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// Copyright (c) The Diem Core Contributors
// SPDX-License-Identifier: Apache-2.0

use crate::{Sleep, SleepTrait, ZERO_DURATION};
use futures::{
    future::Future,
    ready,
    stream::{FusedStream, Stream},
};
use pin_project::pin_project;
use std::{
    pin::Pin,
    task::{Context, Poll},
    time::Duration,
};

/// Stream returned by [`TimeService::interval`](crate::TimeService::interval).
///
/// Mostly taken from [`tokio::time::Interval`] but uses our `Sleep` future.
#[pin_project]
#[must_use = "streams do nothing unless you `.await` or poll them"]
#[derive(Debug)]
pub struct Interval {
    #[pin]
    delay: Sleep,
    period: Duration,
}

impl Interval {
    pub fn new(delay: Sleep, period: Duration) -> Self {
        assert!(period > ZERO_DURATION, "`period` must be non-zero.");

        Self { delay, period }
    }
}

impl Stream for Interval {
    type Item = ();

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let mut this = self.project();

        // Wait for the delay to be done
        ready!(this.delay.as_mut().poll(cx));

        // Reset the delay before next round
        this.delay.reset(*this.period);

        Poll::Ready(Some(()))
    }
}

impl FusedStream for Interval {
    /// We implement [`FusedStream`] here to make it more convenient for API
    /// consumers when using an [`Interval`] inside a `futures::select!`.
    ///
    /// Note: an [`Interval`] stream never ends, so this function always returns
    /// `false`.
    fn is_terminated(&self) -> bool {
        false
    }
}