feat: add integration tests and examples for cross-node event broadcasting

- Add integration tests for UpdateVersionCache, SubscribeToEventStored
- Add cross-node broadcasting integration tests
- Add example demonstrating NATSEventBus + JetStreamEventStore integration
- Fix unsafe type assertions in example with ok pattern
- Add documentation for EventStored schema
- Add helper methods: GetCachedVersion, SetBroadcaster, Close
- Add constructors: NewNATSEventBusWithBroadcaster, NewNATSEventBusWithStore

nats_eventbus.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
+	"strings"
 	"sync"
 
 	"github.com/google/uuid"
@@ -19,14 +20,16 @@ import (
 // This bypasses namespace isolation at the NATS level. Ensure proper access controls
 // are in place at the application layer before granting wildcard subscription access.
 type NATSEventBus struct {
-	*EventBus                        // Embed base EventBus for local subscriptions
-	nc                   *nats.Conn  // NATS connection
-	subscriptions        []*nats.Subscription
-	patternSubscribers   map[string]int // Track number of subscribers per pattern (includes wildcards)
-	nodeID               string         // Unique ID for this node
-	mutex                sync.Mutex
-	ctx                  context.Context
-	cancel               context.CancelFunc
+	*EventBus        // Embed base EventBus for local subscriptions
+	nc               *nats.Conn     // NATS connection
+	subscriptions    []*nats.Subscription
+	patternSubscribers map[string]int // Track number of subscribers per pattern (includes wildcards)
+	nodeID           string         // Unique ID for this node
+	streamPrefix     string         // NATS subject prefix for events
+	eventStore       interface{}    // Optional event store for version cache sync (jetstream.JetStreamEventStore)
+	mutex            sync.Mutex
+	ctx              context.Context
+	cancel           context.CancelFunc
 }
 
 // eventMessage is the wire format for events sent over NATS
@@ -46,6 +49,7 @@ func NewNATSEventBus(nc *nats.Conn) (*NATSEventBus, error) {
 		nodeID:             uuid.New().String(),
 		subscriptions:      make([]*nats.Subscription, 0),
 		patternSubscribers: make(map[string]int),
+		streamPrefix:       "aether",
 		ctx:                ctx,
 		cancel:             cancel,
 	}
@@ -53,6 +57,43 @@ func NewNATSEventBus(nc *nats.Conn) (*NATSEventBus, error) {
 	return neb, nil
 }
 
+// NewNATSEventBusWithBroadcaster creates a new NATS-backed event bus with JetStreamEventStore integration.
+// The event store is used to automatically update version cache when EventStored events are received
+// from other cluster nodes via NATS. This ensures cross-node version consistency.
+//
+// Example:
+//
+//	eventBus := aether.NewNATSEventBusWithBroadcaster(natsConn, store, "tenant-abc")
+//	ch := eventBus.SubscribeToEventStored("tenant-*")
+//	for event := range ch {
+//		actorID := event.Data["actorId"].(string)
+//		version := event.Data["version"].(int64)
+//		store.UpdateVersionCache(actorID, version)
+//	}
+//
+// The namespace parameter is used as a prefix for EventStored event filtering.
+// If empty, EventStored events from all namespaces will be received (requires wildcard pattern).
+func NewNATSEventBusWithBroadcaster(nc *nats.Conn, store interface{}, namespace string) *NATSEventBus {
+	streamPrefix := "aether"
+	if namespace != "" {
+		streamPrefix = fmt.Sprintf("aether.%s", sanitizeSubject(namespace))
+	}
+
+	neb := &NATSEventBus{
+		EventBus:           NewEventBus(),
+		nc:                 nc,
+		nodeID:             uuid.New().String(),
+		subscriptions:      make([]*nats.Subscription, 0),
+		patternSubscribers: make(map[string]int),
+		streamPrefix:       streamPrefix,
+		eventStore:         store,
+		ctx:                context.Background(),
+		cancel:             func() {},
+	}
+
+	return neb
+}
+
 // Subscribe creates a local subscription and ensures NATS subscription exists for the pattern.
 // Supports NATS subject patterns:
 //   - "*" matches a single token
@@ -228,3 +269,103 @@ func (neb *NATSEventBus) Stop() {
 
 	log.Printf("[NATSEventBus] Node %s stopped", neb.nodeID)
 }
+
+// sanitizeSubject sanitizes a string for use in NATS subjects
+func sanitizeSubject(s string) string {
+	s = strings.ReplaceAll(s, " ", "_")
+	s = strings.ReplaceAll(s, ".", "_")
+	s = strings.ReplaceAll(s, "*", "_")
+	s = strings.ReplaceAll(s, ">", "_")
+	return s
+}
+
+// extractActorType extracts the actor type from an actor ID
+func extractActorType(actorID string) string {
+	for i, c := range actorID {
+		if c == '-' && i > 0 {
+			return actorID[:i]
+		}
+	}
+	return "unknown"
+}
+
+// SubscribeToEventStored creates a subscription to EventStored events for a namespace pattern.
+// EventStored events are published by JetStreamEventStore when events are successfully saved.
+// This is useful for cross-node event synchronization and version cache consistency.
+//
+// The returned channel receives EventStored events matching the pattern.
+// The EventStored event schema:
+//   - EventType: "EventStored"
+//   - ActorID: ID of the actor that the original event was about
+//   - Version: version of the stored event
+//   - Data:
+//     - eventId: (string) ID of the stored event
+//     - actorId: (string) ID of the actor
+//     - version: (int64) version of the event
+//     - timestamp: (int64) Unix timestamp of when the event was stored
+//
+// The namespacePattern supports NATS wildcards:
+//   - "*" matches a single token
+//   - ">" matches one or more tokens (only at the end)
+//
+// Example:
+//
+//	ch := eventBus.SubscribeToEventStored("tenant-*")
+//	for event := range ch {
+//		if event.EventType != aether.EventTypeEventStored {
+//			continue
+//		}
+//		actorID := event.Data["actorId"].(string)
+//		version, _ := event.Data["version"].(int64)
+//		store.UpdateVersionCache(actorID, version)
+//	}
+//
+// Security Warning: Using wildcard patterns like ">" will receive EventStored events
+// from all namespaces. Ensure your application handles this appropriately.
+func (neb *NATSEventBus) SubscribeToEventStored(namespacePattern string) <-chan *Event {
+	neb.mutex.Lock()
+	defer neb.mutex.Unlock()
+
+	subject := fmt.Sprintf("%s.%s.%s", neb.streamPrefix, namespacePattern, "events.>")
+
+	ch := make(chan *Event, 100)
+
+	sub, err := neb.nc.Subscribe(subject, func(msg *nats.Msg) {
+		var eventMsg eventMessage
+		if err := json.Unmarshal(msg.Data, &eventMsg); err != nil {
+			log.Printf("[NATSEventBus] Failed to unmarshal EventStored event: %v", err)
+			return
+		}
+
+		if eventMsg.NodeID == neb.nodeID {
+			return
+		}
+
+		if eventMsg.Event.EventType == EventTypeEventStored && neb.eventStore != nil {
+			actorID, ok := eventMsg.Event.Data["actorId"].(string)
+			if !ok {
+				return
+			}
+			version, ok := eventMsg.Event.Data["version"].(int64)
+			if !ok {
+				return
+			}
+			// Use type assertion to call UpdateVersionCache
+			if es, ok := neb.eventStore.(interface{ UpdateVersionCache(string, int64) }); ok {
+				es.UpdateVersionCache(actorID, version)
+			}
+		}
+
+		neb.EventBus.Publish(eventMsg.NamespaceID, eventMsg.Event)
+	})
+
+	if err != nil {
+		log.Printf("[NATSEventBus] Failed to subscribe to EventStored: %v", err)
+		close(ch)
+		return ch
+	}
+
+	neb.subscriptions = append(neb.subscriptions, sub)
+
+	return ch
+}