Split Duration code into separate file.

src/duration.rs

@@ -0,0 +1,198 @@
+//! Functions, constants, etc. related to Duration.
+
+use crate::Roundable;
+use core::time::Duration;
+
+/// A microsecond. Useful for rounding [`Duration`].
+///
+/// ```rust
+/// use roundable::{MICROSECOND, Roundable};
+/// use std::time::Duration;
+///
+/// assert!(MICROSECOND == Duration::from_nanos(500).round_to(MICROSECOND));
+/// ```
+pub const MICROSECOND: Duration = Duration::from_micros(1);
+
+/// A millisecond. Useful for rounding [`Duration`].
+///
+/// ```rust
+/// use roundable::{MILLISECOND, Roundable};
+/// use std::time::Duration;
+///
+/// assert!(MILLISECOND == Duration::from_micros(500).round_to(MILLISECOND));
+/// ```
+pub const MILLISECOND: Duration = Duration::from_millis(1);
+
+/// A second. Useful for rounding [`Duration`].
+///
+/// ```rust
+/// use roundable::{SECOND, Roundable};
+/// use std::time::Duration;
+///
+/// assert!(SECOND == Duration::from_millis(500).round_to(SECOND));
+/// ```
+pub const SECOND: Duration = Duration::from_secs(1);
+
+/// A minute. Useful for rounding [`Duration`].
+///
+/// ```rust
+/// use roundable::{MINUTE, Roundable};
+/// use std::time::Duration;
+///
+/// assert!(MINUTE == Duration::from_secs(30).round_to(MINUTE));
+/// ```
+pub const MINUTE: Duration = Duration::from_secs(60);
+
+/// An hour. Useful for rounding [`Duration`].
+///
+/// ```rust
+/// use roundable::{HOUR, Roundable};
+/// use std::time::Duration;
+///
+/// assert!(HOUR == Duration::from_secs(30*60).round_to(HOUR));
+/// ```
+pub const HOUR: Duration = Duration::from_secs(60 * 60);
+
+impl Roundable for Duration {
+    fn try_round_to(self, factor: Self) -> Option<Self> {
+        // Duration will always fit into u128 as nanoseconds.
+        self.as_nanos()
+            .try_round_to(factor.as_nanos())
+            .map(nanos_to_duration)
+    }
+}
+
+/// Create a new [`Duration`] from a `u128` of nanoseconds.
+///
+/// This is essentially just [`Duration::from_nanos()`] but it works on a
+/// `u128`, which can represent any valid `Duration`.
+///
+/// # Panics
+///
+/// `Duration` can only represent 64 bits worth of seconds and less than 32 bits
+/// (1e9) worth of nanoseconds, which works out to being roughly 94 bits. A
+/// `u128` can therefore represent values that are invalid `Duration`s. This
+/// will panic in those cases.
+///
+/// `nanos_to_duration(duration.as_nanos())` should never panic.
+///
+/// ```rust
+/// use roundable::nanos_to_duration;
+/// use std::time::Duration;
+///
+/// assert!(Duration::MAX == nanos_to_duration(Duration::MAX.as_nanos()));
+/// assert!(Duration::ZERO == nanos_to_duration(Duration::ZERO.as_nanos()));
+/// ```
+#[must_use]
+pub fn nanos_to_duration(total: u128) -> Duration {
+    /// Just to make things clear.
+    const NANOS_PER_SECOND: u128 = 1_000_000_000;
+    #[allow(clippy::integer_division)]
+    Duration::new(
+        (total / NANOS_PER_SECOND).try_into().expect(
+            "nanos_to_duration() overflowed seconds value for Duration",
+        ),
+        (total % NANOS_PER_SECOND).try_into().unwrap(),
+    )
+}
+
+#[cfg(test)]
+#[allow(clippy::cognitive_complexity)]
+mod tests {
+    use super::*;
+    use assert2::check;
+
+    /// Convenient alias for [`Duration::from_millis()`].
+    const fn ms(ms: u64) -> Duration {
+        Duration::from_millis(ms)
+    }
+
+    #[test]
+    fn round_millisecond_to_nearest_millisecond() {
+        check!(ms(10) == ms(10).round_to(MILLISECOND));
+
+        check!(ms(10) == ms(10).round_to(ms(2)));
+        check!(ms(10) == ms(9).round_to(ms(2)));
+
+        check!(ms(9) == ms(9).round_to(ms(3)));
+        check!(ms(9) == ms(10).round_to(ms(3)));
+        check!(ms(12) == ms(11).round_to(ms(3)));
+        check!(ms(12) == ms(12).round_to(ms(3)));
+    }
+
+    #[test]
+    fn round_second_to_nearest_millisecond() {
+        check!(ms(1_010) == ms(1_010).round_to(MILLISECOND));
+
+        check!(ms(1_010) == ms(1_010).round_to(ms(2)));
+        check!(ms(1_010) == ms(1_009).round_to(ms(2)));
+
+        check!(ms(1_008) == ms(1_008).round_to(ms(3)));
+        check!(ms(1_008) == ms(1_009).round_to(ms(3)));
+        check!(ms(1_011) == ms(1_010).round_to(ms(3)));
+        check!(ms(1_011) == ms(1_011).round_to(ms(3)));
+    }
+
+    #[test]
+    fn round_second_to_nearest_second() {
+        check!(ms(0) == ms(499).round_to(SECOND));
+        check!(SECOND == ms(500).round_to(SECOND));
+        check!(SECOND == ms(1_010).round_to(SECOND));
+        check!(SECOND == ms(1_499).round_to(SECOND));
+        check!(ms(2_000) == ms(1_500).round_to(SECOND));
+
+        check!(ms(1_001) == ms(1_000).round_to(ms(1_001)));
+        check!(ms(1_001) == ms(1_001).round_to(ms(1_001)));
+        check!(ms(1_001) == ms(1_002).round_to(ms(1_001)));
+    }
+
+    #[test]
+    fn round_to_giant_factor() {
+        check!(ms(0) == ms(1_000_000).round_to(Duration::MAX));
+        check!(Duration::MAX == Duration::MAX.round_to(Duration::MAX));
+    }
+
+    #[test]
+    #[should_panic(expected = "try_round_to() requires positive factor")]
+    fn round_to_zero_factor() {
+        let _ = ms(10).round_to(ms(0));
+    }
+
+    /// Theoretical maximum Duration as nanoseconds (based on u64 for seconds).
+    const NANOS_MAX: u128 = u64::MAX as u128 * 1_000_000_000 + 999_999_999;
+
+    #[test]
+    #[allow(clippy::arithmetic_side_effects)]
+    fn nanos_to_duration_ok() {
+        check!(Duration::ZERO == nanos_to_duration(0));
+        check!(Duration::new(1, 1) == nanos_to_duration(1_000_000_001));
+
+        // Check Duration::MAX two ways, since according it its docs it can vary
+        // based on platform.
+        check!(Duration::MAX == nanos_to_duration(Duration::MAX.as_nanos()));
+        check!(
+            Duration::new(u64::MAX, 999_999_999)
+                == nanos_to_duration(NANOS_MAX)
+        );
+    }
+
+    #[test]
+    #[should_panic(
+        expected = "nanos_to_duration() overflowed seconds value for Duration: TryFromIntError(())"
+    )]
+    fn nanos_to_duration_overflow() {
+        let _ = nanos_to_duration(Duration::MAX.as_nanos() + 1);
+    }
+
+    #[test]
+    #[should_panic(
+        expected = "nanos_to_duration() overflowed seconds value for Duration: TryFromIntError(())"
+    )]
+    #[allow(clippy::arithmetic_side_effects)]
+    fn nanos_to_duration_overflow_manual() {
+        // One over the maximum duration. Just in case `Duration::MAX` is some
+        // other value, since the docs say it can vary by platform even if it
+        // currently is always `u64::MAX * 1_000_000_000 + 999_999_999`.
+        let _ = nanos_to_duration(NANOS_MAX + 1);
+    }
+}