A Multi-Calendar-System DateTime Service based on Moment.js (and moment-jalaali)

datetime.js

define(['ng', 'moment-jalaali'],
  function(ng, moment) {
    var mod = ng.module('app.service.datetime', []);

    mod.run(['$rootScope', function($rootScope) {
      $rootScope.$on('$languageChangeSuccess', function(evt, newLang) {
        if(newLang === 'fa') moment.loadPersian();
        else moment.locale('en');
      });
    }]);

    mod.service('calendarSystem', function() {
      var availableSystems = {
        GREGORIAN: 0,
        JALALI: 1
      };
      var currentSystem = 0;

      var findByValue = function(value) {
        for(key in availableSystems)
          if(value === availableSystems[key])
            return key;
        return null;
      };

      return {
        SYSTEM: availableSystems,
        set: function(value) {
          if(!ng.isNumber(value))
            throw new TypeError('A system must be represented with it\'s corresponding integer value.');
          if(!findByValue(value))
            throw new Error('The provided system is not defined!');
          currentSystem = value;
        },
        get: function() {
          return currentSystem;
        },
        toString: function() {
          var key = findByValue(currentSystem);
          if(key)
            return key.substr(0, 1) + key.substr(1).toLowerCase();
          else
            return "Unknown";
        }
      };
    });

    // TODO: Switch to mod.provider and join-in the calendarSystem service
    mod.factory('datetimeService', ['calendarSystem', function(calendarSystem) {
      // TODO: Add support for forced Gregorian formatting like Jalali (jM -> gM OR use parameters)
      // var formattingTokens = /(\\)?(j|g)?(Mo|MM?M?M?|Do|DDDo|DD?D?D?|w[o|w]?|YYYYY|YYYY|YY|gg(ggg?)?|)/g,
      var formattingTokens = /(\\)?(Mo|MM?M?M?|Do|DDDo|DD?D?D?|w[o|w]?|YYYYY|YYYY|YY|gg(ggg?)?|)/g,
          sharedTokens = ['M', 'MM', 'MMM', 'MMMM', 'D', 'DD', 'DDD', 'w', 'YY', 'YYYY', 'YYYYY', 'gg', 'gggg', 'ggggg'];

      // Bind directly
      var _simpleBind = function(fn) {
        return function() {
          var result = this.$moment[fn].apply(this.$moment, arguments);
          return moment.isMoment(result) ? this : result;
        };
      };
      // Bind to jFn or fn based on calendar system flag
      var _gjBind = function(fn) {
        var jFn = 'j' + fn.substr(0, 1).toUpperCase() + fn.substr(1);
        return function() {
          var result = this.$moment[this.isJalali ? jFn : fn].apply(this.$moment, arguments);
          return moment.isMoment(result) ? this : result;
        }
      };
      // Bind directly but reformat specified parameter
      var _gjParamBind = function(fn, paramIndex) {
        return function() {
          if(this.isJalali) {
            var value = arguments[paramIndex];
            arguments[paramIndex] = 'j' + value;
          }
          var result = this.$moment[fn].apply(this.$moment, arguments);
          return moment.isMoment(result) ? this : result;
        }
      };

      function DTS() {
        // General functions
        this.isDSTShifted = _simpleBind('isDSTShifted');
        this.invalidAt    = _simpleBind('invalidAt');
        this.isValid      = _simpleBind('isValid');
        this.local        = _simpleBind('local');
        this.parsingFlags = _simpleBind('parsingFlags');
        this.unix         = _simpleBind('unix');
        this.utc          = _simpleBind('utc');
        this.weekday      = _simpleBind('weekday');

        this.toString     = _simpleBind('toString');
        this.toDate       = _simpleBind('toDate');
        this.toISOString  = _simpleBind('toISOString');
        this.toArray      = _simpleBind('toArray');
        this.valueOf      = _simpleBind('valueOf');

        // Calculating functions
        this.add          = _gjParamBind('add', 1); // reformats add(1, 'month') to add(1, 'jMonth') if the jalali flag is set
        this.endOf        = _gjParamBind('endOf', 0);
        this.startOf      = _gjParamBind('startOf', 0);
        this.subtract     = _gjParamBind('subtract', 1);

        // Shared date functions
        this.date      = _gjBind('date'); // reformats date(...) to jDate(...) if the jalali flag is set
        this.dates     = _gjBind('dates');
        this.dayOfYear = _gjBind('dayOfYear');
        this.month     = _gjBind('month');
        this.months    = _gjBind('months');
        this.week      = _gjBind('week');
        this.weekYear  = _gjBind('weekYear');
        this.weeks     = _gjBind('weeks');
        this.year      = _gjBind('year');
        this.years     = _gjBind('years');

        // Gregorian-specific functions
        this.gDate      = _simpleBind('date');
        this.gDates     = _simpleBind('dates');
        this.gDayOfYear = _simpleBind('dayOfYear');
        this.gMonth     = _simpleBind('month');
        this.gMonths    = _simpleBind('months');
        this.gWeek      = _simpleBind('week');
        this.gWeekYear  = _simpleBind('weekYear');
        this.gWeeks     = _simpleBind('weeks');
        this.gYear      = _simpleBind('year');
        this.gYears     = _simpleBind('years');

        // Jalali-specific functions
        this.jDate      = _simpleBind('jDate');
        this.jDates     = _simpleBind('jDates');
        this.jDayOfYear = _simpleBind('jDayOfYear');
        this.jMonth     = _simpleBind('jMonth');
        this.jMonths    = _simpleBind('jMonths');
        this.jWeek      = _simpleBind('jWeek');
        this.jWeekYear  = _simpleBind('jWeekYear');
        this.jWeeks     = _simpleBind('jWeeks');
        this.jYear      = _simpleBind('jYear');
        this.jYears     = _simpleBind('jYears');

        // Special bindings

        this.clone = function() {
          var dts = new DateTimeService();
          dts.$moment = this.$moment.clone.call(this.$moment);
          dts.isJalali = this.isJalali;
          return dts;
        };

        this.format = function(format) {
          if (this.isJalali) {
            format = format.replace(formattingTokens, function(m) {
              return (sharedTokens.indexOf(m) > -1 ? 'j' : '') + m;
            });
          }
          return this.$moment.format.apply(this.$moment, arguments);
        };

        // TODO: Replace with the following line when jMoment.isSame is available in jMoment
        //       this.isSame = _gjParamBind('isSame', 1);
        this.isSame = function(input, units) {
          var inputMs;
          units = (units || 'millisecond').toLowerCase();
          if (units === 'millisecond') {
            input = DateTimeService(input);
            return +this === +input;
          } else {
            inputMs = +DateTimeService(input);
            return +(this.clone().startOf(units)) <= inputMs && inputMs <= +(this.clone().endOf(units));
          }
        };
      };

      function DateTimeService(input, format, lang, utc) {
        if(input instanceof DTS) return input;

        var dts = new DTS;

        if(utc)
          dts.$moment = moment.utc(input, format, lang);
        else
          dts.$moment = moment(input, format, lang);

        dts.isJalali = calendarSystem.get() === calendarSystem.SYSTEM.JALALI;

        return dts;
      };

      return DateTimeService;
    }]);

    return mod;
  });