main.py

# Chess FEN Parser and Board Renderer

def parse_fen(fen):
    """Parses a FEN string and returns a dictionary with board state and game info."""
    # Split the FEN string into its components
    fields = fen.strip().split()
    if len(fields) != 6:
        raise ValueError("Invalid FEN: Incorrect number of fields.")

    piece_placement, active_color, castling_availability, en_passant_target, halfmove_clock, fullmove_number = fields

    # Create the board matrix and piece positions
    board = []
    piece_positions = {'White': {}, 'Black': {}, 'Empty': []}
    ranks = piece_placement.split('/')
    if len(ranks) != 8:
        raise ValueError("Invalid FEN: Incorrect number of ranks.")

    for rank_index, rank in enumerate(ranks):
        board_row = []
        file_index = 0  # Files from 'a' to 'h'
        for char in rank:
            if char.isdigit():
                empty_squares = int(char)
                for _ in range(empty_squares):
                    board_row.append('.')
                    file_char = chr(ord('a') + file_index)
                    rank_char = 8 - rank_index
                    position = f"{file_char}{rank_char}"
                    piece_positions['Empty'].append(position)
                    file_index += 1
            else:
                board_row.append(char)
                color = 'White' if char.isupper() else 'Black'
                piece = char.upper()
                file_char = chr(ord('a') + file_index)
                rank_char = 8 - rank_index
                position = f"{file_char}{rank_char}"
                if piece not in piece_positions[color]:
                    piece_positions[color][piece] = []
                piece_positions[color][piece].append(position)
                file_index += 1
        if len(board_row) != 8:
            raise ValueError("Invalid FEN: Incorrect number of files in a rank.")
        board.append(board_row)

    game_info = {
        'active_color': 'White' if active_color == 'w' else 'Black',
        'castling_availability': castling_availability if castling_availability != '-' else 'None',
        'en_passant_target': en_passant_target if en_passant_target != '-' else 'None',
        'halfmove_clock': int(halfmove_clock),
        'fullmove_number': int(fullmove_number)
    }

    return board, piece_positions, game_info

def render_board(board):
    """Renders the board matrix into an ASCII diagram with labels on all sides."""
    files = '  a  b  c  d  e  f  g  h  '
    print("    " + files)
    print("   +" + "----" * 8 + "+")
    for rank_index, rank in enumerate(board):
        rank_number = 8 - rank_index
        rank_str = f"{rank_number} |"
        for piece in rank:
            rank_str += f" {piece} |"
        rank_str += f" {rank_number}"
        print(rank_str)
        print("   +" + "----" * 8 + "+")
    print("    " + files)

def list_piece_positions(piece_positions):
    """Lists the positions of each piece, including empty squares."""
    for color in ['White', 'Black']:
        print(f"{color} Pieces:")
        if piece_positions[color]:
            for piece in sorted(piece_positions[color].keys()):
                positions = ', '.join(sorted(piece_positions[color][piece]))
                piece_name = piece_full_name(piece)
                print(f"- {piece_name}: {positions}")
        else:
            print("- None")
        print()
    # List empty squares
    print("Empty Squares:")
    if piece_positions['Empty']:
        empty_positions = ', '.join(sorted(piece_positions['Empty']))
        print(f"- {empty_positions}")
    else:
        print("- None")
    print()

def piece_full_name(piece_symbol):
    """Returns the full name of a piece given its symbol."""
    names = {'K': 'King', 'Q': 'Queen', 'R': 'Rook',
             'B': 'Bishop', 'N': 'Knight', 'P': 'Pawn'}
    return names.get(piece_symbol, 'Unknown')

def display_game_info(game_info):
    """Displays human-readable game information."""
    print("Game Information:")
    print(f"- Active Color: {game_info['active_color']}")
    print(f"- Castling Availability: {game_info['castling_availability']}")
    print(f"- En Passant Target Square: {game_info['en_passant_target']}")
    print(f"- Halfmove Clock: {game_info['halfmove_clock']}")
    print(f"- Fullmove Number: {game_info['fullmove_number']}")
    print()

def main():
    fen = input("<FEN String>\n")
    print("</FEN String>")
    try:
        board, piece_positions, game_info = parse_fen(fen)
        print("<ASCII Diagram of the Board>")
        render_board(board)
        print("</ASCII Diagram of the Board>")
        print("<Piece Positions>")
        list_piece_positions(piece_positions)
        print("</Piece Positions>")
        print("<Game Information>")
        display_game_info(game_info)
        print("</Game Information>")
        print("<Instruction>")
        print(f"Find the best, valid move for {game_info['active_color']}.")
        print("</Instruction>")
    except ValueError as e:
        print(f"Error: {e}")

if __name__ == "__main__":
    main()