
  var opt = {
    img_id: '__thatping_tracking',
    uid_prefix: 'tht_',
    uid_randbase: '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.split(''),
    uid_randlen: 12,
    ping_before:  'http://d.thatsping.jp/?',
    ping_after: ''
  };
  if(d.getElementById(opt.img_id)) return;
  var links = d.getElementsByTagName('link'), type_re = new RegExp('xml', 'i'), feed = '', uid = opt.uid_prefix;
  for(var i = 0, len = links.length; i < len; i ++){
    var rel = links[i].getAttribute("rel"), type = links[i].getAttribute('type');
    if(typeof rel == 'string' && rel.toLowerCase() == 'alternate' && typeof type == 'string' && type.match(type_re)){
      feed = links[i].getAttribute('href');
      break;
    }
  }
  for(var i = 0; i < opt.uid_randlen; i ++){
    uid += opt.uid_randbase[~~(Math.random() * opt.uid_randbase.length)];
  }
  var titles = d.getElementsByTagName('title');
  var send_data = {
    i: uid,
    n: titles.length ? titles[0].innerHTML : d.title,
    u: location.href,
    r: document.referrer,
    f: feed,
    t: 0
  };
  if(stayTime > 30){
    stayTime = 30;
  }
  send_data.t = stayTime;
  // send ping if the stay time is more than 5 min.
  if(stayTime >= 5){
    new Image().src = opt.ping_before + encodeURIComponent(toJSON(send_data)) + opt.ping_after;
  }
}

// add event listener to privent the default event handler from overwriting
tht_addEvent(window, "load", tht_load);
tht_addEvent(window, "unload", tht_unload);