extract_moves.py

import chess.pgn
import chess
import numpy as np
from tqdm.notebook import tqdm


def extract_moves_from_pgn(pgn_path:str, max_games=None) -> np.ndarray:
    all_moves = []

    def is_improper_piece(piece_type):
        return piece_type in {chess.PAWN, chess.ROOK, chess.KING}

    def make_starting_position_move(board):
        setup = ['X', '->']
        parts = []

        for square in chess.SQUARES:
            piece = board.piece_at(square)
            if piece:
                color = 'w' if piece.color == chess.WHITE else 'b'
                symbol = piece.symbol().upper()
                square_name = chess.square_name(square)
                if is_improper_piece(piece.piece_type):
                    piece_id = f"{symbol.lower()}{color}"
                else:
                    piece_id = f"{symbol}{color}"
                parts.extend([piece_id, square_name])

        for i in range(0, len(parts), 2):
            if i > 0:
                setup.append('&')
            setup.extend(parts[i:i+2])

        return setup

    def get_piece_id(piece, color, square, moved_from):
        symbol = piece.symbol().upper()
        if square not in moved_from and is_improper_piece(piece.piece_type):
            return f"{symbol.lower()}{color}"
        return f"{symbol}{color}"

    with open(pgn_path) as pgn:
        progress   = tqdm(desc="Processing Games", unit="games", dynamic_ncols=True, leave=True)
        game_count = 0
        while True:
            game = chess.pgn.read_game(pgn)
            if game is None or (max_games is not None and game_count >= max_games):
                    break
            game_count += 1

            fen = game.headers.get("FEN", chess.STARTING_FEN)
            board = chess.Board(fen)

            moved_from = set()
            game_moves = []

            game_moves.append(['<S>'])
            game_moves.append(make_starting_position_move(board))

            for move in game.mainline_moves():
                from_sq = move.from_square
                to_sq = move.to_square
                from_sq_name = chess.square_name(from_sq)
                to_sq_name = chess.square_name(to_sq)

                moving_piece = board.piece_at(from_sq)
                color = 'w' if moving_piece.color == chess.WHITE else 'b'
                piece_id_before = get_piece_id(moving_piece, color, from_sq_name, moved_from)

                # fallback castling detection if castling_rook_square() is not available
                if board.is_castling(move):
                    king_move = [piece_id_before, from_sq_name, '->', piece_id_before, to_sq_name]

                    fen_before = board.fen()
                    board_before = chess.Board(fen_before)
                    rooks_before = set(sq for sq in board_before.pieces(chess.ROOK, moving_piece.color))

                    board.push(move)

                    rooks_after = set(sq for sq in board.pieces(chess.ROOK, moving_piece.color))

                    rook_from_sq = list(rooks_before - rooks_after)
                    rook_to_sq = list(rooks_after - rooks_before)

                    if not rook_from_sq and not rook_to_sq:
                        # ✅ Rook didn't move (legal in Chess960), no second action needed
                        moved_from.add(from_sq_name)
                        game_moves.append(king_move)
                        continue

                    if len(rook_from_sq) == 1 and len(rook_to_sq) == 1:
                        rook_from = chess.square_name(rook_from_sq[0])
                        rook_to = chess.square_name(rook_to_sq[0])
                        rook_piece = board.piece_at(rook_to_sq[0])
                        rook_id = get_piece_id(rook_piece, color, rook_from, moved_from)

                        rook_move = [rook_id, rook_from, '->', rook_id, rook_to]
                        action = king_move + ['&'] + rook_move
                        moved_from.update([from_sq_name, rook_from])
                        game_moves.append(action)
                        continue

                    # Still couldn't determine rook move
                    print(f"\n⚠️  Warning: Could not determine rook move during castling at {from_sq_name}->{to_sq_name}")
                    print("→ PGN headers:")
                    for key, val in game.headers.items():
                        print(f"[{key} \"{val}\"]")
                    print("→ Current FEN before move:")
                    print(fen_before)
                    print("→ Move UCI:", move.uci())
                    print("→ Rooks before:", [chess.square_name(sq) for sq in rooks_before])
                    print("→ Rooks after:", [chess.square_name(sq) for sq in rooks_after])
                    print("→ Difference:")
                    print("    Disappeared:", [chess.square_name(sq) for sq in rooks_before - rooks_after])
                    print("    Appeared:", [chess.square_name(sq) for sq in rooks_after - rooks_before])
                    print()

                    game_moves.append(king_move)
                    continue

                captured_piece = board.piece_at(to_sq)
                board.push(move)

                new_piece = board.piece_at(to_sq)
                piece_id_after = f"{new_piece.symbol().upper()}{color}"

                action = [piece_id_before, from_sq_name, '->', piece_id_after, to_sq_name]
                moved_from.add(from_sq_name)

                if board.is_en_passant(move):
                    capture_sq = chess.square_name(to_sq + (8 if color == 'b' else -8))
                    action += ['&', f"P{'w' if color == 'b' else 'b'}", capture_sq, '->', 'X']

                elif captured_piece:
                    captured_id = f"{captured_piece.symbol().upper()}{'w' if captured_piece.color == chess.WHITE else 'b'}"
                    action += ['&', captured_id, to_sq_name, '->', 'X']

                game_moves.append(action)

            result = game.headers.get("Result", "*")
            game_moves.append([result])
            game_moves.append(['<E>'])

            all_moves.extend(game_moves)
            progress.update(1)
            
            
        progress.close()


    # 🔽 Final flattening step to yield List[str]
    flattened = []
    for move in all_moves:
        flattened.extend(move)
        flattened.append(',')  # comma delimiter

    if flattened:
        flattened.pop()  # Remove last comma


    # Step 2: Token dictionary
    NORMALIZE_MAP = {
    '½-½': '1/2-1/2',
    '1-0': '1-0',
    '0-1': '0-1',
    # Just in case someone uses space around dashes
    '1 - 0': '1-0',
    '0 - 1': '0-1',
    '1/2 - 1/2': '1/2-1/2',
    '½ - ½': '1/2-1/2',
    }
    tokens   = ['<S>', '<E>', '->', '&', ',', 'X']
    files    = 'abcdefgh'
    ranks    = '12345678'
    squares  = [f + r for r in ranks for f in files]
    tokens  += squares
    pieces   = ['P', 'p', 'R', 'r', 'N', 'B', 'Q', 'K', 'k']
    colors   = ['w', 'b']
    tokens  += [p + c for p in pieces for c in colors]
    annotations = ['!!', '!', '!?', '?!', '?', '??', '+', '#', '+−', '−+']
    results     = ['1-0', '0-1', '1/2-1/2']
    tokens     += annotations + results
    str_2_int = {token: idx for idx, token in enumerate(tokens)}

    # Step 3: Convert to integer list
    int_tokens = []
    for token in flattened:
        token = NORMALIZE_MAP.get(token, token)  # normalize if needed
        if token in str_2_int:
            int_tokens.append(str_2_int[token])
        else:
            raise ValueError(f"Unknown token: {token}")

    # Step 4: Convert to numpy array
    arr = np.array(int_tokens, dtype=np.int8)

    return arr