'use strict';

const crypto = require('crypto');

// カードは "As"（スペードのA）, "Td"（ダイヤの10）のような2文字
const RANKS = '23456789TJQKA';
const SUITS = 'shdc';

// 暗号論的乱数で Fisher-Yates シャッフル（山札はサーバの外に出さない）
function newDeck() {
  const deck = [];
  for (const r of RANKS) for (const s of SUITS) deck.push(r + s);
  for (let i = deck.length - 1; i > 0; i--) {
    const j = crypto.randomInt(i + 1);
    [deck[i], deck[j]] = [deck[j], deck[i]];
  }
  return deck;
}

const rankValue = (card) => RANKS.indexOf(card[0]) + 2;

// 5枚の役の強さ。配列を先頭から比較して大きいほうが強い
// [役の種類(0〜8), 比較用の数字...]
function score5(cards) {
  const vals = cards.map(rankValue).sort((a, b) => b - a);
  const flush = cards.every((c) => c[1] === cards[0][1]);

  let straightHigh = 0;
  if (new Set(vals).size === 5) {
    if (vals[0] - vals[4] === 4) straightHigh = vals[0];
    else if (vals[0] === 14 && vals[1] === 5) straightHigh = 5; // A-2-3-4-5
  }
  if (straightHigh && flush) return [8, straightHigh];

  // 枚数の多い順、同じ枚数なら数字の大きい順
  const counts = new Map();
  for (const v of vals) counts.set(v, (counts.get(v) || 0) + 1);
  const groups = [...counts].sort((a, b) => b[1] - a[1] || b[0] - a[0]);
  const byGroup = groups.map((g) => g[0]);

  if (groups[0][1] === 4) return [7, ...byGroup];
  if (groups[0][1] === 3 && groups[1][1] === 2) return [6, ...byGroup];
  if (flush) return [5, ...vals];
  if (straightHigh) return [4, straightHigh];
  if (groups[0][1] === 3) return [3, ...byGroup];
  if (groups[0][1] === 2 && groups[1][1] === 2) return [2, ...byGroup];
  if (groups[0][1] === 2) return [1, ...byGroup];
  return [0, ...vals];
}

function compareScore(a, b) {
  for (let i = 0; i < Math.max(a.length, b.length); i++) {
    const d = (a[i] || 0) - (b[i] || 0);
    if (d) return d;
  }
  return 0;
}

const HAND_NAMES = [
  'ハイカード',
  'ワンペア',
  'ツーペア',
  'スリーカード',
  'ストレート',
  'フラッシュ',
  'フルハウス',
  'フォーカード',
  'ストレートフラッシュ',
];

function handName(score) {
  if (score[0] === 8 && score[1] === 14) return 'ロイヤルフラッシュ';
  return HAND_NAMES[score[0]];
}

// 5〜7枚から最も強い5枚を選ぶ
function bestHand(cards) {
  let best = null;
  const n = cards.length;
  const pick = (start, chosen) => {
    if (chosen.length === 5) {
      const score = score5(chosen);
      if (!best || compareScore(score, best.score) > 0) best = { score, cards: chosen.slice() };
      return;
    }
    for (let i = start; i <= n - (5 - chosen.length); i++) {
      chosen.push(cards[i]);
      pick(i + 1, chosen);
      chosen.pop();
    }
  };
  pick(0, []);
  return best && { score: best.score, cards: best.cards, name: handName(best.score) };
}

module.exports = { newDeck, score5, compareScore, bestHand, handName };