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use super::{Clock, Reference};

use std::prelude::v1::*;

use crate::nanos::Nanos;
use std::ops::Add;
use std::time::{Duration, Instant, SystemTime};

/// The monotonic clock implemented by [`Instant`].
#[derive(Clone, Debug, Default)]
pub struct MonotonicClock;

impl Add<Nanos> for Instant {
    type Output = Instant;

    fn add(self, other: Nanos) -> Instant {
        let other: Duration = other.into();
        self + other
    }
}

impl Reference for Instant {
    fn duration_since(&self, earlier: Self) -> Nanos {
        if earlier < *self {
            (*self - earlier).into()
        } else {
            Nanos::from(Duration::new(0, 0))
        }
    }

    fn saturating_sub(&self, duration: Nanos) -> Self {
        self.checked_sub(duration.into()).unwrap_or(*self)
    }
}

impl Clock for MonotonicClock {
    type Instant = Instant;

    fn now(&self) -> Self::Instant {
        Instant::now()
    }
}

/// The non-monotonic clock implemented by [`SystemTime`].
#[derive(Clone, Debug, Default)]
pub struct SystemClock;

impl Reference for SystemTime {
    /// Returns the difference in times between the two
    /// SystemTimes. Due to the fallible nature of SystemTimes,
    /// returns the zero duration if a negative duration would
    /// result (e.g. due to system clock adjustments).
    fn duration_since(&self, earlier: Self) -> Nanos {
        self.duration_since(earlier)
            .unwrap_or_else(|_| Duration::new(0, 0))
            .into()
    }

    fn saturating_sub(&self, duration: Nanos) -> Self {
        self.checked_sub(duration.into()).unwrap_or(*self)
    }
}

impl Add<Nanos> for SystemTime {
    type Output = SystemTime;

    fn add(self, other: Nanos) -> SystemTime {
        let other: Duration = other.into();
        self + other
    }
}

impl Clock for SystemClock {
    type Instant = SystemTime;

    fn now(&self) -> Self::Instant {
        SystemTime::now()
    }
}

/// Identifies clocks that run similarly to the monotonic realtime clock.
///
/// Clocks implementing this trait can be used with rate-limiters functions that operate
/// asynchronously.
pub trait ReasonablyRealtime: Clock {
    /// Returns a reference point at the start of an operation.
    fn reference_point(&self) -> Self::Instant {
        self.now()
    }
}

impl ReasonablyRealtime for MonotonicClock {}

impl ReasonablyRealtime for SystemClock {}