🔄 Event-Driven Simplicity Refactor Plan

🎯 Goal

Achieve a simple, maintainable, and robust event-driven architecture by:

• Eliminating switch/case control flow in event dispatching
• Preventing infinite event loops
• Enforcing single-responsibility handlers
• Documenting event chains for clarity

---

📐 Refactor Steps

1. Replace Switch/Case with Event Handler Registry

• Before: Event dispatch uses switch/case or if/else to route events.
• After: Use a registry:

map[EventType][]HandlerFunc

• Handlers are registered for each event type.
• On event emission, all registered handlers are invoked.

---

2. Guard Against Infinite Event Loops

• Add a propagation context or depth counter to each event.
• Limit event chain depth or track event IDs to prevent re-processing.
• Optionally, use middleware to wrap handlers with loop protection.

---

3. Enforce Single Responsibility in Handlers

• Each handler should:
• Handle one event type
• Perform one business action
• Optionally emit one follow-up event
• Split complex handlers into smaller, focused ones.

---

4. Document and Visualize Event Chains

• Use Mermaid diagrams or sequence charts to show event flows.
• Document which events trigger which handlers and what follow-up events are emitted.

---

🖼️ Event Flow Example

flowchart TD
    A["DepositInitiated Event"] --> B["DepositValidationHandler"]
    B --> C["DepositPersistenceHandler"]
    C --> D["DepositConversionHandler"]
    D --> E["DepositCompletedHandler"]

    subgraph Legend
      direction LR
      L1["Event"] -- triggers --> L2["Handler"]
    end

    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#bbf,stroke:#333,stroke-width:2px
    style C fill:#bbf,stroke:#333,stroke-width:2px
    style D fill:#bbf,stroke:#333,stroke-width:2px
    style E fill:#bbf,stroke:#333,stroke-width:2px
    style Legend fill:#fff,stroke:#333,stroke-width:1px

---

5. Refactor Event Bus Interface

• Define an interface in pkg/eventbus:

type EventBus interface {
    Register(eventType string, handler HandlerFunc)
    Emit(ctx context.Context, event Event) error
}

• Implement the registry pattern in infra/eventbus.

---

6. Testing and Validation

• Write tests for:
• Event registration and dispatch
• Loop protection
• Event chain correctness

---

Example: Event Handler Registry

type HandlerFunc func(ctx context.Context, event Event) error

type EventBus struct {
    handlers map[string][]HandlerFunc
}

func (eb *EventBus) Register(eventType string, handler HandlerFunc) {
    eb.handlers[eventType] = append(eb.handlers[eventType], handler)
}

func (eb *EventBus) Emit(ctx context.Context, event Event) error {
    for _, handler := range eb.handlers[event.Type()] {
        if err := handler(ctx, event); err != nil {
            return err
        }
    }
    return nil
}

---

Next Steps

1. Refactor event dispatch to use a registry.
2. Add loop protection/context to events.
3. Refactor handlers for single responsibility.
4. Document event flows.
5. Update tests.