public static IEventObservable <TEvent, IEventContext, TModel> GetEventObservable <TEvent, TModel>(this IRouter <TModel> router, IEventHoldingStrategy <TEvent, TModel> strategy)
where TEvent : IIdentifiableEvent
where TModel : IHeldEventStore
{
return(EventObservable.Create <TEvent, IEventContext, TModel>(
o =>
{
var heldEvents = new Dictionary <Guid, HeldEventData <TEvent> >();
var releasedEvents = new HashSet <Guid>();
var disposables = new CollectionDisposable();
disposables.Add(router.GetEventObservable <TEvent>(ObservationStage.Preview).Observe((e, c, m) =>
{
// Have we already re-published this event? If so we don't want to hold it again.
if (releasedEvents.Contains(e.Id))
{
releasedEvents.Remove(e.Id);
o.OnNext(e, c, m);
}
else
{
var shouldHoldEvent = strategy.ShouldHold(e, c, m);
if (shouldHoldEvent)
{
// Cancel the event so no other observers will receive it.
c.Cancel();
// Model that we've cancelled it, other code can now reflect the newly modelled values.
// That is other code needs to determine what to do with these held events on the model.
// When it figures that out it should raise a HeldEventActionEvent so we can proceed here.
IEventDescription eventDescription = strategy.GetEventDescription(e, m);
m.AddHeldEventDescription(eventDescription);
// finally we hold the event locally
heldEvents.Add(e.Id, new HeldEventData <TEvent>(eventDescription, e));
}
}
}));
disposables.Add(router.GetEventObservable <HeldEventActionEvent>().Observe((e, c, m) =>
{
HeldEventData <TEvent> heldEventData;
// Since we're listening to a pipe of all events we need to filter out anything we don't know about.
if (heldEvents.TryGetValue(e.EventId, out heldEventData))
{
// We're received an event to clean up.
heldEvents.Remove(e.EventId);
m.RemoveHeldEventDescription(heldEventData.EventDescription);
if (e.Action == HeldEventAction.Release)
{
// Temporarily store the event we're republishing so we don't re-hold it
releasedEvents.Add(e.EventId);
router.PublishEvent(heldEventData.Event);
}
}
}));
return disposables;
}
));
}
private static IEventObservable <TEvent, TContext, TModel> MergeInternal <TEvent, TContext, TModel>(IEnumerable <IEventObservable <TEvent, TContext, TModel> > sources)
{
return(Create <TEvent, TContext, TModel>(
o =>
{
var disposables = new CollectionDisposable();
foreach (IEventObservable <TEvent, TContext, TModel> source in sources)
{
disposables.Add(source.Observe(o));
}
return disposables;
}
));
}
