'use strict';

Object.defineProperty(exports, '__esModule', { value: true });

/**
 * @private
 */
function _toYear (year) {
  if (!year) {
    year = new Date().getFullYear();
  } else if (year instanceof Date) {
    year = year.getFullYear();
  } else if (typeof year === 'string') {
    year = parseInt(year, 10);
  }
  return year
}

function pre (num, l) {
  l = l || 2;
  const s = '0000' + num;
  return s.substr(s.length - l, l)
}

class EasterDate {
  constructor (year, month, day) {
    this.year = year;
    this.month = month;
    this.day = day;
  }

  toString () {
    return [pre(this.year, 4), pre(this.month), pre(this.day)].join('-')
  }
}

/**
 * from https://de.wikipedia.org/wiki/Gau%C3%9Fsche_Osterformel
 * ergänzte Formel
 */
function _easter (year, julian, gregorian) {
  year = _toYear(year);

  const k = Math.floor(year / 100);
  let m = 15 + Math.floor((3 * k + 3) / 4) - Math.floor((8 * k + 13) / 25);
  let s = 2 - Math.floor((3 * k + 3) / 4);
  if (julian) {
    m = 15;
    s = 0;
  }
  const a = year % 19;
  const d = (19 * a + m) % 30;
  const r = Math.floor((d + a / 11) / 29);
  const og = 21 + d - r;
  const sz = 7 - Math.floor(year + year / 4 + s) % 7;
  const oe = 7 - (og - sz) % 7;
  let os = og + oe;
  if (gregorian) {
    os = os + Math.floor(year / 100) - Math.floor(year / 400) - 2;
  }
  //                        1   2   3   4   5   6   7   8
  const daysPerMonth = [0, 31, 28, 31, 30, 31, 30, 31, 31];
  let day = os;
  let month;
  for (month = 3; month < 8; month++) {
    if (day <= daysPerMonth[month]) {
      break
    }
    day -= daysPerMonth[month];
  }

  return new EasterDate(year, month, day)
}

/**
 * Calculate easter sunday in the gregorian calendar
 * @param {Date|Number} year
 * @return {EasterDate}
 */
function gregorianEaster (year) {
  return _easter(year)
}

/**
 * Calculate easter sunday in the gregorian calendar (Shortcut for
 * `gregorianEaster`)
 * @param {Date|Number} year
 * @return {EasterDate}
 */
const easter = gregorianEaster;

/**
 * Calculate easter sunday in the julian calendar
 * @param {Date|Number} year
 * @return {EasterDate}
 */
function julianEaster (year) {
  return _easter(year, true)
}

/**
 * Orthodox Easter in gregorian calender
 * @param {Date|Number} year
 * @return {EasterDate}
 */
function orthodoxEaster (year) {
  return _easter(year, true, true)
}

var index = {
  easter,
  gregorianEaster,
  julianEaster,
  orthodoxEaster
};

exports.EasterDate = EasterDate;
exports.default = index;
exports.easter = easter;
exports.gregorianEaster = gregorianEaster;
exports.julianEaster = julianEaster;
exports.orthodoxEaster = orthodoxEaster;