moon/lib/lunar.ts

/**
 * Lunar Calculation Engine
 * Based on Jean Meeus' Astronomical Algorithms
 * Calculates moon phases, illumination, age, and positions
 */

// Synodic month (average lunation period) in days
const SYNODIC_MONTH = 29.53058868;

// Known new moon reference: January 6, 2000, 18:14 UTC (Julian date)
const KNOWN_NEW_MOON_JD = 2451550.1;

export type MoonPhaseName = 'new_moon' | 'waxing_crescent' | 'first_quarter' | 'waxing_gibbous' | 'full_moon' | 'waning_gibbous' | 'last_quarter' | 'waning_crescent';

export interface MoonPhaseInfo {
  phase: number; // 0-1 (0 = new moon, 0.5 = full moon)
  phaseName: MoonPhaseName;
  illumination: number; // 0-100%
  age: number; // days since new moon
  emoji: string;
  angleDeg: number; // 0-360
}

export interface MoonEvent {
  date: Date;
  phase: 'new_moon' | 'first_quarter' | 'full_moon' | 'last_quarter';
  name: string;
}

export interface FullMoonInfo {
  date: Date;
  traditionalName: string;
  month: number;
}

/**
 * Convert a Date to Julian Date
 */
export function dateToJD(date: Date): number {
  const y = date.getUTCFullYear();
  const m = date.getUTCMonth() + 1;
  const d = date.getUTCDate() + date.getUTCHours() / 24 + date.getUTCMinutes() / 1440 + date.getUTCSeconds() / 86400;

  let yr = y;
  let mo = m;
  if (mo <= 2) {
    yr -= 1;
    mo += 12;
  }

  const A = Math.floor(yr / 100);
  const B = 2 - A + Math.floor(A / 4);

  return Math.floor(365.25 * (yr + 4716)) + Math.floor(30.6001 * (mo + 1)) + d + B - 1524.5;
}

/**
 * Convert Julian Date to Date
 */
export function jdToDate(jd: number): Date {
  const z = Math.floor(jd + 0.5);
  const f = jd + 0.5 - z;
  let A: number;

  if (z < 2299161) {
    A = z;
  } else {
    const alpha = Math.floor((z - 1867216.25) / 36524.25);
    A = z + 1 + alpha - Math.floor(alpha / 4);
  }

  const B = A + 1524;
  const C = Math.floor((B - 122.1) / 365.25);
  const D = Math.floor(365.25 * C);
  const E = Math.floor((B - D) / 30.6001);

  const day = B - D - Math.floor(30.6001 * E);
  const month = E < 14 ? E - 1 : E - 13;
  const year = month > 2 ? C - 4716 : C - 4715;

  const hours = f * 24;
  const h = Math.floor(hours);
  const mins = Math.floor((hours - h) * 60);
  const secs = Math.floor(((hours - h) * 60 - mins) * 60);

  return new Date(Date.UTC(year, month - 1, day, h, mins, secs));
}

/**
 * Calculate moon phase for a given date
 * Returns a value between 0 and 1 (0 = new moon, 0.5 = full moon)
 */
export function getMoonPhase(date: Date): number {
  const jd = dateToJD(date);
  const daysSinceNew = jd - KNOWN_NEW_MOON_JD;
  const cycles = daysSinceNew / SYNODIC_MONTH;
  const phase = cycles - Math.floor(cycles);
  return phase < 0 ? phase + 1 : phase;
}

/**
 * Get detailed moon phase information
 */
export function getMoonPhaseInfo(date: Date): MoonPhaseInfo {
  const phase = getMoonPhase(date);
  const age = phase * SYNODIC_MONTH;
  const angleDeg = phase * 360;

  // Illumination (simplified: 0 at new moon, 100 at full moon)
  const illumination = Math.round((1 - Math.cos(phase * 2 * Math.PI)) / 2 * 100);

  let phaseName: MoonPhaseName;
  let emoji: string;

  if (phase < 0.0625) {
    phaseName = 'new_moon';
    emoji = '🌑';
  } else if (phase < 0.1875) {
    phaseName = 'waxing_crescent';
    emoji = '🌒';
  } else if (phase < 0.3125) {
    phaseName = 'first_quarter';
    emoji = '🌓';
  } else if (phase < 0.4375) {
    phaseName = 'waxing_gibbous';
    emoji = '🌔';
  } else if (phase < 0.5625) {
    phaseName = 'full_moon';
    emoji = '🌕';
  } else if (phase < 0.6875) {
    phaseName = 'waning_gibbous';
    emoji = '🌖';
  } else if (phase < 0.8125) {
    phaseName = 'last_quarter';
    emoji = '🌗';
  } else if (phase < 0.9375) {
    phaseName = 'waning_crescent';
    emoji = '🌘';
  } else {
    phaseName = 'new_moon';
    emoji = '🌑';
  }

  return { phase, phaseName, illumination, age, emoji, angleDeg };
}

/**
 * Calculate more precise moon phase times using iterative refinement
 * targetPhase: 0 = new, 0.25 = first quarter, 0.5 = full, 0.75 = last quarter
 */
function findPhaseEvent(startJD: number, targetPhase: number): number {
  // Search forward from startJD
  let jd = startJD;
  const step = 1; // 1 day step

  // Coarse search
  let prevDiff = 999;
  for (let i = 0; i < 35; i++) {
    const daysSinceNew = (jd + i * step) - KNOWN_NEW_MOON_JD;
    const cycles = daysSinceNew / SYNODIC_MONTH;
    const phase = cycles - Math.floor(cycles);
    let diff = phase - targetPhase;
    if (diff < -0.5) diff += 1;
    if (diff > 0.5) diff -= 1;
    const absDiff = Math.abs(diff);

    if (absDiff < prevDiff) {
      prevDiff = absDiff;
      jd = startJD + i * step;
    }
  }

  // Fine search: binary search refinement
  let lo = jd - 1;
  let hi = jd + 1;

  for (let iter = 0; iter < 50; iter++) {
    const mid = (lo + hi) / 2;
    const daysSinceNew = mid - KNOWN_NEW_MOON_JD;
    const cycles = daysSinceNew / SYNODIC_MONTH;
    const phase = cycles - Math.floor(cycles);
    let diff = phase - targetPhase;
    if (diff < -0.5) diff += 1;
    if (diff > 0.5) diff -= 1;

    if (Math.abs(diff) < 0.00001) break;

    if (diff < 0) {
      lo = mid;
    } else {
      hi = mid;
    }
  }

  return (lo + hi) / 2;
}

/**
 * Get all moon phase events for a given year
 */
export function getMoonEventsForYear(year: number): MoonEvent[] {
  const events: MoonEvent[] = [];
  const startJD = dateToJD(new Date(Date.UTC(year, 0, 1)));
  const endJD = dateToJD(new Date(Date.UTC(year, 11, 31, 23, 59, 59)));

  const phases: { target: number; name: 'new_moon' | 'first_quarter' | 'full_moon' | 'last_quarter' }[] = [
    { target: 0, name: 'new_moon' },
    { target: 0.25, name: 'first_quarter' },
    { target: 0.5, name: 'full_moon' },
    { target: 0.75, name: 'last_quarter' },
  ];

  // Start from a bit before the year to catch early events
  const searchStart = startJD - 35;

  for (const { target, name } of phases) {
    // Find all occurrences through the year
    let currentJD = searchStart;
    while (currentJD < endJD + 1) {
      const eventJD = findPhaseEvent(currentJD, target);
      if (eventJD >= startJD && eventJD <= endJD + 1) {
        const date = jdToDate(eventJD);
        if (date.getUTCFullYear() === year) {
          events.push({ date, phase: name, name });
        }
      }
      currentJD = eventJD + 25; // Jump ~25 days to find next cycle
    }
  }

  // Sort by date
  events.sort((a, b) => a.date.getTime() - b.date.getTime());

  // Remove duplicates (same phase within 2 days)
  const filtered: MoonEvent[] = [];
  for (const event of events) {
    const isDuplicate = filtered.some(
      (e) => e.phase === event.phase && Math.abs(e.date.getTime() - event.date.getTime()) < 2 * 24 * 60 * 60 * 1000
    );
    if (!isDuplicate) {
      filtered.push(event);
    }
  }

  return filtered;
}

/**
 * Get the next full moon from a given date
 */
export function getNextFullMoon(from: Date = new Date()): Date {
  const jd = dateToJD(from);
  const eventJD = findPhaseEvent(jd, 0.5);
  const result = jdToDate(eventJD);

  // If result is in the past, search from a bit later
  if (result.getTime() < from.getTime()) {
    const nextJD = findPhaseEvent(jd + 25, 0.5);
    return jdToDate(nextJD);
  }

  return result;
}

/**
 * Get the next new moon from a given date
 */
export function getNextNewMoon(from: Date = new Date()): Date {
  const jd = dateToJD(from);
  const eventJD = findPhaseEvent(jd, 0);
  const result = jdToDate(eventJD);

  if (result.getTime() < from.getTime()) {
    const nextJD = findPhaseEvent(jd + 25, 0);
    return jdToDate(nextJD);
  }

  return result;
}

/**
 * Traditional full moon names by month (Northern Hemisphere)
 */
export const FULL_MOON_NAMES: Record<number, { en: string; fr: string; es: string; de: string; pt: string; it: string; ja: string; zh: string; ar: string; ru: string; hi: string }> = {
  1: {
    en: 'Wolf Moon', fr: 'Lune du Loup', es: 'Luna del Lobo', de: 'Wolfsmond',
    pt: 'Lua do Lobo', it: 'Luna del Lupo', ja: 'ウルフムーン', zh: '狼月',
    ar: 'قمر الذئب', ru: 'Волчья Луна', hi: 'भेड़िया चंद्रमा'
  },
  2: {
    en: 'Snow Moon', fr: 'Lune de Neige', es: 'Luna de Nieve', de: 'Schneemond',
    pt: 'Lua da Neve', it: 'Luna della Neve', ja: 'スノームーン', zh: '雪月',
    ar: 'قمر الثلج', ru: 'Снежная Луна', hi: 'हिम चंद्रमा'
  },
  3: {
    en: 'Worm Moon', fr: 'Lune du Ver', es: 'Luna del Gusano', de: 'Wurmmond',
    pt: 'Lua da Minhoca', it: 'Luna del Verme', ja: 'ワームムーン', zh: '蠕虫月',
    ar: 'قمر الدودة', ru: 'Червячная Луна', hi: 'कीट चंद्रमा'
  },
  4: {
    en: 'Pink Moon', fr: 'Lune Rose', es: 'Luna Rosa', de: 'Rosa Mond',
    pt: 'Lua Rosa', it: 'Luna Rosa', ja: 'ピンクムーン', zh: '粉红月',
    ar: 'القمر الوردي', ru: 'Розовая Луна', hi: 'गुलाबी चंद्रमा'
  },
  5: {
    en: 'Flower Moon', fr: 'Lune des Fleurs', es: 'Luna de las Flores', de: 'Blumenmond',
    pt: 'Lua das Flores', it: 'Luna dei Fiori', ja: 'フラワームーン', zh: '花月',
    ar: 'قمر الزهور', ru: 'Цветочная Луна', hi: 'फूल चंद्रमा'
  },
  6: {
    en: 'Strawberry Moon', fr: 'Lune des Fraises', es: 'Luna de Fresa', de: 'Erdbeermond',
    pt: 'Lua do Morango', it: 'Luna delle Fragole', ja: 'ストロベリームーン', zh: '草莓月',
    ar: 'قمر الفراولة', ru: 'Клубничная Луна', hi: 'स्ट्रॉबेरी चंद्रमा'
  },
  7: {
    en: 'Buck Moon', fr: 'Lune du Cerf', es: 'Luna del Ciervo', de: 'Bockmond',
    pt: 'Lua do Cervo', it: 'Luna del Cervo', ja: 'バックムーン', zh: '雄鹿月',
    ar: 'قمر الغزال', ru: 'Оленья Луна', hi: 'हिरण चंद्रमा'
  },
  8: {
    en: 'Sturgeon Moon', fr: 'Lune de l\'Esturgeon', es: 'Luna del Esturión', de: 'Störmond',
    pt: 'Lua do Esturjão', it: 'Luna dello Storione', ja: 'スタージョンムーン', zh: '鲟鱼月',
    ar: 'قمر سمك الحفش', ru: 'Осетровая Луна', hi: 'स्टर्जन चंद्रमा'
  },
  9: {
    en: 'Harvest Moon', fr: 'Lune des Moissons', es: 'Luna de la Cosecha', de: 'Erntemond',
    pt: 'Lua da Colheita', it: 'Luna del Raccolto', ja: 'ハーベストムーン', zh: '收获月',
    ar: 'قمر الحصاد', ru: 'Луна Урожая', hi: 'फसल चंद्रमा'
  },
  10: {
    en: 'Hunter\'s Moon', fr: 'Lune du Chasseur', es: 'Luna del Cazador', de: 'Jägermond',
    pt: 'Lua do Caçador', it: 'Luna del Cacciatore', ja: 'ハンターズムーン', zh: '猎人月',
    ar: 'قمر الصياد', ru: 'Охотничья Луна', hi: 'शिकारी चंद्रमा'
  },
  11: {
    en: 'Beaver Moon', fr: 'Lune du Castor', es: 'Luna del Castor', de: 'Bibermond',
    pt: 'Lua do Castor', it: 'Luna del Castoro', ja: 'ビーバームーン', zh: '海狸月',
    ar: 'قمر القندس', ru: 'Бобровая Луна', hi: 'बीवर चंद्रमा'
  },
  12: {
    en: 'Cold Moon', fr: 'Lune Froide', es: 'Luna Fría', de: 'Kalter Mond',
    pt: 'Lua Fria', it: 'Luna Fredda', ja: 'コールドムーン', zh: '冷月',
    ar: 'القمر البارد', ru: 'Холодная Луна', hi: 'ठंडा चंद्रमा'
  },
};

/**
 * Get full moons for a given year with traditional names
 */
export function getFullMoonsForYear(year: number): FullMoonInfo[] {
  const events = getMoonEventsForYear(year);
  return events
    .filter((e) => e.phase === 'full_moon')
    .map((e) => ({
      date: e.date,
      traditionalName: FULL_MOON_NAMES[e.date.getUTCMonth() + 1]?.en || 'Full Moon',
      month: e.date.getUTCMonth() + 1,
    }));
}

/**
 * Calculate approximate moon position (simplified)
 * Returns ecliptic longitude in degrees
 */
export function getMoonEclipticLongitude(date: Date): number {
  const jd = dateToJD(date);
  const T = (jd - 2451545.0) / 36525; // Julian centuries from J2000

  // Mean longitude of the Moon
  let L0 = 218.3165 + 481267.8813 * T;
  L0 = L0 % 360;
  if (L0 < 0) L0 += 360;

  return L0;
}

/**
 * Calculate approximate moon declination (for visibility map)
 */
export function getMoonDeclination(date: Date): number {
  const jd = dateToJD(date);
  const T = (jd - 2451545.0) / 36525;

  // Simplified calculation
  const D = (297.85 + 445267.1115 * T) % 360;
  const M = (357.53 + 35999.0503 * T) % 360;
  const Mp = (134.96 + 477198.8676 * T) % 360;
  const F = (93.27 + 483202.0175 * T) % 360;

  const dRad = D * Math.PI / 180;
  const mRad = M * Math.PI / 180;
  const mpRad = Mp * Math.PI / 180;
  const fRad = F * Math.PI / 180;

  // Moon's ecliptic latitude (simplified)
  const beta = 5.128 * Math.sin(fRad)
    + 0.2806 * Math.sin(mpRad + fRad)
    + 0.2777 * Math.sin(mpRad - fRad)
    + 0.1732 * Math.sin(2 * dRad - fRad);

  // Ecliptic longitude (simplified)
  let lambda = 218.32 + 481267.883 * T
    + 6.29 * Math.sin(mpRad)
    - 1.27 * Math.sin(2 * dRad - mpRad)
    + 0.66 * Math.sin(2 * dRad)
    + 0.21 * Math.sin(2 * mpRad)
    - 0.19 * Math.sin(mRad)
    - 0.11 * Math.sin(2 * fRad);
  lambda = lambda % 360;

  // Obliquity of ecliptic
  const epsilon = 23.439 - 0.00000036 * (jd - 2451545.0);
  const epsRad = epsilon * Math.PI / 180;
  const lambdaRad = lambda * Math.PI / 180;
  const betaRad = beta * Math.PI / 180;

  // Declination
  const declination = Math.asin(
    Math.sin(betaRad) * Math.cos(epsRad) + Math.cos(betaRad) * Math.sin(epsRad) * Math.sin(lambdaRad)
  ) * 180 / Math.PI;

  return declination;
}

/**
 * Calculate moon right ascension (for visibility)
 */
export function getMoonRightAscension(date: Date): number {
  const jd = dateToJD(date);
  const T = (jd - 2451545.0) / 36525;

  const Mp = (134.96 + 477198.8676 * T) % 360;
  const D = (297.85 + 445267.1115 * T) % 360;
  const M = (357.53 + 35999.0503 * T) % 360;
  const F = (93.27 + 483202.0175 * T) % 360;

  const mpRad = Mp * Math.PI / 180;
  const dRad = D * Math.PI / 180;
  const mRad = M * Math.PI / 180;
  const fRad = F * Math.PI / 180;

  let lambda = 218.32 + 481267.883 * T
    + 6.29 * Math.sin(mpRad)
    - 1.27 * Math.sin(2 * dRad - mpRad)
    + 0.66 * Math.sin(2 * dRad)
    + 0.21 * Math.sin(2 * mpRad)
    - 0.19 * Math.sin(mRad)
    - 0.11 * Math.sin(2 * fRad);
  lambda = lambda % 360;

  const beta = 5.128 * Math.sin(fRad);

  const epsilon = 23.439 - 0.00000036 * (jd - 2451545.0);
  const epsRad = epsilon * Math.PI / 180;
  const lambdaRad = lambda * Math.PI / 180;
  const betaRad = beta * Math.PI / 180;

  const ra = Math.atan2(
    Math.sin(lambdaRad) * Math.cos(epsRad) - Math.tan(betaRad) * Math.sin(epsRad),
    Math.cos(lambdaRad)
  ) * 180 / Math.PI;

  return ((ra % 360) + 360) % 360;
}

/**
 * Countdown to next full moon
 */
export function getCountdownToNextFullMoon(from: Date = new Date()): { days: number; hours: number; minutes: number; seconds: number; totalMs: number } {
  const nextFull = getNextFullMoon(from);
  const totalMs = nextFull.getTime() - from.getTime();

  if (totalMs <= 0) return { days: 0, hours: 0, minutes: 0, seconds: 0, totalMs: 0 };

  const days = Math.floor(totalMs / (1000 * 60 * 60 * 24));
  const hours = Math.floor((totalMs % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
  const minutes = Math.floor((totalMs % (1000 * 60 * 60)) / (1000 * 60));
  const seconds = Math.floor((totalMs % (1000 * 60)) / 1000);

  return { days, hours, minutes, seconds, totalMs };
}

/**
 * Get moon events for a specific month
 */
export function getMoonEventsForMonth(year: number, month: number): MoonEvent[] {
  const allEvents = getMoonEventsForYear(year);
  return allEvents.filter(e => e.date.getUTCMonth() + 1 === month);
}

/**
 * Get zodiac sign based on ecliptic longitude
 */
export function getMoonZodiacSign(date: Date): string {
  const lon = getMoonEclipticLongitude(date);
  const signs = ['Aries', 'Taurus', 'Gemini', 'Cancer', 'Leo', 'Virgo',
    'Libra', 'Scorpio', 'Sagittarius', 'Capricorn', 'Aquarius', 'Pisces'];
  const index = Math.floor(lon / 30) % 12;
  return signs[index];
}