private void Log(string s) {
if (_logFilename == null) return;
if (s == null) {
Directory.CreateDirectory(Path.GetDirectoryName(_logFilename) ?? "");
File.WriteAllBytes(_logFilename, new byte[0]);
} else {
using (var writer = new StreamWriter(_logFilename, true)) {
writer.WriteLine($"{Time()}: {s}");
}
}
}