class OthelloEnv(MultiTurnEnv):
    def env_response(self, model_output, state):
        move = parse_move(model_output)

        if not is_valid(move, state.board):
            state.penalty += INVALID_MOVE_PENALTY
            return error_message(move), state          # same turn, retry

        state.board = apply_move(state.board, move, player="black")

        if not game_over(state.board):
            white_move = opponent_engine(state.board, state.difficulty)
            state.board = apply_move(state.board, white_move, player="white")

        return render_board(state.board), state