kandanapp/kandan

/**
 * Returns a description of this date in relative terms.

 * 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'
 *
 * new Date("Nov 25, 2009").toRelativeTime()
 * --> '2 days from now'
 *
 * // One second ago
 * new Date("Nov 23 2009 17:36:50 GMT-0500 (EST)").toRelativeTime()
 * --> '1 second ago'
 *
 * toRelativeTime() takes an optional argument - a configuration object.
 * It can have the following properties:
 * - now - Date object that defines "now" for the purpose of conversion.
 *         By default, current date & time is used (i.e. new Date())
 * - nowThreshold - Threshold in milliseconds which is considered "Just now"
 *                  for times in the past or "Right now" for now or the immediate future
 * - smartDays - If enabled, dates within a week of now will use Today/Yesterday/Tomorrow
 *               or weekdays along with time, e.g. "Thursday at 15:10:34"
 *               rather than "4 days ago" or "Tomorrow at 20:12:01"
 *               instead of "1 day from now"
 *
 * If a single number is given as argument, it is interpreted as nowThreshold:
 *
 * // 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'
 *
 * // One second in the future, now setting a now_threshold to 5 seconds
 * new Date("Nov 23 2009 17:36:52 GMT-0500 (EST)").toRelativeTime(5000)
 * --> 'Right now'
 *
 */
 Date.prototype.toRelativeTime = (function() {

  var _ = function(options) {
    var opts = processOptions(options);

    var now = opts.now || new Date();
    var delta = now - this;
    var future = (delta <= 0);
    delta = Math.abs(delta);

    // special cases controlled by options
    if (delta <= opts.nowThreshold) {
      return future ? 'Right now' : 'Just now';
    }
    if (opts.smartDays && delta <= 6 * MS_IN_DAY) {
      return toSmartDays(this, now);
    }

    var units = null;
    for (var key in CONVERSIONS) {
      if (delta < CONVERSIONS[key])
        break;
      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, future ? "from now" : "ago"].join(" ");
  };

  var processOptions = function(arg) {
    if (!arg) arg = 0;
    if (typeof arg === 'string') {
      arg = parseInt(arg, 10);
    }
    if (typeof arg === 'number') {
      if (isNaN(arg)) arg = 0;
      return {nowThreshold: arg};
    }
    return arg;
  };

  var toSmartDays = function(date, now) {
    var day;
    var weekday = date.getDay(),
        dayDiff = weekday - now.getDay();
    if (dayDiff == 0)       day = 'Today';
    else if (dayDiff == -1) day = 'Yesterday';
    else if (dayDiff == 1)  day = 'Tomorrow';
    else                    day = WEEKDAYS[weekday];
    return day + " at " + date.toLocaleTimeString();
  };

  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
  };
  var MS_IN_DAY = (CONVERSIONS.millisecond * CONVERSIONS.second * CONVERSIONS.minute * CONVERSIONS.hour * CONVERSIONS.day);

  var WEEKDAYS = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

  return _;

})();



/*
 * 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));
};