libsaria: Alert the PlaylistRenderer when the playlist becomes empty

This allows for bookkeeping and other cleanup (schedule playlist
removal, remove from UI, and so on).

Signed-off-by: Bryan Schumaker <bjschuma@gmail.com>

include/libsaria/renderer.h

@@ -9,6 +9,7 @@ namespace libsaria
 	class PlaylistRenderer {
 		private:
 			Playlist *playlist;
+			virtual void on_playlist_empty();
 
 		public:
 			PlaylistRenderer();
@@ -16,6 +17,7 @@ namespace libsaria
 
 			void set_playlist(Playlist *);
 			Playlist *get_playlist();
+			void playlist_empty();
 
 			void fill();
 			virtual void insert(Track *) = 0;

libsaria/playlist/next.cpp

@@ -89,8 +89,11 @@ namespace libsaria
 		if (flags & PL_DRAIN) {
 			index = distance(cur, plist.begin());
 			plist.erase(cur);
-			if (renderer)
+			if (renderer) {
 				renderer->index_removed(index);
+				if (plist.size() == 0)
+					renderer->playlist_empty();
+			}
 			cur = plist.end();
 			save();
 		}

libsaria/playlist/playlist.cpp

@@ -89,6 +89,9 @@ namespace libsaria
 			removed++;
 		}
 		save();
+
+		if (renderer && (plist.size() == 0))
+			renderer->playlist_empty();
 	}
 
 	void Playlist::rm_track(Track *track)

libsaria/playlist/renderer.cpp

@@ -31,4 +31,18 @@ namespace libsaria
 		playlist->for_each_insert();
 	}
 
+	void PlaylistRenderer::playlist_empty()
+	{
+		on_playlist_empty();
+	}
+
+	void PlaylistRenderer::on_playlist_empty()
+	{
+		/*
+		 * This function is meant to be overridden by
+		 * inherited classes so they can do whatever
+		 * cleanup is necessary on the UI end.
+		 */
+	}
+
 }; /* Namespace: libsaria */