def main():
    """Главная функция запуска бота."""
    if not check_tokens():
        exit()
    bot = telegram.Bot(token=TELEGRAM_TOKEN)
    current_timestamp = 0
    previous_hw_info = {}
    while True:
        try:
            response = get_api_answer(current_timestamp)
            current_hw_info = check_response(response)[0]
            if previous_hw_info == current_hw_info:
                _logger.debug('Статус работы не изменился.')
            if previous_hw_info:
                _logger.debug('Изменился статус работы')
                send_message(bot, parse_status(current_hw_info))
            previous_hw_info = current_hw_info
            current_timestamp = to_unix(current_hw_info.get('date_updated'))
        except RequestExceptionError as error:
            _logger.error(error)
            current_error = f'Сбой в работе программы: {error}'
            send_message(bot, current_error)
        except SendMessageError as error:
            _logger.error(error)
        finally:
            time.sleep(RETRY_PERIOD)