// Go Fish — pure state engine. No Phaser imports.
//
// Pairs variant rules:
//  - Standard 52-card deck. 4 players, 7 cards each. Remainder is the pool.
//  - On your turn, pick an opponent and ask for a rank you hold.
//  - If they hold any of that rank, they hand over ALL cards of that rank;
//    you then check your hand for pairs (any 2 cards of the same rank are
//    immediately scored as a pair). You then ask again.
//  - If they don't, "Go Fish": draw 1 from the pool. If the drawn card matches
//    the asked rank ("lucky fish"), keep going. Otherwise the turn passes.
//  - If your hand goes empty mid-game and the pool has cards, you draw up to
//    5 to refill. If the pool is empty you sit out for the rest of the game.
//  - Game ends when the pool is empty AND every player has ≤ 1 card (no more
//    pairs possible). Most pairs wins; ties allowed.

import { SUITS, RANKS, Card } from '../cards/Deck.js';

export const HAND_DEAL = 7;
export const REFILL_TARGET = 5;

// Mulberry32 — seedable PRNG (mirrors Phase10).
function rng(seed) {
  let a = (seed >>> 0) || 1;
  return () => {
    a = (a + 0x6d2b79f5) >>> 0;
    let t = a;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

function shuffle(arr, seed) {
  const rand = seed === undefined ? Math.random : rng(seed);
  for (let i = arr.length - 1; i > 0; i--) {
    const j = Math.floor(rand() * (i + 1));
    [arr[i], arr[j]] = [arr[j], arr[i]];
  }
}

function buildDeck() {
  const cards = [];
  let id = 0;
  for (const suit of SUITS) {
    for (const rank of RANKS) {
      const c = new Card(rank, suit);
      c.id = id++;
      cards.push(c);
    }
  }
  return cards;
}

function cloneCard(c) {
  const out = new Card(c.rank, c.suit);
  out.id = c.id;
  return out;
}

export function cloneState(state) {
  return {
    players: state.players.map((p) => ({
      seat: p.seat,
      hand: p.hand.map(cloneCard),
      pairs: p.pairs,
      pairedRanks: p.pairedRanks.slice(),
      sittingOut: p.sittingOut,
    })),
    pool: state.pool.map(cloneCard),
    currentPlayer: state.currentPlayer,
    phase: state.phase,
    lastAsk: state.lastAsk ? { ...state.lastAsk } : null,
    log: state.log.map((e) => ({ ...e })),
    winnerSeats: state.winnerSeats.slice(),
    seed: state.seed,
    turnCount: state.turnCount,
  };
}

export function createInitialState({ playerCount = 4, seed } = {}) {
  if (playerCount < 2 || playerCount > 4) {
    throw new Error(`Go Fish supports 2..4 players, got ${playerCount}`);
  }
  const deck = buildDeck();
  shuffle(deck, seed);
  const players = [];
  for (let i = 0; i < playerCount; i++) {
    players.push({
      seat: i,
      hand: deck.splice(0, HAND_DEAL),
      pairs: 0,
      pairedRanks: [],
      sittingOut: false,
    });
  }
  const state = {
    players,
    pool: deck,
    currentPlayer: 0,
    phase: 'play',
    lastAsk: null,
    log: [],
    winnerSeats: [],
    seed: seed ?? null,
    turnCount: 0,
  };
  // Any starting pairs are scored immediately.
  for (const p of state.players) collectPairs(p, state);
  // Edge: if a player was dealt all duplicates and now has 0 cards, refill.
  for (const p of state.players) ensureHasCards(state, p.seat);
  checkGameOver(state);
  return state;
}

export function legalRanksToAsk(state, seat) {
  const set = new Set();
  for (const c of state.players[seat].hand) set.add(c.rank);
  return [...set];
}

export function canAsk(state, seat) {
  if (state.phase !== 'play') return false;
  if (state.currentPlayer !== seat) return false;
  if (state.players[seat].sittingOut) return false;
  return state.players[seat].hand.length > 0;
}

/**
 * Ask `targetSeat` for `rank`. The asker (currentPlayer) must hold at least
 * one card of that rank. Returns a new state plus a description of what
 * happened so the UI can animate it.
 */
export function applyAsk(state, targetSeat, rank) {
  if (state.phase !== 'play') return state;
  const askerSeat = state.currentPlayer;
  if (targetSeat === askerSeat) return state;
  const next = cloneState(state);
  const asker = next.players[askerSeat];
  const target = next.players[targetSeat];
  if (!asker || !target) return state;
  if (target.sittingOut) return state;
  if (!asker.hand.some((c) => c.rank === rank)) return state;

  // Transfer all of `rank` from target to asker.
  const matches = target.hand.filter((c) => c.rank === rank);
  if (matches.length > 0) {
    target.hand = target.hand.filter((c) => c.rank !== rank);
    asker.hand.push(...matches);
    const { count: newPairs, pairedCards } = collectPairs(asker, next);
    next.lastAsk = {
      askerSeat, targetSeat, rank,
      result: 'catch',
      cardsTransferred: matches.map(cloneCard),
      drawnCard: null,
      newPairs,
      pairedCards,
    };
    next.log.push({ kind: 'ask', askerSeat, targetSeat, rank, result: 'catch', count: matches.length });
    // Asker may have emptied target's hand — refill them now (before asker's next ask).
    ensureHasCards(next, targetSeat);
    // Asker may have emptied own hand by pairing — refill them too.
    ensureHasCards(next, askerSeat);
    // If asker still has no cards or can't ask, advance turn.
    if (!canAsk(next, askerSeat)) advanceTurn(next);
    checkGameOver(next);
    return next;
  }

  // Miss — Go Fish.
  next.log.push({ kind: 'ask', askerSeat, targetSeat, rank, result: 'fish', count: 0 });

  if (next.pool.length > 0) {
    // Pause — player must interactively pick a card from the scattered pool.
    next.phase = 'pick';
    next.lastAsk = {
      askerSeat, targetSeat, rank,
      result: 'fish',
      cardsTransferred: [],
      drawnCard: null,
      newPairs: 0,
      pairedCards: [],
    };
    return next;
  }

  // Pool is empty — no card to draw, advance turn immediately.
  next.lastAsk = {
    askerSeat, targetSeat, rank,
    result: 'fish',
    cardsTransferred: [],
    drawnCard: null,
    newPairs: 0,
    pairedCards: [],
  };
  ensureHasCards(next, askerSeat);
  advanceTurn(next);
  checkGameOver(next);
  return next;
}

/**
 * Complete the interactive "Go Fish" draw. `cardId` is the id of the card the
 * player (or AI) chose from the scattered pool. Only valid when phase === 'pick'.
 */
export function applyFishPick(state, cardId) {
  if (state.phase !== 'pick') return state;
  const { askerSeat, targetSeat, rank } = state.lastAsk;
  const next = cloneState(state);
  const poolIdx = next.pool.findIndex((c) => c.id === cardId);
  if (poolIdx === -1) return state;
  const [drawnCard] = next.pool.splice(poolIdx, 1);
  const asker = next.players[askerSeat];
  asker.hand.push(drawnCard);
  const lucky = drawnCard.rank === rank;
  const { count: newPairs, pairedCards } = collectPairs(asker, next);
  next.lastAsk = {
    askerSeat, targetSeat, rank,
    result: lucky ? 'lucky' : 'fish',
    cardsTransferred: [],
    drawnCard: cloneCard(drawnCard),
    newPairs,
    pairedCards,
  };
  if (lucky) next.log.push({ kind: 'lucky', askerSeat, rank });
  next.phase = 'play';
  ensureHasCards(next, askerSeat);
  if (!lucky || !canAsk(next, askerSeat)) advanceTurn(next);
  checkGameOver(next);
  return next;
}

/**
 * Repeatedly remove any 2 cards of the same rank from the player's hand and
 * increment their pair count. Returns { count, pairedCards } where pairedCards
 * holds clones of each removed card for animation purposes.
 */
function collectPairs(player, state) {
  let collected = 0;
  const pairedCards = [];
  while (true) {
    const byRank = new Map();
    let foundRank = null;
    for (const c of player.hand) {
      const list = byRank.get(c.rank) ?? [];
      list.push(c);
      byRank.set(c.rank, list);
      if (list.length >= 2) { foundRank = c.rank; break; }
    }
    if (!foundRank) break;
    const pair = byRank.get(foundRank);
    pairedCards.push(cloneCard(pair[0]), cloneCard(pair[1]));
    const idsToRemove = new Set([pair[0].id, pair[1].id]);
    player.hand = player.hand.filter((c) => !idsToRemove.has(c.id));
    player.pairs += 1;
    player.pairedRanks.push(foundRank);
    collected += 1;
    if (state) state.log.push({ kind: 'pair', seat: player.seat, rank: foundRank });
  }
  return { count: collected, pairedCards };
}

/**
 * If the player's hand is empty, draw up to REFILL_TARGET from the pool.
 * If still empty afterward, mark them as sitting out.
 */
function ensureHasCards(state, seat) {
  const player = state.players[seat];
  if (player.sittingOut) return;
  if (player.hand.length > 0) return;
  while (player.hand.length < REFILL_TARGET && state.pool.length > 0) {
    player.hand.push(state.pool.pop());
  }
  if (player.hand.length > 0) {
    state.log.push({ kind: 'refill', seat, count: player.hand.length });
    collectPairs(player, state);
  }
  if (player.hand.length === 0) {
    player.sittingOut = true;
    state.log.push({ kind: 'sitout', seat });
  }
}

function advanceTurn(state) {
  state.turnCount += 1;
  const N = state.players.length;
  let next = (state.currentPlayer + 1) % N;
  let safety = N + 1;
  while (safety-- > 0) {
    const p = state.players[next];
    if (!p.sittingOut && p.hand.length > 0) {
      state.currentPlayer = next;
      return;
    }
    next = (next + 1) % N;
  }
  // No-one can play — game over will be detected separately.
}

function checkGameOver(state) {
  if (state.phase !== 'play') return;
  // A player can make progress if (a) they have ≥1 card AND the pool has ≥1
  // card (they can fish) OR (b) the pool is empty but they share a rank with
  // another player they could ask for. Otherwise no progress is possible.
  const anyoneCanAct = state.players.some((p) => {
    if (p.sittingOut) return false;
    if (p.hand.length === 0) return false;
    if (state.pool.length > 0) return true;
    return state.players.some(
      (q) => q !== p && !q.sittingOut && q.hand.some((c) => p.hand.some((d) => d.rank === c.rank)),
    );
  });
  if (!anyoneCanAct) {
    state.phase = 'gameOver';
    const max = Math.max(...state.players.map((p) => p.pairs));
    state.winnerSeats = state.players.filter((p) => p.pairs === max).map((p) => p.seat);
  }
}

export function isGameOver(state) {
  return state.phase === 'gameOver';
}