playlist-to-session bridge

internal/playback/playlist_navigation.go

@@ -23,6 +23,7 @@ type PlaylistState struct {
 var (
 	ErrPlaylistEmpty           = errors.New("playlist is empty")
 	ErrPlaylistIndexOutOfRange = errors.New("playlist index is out of range")
+	ErrPlaylistNoSelection     = errors.New("playlist has no selected entry")
 	ErrUnknownPlaylistCommand  = errors.New("unknown playlist command")
 )
 
@@ -91,3 +92,39 @@ func (s PlaylistState) Entry(playlist Playlist) (PlaylistEntry, bool) {
 	}
 	return playlist.Entries[s.CurrentIndex], true
 }
+
+func ApplyPlaylistSelection(
+	playlist Playlist,
+	current PlaylistState,
+	command PlaylistCommand,
+	retry RetryPolicy,
+) (
+	next PlaylistState,
+	sessionCommand SessionCommand,
+	apply bool,
+	err error,
+) {
+	next, err = ApplyPlaylistCommand(playlist, current, command)
+	if err != nil {
+		return current, SessionCommand{}, false, err
+	}
+
+	apply = command.Kind == PlaylistSelect || next != current
+	if !apply {
+		return next, SessionCommand{}, false, nil
+	}
+
+	entry, ok := next.Entry(playlist)
+	if !ok {
+		return current, SessionCommand{}, false, ErrPlaylistNoSelection
+	}
+	session := entry.SessionConfig(retry)
+	if err := session.Validate(); err != nil {
+		return current, SessionCommand{}, false, err
+	}
+
+	return next, SessionCommand{
+		Kind:    CommandSetSession,
+		Session: session,
+	}, true, nil
+}