implemented NATS event bus, websocket hub upgrade, and audit log

internal/events/bus.go

@@ -0,0 +1,87 @@
+package events
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/nats-io/nats.go"
+)
+
+// EventBus is the platform event bus interface.
+// Publish sends a typed payload to the given subject.
+// Subscribe registers a handler for a subject pattern (supports NATS wildcards).
+// The returned func() unsubscribes when called.
+type EventBus interface {
+	Publish(subject string, payload any) error
+	Subscribe(subject string, handler func(subject string, data []byte)) (func(), error)
+	Close()
+}
+
+// NATSBus is the NATS-backed EventBus. Events are published to core NATS subjects.
+// Phase 2A uses core NATS (ephemeral). Phase 2B will add JetStream for CI durability.
+type NATSBus struct {
+	nc *nats.Conn
+}
+
+func NewNATSBus(url string) (*NATSBus, error) {
+	nc, err := nats.Connect(url,
+		nats.MaxReconnects(-1),
+		nats.ReconnectWait(2*time.Second),
+		nats.DisconnectErrHandler(func(_ *nats.Conn, err error) {
+			if err != nil {
+				log.Printf("nats: disconnected: %v", err)
+			}
+		}),
+		nats.ReconnectHandler(func(_ *nats.Conn) {
+			log.Printf("nats: reconnected")
+		}),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("nats connect %s: %w", url, err)
+	}
+	log.Printf("nats: connected to %s", url)
+	return &NATSBus{nc: nc}, nil
+}
+
+func (b *NATSBus) Publish(subject string, payload any) error {
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal: %w", err)
+	}
+	return b.nc.Publish(subject, data)
+}
+
+func (b *NATSBus) Subscribe(subject string, handler func(subject string, data []byte)) (func(), error) {
+	sub, err := b.nc.Subscribe(subject, func(msg *nats.Msg) {
+		handler(msg.Subject, msg.Data)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return func() { sub.Unsubscribe() }, nil //nolint:errcheck
+}
+
+func (b *NATSBus) Close() {
+	if err := b.nc.Drain(); err != nil {
+		log.Printf("nats: drain: %v", err)
+	}
+}
+
+// NoOpBus is a no-op EventBus used when NATS_URL is not configured.
+// Events are silently dropped. The app works normally; just no real-time push.
+type NoOpBus struct{}
+
+func (NoOpBus) Publish(_ string, _ any) error                              { return nil }
+func (NoOpBus) Subscribe(_ string, _ func(string, []byte)) (func(), error) { return func() {}, nil }
+func (NoOpBus) Close()                                                      {}
+
+// New returns a NATSBus if url is non-empty, otherwise a NoOpBus.
+func New(url string) (EventBus, error) {
+	if url == "" {
+		log.Printf("events: NATS_URL not set — using no-op bus (real-time push disabled)")
+		return NoOpBus{}, nil
+	}
+	return NewNATSBus(url)
+}