private long?GetLimiterCount(TimeSpan span)
        {
            Limiter item   = Limiters.FirstOrDefault(l => l.Period == span);
            long?   result = null;

            if (item != null)
            {
                result = item.Count;
            }

            return(result);
        }
        private void SetLimiter(TimeSpan span, long?count)
        {
            Limiter item = Limiters.FirstOrDefault(l => l.Period == span);

            if (item != null)
            {
                _limits.Remove(item);
            }

            if (!count.HasValue)
            {
                return;
            }

            item = new Limiter
            {
                Count  = count.Value,
                Period = span
            };

            _limits.Add(item);
        }