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

use crate::{
    clock::{self},
    state::keyed::KeyedStateStore,
    Jitter, RateLimiter,
};
use futures_timer::Delay;
use std::hash::Hash;

#[cfg(feature = "std")]
/// # Keyed rate limiters - `async`/`await`
impl<K, S, C> RateLimiter<K, S, C>
where
    K: Hash + Eq + Clone,
    S: KeyedStateStore<K>,
    C: clock::ReasonablyRealtime,
{
    /// Asynchronously resolves as soon as the rate limiter allows it.
    ///
    /// When polled, the returned future either resolves immediately (in the case where the rate
    /// limiter allows it), or else triggers an asynchronous delay, after which the rate limiter
    /// is polled again. This means that the future might resolve at some later time (depending
    /// on what other measurements are made on the rate limiter).
    ///
    /// If multiple futures are dispatched against the rate limiter, it is advisable to use
    /// [`until_ready_with_jitter`](#method.until_ready_with_jitter), to avoid thundering herds.
    pub async fn until_key_ready(&self, key: &K) {
        self.until_key_ready_with_jitter(key, Jitter::NONE).await;
    }

    /// Asynchronously resolves as soon as the rate limiter allows it, with a randomized wait
    /// period.
    ///
    /// When polled, the returned future either resolves immediately (in the case where the rate
    /// limiter allows it), or else triggers an asynchronous delay, after which the rate limiter
    /// is polled again. This means that the future might resolve at some later time (depending
    /// on what other measurements are made on the rate limiter).
    ///
    /// This method allows for a randomized additional delay between polls of the rate limiter,
    /// which can help reduce the likelihood of thundering herd effects if multiple tasks try to
    /// wait on the same rate limiter.
    pub async fn until_key_ready_with_jitter(&self, key: &K, jitter: Jitter) {
        while let Err(negative) = self.check_key(key) {
            let delay = Delay::new(jitter + negative.wait_time_from(self.clock.now()));
            delay.await;
        }
    }
}