command/playlist: move code to SearchInsertIntoPlaylist()

src/command/PlaylistCommands.cxx

@@ -231,15 +231,12 @@ handle_playlistadd_position(Client &client, const char *playlist_name,
 		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){
+		SearchInsertIntoPlaylist(client.GetDatabaseOrThrow(),
-			editor.Insert(position,
+					 client.GetStorage(),
-				      DatabaseDetachSong(storage, song));
+					 selection,
-			++position;
+					 editor, position);
-		});
 #else
 		(void)client;
 		r.Error(ACK_ERROR_NO_EXIST, "No database");

src/db/DatabasePlaylist.cxx

@@ -41,3 +41,18 @@ search_add_to_playlist(const Database &db, const Storage *storage,
 	const auto f = [=](auto && arg1) { return AddSong(storage, playlist_path_utf8, arg1); };
 	db.Visit(selection, f);
 }
+
+void
+SearchInsertIntoPlaylist(const Database &db, const Storage *storage,
+			 const DatabaseSelection &selection,
+			 PlaylistFileEditor &playlist,
+			 unsigned position)
+{
+	assert(position <= playlist.size());
+
+	db.Visit(selection, [&playlist, &position, storage](const auto &song){
+		playlist.Insert(position,
+				DatabaseDetachSong(storage, song));
+		++position;
+	});
+}

src/db/DatabasePlaylist.hxx

@@ -25,6 +25,7 @@
 class Database;
 class Storage;
 struct DatabaseSelection;
+class PlaylistFileEditor;
 
 gcc_nonnull(3)
 void
@@ -32,4 +33,10 @@ search_add_to_playlist(const Database &db, const Storage *storage,
 		       const char *playlist_path_utf8,
 		       const DatabaseSelection &selection);
 
+void
+SearchInsertIntoPlaylist(const Database &db, const Storage *storage,
+			 const DatabaseSelection &selection,
+			 PlaylistFileEditor &playlist,
+			 unsigned position);
+
 #endif