session plan

internal/playback/session_plan.go

@@ -0,0 +1,76 @@
+package playback
+
+import "fmt"
+
+type SessionTopology uint8
+
+const (
+	TopologyIdle SessionTopology = iota
+	TopologyIndependent
+	TopologySynchronized
+)
+
+type SyncPredicate func(video, audio FeedConfig) bool
+
+type SessionPlan struct {
+	Topology SessionTopology
+
+	// Desired states for independent slots.
+	Video FeedConfig
+	Audio FeedConfig
+
+	// Desired state for the synchronized slot.
+	Sync SyncPairConfig
+}
+
+func BuildSessionPlan(
+	desired SessionConfig,
+	canSync SyncPredicate,
+) (SessionPlan, error) {
+	if err := desired.Validate(); err != nil {
+		return SessionPlan{}, fmt.Errorf("validate desired session: %w", err)
+	}
+
+	if desired.SyncRequested &&
+		desired.Video.Active &&
+		desired.Audio.Active &&
+		canSync != nil &&
+		canSync(desired.Video, desired.Audio) {
+		return SessionPlan{
+			Topology: TopologySynchronized,
+			Video:    stoppedFeed(desired.Video),
+			Audio:    stoppedFeed(desired.Audio),
+			Sync: SyncPairConfig{
+				Video: desired.Video,
+				Audio: desired.Audio,
+			},
+		}, nil
+	}
+
+	if desired.Video.Active || desired.Audio.Active {
+		return SessionPlan{
+			Topology: TopologyIndependent,
+			Video:    desired.Video,
+			Audio:    desired.Audio,
+			Sync: SyncPairConfig{
+				Video: stoppedFeed(desired.Video),
+				Audio: stoppedFeed(desired.Audio),
+			},
+		}, nil
+	}
+
+	return SessionPlan{
+		Topology: TopologyIdle,
+		Video:    stoppedFeed(desired.Video),
+		Audio:    stoppedFeed(desired.Audio),
+		Sync: SyncPairConfig{
+			Video: stoppedFeed(desired.Video),
+			Audio: stoppedFeed(desired.Audio),
+		},
+	}, nil
+}
+
+func stoppedFeed(config FeedConfig) FeedConfig {
+	config.Active = false
+	return config
+}