helpers: restore old behavior when playing a song already in playlist

src/helpers.cpp

@@ -103,12 +103,20 @@ bool addSongToPlaylist(const MPD::Song &s, bool play, int position)
 {
 	bool result = false;
 	if (Config.space_add_mode == SpaceAddMode::AddRemove
-	&&  !play
 	&&  myPlaylist->checkForSong(s)
 	   )
 	{
 		result = true;
-		removeSongFromPlaylist(myPlaylist->main(), s);
+		if (play)
+		{
+			const auto begin = myPlaylist->main().beginV(), end = myPlaylist->main().endV();
+			auto it = find_map_first(begin, end, s, [](const MPD::Song &found) {
+				Mpd.PlayID(found.getID());
+			});
+			assert(it != end);
+		}
+		else
+			removeSongFromPlaylist(myPlaylist->main(), s);
 		return result;
 	}
 	int id = Mpd.AddSong(s, position);

src/utility/functional.h

@@ -61,6 +61,26 @@ struct pointer_extractor
 	ValueT *operator()(ValueT &v) const { return &v; }
 };
 
+/// Map over the first element in range satisfying the predicate.
+template <typename InputIterator, typename PredicateT, typename MapT>
+InputIterator find_map_first(InputIterator first, InputIterator last, PredicateT &&p, MapT &&f)
+{
+	auto it = std::find(first, last, std::forward<PredicateT>(p));
+	if (it != last)
+		f(*it);
+	return it;
+}
+
+/// Map over all elements in range satisfying the predicate.
+template <typename InputIterator, typename PredicateT, typename MapT>
+void find_map_all(InputIterator first, InputIterator last, PredicateT &&p, MapT &&f)
+{
+	InputIterator it = first;
+	do
+		it = find_map_first(it, last, p, f);
+	while (it != last);
+}
+
 // identity function object
 struct id_
 {