Configurable Event Bus support

[reypader]

I was wondering how the team envisioned a configurable event bus that can delegate to an external pub/sub and queueing mechanism like AMQP, Amazon SQS/SNS, Google Cloud Pub/Sub (I believe it's queued internally).

I was planning to just extend the event bus and override certain methods. However, I believe if we can instead allow injection of a publisher/subscriber in the event bus, it would allow users to do as they please on the event handling.

export class EventBus extends ObservableBus<IEvent> implements IEventBus {
    publish<T extends IEvent>(event: T) {
            if(this.eventPublisher){
                ...publish to external queue...
            } else {
                this.subject$.next(event);
            }
    }

    bind<T extends IEvent>(handler: IEventHandler<IEvent>, name: string) {
            const stream$ = name ? this.ofEventName(name) : this.subject$;
            stream$.subscribe(event => handler.handle(event));
            
            if(this.eventSubscriber){
                ...subscribe a worker to the external queue...
                ...once a message is consumed call "this.subject$.next(event);"...
            }
    }
}

Instead of the clunky if-else blocks, we can have a "DefaultPublisher" and "DefaultSubscriber" that immediately consumes a published messaged and thus, immediately triggering this.subject$.next(event) similar to how it is right now.

Any thoughts?

[reypader]

I'm currently testing some changes for this on my fork but when I tried using it in the example, I'm getting the error Error: Cannot find module 'multer'.

This is after I tried installing @types/node on nest-cqrs since running npm run compile fails due to

node_modules/@nestjs/common/interfaces/external/multer-options.interface.d.ts(1,23): error TS2688: Cannot find type definition file for 'node'.
node_modules/@nestjs/common/interfaces/external/multer-options.interface.d.ts(46,17): error TS2304: Cannot find name 'Buffer'.

It's actually the first time I've tried using local typescript modules; always been a leecher. Any tips on how you guys test this locally?

[kamilmysliwiec]

Let's track this feature in your pull request: #12