Rounding a Duration to the nearest second based on desired precision - dart

Question

I recently started working with Dart, and was trying to format a countdown clock with numbers in a per-second precision.
When counting down time, there's often a precise-yet-imperfect way of representing the time - so if I started a Duration at 2 minutes, and asked to show the current time after one second has elapsed, it is almost guaranteed that the precision of the timer will report at 1:58:999999 (example), and if use Duration.inSeconds() to emit the value, it will be 118 (seconds) which is due to how the ~/ operator works, since it's rounding down to integers based on the Duration's microseconds.
If I render the value as a clock, I'll see the clock go from "2:00" to "1:58" after one second, and will end up displaying "0:00" twice, until the countdown is truly at 0:00:00.
As a human, this appears like the clock is skipping, so I figured since the delta is so small, I should round up to the nearest second, and that would be accurate enough for a countdown timer, and handle the slight imprecision measured in micro/milli-seconds to better serve the viewer.
I came up with this secondRounder approach:
Duration secondRounder(Duration duration) {
int roundedDuration;
if (duration.inMilliseconds > (duration.inSeconds * 1000)) {
roundedDuration = duration.inSeconds + 1;
} else {
roundedDuration = duration.inSeconds;
}
return new Duration(seconds: roundedDuration);
}
This can also be run in this DartPad: https://dartpad.dartlang.org/2a08161c5f889e018938316237c0e810
As I'm yet unfamiliar with all of the methods, I've read through a lot of the docs, and this is the best I've come up with so far. I think I was looking for a method that might looks like:
roundedDuration = duration.ceil(nearest: millisecond)
Is there a better way to go about solving this that I haven't figured out yet?

Answer 1

You can "add" your own method to Duration as an extension method:
extension RoundDurationExtension on Duration {
/// Rounds the time of this duration up to the nearest multiple of [to].
Duration ceil(Duration to) {
int us = this.inMicroseconds;
int toUs = to.inMicroseconds.abs(); // Ignore if [to] is negative.
int mod = us % toUs;
if (mod != 0) {
return Duration(microseconds: us - mod + toUs);
}
return this;
}
}
That should allow you to write myDuration = myDuration.ceil(Duration(seconds: 1)); and round the myDuration up to the nearest second.

Answer 2

The best solution according to the documentation is to use .toStringAsFixed() function
https://api.dart.dev/stable/2.4.0/dart-core/num/toStringAsFixed.html
Examples from the Documentation
1.toStringAsFixed(3); // 1.000
(4321.12345678).toStringAsFixed(3); // 4321.123
(4321.12345678).toStringAsFixed(5); // 4321.12346
123456789012345678901.toStringAsFixed(3); // 123456789012345683968.000
1000000000000000000000.toStringAsFixed(3); // 1e+21
5.25.toStringAsFixed(0); // 5

Answer 3

Another more flexible option can be...
You can use this function to roundup the time.
DateTime alignDateTime(DateTime dt, Duration alignment,
[bool roundUp = false]) {
assert(alignment >= Duration.zero);
if (alignment == Duration.zero) return dt;
final correction = Duration(
days: 0,
hours: alignment.inDays > 0
? dt.hour
: alignment.inHours > 0
? dt.hour % alignment.inHours
: 0,
minutes: alignment.inHours > 0
? dt.minute
: alignment.inMinutes > 0
? dt.minute % alignment.inMinutes
: 0,
seconds: alignment.inMinutes > 0
? dt.second
: alignment.inSeconds > 0
? dt.second % alignment.inSeconds
: 0,
milliseconds: alignment.inSeconds > 0
? dt.millisecond
: alignment.inMilliseconds > 0
? dt.millisecond % alignment.inMilliseconds
: 0,
microseconds: alignment.inMilliseconds > 0 ? dt.microsecond : 0);
if (correction == Duration.zero) return dt;
final corrected = dt.subtract(correction);
final result = roundUp ? corrected.add(alignment) : corrected;
return result;
}
and then use it the following way
void main() {
DateTime dt = DateTime.now();
var newDate = alignDateTime(dt,Duration(minutes:30));
print(dt); // prints 2022-01-07 15:35:56.288
print(newDate); // prints 2022-01-07 15:30:00.000
}