/**
 * Earth's hemispheres.
 *
 * @typedef {string} Hemisphere
 * @enum {Hemisphere}
 */
const Hemisphere = {
  NORTHERN: "Northern",
  SOUTHERN: "Southern",
};

/**
 * Enumeration of lunar phases as emoji
 *
 * @typedef {string} LunarEmoji
 */
const LunarEmoji = {
  /**
   * Enumeration of lunar phases as emoji for the Northern Hemisphere.
   * @num {LunarPhase}
   */
  NorthernHemisphere: {
    NEW: "🌑",
    WAXING_CRESCENT: "🌒",
    FIRST_QUARTER: "🌓",
    WAXING_GIBBOUS: "🌔",
    FULL: "🌕",
    WANING_GIBBOUS: "🌖",
    LAST_QUARTER: "🌗",
    WANING_CRESCENT: "🌘",
  },

  /**
   * Enumeration of lunar phases as emoji for the Southern Hemisphere.
   * @num {LunarPhase}
   */
  SouthernHemisphere: {
    NEW: "🌑",
    WAXING_CRESCENT: "🌘",
    FIRST_QUARTER: "🌗",
    WAXING_GIBBOUS: "🌖",
    FULL: "🌕",
    WANING_GIBBOUS: "🌔",
    LAST_QUARTER: "🌓",
    WANING_CRESCENT: "🌒",
  },
};

/**
 * Lunar month, time between two successive syzygies of the
 * same type: new moons or full moons
 *
 * @typedef {string} LunarMonth
 * @enum {LunarMonth}
 */
const LunarMonth = {
  ANOMALISTIC: "Anomalistic",
  DRACONIC: "Draconic",
  SIDEREAL: "Sidereal",
  SYNODIC: "Synodic",
  TROPICAL: "Tropical",
};

/**
 * Enumeration of lunar phases
 *
 * @typedef {string} LunarPhase
 * @enum {LunarPhase}
 */
const LunarPhase = {
  NEW: "New",
  WAXING_CRESCENT: "Waxing Crescent",
  FIRST_QUARTER: "First Quarter",
  WAXING_GIBBOUS: "Waxing Gibbous",
  FULL: "Full",
  WANING_GIBBOUS: "Waning Gibbous",
  LAST_QUARTER: "Last Quarter",
  WANING_CRESCENT: "Waning Crescent",
};

/**
 * Units of measure
 *
 * @typedef {string} Unit
 * @enum {Unit}
 */
const Unit = {
  EARTH_RADII: "Earth Radii",
  KILOMETERS: "km",
  MILES: "m",
};

/**
 * Timestamp epoch, January 1, 1970, in Julian Days.
 * @type {number}
 */
const EPOCH = 2440587.5;

/**
 * Lunation 1 as the first new moon of 1923 at approximately
 * 02:41 UTC, January 17, 1923 per Ernest William Brown's lunar theory.
 * @type {number}
 */
const LUNATION_BASE_JULIAN_DAY = 2423436.6115277777;

/**
 * Length of one phase (1/8 of a synodic month) in Earth days.
 * @type {number}
 */
const PHASE_LENGTH = 3.69132346322;

/**
 * Orbital period of the Moon from perigee to apogee and back to perigee
 * @type {number}
 */
const ANOMALISTIC_MONTH = 27.55454988;

/**
 * Length of one synodic month - lunation, or days for the phases to complete a cycle.
 * Time between two identical syzygies, equivalent of 29.53059 Earth days.
 *
 * Based on Mean Synodic Month, 2000 AD mean solar days.
 * @type {number}
 */
const SYNODIC_MONTH = 29.53058770576;

var Time = /*#__PURE__*/Object.freeze({
  __proto__: null,
  EPOCH: EPOCH,
  LUNATION_BASE_JULIAN_DAY: LUNATION_BASE_JULIAN_DAY,
  PHASE_LENGTH: PHASE_LENGTH,
  ANOMALISTIC_MONTH: ANOMALISTIC_MONTH,
  SYNODIC_MONTH: SYNODIC_MONTH
});

/**
 * Normalization utility for percentage calculations.
 *
 * @param {number} value Percent value.
 * @returns {number} Normalized value
 */
const normalize = (value) => {
  value -= Math.floor(value);
  if (value < 0) {
    value += 1;
  }

  return value;
};

/**
 * Julian day from Gregorian date.
 * @param {Date} date Gregorian date to convert to Julian day.
 * @returns {number} Julian Day
 */
const fromDate = (date = new Date()) => {
  const time = date.getTime();
  return time / 86400000 - date.getTimezoneOffset() / 1440 + EPOCH;
};

/**
 * Gregorian date from Julian day
 * @param {number} julian Julian dat to convert to Gregorian date
 * @returns {Date} Gregorian date
 */
const toDate = (julian) => {
  let date = new Date();
  date.setTime((julian - EPOCH + date.getTimezoneOffset() / 1440) * 86400000);
  return date;
};

var JulianDay = /*#__PURE__*/Object.freeze({
  __proto__: null,
  fromDate: fromDate,
  toDate: toDate
});

/**
 * Moon's age, or Earth days since the last new moon.
 *
 * @param {Date} date Date used for calculation.
 * @returns {number} Age of the moon, normalized within a 29.53059 Earth days calendar.
 */
const lunarAge = (date = new Date()) => {
  const percent = lunarAgePercent(date);
  return percent * SYNODIC_MONTH;
};

/**
 * Percentage through the lunar synodic month.
 *
 * @param {Date} date Date used for calculation.
 * @returns {number} Percentage through the lunar month.
 */
const lunarAgePercent = (date = new Date()) => {
  return normalize((fromDate(date) - 2451550.1) / SYNODIC_MONTH);
};

/**
 * Brown Lunation Number (BLN), per Ernest William Brown's lunar theory,
 * defining Lunation 1 as the first new moon of 1923 at
 * approximately 02:41 UTC, January 17, 1923.
 *
 * @param {Date} date Date used for calculation.
 * @returns {number} Lunation Number
 */
const lunationNumber = (date = new Date()) => {
  return Math.round((fromDate(date) - LUNATION_BASE_JULIAN_DAY) / SYNODIC_MONTH) + 1;
};

/**
 * Distance to the moon measured in units of Earth radii, with
 * perigee at 56 and apogee at 63.8.
 *
 * @param {Date} date Date used for calculation
 * @returns {number} Distance to the moon in Earth radii
 */
const lunarDistance = (date = new Date()) => {
  const julian = fromDate(date);
  const agePercent = lunarAgePercent(date);
  const radians = agePercent * 2 * Math.PI;
  const percent = 2 * Math.PI * normalize((julian - 2451562.2) / ANOMALISTIC_MONTH);

  return 60.4 - 3.3 * Math.cos(percent) - 0.6 * Math.cos(2 * radians - percent) - 0.5 * Math.cos(2 * radians);
};

/**
 * Name of the lunar phase per date submitted.
 *
 * @param {Date} date Date used to calculate lunar phase.
 * @returns {string} Name as string of the current lunar phase.
 */
const lunarPhase = (date = new Date()) => {
  const age = lunarAge(date);

  if (age < 1.84566173161) return LunarPhase.NEW;
  else if (age < 5.53698519483) return LunarPhase.WAXING_CRESCENT;
  else if (age < 9.22830865805) return LunarPhase.FIRST_QUARTER;
  else if (age < 12.91963212127) return LunarPhase.WAXING_GIBBOUS;
  else if (age < 16.61095558449) return LunarPhase.FULL;
  else if (age < 20.30227904771) return LunarPhase.WANING_GIBBOUS;
  else if (age < 23.99360251093) return LunarPhase.LAST_QUARTER;
  else if (age < 27.68492597415) return LunarPhase.WANING_CRESCENT;

  return LunarPhase.NEW;
};

/**
 * Emoji of the lunar phase per date submitted.
 *
 * @param {Date} date Date used to calculate lunar phase.
 * @param {Hemisphere} hemisphere Northern or Southern Hemisphere.
 * @returns Emoji of the current lunar phase.
 */
const lunarPhaseEmoji = (date = new Date(), hemisphere = Hemisphere.NORTHERN) => {
  const phase = lunarPhase(date);

  return emojiForLunarPhase(phase, hemisphere);
};

/**
 * Emoji for specified lunar phase.
 *
 * @param {LunarPhase} phase Lunar phase, per the LunarPhase enum
 * @param {Hemisphere} hemisphere Northern or Southern Hemisphere.
 * @returns {string} Emoji of the current lunar phase.
 */
const emojiForLunarPhase = (phase, hemisphere = Hemisphere.NORTHERN) => {
  let emoji;

  if (hemisphere === Hemisphere.SOUTHERN) {
    emoji = LunarEmoji.SouthernHemisphere;
  } else {
    emoji = LunarEmoji.NorthernHemisphere;
  }

  switch (phase) {
    case LunarPhase.WANING_CRESCENT:
      return emoji["WANING_CRESCENT"];
    case LunarPhase.LAST_QUARTER:
      return emoji["LAST_QUARTER"];
    case LunarPhase.WANING_GIBBOUS:
      return emoji["WANING_GIBBOUS"];
    case LunarPhase.FULL:
      return emoji["FULL"];
    case LunarPhase.WAXING_GIBBOUS:
      return emoji["WAXING_GIBBOUS"];
    case LunarPhase.FIRST_QUARTER:
      return emoji["FIRST_QUARTER"];
    case LunarPhase.WAXING_CRESCENT:
      return emoji["WAXING_CRESCENT"];

    default:
    case LunarPhase.NEW:
      return emoji["NEW"];
  }
};

/**
 * Whether the moon is currently waxing (growing).
 *
 * @param {Date} date Date used for calculation.
 * @returns {boolean} True if moon is waxing.
 */
const isWaxing = (date = new Date()) => {
  const age = lunarAge(date);
  return age <= 14.765;
};

/**
 * Whether the moon is currently waning (shrinking).
 *
 * @param {Date} date Date used for calculation.
 * @returns {boolean} True if moon is waning.
 */
const isWaning = (date = new Date()) => {
  const age = lunarAge(date);
  return age > 14.765;
};

var Moon = /*#__PURE__*/Object.freeze({
  __proto__: null,
  lunarAge: lunarAge,
  lunarAgePercent: lunarAgePercent,
  lunationNumber: lunationNumber,
  lunarDistance: lunarDistance,
  lunarPhase: lunarPhase,
  lunarPhaseEmoji: lunarPhaseEmoji,
  emojiForLunarPhase: emojiForLunarPhase,
  isWaxing: isWaxing,
  isWaning: isWaning
});

export { Hemisphere, JulianDay, LunarEmoji, LunarMonth, LunarPhase, Moon, Time, Unit };
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