/**
 * Divisional Chart (Varga) Calculator
 * Computes planet positions in any of the 16 Shodashvarga divisional charts.
 */

import { SIGN_NAMES } from '../core/constants';
import { getChartInfo } from './charts';

// ── Types ───────────────────────────────────────────────────────────────────

export interface DivisionalPosition {
  planet: string;
  d1SignNumber: number;      // Original sign in D1 (1-12)
  d1Degree: number;          // Degree in D1 sign (0-30)
  vargaSignNumber: number;   // Sign in this divisional chart (1-12)
  vargaSignName: string;
  vargaDegree: number;       // Degree within varga division
}

export interface DivisionalChart {
  name: string;              // e.g. "Navamsa (D9)"
  division: number;          // e.g. 9
  planets: DivisionalPosition[];
  lagnaSign: { number: number; name: string };
}

export interface PlanetInput {
  name: string;
  signNumber: number;        // 1-12
  degreeInSign: number;      // 0-30
}

// ── Helpers ─────────────────────────────────────────────────────────────────

/** Normalise a sign number to 1-12. */
function normSign(n: number): number {
  return ((n - 1) % 12 + 12) % 12 + 1;
}

/** Get element of a sign: 'fire' | 'earth' | 'air' | 'water'. */
function signElement(signNumber: number): 'fire' | 'earth' | 'air' | 'water' {
  const mod = ((signNumber - 1) % 4);
  return (['fire', 'earth', 'air', 'water'] as const)[mod];
}

/** Is sign odd (1,3,5,...) or even (2,4,6,...)? */
function isOddSign(signNumber: number): boolean {
  return signNumber % 2 === 1;
}

// ── Division-specific calculators ───────────────────────────────────────────

/**
 * D2 (Hora): 2 parts of 15 deg.
 * Odd signs: 0-15 = Leo(5), 15-30 = Cancer(4)
 * Even signs: 0-15 = Cancer(4), 15-30 = Leo(5)
 */
function calcD2(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const part = deg < 15 ? 0 : 1;
  const odd = isOddSign(sign);
  let vargaSign: number;
  if (odd) {
    vargaSign = part === 0 ? 5 : 4;  // Leo, Cancer
  } else {
    vargaSign = part === 0 ? 4 : 5;  // Cancer, Leo
  }
  return { vargaSign, vargaDeg: deg - part * 15 };
}

/**
 * D3 (Drekkana): 3 parts of 10 deg.
 * 1st (0-10): same sign
 * 2nd (10-20): 5th sign from it
 * 3rd (20-30): 9th sign from it
 */
function calcD3(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partIndex = Math.min(Math.floor(deg / 10), 2);
  const offsets = [0, 4, 8]; // 1st, 5th, 9th from sign
  const vargaSign = normSign(sign + offsets[partIndex]);
  return { vargaSign, vargaDeg: deg - partIndex * 10 };
}

/**
 * D4 (Chaturthamsa): 4 parts of 7.5 deg.
 * Part N (0-indexed) -> sign = original + (N * 3)
 */
function calcD4(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partIndex = Math.min(Math.floor(deg / 7.5), 3);
  const vargaSign = normSign(sign + partIndex * 3);
  return { vargaSign, vargaDeg: deg - partIndex * 7.5 };
}

/**
 * D7 (Saptamsa): 7 parts of 4.2857 deg.
 * Odd signs: start from same sign, advance +1 per division
 * Even signs: start from 7th sign, advance +1 per division
 */
function calcD7(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 30 / 7;
  const partIndex = Math.min(Math.floor(deg / partSize), 6);
  const startSign = isOddSign(sign) ? sign : normSign(sign + 6);
  const vargaSign = normSign(startSign + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D9 (Navamsa): 9 parts of 3.333 deg.
 * Fire signs (1,5,9): start from Aries (1)
 * Earth signs (2,6,10): start from Capricorn (10)
 * Air signs (3,7,11): start from Libra (7)
 * Water signs (4,8,12): start from Cancer (4)
 */
function calcD9(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 30 / 9;
  const partIndex = Math.min(Math.floor(deg / partSize), 8);
  const elem = signElement(sign);
  const startMap: Record<string, number> = { fire: 1, earth: 10, air: 7, water: 4 };
  const vargaSign = normSign(startMap[elem] + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D10 (Dasamsa): 10 parts of 3 deg.
 * Odd signs: start from same sign
 * Even signs: start from 9th sign
 */
function calcD10(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 3;
  const partIndex = Math.min(Math.floor(deg / partSize), 9);
  const startSign = isOddSign(sign) ? sign : normSign(sign + 8);
  const vargaSign = normSign(startSign + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D12 (Dwadasamsa): 12 parts of 2.5 deg.
 * Start from same sign, advance +1 per division.
 */
function calcD12(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 2.5;
  const partIndex = Math.min(Math.floor(deg / partSize), 11);
  const vargaSign = normSign(sign + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D16 (Shodasamsa): 16 parts of 1.875 deg.
 * Fire signs: start Aries(1), Earth: Leo(5), Air: Sagittarius(9), Water: Aries(1)
 */
function calcD16(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 30 / 16;
  const partIndex = Math.min(Math.floor(deg / partSize), 15);
  const elem = signElement(sign);
  const startMap: Record<string, number> = { fire: 1, earth: 5, air: 9, water: 1 };
  const vargaSign = normSign(startMap[elem] + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D20 (Vimsamsa): 20 parts of 1.5 deg.
 * Fire signs: start Aries(1), Earth: Sagittarius(9), Air: Leo(5)
 * Water signs: follow the fire cycle → Aries(1)
 */
function calcD20(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 1.5;
  const partIndex = Math.min(Math.floor(deg / partSize), 19);
  const elem = signElement(sign);
  const startMap: Record<string, number> = { fire: 1, earth: 9, air: 5, water: 1 };
  const vargaSign = normSign(startMap[elem] + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D24 (Chaturvimsamsa): 24 parts of 1.25 deg.
 * Odd signs: start Leo(5), Even signs: start Cancer(4)
 */
function calcD24(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 30 / 24;
  const partIndex = Math.min(Math.floor(deg / partSize), 23);
  const startSign = isOddSign(sign) ? 5 : 4;
  const vargaSign = normSign(startSign + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D27 (Saptavimsamsa/Bhamsa): 27 parts of 1.111 deg.
 * Fire: Aries(1), Earth: Cancer(4), Air: Libra(7), Water: Capricorn(10)
 */
function calcD27(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 30 / 27;
  const partIndex = Math.min(Math.floor(deg / partSize), 26);
  const elem = signElement(sign);
  const startMap: Record<string, number> = { fire: 1, earth: 4, air: 7, water: 10 };
  const vargaSign = normSign(startMap[elem] + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D30 (Trimsamsa): Irregular division (not equal parts).
 * Odd signs: 0-5 Mars(Aries/1), 5-10 Saturn(Aquarius/11), 10-18 Jupiter(Sagittarius/9),
 *            18-25 Mercury(Gemini/3), 25-30 Venus(Taurus/2)
 * Even signs: 0-5 Venus(Taurus/2), 5-12 Mercury(Virgo/6), 12-20 Jupiter(Pisces/12),
 *             20-25 Saturn(Capricorn/10), 25-30 Mars(Scorpio/8)
 */
function calcD30(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  if (isOddSign(sign)) {
    if (deg < 5)  return { vargaSign: 1,  vargaDeg: deg };
    if (deg < 10) return { vargaSign: 11, vargaDeg: deg - 5 };
    if (deg < 18) return { vargaSign: 9,  vargaDeg: deg - 10 };
    if (deg < 25) return { vargaSign: 3,  vargaDeg: deg - 18 };
    return { vargaSign: 2, vargaDeg: deg - 25 };
  } else {
    if (deg < 5)  return { vargaSign: 2,  vargaDeg: deg };
    if (deg < 12) return { vargaSign: 6,  vargaDeg: deg - 5 };
    if (deg < 20) return { vargaSign: 12, vargaDeg: deg - 12 };
    if (deg < 25) return { vargaSign: 10, vargaDeg: deg - 20 };
    return { vargaSign: 8, vargaDeg: deg - 25 };
  }
}

/**
 * D40 (Khavedamsa): 40 parts of 0.75 deg.
 * Odd signs: start Aries(1), Even signs: start Libra(7)
 */
function calcD40(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 0.75;
  const partIndex = Math.min(Math.floor(deg / partSize), 39);
  const startSign = isOddSign(sign) ? 1 : 7;
  const vargaSign = normSign(startSign + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D45 (Akshavedamsa): 45 parts of 0.667 deg.
 * Fire: Aries(1), Earth: Leo(5), Air: Sagittarius(9), Water: Aries(1)
 */
function calcD45(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 30 / 45;
  const partIndex = Math.min(Math.floor(deg / partSize), 44);
  const elem = signElement(sign);
  const startMap: Record<string, number> = { fire: 1, earth: 5, air: 9, water: 1 };
  const vargaSign = normSign(startMap[elem] + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

/**
 * D60 (Shashtiamsa): 60 parts of 0.5 deg.
 * Start from same sign, advance +1 per division.
 */
function calcD60(sign: number, deg: number): { vargaSign: number; vargaDeg: number } {
  const partSize = 0.5;
  const partIndex = Math.min(Math.floor(deg / partSize), 59);
  const vargaSign = normSign(sign + partIndex);
  return { vargaSign, vargaDeg: deg - partIndex * partSize };
}

// ── Calculator dispatch ─────────────────────────────────────────────────────

type DivisionCalc = (sign: number, deg: number) => { vargaSign: number; vargaDeg: number };

const DIVISION_CALCULATORS: Record<number, DivisionCalc> = {
  2:  calcD2,
  3:  calcD3,
  4:  calcD4,
  7:  calcD7,
  9:  calcD9,
  10: calcD10,
  12: calcD12,
  16: calcD16,
  20: calcD20,
  24: calcD24,
  27: calcD27,
  30: calcD30,
  40: calcD40,
  45: calcD45,
  60: calcD60,
};

/**
 * Compute a single planet's varga position for a given division.
 */
function computeVargaPosition(
  division: number,
  sign: number,
  deg: number,
): { vargaSign: number; vargaDeg: number } {
  // D1 is the birth chart itself
  if (division === 1) {
    return { vargaSign: sign, vargaDeg: deg };
  }

  const calc = DIVISION_CALCULATORS[division];
  if (!calc) {
    throw new Error(`Unsupported divisional chart: D${division}`);
  }
  return calc(sign, deg);
}

// ── Public API ──────────────────────────────────────────────────────────────

/**
 * Calculate a divisional chart for a given division number.
 * @param division - The division number (1, 2, 3, 4, 7, 9, 10, 12, 16, 20, 24, 27, 30, 40, 45, 60)
 * @param planets - Array of {name, signNumber (1-12), degreeInSign (0-30)}
 * @param lagnaSignNumber - Lagna sign number (1-12)
 * @param lagnaDegree - Lagna degree in sign (0-30)
 */
export function calculateDivisionalChart(
  division: number,
  planets: PlanetInput[],
  lagnaSignNumber: number,
  lagnaDegree: number,
): DivisionalChart {
  const chartInfo = getChartInfo(division);
  const chartName = chartInfo
    ? `${chartInfo.name} (${chartInfo.shortName})`
    : `D${division}`;

  // Calculate lagna position in this varga
  const lagnaVarga = computeVargaPosition(division, lagnaSignNumber, lagnaDegree);

  // Calculate each planet
  const positions: DivisionalPosition[] = planets.map(p => {
    const result = computeVargaPosition(division, p.signNumber, p.degreeInSign);
    return {
      planet: p.name,
      d1SignNumber: p.signNumber,
      d1Degree: p.degreeInSign,
      vargaSignNumber: result.vargaSign,
      vargaSignName: SIGN_NAMES[result.vargaSign] || `Sign-${result.vargaSign}`,
      vargaDegree: result.vargaDeg,
    };
  });

  return {
    name: chartName,
    division,
    planets: positions,
    lagnaSign: {
      number: lagnaVarga.vargaSign,
      name: SIGN_NAMES[lagnaVarga.vargaSign] || `Sign-${lagnaVarga.vargaSign}`,
    },
  };
}