/*
 * World Calendars
 * https://github.com/alexcjohnson/world-calendars
 *
 * Batch-converted from kbwood/calendars
 * Many thanks to Keith Wood and all of the contributors to the original project!
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

/* http://keith-wood.name/calendars.html
   Calendars for jQuery v2.0.2.
   Written by Keith Wood (wood.keith{at}optusnet.com.au) August 2009.
   Available under the MIT (http://keith-wood.name/licence.html) license. 
   Please attribute the author if you use it. */

var assign = require('object-assign');


function Calendars() {
    this.regionalOptions = [];
    this.regionalOptions[''] = {
        invalidCalendar: 'Calendar {0} not found',
        invalidDate: 'Invalid {0} date',
        invalidMonth: 'Invalid {0} month',
        invalidYear: 'Invalid {0} year',
        differentCalendars: 'Cannot mix {0} and {1} dates'
    };
    this.local = this.regionalOptions[''];
    this.calendars = {};
    this._localCals = {};
}

/** Create the calendars plugin.
    <p>Provides support for various world calendars in a consistent manner.</p>
     @class Calendars
    @example _exports.instance('julian').newDate(2014, 12, 25) */
assign(Calendars.prototype, {

    /** Obtain a calendar implementation and localisation.
        @memberof Calendars
        @param [name='gregorian'] {string} The name of the calendar, e.g. 'gregorian', 'persian', 'islamic'.
        @param [language=''] {string} The language code to use for localisation (default is English).
        @return {Calendar} The calendar and localisation.
        @throws Error if calendar not found. */
    instance: function(name, language) {
        name = (name || 'gregorian').toLowerCase();
        language = language || '';
        var cal = this._localCals[name + '-' + language];
        if (!cal && this.calendars[name]) {
            cal = new this.calendars[name](language);
            this._localCals[name + '-' + language] = cal;
        }
        if (!cal) {
            throw (this.local.invalidCalendar || this.regionalOptions[''].invalidCalendar).
                replace(/\{0\}/, name);
        }
        return cal;
    },

    /** Create a new date - for today if no other parameters given.
        @memberof Calendars
        @param year {CDate|number} The date to copy or the year for the date.
        @param [month] {number} The month for the date.
        @param [day] {number} The day for the date.
        @param [calendar='gregorian'] {BaseCalendar|string} The underlying calendar or the name of the calendar.
        @param [language=''] {string} The language to use for localisation (default English).
        @return {CDate} The new date.
        @throws Error if an invalid date. */
    newDate: function(year, month, day, calendar, language) {
        calendar = (year != null && year.year ? year.calendar() : (typeof calendar === 'string' ?
            this.instance(calendar, language) : calendar)) || this.instance();
        return calendar.newDate(year, month, day);
    },
    
    /** A simple digit substitution function for localising numbers via the Calendar digits option.
        @member Calendars
        @param digits {string[]} The substitute digits, for 0 through 9.
        @return {function} The substitution function. */
    substituteDigits: function(digits) {
        return function(value) {
            return (value + '').replace(/[0-9]/g, function(digit) {
                return digits[digit];
            });
        }
    },
    
    /** Digit substitution function for localising Chinese style numbers via the Calendar digits option.
        @member Calendars
        @param digits {string[]} The substitute digits, for 0 through 9.
        @param powers {string[]} The characters denoting powers of 10, i.e. 1, 10, 100, 1000.
        @return {function} The substitution function. */
    substituteChineseDigits: function(digits, powers) {
        return function(value) {
            var localNumber = '';
            var power = 0;
            while (value > 0) {
                var units = value % 10;
                localNumber = (units === 0 ? '' : digits[units] + powers[power]) + localNumber;
                power++;
                value = Math.floor(value / 10);
            }
            if (localNumber.indexOf(digits[1] + powers[1]) === 0) {
                localNumber = localNumber.substr(1);
            }
            return localNumber || digits[0];
        }
    }
});

/** Generic date, based on a particular calendar.
    @class CDate
    @param calendar {BaseCalendar} The underlying calendar implementation.
    @param year {number} The year for this date.
    @param month {number} The month for this date.
    @param day {number} The day for this date.
    @return {CDate} The date object.
    @throws Error if an invalid date. */
function CDate(calendar, year, month, day) {
    this._calendar = calendar;
    this._year = year;
    this._month = month;
    this._day = day;
    if (this._calendar._validateLevel === 0 &&
            !this._calendar.isValid(this._year, this._month, this._day)) {
        throw (_exports.local.invalidDate || _exports.regionalOptions[''].invalidDate).
            replace(/\{0\}/, this._calendar.local.name);
    }
}

/** Pad a numeric value with leading zeroes.
    @private
    @param value {number} The number to format.
    @param length {number} The minimum length.
    @return {string} The formatted number. */
function pad(value, length) {
    value = '' + value;
    return '000000'.substring(0, length - value.length) + value;
}

assign(CDate.prototype, {

    /** Create a new date.
        @memberof CDate
        @param [year] {CDate|number} The date to copy or the year for the date (default this date).
        @param [month] {number} The month for the date.
        @param [day] {number} The day for the date.
        @return {CDate} The new date.
        @throws Error if an invalid date. */
    newDate: function(year, month, day) {
        return this._calendar.newDate((year == null ? this : year), month, day);
    },

    /** Set or retrieve the year for this date.
        @memberof CDate
        @param [year] {number} The year for the date.
        @return {number|CDate} The date's year (if no parameter) or the updated date.
        @throws Error if an invalid date. */
    year: function(year) {
        return (arguments.length === 0 ? this._year : this.set(year, 'y'));
    },

    /** Set or retrieve the month for this date.
        @memberof CDate
        @param [month] {number} The month for the date.
        @return {number|CDate} The date's month (if no parameter) or the updated date.
        @throws Error if an invalid date. */
    month: function(month) {
        return (arguments.length === 0 ? this._month : this.set(month, 'm'));
    },

    /** Set or retrieve the day for this date.
        @memberof CDate
        @param [day] {number} The day for the date.
        @return {number|CData} The date's day (if no parameter) or the updated date.
        @throws Error if an invalid date. */
    day: function(day) {
        return (arguments.length === 0 ? this._day : this.set(day, 'd'));
    },

    /** Set new values for this date.
        @memberof CDate
        @param year {number} The year for the date.
        @param month {number} The month for the date.
        @param day {number} The day for the date.
        @return {CDate} The updated date.
        @throws Error if an invalid date. */
    date: function(year, month, day) {
        if (!this._calendar.isValid(year, month, day)) {
            throw (_exports.local.invalidDate || _exports.regionalOptions[''].invalidDate).
                replace(/\{0\}/, this._calendar.local.name);
        }
        this._year = year;
        this._month = month;
        this._day = day;
        return this;
    },

    /** Determine whether this date is in a leap year.
        @memberof CDate
        @return {boolean} <code>true</code> if this is a leap year, <code>false</code> if not. */
    leapYear: function() {
        return this._calendar.leapYear(this);
    },

    /** Retrieve the epoch designator for this date, e.g. BCE or CE.
        @memberof CDate
        @return {string} The current epoch. */
    epoch: function() {
        return this._calendar.epoch(this);
    },

    /** Format the year, if not a simple sequential number.
        @memberof CDate
        @return {string} The formatted year. */
    formatYear: function() {
        return this._calendar.formatYear(this);
    },

    /** Retrieve the month of the year for this date,
        i.e. the month's position within a numbered year.
        @memberof CDate
        @return {number} The month of the year: <code>minMonth</code> to months per year. */
    monthOfYear: function() {
        return this._calendar.monthOfYear(this);
    },

    /** Retrieve the week of the year for this date.
        @memberof CDate
        @return {number} The week of the year: 1 to weeks per year. */
    weekOfYear: function() {
        return this._calendar.weekOfYear(this);
    },

    /** Retrieve the number of days in the year for this date.
        @memberof CDate
        @return {number} The number of days in this year. */
    daysInYear: function() {
        return this._calendar.daysInYear(this);
    },

    /** Retrieve the day of the year for this date.
        @memberof CDate
        @return {number} The day of the year: 1 to days per year. */
    dayOfYear: function() {
        return this._calendar.dayOfYear(this);
    },

    /** Retrieve the number of days in the month for this date.
        @memberof CDate
        @return {number} The number of days. */
    daysInMonth: function() {
        return this._calendar.daysInMonth(this);
    },

    /** Retrieve the day of the week for this date.
        @memberof CDate
        @return {number} The day of the week: 0 to number of days - 1. */
    dayOfWeek: function() {
        return this._calendar.dayOfWeek(this);
    },

    /** Determine whether this date is a week day.
        @memberof CDate
        @return {boolean} <code>true</code> if a week day, <code>false</code> if not. */
    weekDay: function() {
        return this._calendar.weekDay(this);
    },

    /** Retrieve additional information about this date.
        @memberof CDate
        @return {object} Additional information - contents depends on calendar. */
    extraInfo: function() {
        return this._calendar.extraInfo(this);
    },

    /** Add period(s) to a date.
        @memberof CDate
        @param offset {number} The number of periods to adjust by.
        @param period {string} One of 'y' for year, 'm' for month, 'w' for week, 'd' for day.
        @return {CDate} The updated date. */
    add: function(offset, period) {
        return this._calendar.add(this, offset, period);
    },

    /** Set a portion of the date.
        @memberof CDate
        @param value {number} The new value for the period.
        @param period {string} One of 'y' for year, 'm' for month, 'd' for day.
        @return {CDate} The updated date.
        @throws Error if not a valid date. */
    set: function(value, period) {
        return this._calendar.set(this, value, period);
    },

    /** Compare this date to another date.
        @memberof CDate
        @param date {CDate} The other date.
        @return {number} -1 if this date is before the other date,
                0 if they are equal, or +1 if this date is after the other date. */
    compareTo: function(date) {
        if (this._calendar.name !== date._calendar.name) {
            throw (_exports.local.differentCalendars || _exports.regionalOptions[''].differentCalendars).
                replace(/\{0\}/, this._calendar.local.name).replace(/\{1\}/, date._calendar.local.name);
        }
        var c = (this._year !== date._year ? this._year - date._year :
            this._month !== date._month ? this.monthOfYear() - date.monthOfYear() :
            this._day - date._day);
        return (c === 0 ? 0 : (c < 0 ? -1 : +1));
    },

    /** Retrieve the calendar backing this date.
        @memberof CDate
        @return {BaseCalendar} The calendar implementation. */
    calendar: function() {
        return this._calendar;
    },

    /** Retrieve the Julian date equivalent for this date,
        i.e. days since January 1, 4713 BCE Greenwich noon.
        @memberof CDate
        @return {number} The equivalent Julian date. */
    toJD: function() {
        return this._calendar.toJD(this);
    },

    /** Create a new date from a Julian date.
        @memberof CDate
        @param jd {number} The Julian date to convert.
        @return {CDate} The equivalent date. */
    fromJD: function(jd) {
        return this._calendar.fromJD(jd);
    },

    /** Convert this date to a standard (Gregorian) JavaScript Date.
        @memberof CDate
        @return {Date} The equivalent JavaScript date. */
    toJSDate: function() {
        return this._calendar.toJSDate(this);
    },

    /** Create a new date from a standard (Gregorian) JavaScript Date.
        @memberof CDate
        @param jsd {Date} The JavaScript date to convert.
        @return {CDate} The equivalent date. */
    fromJSDate: function(jsd) {
        return this._calendar.fromJSDate(jsd);
    },

    /** Convert to a string for display.
        @memberof CDate
        @return {string} This date as a string. */
    toString: function() {
        return (this.year() < 0 ? '-' : '') + pad(Math.abs(this.year()), 4) +
            '-' + pad(this.month(), 2) + '-' + pad(this.day(), 2);
    }
});

/** Basic functionality for all calendars.
    Other calendars should extend this:
    <pre>OtherCalendar.prototype = new BaseCalendar;</pre>
    @class BaseCalendar */
function BaseCalendar() {
    this.shortYearCutoff = '+10';
}

assign(BaseCalendar.prototype, {
    _validateLevel: 0, // "Stack" to turn validation on/off

    /** Create a new date within this calendar - today if no parameters given.
        @memberof BaseCalendar
        @param year {CDate|number} The date to duplicate or the year for the date.
        @param [month] {number} The month for the date.
        @param [day] {number} The day for the date.
        @return {CDate} The new date.
        @throws Error if not a valid date or a different calendar used. */
    newDate: function(year, month, day) {
        if (year == null) {
            return this.today();
        }
        if (year.year) {
            this._validate(year, month, day,
                _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
            day = year.day();
            month = year.month();
            year = year.year();
        }
        return new CDate(this, year, month, day);
    },

    /** Create a new date for today.
        @memberof BaseCalendar
        @return {CDate} Today's date. */
    today: function() {
        return this.fromJSDate(new Date());
    },

    /** Retrieve the epoch designator for this date.
        @memberof BaseCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @return {string} The current epoch.
        @throws Error if an invalid year or a different calendar used. */
    epoch: function(year) {
        var date = this._validate(year, this.minMonth, this.minDay,
            _exports.local.invalidYear || _exports.regionalOptions[''].invalidYear);
        return (date.year() < 0 ? this.local.epochs[0] : this.local.epochs[1]);
    },

    /** Format the year, if not a simple sequential number
        @memberof BaseCalendar
        @param year {CDate|number} The date to format or the year to format.
        @return {string} The formatted year.
        @throws Error if an invalid year or a different calendar used. */
    formatYear: function(year) {
        var date = this._validate(year, this.minMonth, this.minDay,
            _exports.local.invalidYear || _exports.regionalOptions[''].invalidYear);
        return (date.year() < 0 ? '-' : '') + pad(Math.abs(date.year()), 4)
    },

    /** Retrieve the number of months in a year.
        @memberof BaseCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @return {number} The number of months.
        @throws Error if an invalid year or a different calendar used. */
    monthsInYear: function(year) {
        this._validate(year, this.minMonth, this.minDay,
            _exports.local.invalidYear || _exports.regionalOptions[''].invalidYear);
        return 12;
    },

    /** Calculate the month's ordinal position within the year -
        for those calendars that don't start at month 1!
        @memberof BaseCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @param month {number} The month to examine.
        @return {number} The ordinal position, starting from <code>minMonth</code>.
        @throws Error if an invalid year/month or a different calendar used. */
    monthOfYear: function(year, month) {
        var date = this._validate(year, month, this.minDay,
            _exports.local.invalidMonth || _exports.regionalOptions[''].invalidMonth);
        return (date.month() + this.monthsInYear(date) - this.firstMonth) %
            this.monthsInYear(date) + this.minMonth;
    },

    /** Calculate actual month from ordinal position, starting from minMonth.
        @memberof BaseCalendar
        @param year {number} The year to examine.
        @param ord {number} The month's ordinal position.
        @return {number} The month's number.
        @throws Error if an invalid year/month. */
    fromMonthOfYear: function(year, ord) {
        var m = (ord + this.firstMonth - 2 * this.minMonth) %
            this.monthsInYear(year) + this.minMonth;
        this._validate(year, m, this.minDay,
            _exports.local.invalidMonth || _exports.regionalOptions[''].invalidMonth);
        return m;
    },

    /** Retrieve the number of days in a year.
        @memberof BaseCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @return {number} The number of days.
        @throws Error if an invalid year or a different calendar used. */
    daysInYear: function(year) {
        var date = this._validate(year, this.minMonth, this.minDay,
            _exports.local.invalidYear || _exports.regionalOptions[''].invalidYear);
        return (this.leapYear(date) ? 366 : 365);
    },

    /** Retrieve the day of the year for a date.
        @memberof BaseCalendar
        @param year {CDate|number} The date to convert or the year to convert.
        @param [month] {number} The month to convert.
        @param [day] {number} The day to convert.
        @return {number} The day of the year.
        @throws Error if an invalid date or a different calendar used. */
    dayOfYear: function(year, month, day) {
        var date = this._validate(year, month, day,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        return date.toJD() - this.newDate(date.year(),
            this.fromMonthOfYear(date.year(), this.minMonth), this.minDay).toJD() + 1;
    },

    /** Retrieve the number of days in a week.
        @memberof BaseCalendar
        @return {number} The number of days. */
    daysInWeek: function() {
        return 7;
    },

    /** Retrieve the day of the week for a date.
        @memberof BaseCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @param [month] {number} The month to examine.
        @param [day] {number} The day to examine.
        @return {number} The day of the week: 0 to number of days - 1.
        @throws Error if an invalid date or a different calendar used. */
    dayOfWeek: function(year, month, day) {
        var date = this._validate(year, month, day,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        return (Math.floor(this.toJD(date)) + 2) % this.daysInWeek();
    },

    /** Retrieve additional information about a date.
        @memberof BaseCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @param [month] {number} The month to examine.
        @param [day] {number} The day to examine.
        @return {object} Additional information - contents depends on calendar.
        @throws Error if an invalid date or a different calendar used. */
    extraInfo: function(year, month, day) {
        this._validate(year, month, day,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        return {};
    },

    /** Add period(s) to a date.
        Cater for no year zero.
        @memberof BaseCalendar
        @param date {CDate} The starting date.
        @param offset {number} The number of periods to adjust by.
        @param period {string} One of 'y' for year, 'm' for month, 'w' for week, 'd' for day.
        @return {CDate} The updated date.
        @throws Error if a different calendar used. */
    add: function(date, offset, period) {
        this._validate(date, this.minMonth, this.minDay,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        return this._correctAdd(date, this._add(date, offset, period), offset, period);
    },

    /** Add period(s) to a date.
        @memberof BaseCalendar
        @private
        @param date {CDate} The starting date.
        @param offset {number} The number of periods to adjust by.
        @param period {string} One of 'y' for year, 'm' for month, 'w' for week, 'd' for day.
        @return {CDate} The updated date. */
    _add: function(date, offset, period) {
        this._validateLevel++;
        if (period === 'd' || period === 'w') {
            var jd = date.toJD() + offset * (period === 'w' ? this.daysInWeek() : 1);
            var d = date.calendar().fromJD(jd);
            this._validateLevel--;
            return [d.year(), d.month(), d.day()];
        }
        try {
            var y = date.year() + (period === 'y' ? offset : 0);
            var m = date.monthOfYear() + (period === 'm' ? offset : 0);
            var d = date.day();// + (period === 'd' ? offset : 0) +
                //(period === 'w' ? offset * this.daysInWeek() : 0);
            var resyncYearMonth = function(calendar) {
                while (m < calendar.minMonth) {
                    y--;
                    m += calendar.monthsInYear(y);
                }
                var yearMonths = calendar.monthsInYear(y);
                while (m > yearMonths - 1 + calendar.minMonth) {
                    y++;
                    m -= yearMonths;
                    yearMonths = calendar.monthsInYear(y);
                }
            };
            if (period === 'y') {
                if (date.month() !== this.fromMonthOfYear(y, m)) { // Hebrew
                    m = this.newDate(y, date.month(), this.minDay).monthOfYear();
                }
                m = Math.min(m, this.monthsInYear(y));
                d = Math.min(d, this.daysInMonth(y, this.fromMonthOfYear(y, m)));
            }
            else if (period === 'm') {
                resyncYearMonth(this);
                d = Math.min(d, this.daysInMonth(y, this.fromMonthOfYear(y, m)));
            }
            var ymd = [y, this.fromMonthOfYear(y, m), d];
            this._validateLevel--;
            return ymd;
        }
        catch (e) {
            this._validateLevel--;
            throw e;
        }
    },

    /** Correct a candidate date after adding period(s) to a date.
        Handle no year zero if necessary.
        @memberof BaseCalendar
        @private
        @param date {CDate} The starting date.
        @param ymd {number[]} The added date.
        @param offset {number} The number of periods to adjust by.
        @param period {string} One of 'y' for year, 'm' for month, 'w' for week, 'd' for day.
        @return {CDate} The updated date. */
    _correctAdd: function(date, ymd, offset, period) {
        if (!this.hasYearZero && (period === 'y' || period === 'm')) {
            if (ymd[0] === 0 || // In year zero
                    (date.year() > 0) !== (ymd[0] > 0)) { // Crossed year zero
                var adj = {y: [1, 1, 'y'], m: [1, this.monthsInYear(-1), 'm'],
                    w: [this.daysInWeek(), this.daysInYear(-1), 'd'],
                    d: [1, this.daysInYear(-1), 'd']}[period];
                var dir = (offset < 0 ? -1 : +1);
                ymd = this._add(date, offset * adj[0] + dir * adj[1], adj[2]);
            }
        }
        return date.date(ymd[0], ymd[1], ymd[2]);
    },

    /** Set a portion of the date.
        @memberof BaseCalendar
        @param date {CDate} The starting date.
        @param value {number} The new value for the period.
        @param period {string} One of 'y' for year, 'm' for month, 'd' for day.
        @return {CDate} The updated date.
        @throws Error if an invalid date or a different calendar used. */
    set: function(date, value, period) {
        this._validate(date, this.minMonth, this.minDay,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        var y = (period === 'y' ? value : date.year());
        var m = (period === 'm' ? value : date.month());
        var d = (period === 'd' ? value : date.day());
        if (period === 'y' || period === 'm') {
            d = Math.min(d, this.daysInMonth(y, m));
        }
        return date.date(y, m, d);
    },

    /** Determine whether a date is valid for this calendar.
        @memberof BaseCalendar
        @param year {number} The year to examine.
        @param month {number} The month to examine.
        @param day {number} The day to examine.
        @return {boolean} <code>true</code> if a valid date, <code>false</code> if not. */
    isValid: function(year, month, day) {
        this._validateLevel++;
        var valid = (this.hasYearZero || year !== 0);
        if (valid) {
            var date = this.newDate(year, month, this.minDay);
            valid = (month >= this.minMonth && month - this.minMonth < this.monthsInYear(date)) &&
                (day >= this.minDay && day - this.minDay < this.daysInMonth(date));
        }
        this._validateLevel--;
        return valid;
    },

    /** Convert the date to a standard (Gregorian) JavaScript Date.
        @memberof BaseCalendar
        @param year {CDate|number} The date to convert or the year to convert.
        @param [month] {number} The month to convert.
        @param [day] {number} The day to convert.
        @return {Date} The equivalent JavaScript date.
        @throws Error if an invalid date or a different calendar used. */
    toJSDate: function(year, month, day) {
        var date = this._validate(year, month, day,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        return _exports.instance().fromJD(this.toJD(date)).toJSDate();
    },

    /** Convert the date from a standard (Gregorian) JavaScript Date.
        @memberof BaseCalendar
        @param jsd {Date} The JavaScript date.
        @return {CDate} The equivalent calendar date. */
    fromJSDate: function(jsd) {
        return this.fromJD(_exports.instance().fromJSDate(jsd).toJD());
    },

    /** Check that a candidate date is from the same calendar and is valid.
        @memberof BaseCalendar
        @private
        @param year {CDate|number} The date to validate or the year to validate.
        @param [month] {number} The month to validate.
        @param [day] {number} The day to validate.
        @param error {string} Rrror message if invalid.
        @throws Error if different calendars used or invalid date. */
    _validate: function(year, month, day, error) {
        if (year.year) {
            if (this._validateLevel === 0 && this.name !== year.calendar().name) {
                throw (_exports.local.differentCalendars || _exports.regionalOptions[''].differentCalendars).
                    replace(/\{0\}/, this.local.name).replace(/\{1\}/, year.calendar().local.name);
            }
            return year;
        }
        try {
            this._validateLevel++;
            if (this._validateLevel === 1 && !this.isValid(year, month, day)) {
                throw error.replace(/\{0\}/, this.local.name);
            }
            var date = this.newDate(year, month, day);
            this._validateLevel--;
            return date;
        }
        catch (e) {
            this._validateLevel--;
            throw e;
        }
    }
});

/** Implementation of the Proleptic Gregorian Calendar.
    See <a href=":http://en.wikipedia.org/wiki/Gregorian_calendar">http://en.wikipedia.org/wiki/Gregorian_calendar</a>
    and <a href="http://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar">http://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar</a>.
    @class GregorianCalendar
    @augments BaseCalendar
    @param [language=''] {string} The language code (default English) for localisation. */
function GregorianCalendar(language) {
    this.local = this.regionalOptions[language] || this.regionalOptions[''];
}

GregorianCalendar.prototype = new BaseCalendar;

assign(GregorianCalendar.prototype, {
    /** The calendar name.
        @memberof GregorianCalendar */
    name: 'Gregorian',
     /** Julian date of start of Gregorian epoch: 1 January 0001 CE.
        @memberof GregorianCalendar */
    jdEpoch: 1721425.5,
     /** Days per month in a common year.
        @memberof GregorianCalendar */
    daysPerMonth: [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31],
     /** <code>true</code> if has a year zero, <code>false</code> if not.
        @memberof GregorianCalendar */
    hasYearZero: false,
    /** The minimum month number.
        @memberof GregorianCalendar */
    minMonth: 1,
    /** The first month in the year.
        @memberof GregorianCalendar */
    firstMonth: 1,
     /** The minimum day number.
        @memberof GregorianCalendar */
    minDay: 1,

    /** Localisations for the plugin.
        Entries are objects indexed by the language code ('' being the default US/English).
        Each object has the following attributes.
        @memberof GregorianCalendar
        @property name {string} The calendar name.
        @property epochs {string[]} The epoch names.
        @property monthNames {string[]} The long names of the months of the year.
        @property monthNamesShort {string[]} The short names of the months of the year.
        @property dayNames {string[]} The long names of the days of the week.
        @property dayNamesShort {string[]} The short names of the days of the week.
        @property dayNamesMin {string[]} The minimal names of the days of the week.
        @property dateFormat {string} The date format for this calendar.
                See the options on <a href="BaseCalendar.html#formatDate"><code>formatDate</code></a> for details.
        @property firstDay {number} The number of the first day of the week, starting at 0.
        @property isRTL {number} <code>true</code> if this localisation reads right-to-left. */
    regionalOptions: { // Localisations
        '': {
            name: 'Gregorian',
            epochs: ['BCE', 'CE'],
            monthNames: ['January', 'February', 'March', 'April', 'May', 'June',
            'July', 'August', 'September', 'October', 'November', 'December'],
            monthNamesShort: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
            dayNames: ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'],
            dayNamesShort: ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'],
            dayNamesMin: ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'],
            digits: null,
            dateFormat: 'mm/dd/yyyy',
            firstDay: 0,
            isRTL: false
        }
    },
    
    /** Determine whether this date is in a leap year.
        @memberof GregorianCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @return {boolean} <code>true</code> if this is a leap year, <code>false</code> if not.
        @throws Error if an invalid year or a different calendar used. */
    leapYear: function(year) {
        var date = this._validate(year, this.minMonth, this.minDay,
            _exports.local.invalidYear || _exports.regionalOptions[''].invalidYear);
        var year = date.year() + (date.year() < 0 ? 1 : 0); // No year zero
        return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
    },

    /** Determine the week of the year for a date - ISO 8601.
        @memberof GregorianCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @param [month] {number} The month to examine.
        @param [day] {number} The day to examine.
        @return {number} The week of the year, starting from 1.
        @throws Error if an invalid date or a different calendar used. */
    weekOfYear: function(year, month, day) {
        // Find Thursday of this week starting on Monday
        var checkDate = this.newDate(year, month, day);
        checkDate.add(4 - (checkDate.dayOfWeek() || 7), 'd');
        return Math.floor((checkDate.dayOfYear() - 1) / 7) + 1;
    },

    /** Retrieve the number of days in a month.
        @memberof GregorianCalendar
        @param year {CDate|number} The date to examine or the year of the month.
        @param [month] {number} The month.
        @return {number} The number of days in this month.
        @throws Error if an invalid month/year or a different calendar used. */
    daysInMonth: function(year, month) {
        var date = this._validate(year, month, this.minDay,
            _exports.local.invalidMonth || _exports.regionalOptions[''].invalidMonth);
        return this.daysPerMonth[date.month() - 1] +
            (date.month() === 2 && this.leapYear(date.year()) ? 1 : 0);
    },

    /** Determine whether this date is a week day.
        @memberof GregorianCalendar
        @param year {CDate|number} The date to examine or the year to examine.
        @param [month] {number} The month to examine.
        @param [day] {number} The day to examine.
        @return {boolean} <code>true</code> if a week day, <code>false</code> if not.
        @throws Error if an invalid date or a different calendar used. */
    weekDay: function(year, month, day) {
        return (this.dayOfWeek(year, month, day) || 7) < 6;
    },

    /** Retrieve the Julian date equivalent for this date,
        i.e. days since January 1, 4713 BCE Greenwich noon.
        @memberof GregorianCalendar
        @param year {CDate|number} The date to convert or the year to convert.
        @param [month] {number} The month to convert.
        @param [day] {number} The day to convert.
        @return {number} The equivalent Julian date.
        @throws Error if an invalid date or a different calendar used. */
    toJD: function(year, month, day) {
        var date = this._validate(year, month, day,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        year = date.year();
        month = date.month();
        day = date.day();
        if (year < 0) { year++; } // No year zero
        // Jean Meeus algorithm, "Astronomical Algorithms", 1991
        if (month < 3) {
            month += 12;
            year--;
        }
        var a = Math.floor(year / 100);
        var b = 2 - a + Math.floor(a / 4);
        return Math.floor(365.25 * (year + 4716)) +
            Math.floor(30.6001 * (month + 1)) + day + b - 1524.5;
    },

    /** Create a new date from a Julian date.
        @memberof GregorianCalendar
        @param jd {number} The Julian date to convert.
        @return {CDate} The equivalent date. */
    fromJD: function(jd) {
        // Jean Meeus algorithm, "Astronomical Algorithms", 1991
        var z = Math.floor(jd + 0.5);
        var a = Math.floor((z - 1867216.25) / 36524.25);
        a = z + 1 + a - Math.floor(a / 4);
        var b = a + 1524;
        var c = Math.floor((b - 122.1) / 365.25);
        var d = Math.floor(365.25 * c);
        var e = Math.floor((b - d) / 30.6001);
        var day = b - d - Math.floor(e * 30.6001);
        var month = e - (e > 13.5 ? 13 : 1);
        var year = c - (month > 2.5 ? 4716 : 4715);
        if (year <= 0) { year--; } // No year zero
        return this.newDate(year, month, day);
    },

    /** Convert this date to a standard (Gregorian) JavaScript Date.
        @memberof GregorianCalendar
        @param year {CDate|number} The date to convert or the year to convert.
        @param [month] {number} The month to convert.
        @param [day] {number} The day to convert.
        @return {Date} The equivalent JavaScript date.
        @throws Error if an invalid date or a different calendar used. */
    toJSDate: function(year, month, day) {
        var date = this._validate(year, month, day,
            _exports.local.invalidDate || _exports.regionalOptions[''].invalidDate);
        var jsd = new Date(date.year(), date.month() - 1, date.day());
        jsd.setHours(0);
        jsd.setMinutes(0);
        jsd.setSeconds(0);
        jsd.setMilliseconds(0);
        // Hours may be non-zero on daylight saving cut-over:
        // > 12 when midnight changeover, but then cannot generate
        // midnight datetime, so jump to 1AM, otherwise reset.
        jsd.setHours(jsd.getHours() > 12 ? jsd.getHours() + 2 : 0);
        return jsd;
    },

    /** Create a new date from a standard (Gregorian) JavaScript Date.
        @memberof GregorianCalendar
        @param jsd {Date} The JavaScript date to convert.
        @return {CDate} The equivalent date. */
    fromJSDate: function(jsd) {
        return this.newDate(jsd.getFullYear(), jsd.getMonth() + 1, jsd.getDate());
    }
});

// Singleton manager
var _exports = module.exports = new Calendars();

// Date template
_exports.cdate = CDate;

// Base calendar template
_exports.baseCalendar = BaseCalendar;

// Gregorian calendar implementation
_exports.calendars.gregorian = GregorianCalendar;