add thread-safe playback status store

internal/playback/status_store.go

@@ -0,0 +1,33 @@
+package playback
+
+import "sync"
+
+type StatusStore struct {
+	mu       sync.RWMutex
+	statuses map[Unit]Status
+}
+
+func NewStatusStore() *StatusStore {
+	return &StatusStore{
+		statuses: make(map[Unit]Status),
+	}
+}
+
+func (s *StatusStore) Observe(status Status) {
+	s.mu.Lock()
+	s.statuses[status.Unit] = status
+	s.mu.Unlock()
+}
+
+func (s *StatusStore) Snapshot(unit Unit) (Status, bool) {
+	s.mu.RLock()
+	status, ok := s.statuses[unit]
+	s.mu.RUnlock()
+	return status, ok
+}
+
+func (s *StatusStore) Clear(unit Unit) {
+	s.mu.Lock()
+	delete(s.statuses, unit)
+	s.mu.Unlock()
+}