PlaylistController

internal/playback/playlist_controller.go

@@ -0,0 +1,102 @@
+package playback
+
+import (
+	"context"
+	"errors"
+	"sync"
+)
+
+type PlaylistController struct {
+	playlist Playlist
+	retry    RetryPolicy
+	sessions chan<- SessionCommand
+
+	mu          sync.RWMutex
+	snapshot    PlaylistSnapshot
+	hasSnapshot bool
+}
+
+type PlaylistSnapshot struct {
+	State PlaylistState
+	Entry PlaylistEntry
+}
+
+var (
+	ErrNilSessionCommandChannel = errors.New("session-command channel is nil")
+)
+
+func NewPlaylistController(
+	playlist Playlist,
+	retry RetryPolicy,
+	sessions chan<- SessionCommand,
+) (*PlaylistController, error) {
+	if err := playlist.Validate(); err != nil {
+		return nil, err
+	}
+	if err := retry.Validate(); err != nil {
+		return nil, err
+	}
+	if sessions == nil {
+		return nil, ErrNilSessionCommandChannel
+	}
+	return &PlaylistController{
+		playlist: playlist,
+		retry:    retry,
+		sessions: sessions,
+	}, nil
+}
+
+func (c *PlaylistController) Run(
+	ctx context.Context,
+	commands <-chan PlaylistCommand,
+) error {
+	state := PlaylistState{}
+	c.publish(state)
+
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+
+		case command, ok := <-commands:
+			if !ok {
+				return nil
+			}
+
+			next, sessionCommand, apply, err := ApplyPlaylistSelection(
+				c.playlist,
+				state,
+				command,
+				c.retry,
+			)
+			if err != nil {
+				continue
+			}
+			if apply {
+				select {
+				case <-ctx.Done():
+					return ctx.Err()
+				case c.sessions <- sessionCommand:
+				}
+			}
+
+			state = next
+			c.publish(state)
+		}
+	}
+}
+
+func (c *PlaylistController) Snapshot() (PlaylistSnapshot, bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.snapshot, c.hasSnapshot
+}
+
+func (c *PlaylistController) publish(state PlaylistState) {
+	entry, _ := state.Entry(c.playlist)
+
+	c.mu.Lock()
+	c.snapshot = PlaylistSnapshot{State: state, Entry: entry}
+	c.hasSnapshot = true
+	c.mu.Unlock()
+}