Play position in stuff like podcasts can now be permanently persisted.

src/playlist_manager.cpp

@@ -104,10 +104,41 @@ Playlist* PlaylistManager::get_playlist_for_id(String id) {
 }
 
 Playlist* PlaylistManager::get_playlist_for_folder(String folder) {
+	Playlist* p;
 	if (!_playlists.count(folder)) {
-		_playlists[folder] = new Playlist(folder);
+		p = new Playlist(folder);
+		_playlists[folder] = p;
+		if (p->persistence == PERSIST_PERMANENTLY) {
+			// TODO Load persistence from file
+			String search = folder;
+			search += "=";
+			SPIMaster::select_sd();
+			if (SD.exists("/_positions.txt")) {
+				File f = SD.open("/_positions.txt", "r");
+				while (true) {
+					String s = f.readStringUntil('\n');
+					if (s.length()==0) break;
+					if (s.startsWith(search)) {
+						s = s.substring(search.length());
+						int idx = s.indexOf(',');
+						String title_index = s.substring(0, idx);
+						uint32_t position = s.substring(idx+1).toInt();
+						p->set_track_by_id(title_index);
+						p->set_position(position);
+						break;
+					}
+				}
+				f.close();
+			}
+			SPIMaster::select_sd(false);
+		}
+	} else {
+		p = _playlists[folder];
+		if (p->persistence == PERSIST_NONE) {
+			p->reset();
+		}
 	}
-	return _playlists[folder];
+	return p;
 }
 
 void PlaylistManager::dump_ids() {
@@ -164,3 +195,40 @@ String PlaylistManager::create_mapping_txt() {
 	}
 	return s;
 }
+
+void PlaylistManager::persist(Playlist* p) {
+	if (p->persistence != PERSIST_PERMANENTLY) return;
+	
+	String search = p->path();
+	search += '=';
+	
+	bool old_file_existed = false;
+	
+	SPIMaster::select_sd();
+	if (SD.exists("_positions.txt")) {
+		SD.rename("/_positions.txt", "/_positions.temp.txt");
+		old_file_existed = true;
+	}
+	File dst = SD.open("/_positions.txt", "w");
+	
+	if (old_file_existed) {
+		File src = SD.open("/_positions.temp.txt", "r");
+	
+		while (true) {
+			String line = src.readStringUntil('\n');
+			line.trim();
+			if (line.startsWith(search)) continue;
+			dst.println(line);
+		}
+		
+		src.close();
+		SD.remove("/_positions.temp.txt");
+	}
+	
+	dst.print(search);
+	dst.print(p->get_current_track_id());
+	dst.print(',');
+	dst.println(p->get_position());
+	dst.close();
+	SPIMaster::select_sd(false);
+}