example strategies

strategies.cs

    public interface ISnapshotStrategy
    {
        bool ShouldTakeSnapshot(long index);
    }

    public class EventsCountStrategy : ISnapshotStrategy
    {
        private readonly int _eventsPerSnapshot;

        public EventsCountStrategy(int eventsPerSnapshot)
        {
            _eventsPerSnapshot = eventsPerSnapshot;
        }

        public bool ShouldTakeSnapshot(long index)
        {
            return index % _eventsPerSnapshot == 0;
        }
    }

    public class NoSnapshots : ISnapshotStrategy {
        public bool ShouldTakeSnapshot(long index)
        {
            return false;
        }
    }

    public class TimeStrategy : ISnapshotStrategy
    {
        private readonly TimeSpan _interval;
        private readonly Func<DateTime> _getNow;
        private DateTime _lastTaken = DateTime.MinValue;

        public TimeStrategy(TimeSpan interval, Func<DateTime> getNow = null)
        {
            _interval = interval;
            _getNow = getNow ?? (() => DateTime.Now);
        }
        
        public bool ShouldTakeSnapshot(long index)
        {
            return _lastTaken.Add(_interval) >= _getNow();
        }
    }