date-ext.js

(function() {

  var DAYS = [
          /* Short */
          'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'
          /* Full */
        , 'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'
        , 'Saturday'
      ]

    , F_ISO_8601 = 'Y-m-d\\TH:i:sP'

    , F_RFC_2822 = 'D, j M Y H:i:s O'

    , MONTHS = [
          /* Short */
          'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct'
        , 'Nov', 'Dec'
          /* Full  */
        , 'January', 'February', 'March', 'April', 'May', 'June', 'July'
        , 'August', 'September', 'October', 'November', 'December'
      ]

    , ORDINALS = ['th', 'st', 'nd', 'rd']

    , R_TOKEN = /\\?[\\dDjlNSwzWFmMntLoYyaABgGhHisueIOPTZcrU]/g

    , R_TIMEZONE = /([A-Z]+)(?=[\-\+]\d{4})/g;

  var tasks = [];

  function addToField(date, field, value) {
    if (value) date['set' + field](date['get' + field]() + value);
    return date;
  }

  function extend(name, proto, func) {
    if (proto) {
      if ('function' !== typeof Date.prototype[name]) {
        Date.prototype[name] = func;
      }
    } else {
      if ('function' !== typeof Date[name]) Date[name] = func;
    }
  }

  function format(date, formatStr, params) {

    if ('string' !== typeof formatStr) formatStr = F_RFC_2822;

    if (!params) {

      var iso = getISODate(date)
        , j = date.getDate()
        , w = date.getDay()
        , n = date.getMonth()
        , Y = date.getFullYear()
        , G = date.getHours()
        , e = date.toString().match(R_TIMEZONE);

      params = {
          /* Day */

          d: pad(j)

        , D: DAYS[w]

        , j: j

        , l: DAYS[w + 7]

        , N: w || 7

        , S: ORDINALS[(j % 10 > 3) ? 0 : (j % 100 - j % 10 !== 10) * j % 10]

        , w: w

        , z: getDayOfYear(date)
          /* Week */

        , W: iso.week
          /* Month */

        , F: MONTHS[n + 12]

        , m: pad(n + 1)

        , M: MONTHS[n]

        , n: n + 1

        , t: getDaysInMonth(date)
          /* Year */

        , L: isLeapYear(date) ? 1 : 0

        , o: iso.year

        , Y: Y

        , y: String(Y).slice(2)
          /* Time */

        , a: (G < 12) ? 'am' : 'pm'

        , A: (G < 12) ? 'AM' : 'PM'

        , B: getSwatchInternetTime(date)

        , g: G % 12 || 12

        , G: G

        , h: pad(G % 12 || 12)

        , H: pad(G)

        , i: pad(date.getMinutes())

        , s: pad(date.getSeconds())

        , u: pad(date.getMilliseconds() * 1000, 6)
          /* Timezone */

        , e: e ? e[0] : ''

        , I: isDaylightSavingTime(date) ? 1 : 0

        , O: parseTimezoneOffset(date)

        , P: parseTimezoneOffset(date, ':')

        , T: e ? e[0] : ''

        , Z: date.getTimezoneOffset() * -60
          /* Full Date/Time */

        , c: ''

        , r: ''

        , U: Math.round(date.getTime() / 1000)
      };

      params.c = format(date, F_ISO_8601, params);
      params.r = format(date, F_RFC_2822, params);
    }

    return formatStr.replace(R_TOKEN, function(str) {
      if ('\\' === str) return str;
      if (0 === str.indexOf('\\')) return str.substr(1);
      return params[str];
    });
  }

  function getDayOfYear(date) {
    var start = new Date(date.getFullYear(), 0, 1);
    return Math.floor((date - start) / 1000 / 60 / 60 / 24);
  }

  function getDaysInMonth(date) {
    return (new Date(date.getFullYear(), date.getMonth() + 1, 0)).getDate();
  }

  function getISODate(date) {

    var copy = new Date(Date.UTC(date.getFullYear(), date.getMonth()
        , date.getDate()))
      , day = copy.getUTCDay();

    copy.setUTCDate(copy.getUTCDate() - (day + 6) % 7 + 3);
    var start = copy.getTime();

    copy.setUTCMonth(0, 4);
    var week = Math.round((start - copy) / (7 * (1000 * 60 * 60 * 24))) + 1;
    return {
        day: day || 7
      , week: week
      , year: copy.getUTCFullYear()
    };
  }

  function getSwatchInternetTime(date) {
    var time = ((date.getUTCHours() + 1) % 24) + (date.getUTCMinutes() / 60)
          + (date.getUTCSeconds() / (60 * 60));
    return Math.floor(time * 1000 / 24);
  }

  function isDaylightSavingTime(date) {
    var start = new Date(date);
    start.setMonth(0, 1);
    return start.getTimezoneOffset() !== date.getTimezoneOffset();
  }

  function isLeapYear(date) {
    return 1 === (new Date(date.getFullYear(), 1, 29)).getMonth();
  }

  function pad(value, size) {
    size  = size || 2;
    value = String(value);
    while (value.length < size) value = '0' + value;
    return value;
  }

  function parseTimezoneOffset(date, separator) {
    var offset = date.getTimezoneOffset()
      , parsed = String(pad(Math.floor(Math.abs(offset) / 60) * 100
          + Math.abs(offset) % 60, 4));
    if (separator) parsed = parsed.slice(0, 2) + separator + parsed.slice(2);
    return ((offset > 0) ? '-' : '+') + parsed;
  }

  function schedule(date, callback, context) {

    if ('string' === typeof callback) {
      context = callback;
      callback = null;
    }
    if ('function' === typeof date) {
      callback = date;
      date = null;
    }
    if (date == null) date = new Date();
    var scheduleId
      , time = date - new Date();

    function wrapper() {
      var idx = tasks.indexOf(scheduleId);
      if (idx > -1) {
        tasks.splice(idx, 1);
        callback.call(context);
      }
    }

    if ('function' === typeof callback) {
      if (time <= 0) {
        callback.call(context);
      } else {
        tasks.push(scheduleId = setTimeout(wrapper, time));
      }
    }
    return scheduleId;
  }

  function unschedule(scheduleId) {
    var idx = tasks.indexOf(scheduleId);
    if (idx > -1) {
      clearTimeout(scheduleId);
      tasks.splice(idx, 1);
      return true;
    }
    return false;
  }

  extend('addDays', true, function(days) {
    return addToField(this, 'Date', days);
  });

  extend('addHours', true, function(hours) {
    return addToField(this, 'Hours', hours);
  });

  extend('addMilliseconds', true, function(milliseconds) {
    return addToField(this, 'Milliseconds', milliseconds);
  });

  extend('addMinutes', true, function(minutes) {
    return addToField(this, 'Minutes', minutes);
  });

  extend('addMonths', true, function(months) {
    return addToField(this, 'Month', months);
  });

  extend('addSeconds', true, function(seconds) {
    return addToField(this, 'Seconds', seconds);
  });

  extend('addYears', true, function(years) {
    return addToField(this, 'FullYear', years);
  });

  extend('clear', true, function() {
    this.clearDate();
    this.clearTime();
    return this;
  });

  extend('clearDate', true, function() {
    this.setFullYear(0, 0, 1);
    return this;
  });

  extend('clearTime', true, function() {
    this.setHours(0, 0, 0, 0);
    return this;
  });

  extend('format', false, function(date, formatStr) {
    return format(date, formatStr);
  });

  extend('format', true, function(formatStr) {
    return format(this, formatStr);
  });

  extend('getDayOfYear', true, function() {
    return getDayOfYear(this);
  });

  extend('getDaysInMonth', true, function() {
    return getDaysInMonth(this);
  });

  extend('getWeekOfYear', true, function() {
    return getISODate(this).week;
  });

  extend('getYearOfWeek', true, function() {  
    return getISODate(this).year;
  });

  extend('isDaylightSavingTime', true, function() {
    return isDaylightSavingTime(this);
  });

  extend('isLeapYear', true, function() {
    return isLeapYear(this);
  });

  extend('schedule', false, function(date, callback, context) {
    return schedule(date, callback, context);
  });

  extend('schedule', true, function(callback, context) {
    return schedule(this, callback, context);
  });

  extend('unschedule', false, unschedule);
  extend('unschedule', true, unschedule);

}());