/**
* https://github.com/jherdman/javascript-relative-time-helpers
*
* Returns a description of this past date in relative terms.
* Takes an optional parameter (default: 0) setting the threshold in ms which
* is considered "Just now".
*
* Examples, where new Date().toString() == "Mon Nov 23 2009 17:36:51 GMT-0500 (EST)":
*
* new Date().toRelativeTime()
* --> 'Just now'
*
* new Date("Nov 21, 2009").toRelativeTime()
* --> '2 days ago'
*
* // One second ago
* new Date("Nov 23 2009 17:36:50 GMT-0500 (EST)").toRelativeTime()
* --> '1 second ago'
*
* // One second ago, now setting a now_threshold to 5 seconds
* new Date("Nov 23 2009 17:36:50 GMT-0500 (EST)").toRelativeTime(5000)
* --> 'Just now'
*
*/
Date.prototype.toRelativeTime = function(now_threshold) {
  var delta = new Date() - this;

  now_threshold = parseInt(now_threshold, 10);

  if (isNaN(now_threshold)) {
    now_threshold = 0;
  }

  if (delta <= now_threshold) {
    return 'Just now';
  }

  var units = null;
  var conversions = {
    millisecond: 1, // ms -> ms
    second: 1000, // ms -> sec
    minute: 60, // sec -> min
    hour: 60, // min -> hour
    day: 24, // hour -> day
    month: 30, // day -> month (roughly)
    year: 12 // month -> year
  };

  for (var key in conversions) {
    if (delta < conversions[key]) {
      break;
    } else {
      units = key; // keeps track of the selected key over the iteration
      delta = delta / conversions[key];
    }
  }

  // pluralize a unit when the difference is greater than 1.
  delta = Math.floor(delta);
  if (delta !== 1) { units += "s"; }
  return [delta, units, "ago"].join(" ");
};

/*
* Wraps up a common pattern used with this plugin whereby you take a String
* representation of a Date, and want back a date object.
*/
Date.fromString = function(str) {
  return new Date(Date.parse(str));
};