Add namespace event filtering (SubscribeWithFilter)

Adds support for filtering events by type or actor pattern within namespace
subscriptions. Key changes:

- Add SubscriptionFilter type with EventTypes and ActorPattern fields
- Add SubscribeWithFilter to EventBroadcaster interface
- Implement filtering in EventBus with full wildcard pattern support preserved
- Implement filtering in NATSEventBus (server-side namespace, client-side filters)
- Add MatchActorPattern function for actor ID pattern matching
- Add comprehensive unit tests for all filtering scenarios

Filter Processing:
- EventTypes: Event must match at least one type in the list (OR within types)
- ActorPattern: Event's ActorID must match the pattern (supports * and > wildcards)
- Multiple filters are combined with AND logic

This implementation works alongside the existing wildcard subscription support:
- Namespace wildcards (* and >) work with event filters
- Filters are applied after namespace pattern matching
- Metrics are properly recorded for filtered subscriptions

Closes #21

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

eventbus_test.go

@@ -414,3 +414,409 @@ func TestEventBus_ConcurrentOperations(t *testing.T) {
 
 	wg.Wait()
 }
+
+// Tests for SubscribeWithFilter functionality
+
+func TestEventBus_SubscribeWithFilter_EventTypes(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Subscribe with filter for specific event types
+	filter := &SubscriptionFilter{
+		EventTypes: []string{"OrderPlaced", "OrderShipped"},
+	}
+	ch := eb.SubscribeWithFilter("orders", filter)
+
+	// Publish events of different types
+	events := []*Event{
+		{ID: "evt-1", EventType: "OrderPlaced", ActorID: "order-1"},
+		{ID: "evt-2", EventType: "OrderCancelled", ActorID: "order-2"}, // Should not be received
+		{ID: "evt-3", EventType: "OrderShipped", ActorID: "order-3"},
+	}
+
+	for _, e := range events {
+		eb.Publish("orders", e)
+	}
+
+	// Should receive evt-1 and evt-3, but not evt-2
+	received := make(map[string]bool)
+	timeout := time.After(100 * time.Millisecond)
+
+	for i := 0; i < 2; i++ {
+		select {
+		case evt := <-ch:
+			received[evt.ID] = true
+		case <-timeout:
+			t.Fatalf("timed out after receiving %d events", len(received))
+		}
+	}
+
+	if !received["evt-1"] || !received["evt-3"] {
+		t.Errorf("expected to receive evt-1 and evt-3, got %v", received)
+	}
+
+	// Verify evt-2 was not received
+	select {
+	case evt := <-ch:
+		t.Errorf("unexpected event received: %s", evt.ID)
+	case <-time.After(50 * time.Millisecond):
+		// Expected
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_ActorPattern(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Subscribe with filter for specific actor pattern
+	filter := &SubscriptionFilter{
+		ActorPattern: "order-*",
+	}
+	ch := eb.SubscribeWithFilter("events", filter)
+
+	// Publish events from different actors
+	events := []*Event{
+		{ID: "evt-1", EventType: "Test", ActorID: "order-123"},
+		{ID: "evt-2", EventType: "Test", ActorID: "user-456"},  // Should not be received
+		{ID: "evt-3", EventType: "Test", ActorID: "order-789"},
+	}
+
+	for _, e := range events {
+		eb.Publish("events", e)
+	}
+
+	// Should receive evt-1 and evt-3, but not evt-2
+	received := make(map[string]bool)
+	timeout := time.After(100 * time.Millisecond)
+
+	for i := 0; i < 2; i++ {
+		select {
+		case evt := <-ch:
+			received[evt.ID] = true
+		case <-timeout:
+			t.Fatalf("timed out after receiving %d events", len(received))
+		}
+	}
+
+	if !received["evt-1"] || !received["evt-3"] {
+		t.Errorf("expected to receive evt-1 and evt-3, got %v", received)
+	}
+
+	// Verify evt-2 was not received
+	select {
+	case evt := <-ch:
+		t.Errorf("unexpected event received: %s", evt.ID)
+	case <-time.After(50 * time.Millisecond):
+		// Expected
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_Combined(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Subscribe with filter for both event type AND actor pattern
+	filter := &SubscriptionFilter{
+		EventTypes:   []string{"OrderPlaced"},
+		ActorPattern: "order-*",
+	}
+	ch := eb.SubscribeWithFilter("orders", filter)
+
+	// Publish events with various combinations
+	events := []*Event{
+		{ID: "evt-1", EventType: "OrderPlaced", ActorID: "order-123"},  // Should be received
+		{ID: "evt-2", EventType: "OrderPlaced", ActorID: "user-456"},   // Wrong actor
+		{ID: "evt-3", EventType: "OrderCancelled", ActorID: "order-789"}, // Wrong type
+		{ID: "evt-4", EventType: "OrderCancelled", ActorID: "user-000"}, // Wrong both
+	}
+
+	for _, e := range events {
+		eb.Publish("orders", e)
+	}
+
+	// Should only receive evt-1
+	select {
+	case evt := <-ch:
+		if evt.ID != "evt-1" {
+			t.Errorf("expected evt-1, got %s", evt.ID)
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("timed out waiting for event")
+	}
+
+	// Verify no more events arrive
+	select {
+	case evt := <-ch:
+		t.Errorf("unexpected event received: %s", evt.ID)
+	case <-time.After(50 * time.Millisecond):
+		// Expected
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_NilFilter(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Subscribe with nil filter - should receive all events
+	ch := eb.SubscribeWithFilter("events", nil)
+
+	events := []*Event{
+		{ID: "evt-1", EventType: "TypeA", ActorID: "actor-1"},
+		{ID: "evt-2", EventType: "TypeB", ActorID: "actor-2"},
+	}
+
+	for _, e := range events {
+		eb.Publish("events", e)
+	}
+
+	received := make(map[string]bool)
+	timeout := time.After(100 * time.Millisecond)
+
+	for i := 0; i < 2; i++ {
+		select {
+		case evt := <-ch:
+			received[evt.ID] = true
+		case <-timeout:
+			t.Fatalf("timed out after receiving %d events", len(received))
+		}
+	}
+
+	if !received["evt-1"] || !received["evt-2"] {
+		t.Errorf("expected all events, got %v", received)
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_EmptyFilter(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Subscribe with empty filter - should receive all events
+	ch := eb.SubscribeWithFilter("events", &SubscriptionFilter{})
+
+	events := []*Event{
+		{ID: "evt-1", EventType: "TypeA", ActorID: "actor-1"},
+		{ID: "evt-2", EventType: "TypeB", ActorID: "actor-2"},
+	}
+
+	for _, e := range events {
+		eb.Publish("events", e)
+	}
+
+	received := make(map[string]bool)
+	timeout := time.After(100 * time.Millisecond)
+
+	for i := 0; i < 2; i++ {
+		select {
+		case evt := <-ch:
+			received[evt.ID] = true
+		case <-timeout:
+			t.Fatalf("timed out after receiving %d events", len(received))
+		}
+	}
+
+	if !received["evt-1"] || !received["evt-2"] {
+		t.Errorf("expected all events, got %v", received)
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_WildcardNamespaceAndFilter(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Subscribe to wildcard namespace pattern with event type filter
+	filter := &SubscriptionFilter{
+		EventTypes: []string{"OrderPlaced"},
+	}
+	ch := eb.SubscribeWithFilter("prod.*", filter)
+
+	// Publish events to different namespaces
+	events := []*Event{
+		{ID: "evt-1", EventType: "OrderPlaced", ActorID: "order-1"},  // prod.orders - should match
+		{ID: "evt-2", EventType: "OrderShipped", ActorID: "order-2"}, // prod.orders - wrong type
+		{ID: "evt-3", EventType: "OrderPlaced", ActorID: "order-3"},  // staging.orders - wrong namespace
+	}
+
+	eb.Publish("prod.orders", events[0])
+	eb.Publish("prod.orders", events[1])
+	eb.Publish("staging.orders", events[2])
+
+	// Should only receive evt-1
+	select {
+	case evt := <-ch:
+		if evt.ID != "evt-1" {
+			t.Errorf("expected evt-1, got %s", evt.ID)
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("timed out waiting for event")
+	}
+
+	// Verify no more events arrive
+	select {
+	case evt := <-ch:
+		t.Errorf("unexpected event received: %s", evt.ID)
+	case <-time.After(50 * time.Millisecond):
+		// Expected
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_MultipleSubscribersWithDifferentFilters(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Two subscribers with different filters on same namespace
+	filter1 := &SubscriptionFilter{EventTypes: []string{"OrderPlaced"}}
+	filter2 := &SubscriptionFilter{EventTypes: []string{"OrderShipped"}}
+	
+	ch1 := eb.SubscribeWithFilter("orders", filter1)
+	ch2 := eb.SubscribeWithFilter("orders", filter2)
+
+	events := []*Event{
+		{ID: "evt-1", EventType: "OrderPlaced", ActorID: "order-1"},
+		{ID: "evt-2", EventType: "OrderShipped", ActorID: "order-2"},
+	}
+
+	for _, e := range events {
+		eb.Publish("orders", e)
+	}
+
+	// ch1 should only receive evt-1
+	select {
+	case evt := <-ch1:
+		if evt.ID != "evt-1" {
+			t.Errorf("ch1: expected evt-1, got %s", evt.ID)
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("ch1 timed out")
+	}
+
+	// ch2 should only receive evt-2
+	select {
+	case evt := <-ch2:
+		if evt.ID != "evt-2" {
+			t.Errorf("ch2: expected evt-2, got %s", evt.ID)
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("ch2 timed out")
+	}
+
+	// Verify no extra events
+	select {
+	case evt := <-ch1:
+		t.Errorf("ch1: unexpected event %s", evt.ID)
+	case evt := <-ch2:
+		t.Errorf("ch2: unexpected event %s", evt.ID)
+	case <-time.After(50 * time.Millisecond):
+		// Expected
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_UnsubscribeFiltered(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	filter := &SubscriptionFilter{EventTypes: []string{"OrderPlaced"}}
+	ch := eb.SubscribeWithFilter("orders", filter)
+
+	// Verify subscription count
+	if eb.SubscriberCount("orders") != 1 {
+		t.Errorf("expected 1 subscriber, got %d", eb.SubscriberCount("orders"))
+	}
+
+	eb.Unsubscribe("orders", ch)
+
+	// Verify unsubscribed
+	if eb.SubscriberCount("orders") != 0 {
+		t.Errorf("expected 0 subscribers, got %d", eb.SubscriberCount("orders"))
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_FilteredAndUnfilteredCoexist(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// One subscriber with filter, one without
+	filter := &SubscriptionFilter{EventTypes: []string{"OrderPlaced"}}
+	chFiltered := eb.SubscribeWithFilter("orders", filter)
+	chUnfiltered := eb.Subscribe("orders")
+
+	events := []*Event{
+		{ID: "evt-1", EventType: "OrderPlaced", ActorID: "order-1"},
+		{ID: "evt-2", EventType: "OrderShipped", ActorID: "order-2"},
+	}
+
+	for _, e := range events {
+		eb.Publish("orders", e)
+	}
+
+	// Filtered subscriber should only receive evt-1
+	select {
+	case evt := <-chFiltered:
+		if evt.ID != "evt-1" {
+			t.Errorf("filtered: expected evt-1, got %s", evt.ID)
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("filtered subscriber timed out")
+	}
+
+	// Unfiltered subscriber should receive both
+	received := make(map[string]bool)
+	timeout := time.After(100 * time.Millisecond)
+	for i := 0; i < 2; i++ {
+		select {
+		case evt := <-chUnfiltered:
+			received[evt.ID] = true
+		case <-timeout:
+			t.Fatalf("unfiltered timed out after %d events", len(received))
+		}
+	}
+
+	if !received["evt-1"] || !received["evt-2"] {
+		t.Errorf("unfiltered expected both events, got %v", received)
+	}
+}
+
+func TestEventBus_SubscribeWithFilter_WildcardGreaterWithFilter(t *testing.T) {
+	eb := NewEventBus()
+	defer eb.Stop()
+
+	// Use > wildcard (matches one or more tokens) with filter
+	filter := &SubscriptionFilter{
+		ActorPattern: "order-*",
+	}
+	ch := eb.SubscribeWithFilter(">", filter)
+
+	events := []*Event{
+		{ID: "evt-1", EventType: "Test", ActorID: "order-123"},
+		{ID: "evt-2", EventType: "Test", ActorID: "user-456"},
+		{ID: "evt-3", EventType: "Test", ActorID: "order-789"},
+	}
+
+	// Publish to different namespaces
+	eb.Publish("tenant-a", events[0])
+	eb.Publish("tenant-b", events[1])
+	eb.Publish("prod.orders", events[2])
+
+	// Should receive evt-1 and evt-3, but not evt-2
+	received := make(map[string]bool)
+	timeout := time.After(100 * time.Millisecond)
+	for i := 0; i < 2; i++ {
+		select {
+		case evt := <-ch:
+			received[evt.ID] = true
+		case <-timeout:
+			t.Fatalf("timed out after %d events", len(received))
+		}
+	}
+
+	if !received["evt-1"] || !received["evt-3"] {
+		t.Errorf("expected evt-1 and evt-3, got %v", received)
+	}
+
+	// Verify no evt-2
+	select {
+	case evt := <-ch:
+		t.Errorf("unexpected event: %s", evt.ID)
+	case <-time.After(50 * time.Millisecond):
+		// Expected
+	}
+}