private static async Task Exercise(IEventStreamHost <int> host)
{
IEventStream <int> streamA = await host.AddAsync("a");
// OpenAtStart returns an observable sequence that produces events from the start of the stream until the stream is sealed.
IObservable <EventStreamSegment <int> > openAtStart = streamA.OpenAtStart();
(from segment in openAtStart from e in segment where e.Data.IsEven() select e).Subscribe(O("a.OpenAtStart(Even)"));
// Schedule a periodic WriteAsync to the stream.
var writer = Observable.Interval(TimeSpan.FromSeconds(0.5)).Subscribe(i =>
{
// WriteAsync writes one-or-more events (automically) to the stream.
Task <EventStreamSegment <int> > written = streamA.WriteAsync((int)i);
});
await Task.Delay(TimeSpan.FromSeconds(3));
// As the stream now contains events, OpenAtStart will produce those events before any other.
(from segment in openAtStart from e in segment where e.Data.IsOdd() select e).Subscribe(O("a.OpenAtStart(Odd)"));
await Task.Delay(TimeSpan.FromSeconds(3));
// OpenAtEnd returns an observable sequence that produces events until the stream is sealed.
IObservable <EventStreamSegment <int> > openAtEnd = streamA.OpenAtEnd();
(from segment in openAtEnd from e in segment select e).Subscribe(O("a.OpenAtEnd(*)"));
await Task.Delay(TimeSpan.FromSeconds(3));
// GetInfoAsync returns a snapshot of information about the stream:
// Sequence: The current sequence number.
// Count: The current number of events.
// Sealed: Indicates if the stream is sealed.
EventStreamInfo info = await streamA.GetInfoAsync();
// OpenAt returns an observable sequence that produces events from the given sequence (inclusive) until the stream is sealed.
long openAtSequence = info.Sequence / 2;
IObservable <EventStreamSegment <int> > openAt = streamA.OpenAt(openAtSequence);
(from segment in openAt from e in segment where e.Data.IsEven() select e).Subscribe(O($"a.OpenAt({openAtSequence},Even)"));
await Task.Delay(TimeSpan.FromSeconds(3));
writer.Dispose();
// Seal the stream, thus notifying observers of completion and preventing further writes.
// The behaviour of the *Open methods is now as follows:
// OpenAtStart: Produces events from the start of the stream and then completes.
// OpenAtEnd: Immediately completes.
// OpenAt: Produces events from the given sequence and then completes.
await streamA.SealAsync();
var streamB = await host.AddAsync("b");
(from segment in streamB.OpenAtEnd() from e in segment select e).Subscribe(O("b.OpenAtEnd(*)"));
// Delete the stream, thus notifying observers of the _error_.
// The behaviour of the *Open methods is now as follows:
// OpenAtStart: Immediately notifies of error.
// OpenAtEnd: Immediately notifies of error.
// OpenAt: Immediately notifies of error.
await streamB.DeleteAsync();
}