db/simple: purge songs for unavailable decoder plugins on update

NEWS

 ver 0.22.2 (not yet released)
 * database
-  - simple: purge virtual directories for unavailable plugins on update
+  - simple: purge songs and virtual directories for unavailable plugins
+    on update
 
 ver 0.22.1 (2020/10/17)
 * decoder

src/SongUpdate.cxx

@@ -23,6 +23,7 @@
 #include "db/plugins/simple/Directory.hxx"
 #include "storage/StorageInterface.hxx"
 #include "storage/FileInfo.hxx"
+#include "decoder/DecoderList.hxx"
 #include "fs/AllocatedPath.hxx"
 #include "fs/FileInfo.hxx"
 #include "tag/Builder.hxx"
@@ -40,6 +41,14 @@
 
 #ifdef ENABLE_DATABASE
 
+bool
+Song::IsPluginAvailable() const noexcept
+{
+	const char *suffix = GetFilenameSuffix();
+	return suffix != nullptr &&
+		decoder_plugins_supports_suffix(suffix);
+}
+
 SongPtr
 Song::LoadFile(Storage &storage, const char *path_utf8, Directory &parent)
 {

src/db/plugins/simple/Song.cxx

@@ -34,6 +34,14 @@ Song::Song(DetachedSong &&other, Directory &_parent) noexcept
 {
 }
 
+const char *
+Song::GetFilenameSuffix() const noexcept
+{
+	return target.empty()
+		? PathTraitsUTF8::GetFilenameSuffix(filename.c_str())
+		: PathTraitsUTF8::GetPathSuffix(target.c_str());
+}
+
 std::string
 Song::GetURI() const noexcept
 {

src/db/plugins/simple/Song.hxx

@@ -108,6 +108,16 @@ struct Song {
 
 	Song(DetachedSong &&other, Directory &_parent) noexcept;
 
+	gcc_pure
+	const char *GetFilenameSuffix() const noexcept;
+
+	/**
+	 * Checks whether the decoder plugin for this song is
+	 * available.
+	 */
+	gcc_pure
+	bool IsPluginAvailable() const noexcept;
+
 	/**
 	 * allocate a new song structure with a local file name and attempt to
 	 * load its metadata.  If all decoder plugin fail to read its meta

src/db/update/Walk.cxx

@@ -111,7 +111,11 @@ UpdateWalk::PurgeDeletedFromDirectory(Directory &directory) noexcept
 
 	directory.ForEachSongSafe([&](Song &song){
 		if (!directory_child_is_regular(storage, directory,
-						song.filename)) {
+						song.filename) ||
+		    !song.IsPluginAvailable()) {
+			/* the song file was deleted (or the decoder
+			   plugin is unavailable) */
+
 			editor.LockDeleteSong(directory, &song);
 
 			modified = true;