chesskit/src/lib/chess.ts

import { EvaluateGameParams, PositionEval } from "@/types/eval";
import { Game } from "@/types/game";
import { Chess, PieceSymbol, Square } from "chess.js";
import { getPositionWinPercentage } from "./engine/helpers/winPercentage";
import { Color } from "@/types/enums";

export const getEvaluateGameParams = (game: Chess): EvaluateGameParams => {
  const history = game.history({ verbose: true });

  const fens = history.map((move) => move.before);
  fens.push(history[history.length - 1].after);

  const uciMoves = history.map(
    (move) => move.from + move.to + (move.promotion || "")
  );

  return { fens, uciMoves };
};

export const getGameFromPgn = (pgn: string): Chess => {
  const game = new Chess();
  game.loadPgn(pgn);

  return game;
};

export const formatGameToDatabase = (game: Chess): Omit<Game, "id"> => {
  const headers: Record<string, string | undefined> = game.header();

  return {
    pgn: game.pgn(),
    event: headers.Event,
    site: headers.Site,
    date: headers.Date,
    round: headers.Round ?? "?",
    white: {
      name: headers.White,
      rating: headers.WhiteElo ? Number(headers.WhiteElo) : undefined,
    },
    black: {
      name: headers.Black,
      rating: headers.BlackElo ? Number(headers.BlackElo) : undefined,
    },
    result: headers.Result,
    termination: headers.Termination,
    timeControl: headers.TimeControl,
  };
};

export const getGameToSave = (game: Chess, board: Chess): Chess => {
  if (game.history().length) return game;
  return setGameHeaders(board);
};

export const setGameHeaders = (
  game: Chess,
  params: { whiteName?: string; blackName?: string; resigned?: Color } = {}
): Chess => {
  game.header("Event", "Freechess Game");
  game.header("Site", "Freechess");
  game.header(
    "Date",
    new Date().toISOString().split("T")[0].replaceAll("-", ".")
  );

  const { whiteName, blackName, resigned } = params;

  if (whiteName) game.header("White", whiteName);
  if (blackName) game.header("Black", blackName);

  const whiteNameToUse = game.header().White || "White";
  const blackNameToUse = game.header().Black || "Black";

  if (resigned) {
    game.header("Result", resigned === "w" ? "0-1" : "1-0");
    game.header(
      "Termination",
      `${resigned === "w" ? blackNameToUse : whiteNameToUse} won by resignation`
    );
  }

  if (!game.isGameOver()) return game;

  if (game.isCheckmate()) {
    game.header("Result", game.turn() === "w" ? "0-1" : "1-0");
    game.header(
      "Termination",
      `${
        game.turn() === "w" ? blackNameToUse : whiteNameToUse
      } won by checkmate`
    );
  }

  if (game.isInsufficientMaterial()) {
    game.header("Result", "1/2-1/2");
    game.header("Termination", "Draw by insufficient material");
  }

  if (game.isStalemate()) {
    game.header("Result", "1/2-1/2");
    game.header("Termination", "Draw by stalemate");
  }

  if (game.isThreefoldRepetition()) {
    game.header("Result", "1/2-1/2");
    game.header("Termination", "Draw by threefold repetition");
  }

  return game;
};

export const moveLineUciToSan = (
  fen: string
): ((moveUci: string) => string) => {
  const game = new Chess(fen);

  return (moveUci: string): string => {
    try {
      const move = game.move(uciMoveParams(moveUci));
      return move.san;
    } catch (e) {
      return moveUci;
    }
  };
};

export const getEvaluationBarValue = (
  position: PositionEval
): { whiteBarPercentage: number; label: string } => {
  const whiteBarPercentage = getPositionWinPercentage(position);
  const bestLine = position.lines[0];

  if (bestLine.mate) {
    return { label: `M${Math.abs(bestLine.mate)}`, whiteBarPercentage };
  }

  const cp = bestLine.cp;
  if (!cp) return { whiteBarPercentage, label: "0.0" };

  const pEval = Math.abs(cp) / 100;
  let label = pEval.toFixed(1);

  if (label.toString().length > 3) {
    label = pEval.toFixed(0);
  }

  return { whiteBarPercentage, label };
};

export const getWhoIsCheckmated = (fen: string): "w" | "b" | null => {
  const game = new Chess(fen);
  if (!game.isCheckmate()) return null;
  return game.turn();
};

export const uciMoveParams = (
  uciMove: string
): {
  from: Square;
  to: Square;
  promotion?: string | undefined;
} => ({
  from: uciMove.slice(0, 2) as Square,
  to: uciMove.slice(2, 4) as Square,
  promotion: uciMove.slice(4, 5) || undefined,
});

export const isSimplePieceRecapture = (
  fen: string,
  uciMoves: [string, string]
): boolean => {
  const game = new Chess(fen);
  const moves = uciMoves.map((uciMove) => uciMoveParams(uciMove));

  if (moves[0].to !== moves[1].to) return false;

  const piece = game.get(moves[0].to);
  if (piece) return true;

  return false;
};

export const getIsPieceSacrifice = (
  fen: string,
  playedMove: string,
  bestLinePvToPlay: string[]
): boolean => {
  if (
    !bestLinePvToPlay.length ||
    bestLinePvToPlay[0].slice(2, 4) !== playedMove.slice(2, 4)
  )
    return false;

  const game = new Chess(fen);
  const whiteToPlay = game.turn() === "w";
  const startingMaterialDifference = getMaterialDifference(fen);

  let moves = [playedMove, ...bestLinePvToPlay];
  if (moves.length % 2 === 1) {
    moves = moves.slice(0, -1);
  }
  let nonCapturingMovesTemp = 1;

  for (const move of moves) {
    const fullMove = game.move(uciMoveParams(move));
    if (fullMove.captured) {
      nonCapturingMovesTemp = 1;
    } else {
      nonCapturingMovesTemp--;
      if (nonCapturingMovesTemp < 0) break;
    }
  }

  const endingMaterialDifference = getMaterialDifference(game.fen());

  const materialDiff = endingMaterialDifference - startingMaterialDifference;
  const materialDiffPlayerRelative = whiteToPlay ? materialDiff : -materialDiff;

  return materialDiffPlayerRelative < 0;
};

export const getMaterialDifference = (fen: string): number => {
  const game = new Chess(fen);
  const board = game.board().flat();

  return board.reduce((acc, square) => {
    if (!square) return acc;
    const piece = square.type;

    if (square.color === "w") {
      return acc + getPieceValue(piece);
    }

    return acc - getPieceValue(piece);
  }, 0);
};

const getPieceValue = (piece: PieceSymbol): number => {
  switch (piece) {
    case "p":
      return 1;
    case "n":
      return 3;
    case "b":
      return 3;
    case "r":
      return 5;
    case "q":
      return 9;
    default:
      return 0;
  }
};

export const getStartingFen = (
  params: { pgn: string } | { game: Chess }
): string => {
  const game = "game" in params ? params.game : getGameFromPgn(params.pgn);

  const history = game.history({ verbose: true });
  if (!history.length) return game.fen();

  return history[0].before;
};

export const isCheck = (fen: string): boolean => {
  const game = new Chess(fen);
  return game.inCheck();
};

export const getCapturedPieces = (
  fen: string,
  color: Color
): Record<string, number | undefined> => {
  const capturedPieces: Record<string, number | undefined> = {};
  if (color === Color.White) {
    capturedPieces.p = 8;
    capturedPieces.r = 2;
    capturedPieces.n = 2;
    capturedPieces.b = 2;
    capturedPieces.q = 1;
  } else {
    capturedPieces.P = 8;
    capturedPieces.R = 2;
    capturedPieces.N = 2;
    capturedPieces.B = 2;
    capturedPieces.Q = 1;
  }

  const fenPiecePlacement = fen.split(" ")[0];
  for (const piece of Object.keys(capturedPieces)) {
    const count = fenPiecePlacement.match(new RegExp(piece, "g"))?.length;
    if (count) capturedPieces[piece] = (capturedPieces[piece] ?? 0) - count;
  }

  return capturedPieces;
};