command/playlist: add position parameter to "playlistadd"

NEWS

 ver 0.23.3 (not yet released)
 * protocol
-  - add optional position parameter to "add"
+  - add optional position parameter to "add" and "playlistadd"
 * output
   - alsa: add option "stop_dsd_silence" to work around DSD DAC noise
 * macOS: fix libfmt related build failure

doc/protocol.rst

@@ -695,7 +695,7 @@ Whenever possible, ids should be used.
     can also be a single file.
 
     The position parameter is the same as in :ref:`addid
-    <command_addid>`.
+    <command_addid>`. [#since_0_23_3]_
 
     Clients that are connected via local socket may add arbitrary
     local files (URI is an absolute path).  Example::
@@ -933,12 +933,15 @@ remote playlists (absolute URI with a supported scheme).
 
 .. _command_playlistadd:
 
-:command:`playlistadd {NAME} {URI}`
+:command:`playlistadd {NAME} {URI} [POSITION]`
     Adds ``URI`` to the playlist
     `NAME.m3u`.
     `NAME.m3u` will be created if it does
     not exist.
 
+    The ``POSITION`` parameter specifies where the songs will be
+    inserted into the playlist. [#since_0_23_3]_
+
 .. _command_playlistclear:
 
 :command:`playlistclear {NAME}`
@@ -1649,3 +1652,4 @@ client-to-client messages are local to the current partition.
 .. [#since_0_22_4] Since :program:`MPD` 0.22.4
 .. [#since_0_23] Since :program:`MPD` 0.23
 .. [#since_0_23_1] Since :program:`MPD` 0.23.1
+.. [#since_0_23_3] Since :program:`MPD` 0.23.3

src/PlaylistFile.cxx

@@ -269,6 +269,29 @@ PlaylistFileEditor::PlaylistFileEditor(const char *name_utf8,
 }
 
 void
+PlaylistFileEditor::Insert(std::size_t i, const char *uri)
+{
+	if (i > size())
+		throw PlaylistError(PlaylistResult::BAD_RANGE, "Bad position");
+
+	if (size() >= playlist_max_length)
+		throw PlaylistError(PlaylistResult::TOO_LARGE,
+				    "Stored playlist is too large");
+
+	contents.emplace(std::next(contents.begin(), i), uri);
+}
+
+void
+PlaylistFileEditor::Insert(std::size_t i, const DetachedSong &song)
+{
+	const char *uri = playlist_saveAbsolutePaths
+		? song.GetRealURI()
+		: song.GetURI();
+
+	Insert(i, uri);
+}
+
+void
 PlaylistFileEditor::MoveIndex(unsigned src, unsigned dest)
 {
 	if (src >= contents.size() || dest >= contents.size())

src/PlaylistFile.hxx

@@ -51,6 +51,13 @@ public:
 	 */
 	explicit PlaylistFileEditor(const char *name_utf8, LoadMode load_mode);
 
+	auto size() const noexcept {
+		return contents.size();
+	}
+
+	void Insert(std::size_t i, const char *uri);
+	void Insert(std::size_t i, const DetachedSong &song);
+
 	void MoveIndex(unsigned src, unsigned dest);
 	void RemoveIndex(unsigned i);
 

src/command/AllCommands.cxx

@@ -157,7 +157,7 @@ static constexpr struct command commands[] = {
 	{ "play", PERMISSION_PLAYER, 0, 1, handle_play },
 	{ "playid", PERMISSION_PLAYER, 0, 1, handle_playid },
 	{ "playlist", PERMISSION_READ, 0, 0, handle_playlist },
-	{ "playlistadd", PERMISSION_CONTROL, 2, 2, handle_playlistadd },
+	{ "playlistadd", PERMISSION_CONTROL, 2, 3, handle_playlistadd },
 	{ "playlistclear", PERMISSION_CONTROL, 1, 1, handle_playlistclear },
 	{ "playlistdelete", PERMISSION_CONTROL, 2, 2, handle_playlistdelete },
 	{ "playlistfind", PERMISSION_READ, 1, -1, handle_playlistfind },

src/command/PlaylistCommands.cxx

@@ -22,8 +22,10 @@
 #include "PositionArg.hxx"
 #include "Request.hxx"
 #include "Instance.hxx"
+#include "db/Interface.hxx"
 #include "db/Selection.hxx"
 #include "db/DatabasePlaylist.hxx"
+#include "db/DatabaseSong.hxx"
 #include "PlaylistSave.hxx"
 #include "PlaylistFile.hxx"
 #include "PlaylistError.hxx"
@@ -201,12 +203,56 @@ handle_playlistclear([[maybe_unused]] Client &client,
 	return CommandResult::OK;
 }
 
+static CommandResult
+handle_playlistadd_position(Client &client, const char *playlist_name,
+			    const char *uri, unsigned position,
+			    Response &r)
+{
+	PlaylistFileEditor editor{
+		playlist_name,
+		PlaylistFileEditor::LoadMode::TRY,
+	};
+
+	if (position > editor.size()) {
+		r.Error(ACK_ERROR_ARG, "Bad position");
+		return CommandResult::ERROR;
+	}
+
+	if (uri_has_scheme(uri)) {
+		editor.Insert(position, uri);
+	} else {
+#ifdef ENABLE_DATABASE
+		const auto &db = client.GetDatabaseOrThrow();
+		const auto *storage = client.GetStorage();
+		const DatabaseSelection selection(uri, true, nullptr);
+
+		db.Visit(selection, [&editor, &position, storage](const auto &song){
+			editor.Insert(position,
+				      DatabaseDetachSong(storage, song));
+			++position;
+		});
+#else
+		(void)client;
+		r.Error(ACK_ERROR_NO_EXIST, "No database");
+		return CommandResult::ERROR;
+#endif
+	}
+
+	editor.Save();
+
+	return CommandResult::OK;
+}
+
 CommandResult
 handle_playlistadd(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	const char *const playlist = args[0];
 	const char *const uri = args[1];
 
+	if (args.size >= 3)
+		return handle_playlistadd_position(client, playlist, uri,
+						   args.ParseUnsigned(2), r);
+
 	if (uri_has_scheme(uri)) {
 		const SongLoader loader(client);
 		spl_append_uri(playlist, loader, uri);