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String _printDuration(Duration duration) {
String twoDigits(int n) => n.toString().padLeft(2, "0");
String twoDigitMinutes = twoDigits(duration.inMinutes.remainder(60));
String twoDigitSeconds = twoDigits(duration.inSeconds.remainder(60));
return "${twoDigits(duration.inHours)}:$twoDigitMinutes:$twoDigitSeconds";
}