use core::{
  task::{Context, Poll},
  time::Duration,
};
use std::time::Instant;

use ::async_io::Timer;
use futures_util::FutureExt;

use crate::time::{AsyncLocalInterval, AsyncLocalIntervalExt};

/// The [`AsyncInterval`] implementation for any runtime based on [`async-io`](async_io), e.g. `async-std` and `smol`.
pub type AsyncIoInterval = Timer;

impl AsyncLocalInterval for Timer {
  fn reset(&mut self, interval: Duration) {
    self.set_after(interval)
  }

  fn reset_at(&mut self, deadline: Instant) {
    self.set_at(deadline);
  }

  fn poll_tick(&mut self, cx: &mut Context<'_>) -> Poll<Instant> {
    self.poll_unpin(cx)
  }
}

impl AsyncLocalIntervalExt for Timer {
  fn interval_local(period: Duration) -> Self
  where
    Self: Sized,
  {
    Timer::interval(period)
  }

  fn interval_local_at(start: Instant, period: Duration) -> Self
  where
    Self: Sized,
  {
    Timer::interval_at(start, period)
  }
}

#[cfg(test)]
mod tests {
  use futures::StreamExt;

  use super::AsyncIoInterval;
  use crate::time::{AsyncInterval, AsyncIntervalExt};
  use std::time::{Duration, Instant};

  const INTERVAL: Duration = Duration::from_millis(100);
  const BOUND: Duration = Duration::from_millis(50);
  const IMMEDIATE: Duration = Duration::from_millis(1);

  #[test]
  fn test_object_safe() {
    let _x: Box<dyn AsyncInterval> = Box::new(AsyncIoInterval::interval(Duration::from_secs(1)));
  }

  #[test]
  fn test_interval() {
    futures::executor::block_on(async {
      let start = Instant::now();
      let interval = <AsyncIoInterval as AsyncIntervalExt>::interval(INTERVAL);
      let mut interval = interval.take(3);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL - BOUND);
      assert!(elapsed >= INTERVAL - BOUND && elapsed <= INTERVAL + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL * 2 - BOUND);
      assert!(elapsed >= INTERVAL * 2 - BOUND && elapsed <= INTERVAL * 2 + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL * 3 - BOUND);
      assert!(elapsed >= INTERVAL * 3 - BOUND && elapsed <= INTERVAL * 3 + BOUND);

      assert!(interval.next().await.is_none());
    });
  }

  #[test]
  fn test_interval_at() {
    futures::executor::block_on(async {
      let start = Instant::now();
      let interval = <AsyncIoInterval as AsyncIntervalExt>::interval_at(Instant::now(), INTERVAL);
      let mut interval = interval.take(4);
      // The first tick is immediate
      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins <= start + IMMEDIATE);
      assert!(elapsed <= IMMEDIATE + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL - BOUND);
      assert!(elapsed >= INTERVAL - BOUND && elapsed <= INTERVAL + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL * 2 - BOUND);
      assert!(elapsed >= INTERVAL * 2 - BOUND && elapsed <= INTERVAL * 2 + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL * 3 - BOUND);
      assert!(elapsed >= INTERVAL * 3 - BOUND && elapsed <= INTERVAL * 3 + BOUND);

      assert!(interval.next().await.is_none());
    });
  }

  #[test]
  fn test_interval_reset() {
    futures::executor::block_on(async {
      let start = Instant::now();
      let mut interval = <AsyncIoInterval as AsyncIntervalExt>::interval(INTERVAL);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL - BOUND);
      assert!(elapsed >= INTERVAL - BOUND && elapsed <= INTERVAL + BOUND);

      // Reset the next tick to 2x
      interval.reset(INTERVAL * 2);
      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      // interval + 2x interval, so 3 here
      assert!(ins >= start + INTERVAL * 3 - BOUND);
      assert!(elapsed >= INTERVAL * 3 - BOUND && elapsed <= INTERVAL * 3 + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      // interval + 2x interval + interval, so 4 here
      assert!(ins >= start + INTERVAL * 4 - BOUND);
      assert!(elapsed >= INTERVAL * 4 - BOUND && elapsed <= INTERVAL * 4 + BOUND);
    });
  }

  #[test]
  fn test_interval_reset_at() {
    futures::executor::block_on(async {
      let start = Instant::now();
      let mut interval = <AsyncIoInterval as AsyncIntervalExt>::interval(INTERVAL);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      assert!(ins >= start + INTERVAL);
      assert!(elapsed >= INTERVAL && elapsed <= INTERVAL + BOUND);

      // Reset the next tick to 2x
      interval.reset_at(start + INTERVAL * 3);
      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      // interval + 2x interval, so 3 here
      assert!(ins >= start + INTERVAL * 3);
      assert!(elapsed >= INTERVAL * 3 - BOUND && elapsed <= INTERVAL * 3 + BOUND);

      let ins = interval.next().await.unwrap();
      let elapsed = start.elapsed();
      // interval + 2x interval + interval, so 4 here
      assert!(ins >= start + INTERVAL * 4 - BOUND);
      assert!(elapsed >= INTERVAL * 4 - BOUND && elapsed <= INTERVAL * 4 + BOUND);
    });
  }
}