thread-safe controller snapshot for GUI, CLI

internal/playback/session_controller.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"sync"
 )
 
 type VideoSlotRunner interface {
@@ -40,11 +41,21 @@ var (
 	ErrSyncSlotRequired  = errors.New("sync slot is required")
 )
 
+type SessionSnapshot struct {
+	Desired    SessionConfig
+	Plan       SessionPlan
+	Generation uint64
+}
+
 type SessionController struct {
 	videoSlot VideoSlotRunner
 	audioSlot AudioSlotRunner
 	syncSlot  SyncSlotRunner
 	canSync   SyncPredicate
+
+	mu          sync.RWMutex
+	snapshot    SessionSnapshot
+	hasSnapshot bool
 }
 
 func NewSessionController(
@@ -100,6 +111,13 @@ func (c *SessionController) Run(
 	desired := initial
 	runtime := c.startSessionRuntime(ctx, plan)
 
+	generation := uint64(1)
+	c.publish(SessionSnapshot{
+		Desired:    initial,
+		Plan:       plan,
+		Generation: generation,
+	})
+
 	for {
 		var runtimeDone <-chan struct{}
 		if runtime != nil {
@@ -144,9 +162,17 @@ func (c *SessionController) Run(
 				return err
 			}
 
+			if plan.Topology != nextPlan.Topology {
+				generation++
+			}
 			desired = nextDesired
 			plan = nextPlan
 			runtime = nextRuntime
+			c.publish(SessionSnapshot{
+				Desired:    desired,
+				Plan:       plan,
+				Generation: generation,
+			})
 		}
 	}
 }
@@ -301,3 +327,18 @@ func sessionRuntimeSendError(ctx context.Context, runtime *sessionRuntime) error
 	<-runtime.done
 	return unexpectedSessionRuntimeError(runtime.result)
 }
+
+func (c *SessionController) Snapshot() (SessionSnapshot, bool) {
+	c.mu.RLock()
+	snapshot := c.snapshot
+	ok := c.hasSnapshot
+	c.mu.RUnlock()
+	return snapshot, ok
+}
+
+func (c *SessionController) publish(snapshot SessionSnapshot) {
+	c.mu.Lock()
+	c.snapshot = snapshot
+	c.hasSnapshot = true
+	c.mu.Unlock()
+}