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//! Temporal quantification.

pub use core::time::Duration;

/// A measurement of a monotonically nondecreasing clock.
/// Opaque and useful only with [`Duration`].
#[derive(Clone, Copy)]
pub struct Instant(Duration);

impl Instant {
    /// Returns an instant corresponding to "now".
    pub fn now() -> Instant {
        Instant(axhal::time::current_time())
    }

    /// Converts an `Instant` to a `Duration` directly.
    pub(crate) fn as_duration(&self) -> Duration {
        self.0
    }

    /// Returns the amount of time elapsed from another instant to this one,
    /// or zero duration if that instant is later than this one.
    ///
    /// # Panics
    ///
    /// Previous rust versions panicked when `earlier` was later than `self`. Currently this
    /// method saturates. Future versions may reintroduce the panic in some circumstances.
    pub fn duration_since(&self, earlier: Instant) -> Duration {
        self.0 - earlier.0
    }

    /// Returns the amount of time elapsed since this instant was created.
    ///
    /// # Panics
    ///
    /// Previous rust versions panicked when the current time was earlier than self. Currently this
    /// method returns a Duration of zero in that case. Future versions may reintroduce the panic.
    pub fn elapsed(&self) -> Duration {
        Instant::now().0 - self.0
    }
}