DatabaseGlue: add function db_is_simple()

Preparing for non-"simple" database plugins.

src/DatabaseGlue.cxx

@@ -87,10 +87,19 @@ GetDatabase()
 	return db;
 }
 
+bool
+db_is_simple(void)
+{
+	assert(db == NULL || db_is_open);
+
+	return dynamic_cast<SimpleDatabase *>(db) != nullptr;
+}
+
 struct directory *
 db_get_root(void)
 {
 	assert(db != NULL);
+	assert(db_is_simple());
 
 	return ((SimpleDatabase *)db)->GetRoot();
 }
@@ -128,6 +137,7 @@ db_save(GError **error_r)
 {
 	assert(db != NULL);
 	assert(db_is_open);
+	assert(db_is_simple());
 
 	return ((SimpleDatabase *)db)->Save(error_r);
 }
@@ -153,6 +163,7 @@ db_get_mtime(void)
 {
 	assert(db != NULL);
 	assert(db_is_open);
+	assert(db_is_simple());
 
 	return ((SimpleDatabase *)db)->GetLastModified();
 }

src/Stats.cxx

@@ -119,14 +119,18 @@ int stats_print(struct client *client)
 		      "songs: %i\n"
 		      "uptime: %li\n"
 		      "playtime: %li\n"
-		      "db_playtime: %li\n"
+		      "db_playtime: %li\n",
-		      "db_update: %li\n",
 		      stats.artist_count,
 		      stats.album_count,
 		      stats.song_count,
 		      (long)g_timer_elapsed(stats.timer, NULL),
 		      (long)(pc_get_total_play_time(client->player_control) + 0.5),
-		      stats.song_duration,
+		      stats.song_duration);
+
+	if (db_is_simple())
+		client_printf(client,
+			      "db_update: %li\n",
 			      (long)db_get_mtime());
+
 	return 0;
 }

src/database.h

@@ -43,9 +43,19 @@ db_init(const struct config_param *path, GError **error_r);
 void
 db_finish(void);
 
+/**
+ * Check whether the default #SimpleDatabasePlugin is used.  This
+ * allows using db_get_root(), db_save(), db_get_mtime() and
+ * db_exists().
+ */
+bool
+db_is_simple(void);
+
 /**
  * Returns the root directory object.  Returns NULL if there is no
  * configured music directory.
+ *
+ * May only be used if db_is_simple() returns true.
  */
 gcc_pure
 struct directory *
@@ -64,18 +74,26 @@ gcc_pure
 struct song *
 db_get_song(const char *file);
 
+/**
+ * May only be used if db_is_simple() returns true.
+ */
 bool
 db_save(GError **error_r);
 
 bool
 db_load(GError **error);
 
+/**
+ * May only be used if db_is_simple() returns true.
+ */
 gcc_pure
 time_t
 db_get_mtime(void);
 
 /**
  * Returns true if there is a valid database file on the disk.
+ *
+ * May only be used if db_is_simple() returns true.
  */
 gcc_pure
 static inline bool

src/update.c

@@ -118,7 +118,7 @@ update_enqueue(const char *path, bool _discard)
 {
 	assert(g_thread_self() == main_task);
 
-	if (!mapper_has_music_directory())
+	if (!db_is_simple() || !mapper_has_music_directory())
 		return 0;
 
 	if (progress != UPDATE_PROGRESS_IDLE) {