db/update: scan CUE playlist contents

This commit adds a PlaylistPlugin attribute "as_folder" which for now
is only enabled in the "CUE" playlist plugin (which handles separate
"*.cue" files).  If a playlist with this flag set is being scanned
during database update, it will be parsed and its contents will be
added to the database.  This allows clients to inspect them like
directories and its contents will be searchable.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/39

NEWS

@@ -12,6 +12,8 @@ ver 0.22 (not yet released)
   - ffmpeg: allow partial reads
 * archive
   - iso9660: support seeking
+* playlist
+  - cue: integrate contents in database
 * decoder
   - mad: remove option "gapless", always do gapless
   - sidplay: add option "default_genre"

src/db/plugins/simple/Directory.hxx

@@ -44,6 +44,12 @@ static constexpr unsigned DEVICE_INARCHIVE = -1;
  */
 static constexpr unsigned DEVICE_CONTAINER = -2;
 
+/**
+ * Virtual directory that is really a playlist file (special value for
+ * Directory::device).
+ */
+static constexpr unsigned DEVICE_PLAYLIST = -3;
+
 class SongFilter;
 
 struct Directory {
@@ -117,6 +123,7 @@ public:
 	 */
 	bool IsReallyAFile() const noexcept {
 		return device == DEVICE_INARCHIVE ||
+			device == DEVICE_PLAYLIST ||
 			device == DEVICE_CONTAINER;
 	}
 

src/db/plugins/simple/DirectorySave.cxx

@@ -50,6 +50,9 @@ DeviceToTypeString(unsigned device) noexcept
 	case DEVICE_CONTAINER:
 		return "container";
 
+	case DEVICE_PLAYLIST:
+		return "playlist";
+
 	default:
 		return nullptr;
 	}
@@ -63,6 +66,8 @@ ParseTypeString(const char *type) noexcept
 		return DEVICE_INARCHIVE;
 	else if (StringIsEqual(type, "container"))
 		return DEVICE_CONTAINER;
+	else if (StringIsEqual(type, "playlist"))
+		return DEVICE_PLAYLIST;
 	else
 		return 0;
 }

src/db/update/Playlist.cxx

@@ -18,24 +18,91 @@
  */
 
 #include "Walk.hxx"
+#include "UpdateDomain.hxx"
 #include "db/DatabaseLock.hxx"
 #include "db/PlaylistVector.hxx"
 #include "db/plugins/simple/Directory.hxx"
+#include "song/DetachedSong.hxx"
+#include "input/InputStream.hxx"
+#include "playlist/PlaylistPlugin.hxx"
 #include "playlist/PlaylistRegistry.hxx"
+#include "playlist/PlaylistStream.hxx"
+#include "playlist/SongEnumerator.hxx"
 #include "storage/FileInfo.hxx"
+#include "storage/StorageInterface.hxx"
+#include "util/StringFormat.hxx"
+#include "Log.hxx"
+
+void
+UpdateWalk::UpdatePlaylistFile(Directory &parent, const char *name,
+			       const StorageFileInfo &info,
+			       const PlaylistPlugin &plugin) noexcept
+{
+	assert(plugin.open_stream);
+
+	Directory *directory =
+		LockMakeVirtualDirectoryIfModified(parent, name, info,
+						   DEVICE_PLAYLIST);
+	if (directory == nullptr)
+		/* not modified */
+		return;
+
+	const auto uri_utf8 = storage.MapUTF8(directory->GetPath());
+
+	FormatDebug(update_domain, "scanning playlist '%s'", uri_utf8.c_str());
+
+	try {
+		Mutex mutex;
+		auto e = plugin.open_stream(InputStream::OpenReady(uri_utf8.c_str(),
+								   mutex));
+		if (!e) {
+			/* unsupported URI? roll back.. */
+			editor.LockDeleteDirectory(directory);
+			return;
+		}
+
+		unsigned track = 0;
+
+		while (true) {
+			auto song = e->NextSong();
+			if (!song)
+				break;
+
+			auto db_song = std::make_unique<Song>(std::move(*song),
+							      *directory);
+			db_song->target = "../" + db_song->filename;
+			db_song->filename = StringFormat<64>("track%04u",
+							     ++track);
+
+			{
+				const ScopeDatabaseLock protect;
+				directory->AddSong(std::move(db_song));
+			}
+		}
+	} catch (...) {
+		FormatError(std::current_exception(),
+			    "Failed to scan playlist '%s'", uri_utf8.c_str());
+		editor.LockDeleteDirectory(directory);
+	}
+}
 
 bool
 UpdateWalk::UpdatePlaylistFile(Directory &directory,
 			       const char *name, const char *suffix,
 			       const StorageFileInfo &info) noexcept
 {
-	if (!playlist_suffix_supported(suffix))
+	const auto *const plugin = FindPlaylistPluginBySuffix(suffix);
+	if (plugin == nullptr)
 		return false;
 
+	if (plugin->as_folder)
+		UpdatePlaylistFile(directory, name, info, *plugin);
+
 	PlaylistInfo pi(name, info.mtime);
 
 	const ScopeDatabaseLock protect;
 	if (directory.playlists.UpdateOrInsert(std::move(pi)))
 		modified = true;
+
 	return true;
 }

src/db/update/Walk.hxx

@@ -30,6 +30,7 @@
 struct StorageFileInfo;
 struct Directory;
 struct ArchivePlugin;
+struct PlaylistPlugin;
 class ArchiveFile;
 class Storage;
 class ExcludeList;
@@ -118,6 +119,10 @@ private:
 	}
 #endif
 
+	void UpdatePlaylistFile(Directory &parent, const char *name,
+				const StorageFileInfo &info,
+				const PlaylistPlugin &plugin) noexcept;
+
 	bool UpdatePlaylistFile(Directory &directory,
 				const char *name, const char *suffix,
 				const StorageFileInfo &info) noexcept;

src/playlist/PlaylistPlugin.hxx

@@ -69,6 +69,12 @@ struct PlaylistPlugin {
 	const char *const*suffixes = nullptr;
 	const char *const*mime_types = nullptr;
 
+	/**
+	 * If true, then playlists of this type are shown in the
+	 * database as folders.
+	 */
+	bool as_folder = false;
+
 	constexpr PlaylistPlugin(const char *_name,
 				 std::unique_ptr<SongEnumerator> (*_open_uri)(const char *uri,
 									      Mutex &mutex)) noexcept
@@ -104,6 +110,12 @@ struct PlaylistPlugin {
 		return copy;
 	}
 
+	constexpr auto WithAsFolder(bool value=true) noexcept {
+		auto copy = *this;
+		copy.as_folder = value;
+		return copy;
+	}
+
 	/**
 	 * Does the plugin announce the specified URI scheme?
 	 */

src/playlist/plugins/CuePlaylistPlugin.cxx

@@ -72,5 +72,6 @@ static const char *const cue_playlist_mime_types[] = {
 
 const PlaylistPlugin cue_playlist_plugin =
 	PlaylistPlugin("cue", cue_playlist_open_stream)
+	.WithAsFolder()
 	.WithSuffixes(cue_playlist_suffixes)
 	.WithMimeTypes(cue_playlist_mime_types);