import type { DuplicateGame } from './game';
import type { GameStatus, GameResult, BoardId } from './types';
import { PLAYERS, PLAYER_BOARDS, BOARD_PLAYERS } from './boards';
import { legalSyncedMoves } from './legality';

/** PROVISIONAL (spec §6): the 50-move rule fires after this many rounds. */
const FIFTY_MOVE_ROUNDS = 50;
const FIFTY_MOVE_PLIES = FIFTY_MOVE_ROUNDS * 4;

function allDraw(): GameResult {
  return { N: 'draw', S: 'draw', E: 'draw', W: 'draw' };
}

/** Evaluate the game from the perspective of the player to move. */
export function evaluateStatus(game: DuplicateGame): GameStatus {
  const player = game.currentPlayer;
  const [a, b] = PLAYER_BOARDS[player];

  const checks: BoardId[] = [];
  if (game.boards[a].inCheck()) checks.push(a);
  if (game.boards[b].inCheck()) checks.push(b);

  const synced = legalSyncedMoves(game);

  if (synced.length === 0) {
    if (checks.length > 0) {
      // Checkmate. PROVISIONAL (spec §6): every opponent delivering a check wins.
      const winners = checks.map((board) =>
        BOARD_PLAYERS[board].w === player
          ? BOARD_PLAYERS[board].b
          : BOARD_PLAYERS[board].w,
      );
      const result = {} as GameResult;
      for (const p of PLAYERS) {
        result[p] = p === player ? 'loss' : winners.includes(p) ? 'win' : 'draw';
      }
      return { state: 'checkmate', result, checks };
    }
    // PROVISIONAL (spec §6): a no-synchronized-move stalemate ends the game, all draw.
    return { state: 'stalemate', result: allDraw(), reason: 'stalemate', checks };
  }

  if (game.repetitionCount() >= 3) {
    return { state: 'draw', result: allDraw(), reason: 'threefold', checks };
  }
  if (game.pliesSinceProgress >= FIFTY_MOVE_PLIES) {
    return { state: 'draw', result: allDraw(), reason: 'fifty-move', checks };
  }

  return { state: 'playing', checks };
}