var header = document.getElementById('title');
var count = getCount();
var title = document.title.replace(/s$/, '');

updateCount(count);
try {
  window.addEventListener('storage', onStorageChange);
} catch(e) {
  window.attachEvent('onstorage', onStorageChange);
}

function updateCount(n) {
  var s = n === 1 ? '' : 's';
  var t = header.innerHTML = document.title = n + ' ' + title + s;
  if (frameElement) { // for bl.ocks.org's parent frame
    parent.document.title = t;
    frameElement.style.height = '125px';
  }
}

function getCount() {
  return JSON.parse(localStorage.unseenNotificationCount || '0');
}

function setCount(n) {
  localStorage.unseenNotificationCount = JSON.stringify(n || 0);
  return count = n;
}

function onStorageChange(e) {
  if (e.key !== 'unseenNotificationCount') return;
  var v = e.newValue;
  updateCount(v);
  try {
    var t = (new Date(e.timeStamp)).toISOString();
    console.log('%s: %s = %s', t, e.key, v);
  } catch(e) {}
}

document.body.addEventListener('click', function(e) {
  switch (e.target.id) {
    case 'clr': return updateCount(setCount(0));
    case 'add': return updateCount(setCount(1 + getCount()));
  }
});