function show_dates_as_local_time() {
  var spans = document.getElementsByTagName('span');
  for (var i=0; i<spans.length; i++) {
    if (spans[i].className.match(/\btypo_date\b/i)) {
      spans[i].innerHTML = get_local_time_for_date(spans[i].title);
    }
  }
}

function get_local_time_for_date(time) {
  system_date = new Date(time);
  user_date = new Date();
  delta_minutes = Math.floor((user_date - system_date) / (60 * 1000));
  if (Math.abs(delta_minutes) <= (8*7*24*60)) { // eight weeks... I'm lazy to count days for longer than that
    distance = distance_of_time_in_words(delta_minutes);
    if (delta_minutes < 0) {
      return 'dans ' + distance;
    } else {
      return 'il y a ' + distance;
    }
  } else {
    return 'le ' + system_date.toLocaleDateString();
  }
}

// a vague copy of rails' inbuilt function, 
// but a bit more friendly with the hours.
function distance_of_time_in_words(minutes) {
  if (minutes.isNaN) return "";
  minutes = Math.abs(minutes);
  if (minutes < 1) return "moins d'une minute";
  if (minutes < 50) return (minutes + ' minute' + (minutes == 1 ? '' : 's'));
  if (minutes < 90) return "une heure";
  if (minutes < 1080) return (Math.round(minutes / 60) + ' heures');
  if (minutes < 1440) return ('un jour');
  if (minutes < 2880) return ('un jour');
  else return (Math.round(minutes / 1440) + ' jours')
}