public async Task <IActionResult> AddRepeat(int?topicId)
        {
            if (topicId.HasValue)
            {
                var topic = await _topicRepository.GetById(topicId.Value);

                if (!ExistsAndAllowedToUse(topic))
                {
                    return(NotFound());
                }

                _scheduler.AddRepeat(topic, DateTime.Now.AddDays(1));
                await _topicRepository.Update(topic);

                return(RedirectToAction(nameof(Topic), new { topicId = topicId }));
            }
            else
            {
                return(NotFound());
            }
        }