@hebcal/hdate/dist/esm/greg.js

converts between Hebrew and Gregorian dates using Rata Die (R.D.) algorithm by Dershowitz and Reingold

/*! @hebcal/hdate v0.22.5, distributed under GPLv2 https://www.gnu.org/licenses/gpl-2.0.txt */
/** @private */
const lengths = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
/** @private */
const monthLengths = [lengths, lengths.slice()];
monthLengths[1][2] = 29;
/**
 * @private
 */
function mod(x, y) {
    return x - y * Math.floor(x / y);
}
/**
 * @private
 */
function quotient(x, y) {
    return Math.floor(x / y);
}
/**
 * @private
 * @param abs - R.D. number of days
 */
function yearFromFixed(abs) {
    const l0 = abs - 1;
    const n400 = quotient(l0, 146097);
    const d1 = mod(l0, 146097);
    const n100 = quotient(d1, 36524);
    const d2 = mod(d1, 36524);
    const n4 = quotient(d2, 1461);
    const d3 = mod(d2, 1461);
    const n1 = quotient(d3, 365);
    const year = 400 * n400 + 100 * n100 + 4 * n4 + n1;
    return n100 !== 4 && n1 !== 4 ? year + 1 : year;
}
/*
const ABS_14SEP1752 = 639797;
const ABS_2SEP1752 = 639785;
*/
/*
 * Formerly in namespace, now top-level
 */
/**
 * Returns true if the Gregorian year is a leap year
 * @param year Gregorian year
 * @example
 * isGregLeapYear(2000); // true
 * isGregLeapYear(2020); // true
 * isGregLeapYear(2023); // false
 * isGregLeapYear(2100); // false (divisible by 100 but not 400)
 */
function isGregLeapYear(year) {
    return !(year % 4) && (!!(year % 100) || !(year % 400));
}
/**
 * Number of days in the Gregorian month for given year
 * @param month Gregorian month (1=January, 12=December)
 * @param year Gregorian year
 * @example
 * daysInGregMonth(2, 2024); // 29 (February in a leap year)
 * daysInGregMonth(2, 2023); // 28
 * daysInGregMonth(7, 2024); // 31 (July)
 */
function daysInGregMonth(month, year) {
    // 1 based months
    return monthLengths[+isGregLeapYear(year)][month];
}
/**
 * Returns true if the object is a Javascript Date
 * @example
 * isDate(new Date()); // true
 * isDate('2024-01-01'); // false
 * isDate(1700000000000); // false
 */
function isDate(obj) {
    // eslint-disable-next-line no-prototype-builtins
    return typeof obj === 'object' && Date.prototype.isPrototypeOf(obj);
}
/**
 * @private
 * @param year
 * @param month (1-12)
 * @param day (1-31)
 */
function toFixed(year, month, day) {
    const py = year - 1;
    return (365 * py +
        quotient(py, 4) -
        quotient(py, 100) +
        quotient(py, 400) +
        quotient(367 * month - 362, 12) +
        (month <= 2 ? 0 : isGregLeapYear(year) ? -1 : -2) +
        day);
}
/**
 * Converts Gregorian date to absolute R.D. (Rata Die) days
 * @param date Gregorian date
 * @example
 * greg2abs(new Date(2008, 10, 13)); // 733359 (13 November 2008)
 * greg2abs(new Date(2005, 3, 2)); // 732038 (2 April 2005)
 */
function greg2abs(date) {
    if (!isDate(date)) {
        throw new TypeError(`not a Date: ${date}`);
    }
    else if (isNaN(date.getTime())) {
        throw new RangeError('Invalid Date');
    }
    const abs = toFixed(date.getFullYear(), date.getMonth() + 1, date.getDate());
    /*
      if (abs < ABS_14SEP1752 && abs > ABS_2SEP1752) {
        throw new RangeError(`Invalid Date: ${date}`);
      }
      */
    return abs;
}
/**
 * Converts from Rata Die (R.D. number) to Gregorian date.
 * See the footnote on page 384 of ``Calendrical Calculations, Part II:
 * Three Historical Calendars'' by E. M. Reingold,  N. Dershowitz, and S. M.
 * Clamen, Software--Practice and Experience, Volume 23, Number 4
 * (April, 1993), pages 383-404 for an explanation.
 *
 * Note that this function returns the daytime portion of the date.
 * For example, the 15th of Cheshvan 5769 began at sundown on
 * 12 November 2008 and continues through 13 November 2008. This
 * function would return only the date 13 November 2008.
 * @param abs - R.D. number of days
 * @example
 * const abs = hebrew2abs(5769, months.CHESHVAN, 15);
 * const date = abs2greg(abs); // 13 November 2008
 * const year = date.getFullYear(); // 2008
 * const monthNum = date.getMonth() + 1; // 11
 * const day = date.getDate(); // 13
 */
function abs2greg(abs) {
    if (typeof abs !== 'number' || isNaN(abs)) {
        throw new TypeError(`not a Number: ${abs}`);
    }
    abs = Math.trunc(abs);
    /*
      if (abs < ABS_14SEP1752 && abs > ABS_2SEP1752) {
        throw new RangeError(`Invalid Date: ${abs}`);
      }
      */
    const year = yearFromFixed(abs);
    const priorDays = abs - toFixed(year, 1, 1);
    const correction = abs < toFixed(year, 3, 1) ? 0 : isGregLeapYear(year) ? 1 : 2;
    const month = quotient(12 * (priorDays + correction) + 373, 367);
    const day = abs - toFixed(year, month, 1) + 1;
    const dt = new Date(year, month - 1, day);
    if (year < 100 && year >= 0) {
        dt.setFullYear(year);
    }
    return dt;
}

export { abs2greg, daysInGregMonth, greg2abs, isDate, isGregLeapYear };
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