add audio slot lifecycle

internal/playback/audio_slot.go

@@ -0,0 +1,93 @@
+package playback
+
+import (
+	"context"
+	"errors"
+	"fmt"
+)
+
+var ErrAudioWorkerRequired = errors.New("audio worker is required")
+
+type AudioSlot struct {
+	worker *AudioWorker
+}
+
+func NewAudioSlot(worker *AudioWorker) (*AudioSlot, error) {
+	if worker == nil {
+		return nil, ErrAudioWorkerRequired
+	}
+	return &AudioSlot{worker: worker}, nil
+}
+
+func (s *AudioSlot) Run(
+	ctx context.Context,
+	initial FeedConfig,
+	commands <-chan FeedConfig,
+) error {
+	if err := initial.Validate(); err != nil {
+		return fmt.Errorf("validate initial audio config: %w", err)
+	}
+
+	var (
+		workerCancel context.CancelFunc
+		workerDone   chan error
+	)
+
+	start := func(config FeedConfig) {
+		workerCtx, cancel := context.WithCancel(ctx)
+		done := make(chan error, 1)
+
+		workerCancel = cancel
+		workerDone = done
+
+		go func() {
+			done <- s.worker.Run(workerCtx, config)
+		}()
+	}
+
+	stop := func() {
+		if workerCancel == nil {
+			return
+		}
+
+		workerCancel()
+		<-workerDone
+
+		workerCancel = nil
+		workerDone = nil
+	}
+
+	if initial.Active {
+		start(initial)
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			stop()
+			return ctx.Err()
+
+		case config, ok := <-commands:
+			if !ok {
+				stop()
+				return nil
+			}
+
+			if err := config.Validate(); err != nil {
+				// Ignore invalid commands without disturbing the current worker.
+				continue
+			}
+
+			stop()
+			if config.Active {
+				start(config)
+			}
+
+		case <-workerDone:
+			// The worker stopped naturally or exhausted its retries.
+			workerCancel()
+			workerCancel = nil
+			workerDone = nil
+		}
+	}
+}