Where's the Event Bus?

[daniser]

Every event driven system usually revolves around event bus as its core component. Spatie's solution doesn't seem to have explicit event bus implementation despite having command bus one. What am I trying to achieve is to attach middleware chain to event bus to handle side effects like Reactors do, but with execution order which can be trusted. I don't know if it's achievable with Reactors out-of-the-box.

My idea is to create single Reactor which hosts and manages pipeline, but:

1. middleware stack must be applied to every event in the system (Reactors in fact are Listeners, which handle specific events);
2. I don't want to reinvent the wheel if there's way to implement same functionality with existing event bus.

[daniser]

To give more context:

I am designing helpdesk system where each ticket have weight which defines ticket processing priority by the operator. The weight is calculated dynamically given initial characteristics of the ticket (TicketCreated event's payload) and further changes during ticket's lifetime. Weight calculation algorithm must be highly configurable. I've named each condition which lead to weight correction a factor. Factor order, conditions and amount of weight correction may be configured by the supervisor.

At first, I've chosen command bus for this matter. In this implementation, factors were just simple middlewares on the command bus which instantly modified command's payload (more specifically weight). Shortly, I decided that I need to track changes applied by the factors to answer a simple question "why is this ticket so important??".
I caught myself on reimplementing event sourcing within command bus😅. Given that event sourcing was already chosen as a backbone of the system, I decided to go another path.

I've tried to attach these middlewares ("factors") to the event bus. Instead of modifying event payload, I planned to issue IncrementTicketWeight command when factor decides to modify the ticket's weight. Every event within TicketAggregateRoot boundary (except maybe some events like TicketWeightIncremented itself) should've been passed through this middleware (factor) stack.

But, the event bus was never found😁.

The last resort is Reactors, but they are more like listeners than middleware, as they doesn't guarantee order of execution and they have 1-to-many relation to events and not many-to-many (correct me if I'm wrong).

Why is order so important?
Example:
One factor may decide to add +100 points to the ticket's weight.
Following factor may decide to multiply weight by 2.
So this brings us to simple arithmetic problem: (w + 100) * 2 vs. w * 2 + 100 will give us different results.

Sorry if my explanations were cumbersome. English is not my first language.