playlist: provide information about "next song"

In random mode, this patch allows clients to see the "next song" in
the queue.

src/command.c

@@ -62,6 +62,8 @@
 #define COMMAND_STATUS_PLAYLIST_LENGTH  "playlistlength"
 #define COMMAND_STATUS_SONG             "song"
 #define COMMAND_STATUS_SONGID           "songid"
+#define COMMAND_STATUS_NEXTSONG         "nextsong"
+#define COMMAND_STATUS_NEXTSONGID       "nextsongid"
 #define COMMAND_STATUS_TIME             "time"
 #define COMMAND_STATUS_BITRATE          "bitrate"
 #define COMMAND_STATUS_ERROR            "error"
@@ -508,6 +510,14 @@ handle_status(struct client *client,
 			      getPlayerErrorStr());
 	}
 
+	song = getPlaylistNextSong(&g_playlist);
+	if (song >= 0) {
+		client_printf(client,
+			      COMMAND_STATUS_NEXTSONG ": %i\n"
+			      COMMAND_STATUS_NEXTSONGID ": %u\n",
+			      song, getPlaylistSongId(&g_playlist, song));
+	}
+
 	return COMMAND_RETURN_OK;
 }
 

src/playlist.c

@@ -334,6 +334,21 @@ int getPlaylistCurrentSong(const struct playlist *playlist)
 	return -1;
 }
 
+int getPlaylistNextSong(const struct playlist *playlist)
+{
+	if (playlist->current >= 0)
+	{
+		if (queue_length(&playlist->queue) > 1)
+			return queue_order_to_position(&playlist->queue,
+					       playlist->current + 1);
+		else if (playlist->queue.repeat == 1)
+			return queue_order_to_position(&playlist->queue,
+					       playlist->current);
+	}
+
+	return -1;
+}
+
 unsigned long
 getPlaylistVersion(const struct playlist *playlist)
 {

src/playlist.h

@@ -180,6 +180,8 @@ void setPlaylistRandomStatus(struct playlist *playlist, bool status);
 
 int getPlaylistCurrentSong(const struct playlist *playlist);
 
+int getPlaylistNextSong(const struct playlist *playlist);
+
 unsigned
 getPlaylistSongId(const struct playlist *playlist, unsigned song);