sticker: don't use classes Directory and Song

Don't depend on the "simple" database plugin.  This fixes an assertion
failure / crash and allows using stickers with other plugins.

src/command/StickerCommands.cxx

@@ -124,24 +124,17 @@ handle_sticker_song(Client &client, int argc, char *argv[])
 	/* find song dir key */
 	} else if (argc == 5 && strcmp(argv[1], "find") == 0) {
 		/* "sticker find song a/directory name" */
+
+		const char *const base_uri = argv[3];
+
 		bool success;
 		struct sticker_song_find_data data = {
 			client,
 			argv[4],
 		};
 
-		db_lock();
-		Directory *directory = db_get_directory(argv[3]);
-		if (directory == nullptr) {
-			db_unlock();
-			command_error(client, ACK_ERROR_NO_EXIST,
-				      "no such directory");
-			return CommandResult::ERROR;
-		}
-
-		success = sticker_song_find(*directory, data.name,
+		success = sticker_song_find(base_uri, data.name,
 					    sticker_song_find_print_cb, &data);
-		db_unlock();
 		if (!success) {
 			command_error(client, ACK_ERROR_SYSTEM,
 				      "failed to set search sticker database");

src/sticker/SongSticker.cxx

@@ -21,8 +21,9 @@
 #include "SongSticker.hxx"
 #include "StickerDatabase.hxx"
 #include "db/LightSong.hxx"
-#include "db/Song.hxx"
-#include "db/Directory.hxx"
+#include "db/DatabaseGlue.hxx"
+#include "db/DatabasePlugin.hxx"
+#include "util/Error.hxx"
 
 #include <glib.h>
 
@@ -66,7 +67,7 @@ sticker_song_get(const LightSong &song)
 }
 
 struct sticker_song_find_data {
-	Directory *directory;
+	const Database *db;
 	const char *base_uri;
 	size_t base_uri_length;
 
@@ -85,24 +86,29 @@ sticker_song_find_cb(const char *uri, const char *value, void *user_data)
 		/* should not happen, ignore silently */
 		return;
 
-	Song *song = data->directory->LookupSong(uri + data->base_uri_length);
-	if (song != nullptr)
-		data->func(song->Export(), value, data->user_data);
+	const Database *db = data->db;
+	const LightSong *song = db->GetSong(uri, IgnoreError());
+	if (song != nullptr) {
+		data->func(*song, value, data->user_data);
+		db->ReturnSong(song);
+	}
 }
 
 bool
-sticker_song_find(Directory &directory, const char *name,
+sticker_song_find(const char *base_uri, const char *name,
 		  void (*func)(const LightSong &song, const char *value,
 			       void *user_data),
 		  void *user_data)
 {
 	struct sticker_song_find_data data;
-	data.directory = &directory;
+	data.db = GetDatabase();
+	assert(data.db != nullptr);
+
 	data.func = func;
 	data.user_data = user_data;
 
 	char *allocated;
-	data.base_uri = directory.GetPath();
+	data.base_uri = base_uri;
 	if (*data.base_uri != 0)
 		/* append slash to base_uri */
 		data.base_uri = allocated =

src/sticker/SongSticker.hxx

@@ -72,13 +72,13 @@ sticker_song_get(const LightSong &song);
  *
  * Caller must lock the #db_mutex.
  *
- * @param directory the base directory to search in
+ * @param base_uri the base directory to search in
  * @param name the name of the sticker
  * @return true on success (even if no sticker was found), false on
  * failure
  */
 bool
-sticker_song_find(Directory &directory, const char *name,
+sticker_song_find(const char *base_uri, const char *name,
 		  void (*func)(const LightSong &song, const char *value,
 			       void *user_data),
 		  void *user_data);