// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

use crate::time::timestamp::Timestamp;
use core::task::Poll;

/// A timer that does not trigger an update in a timer
/// list. These are usually owned by individual components
/// and needs to be explicitly polled.
///
/// Note: The timer doesn't implement Copy to ensure it isn't accidentally moved
///       and have the expiration discarded.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct Timer {
    expiration: Option<Timestamp>,
}

impl Timer {
    /// Sets the timer to expire at the given timestamp
    #[inline]
    pub fn set(&mut self, time: Timestamp) {
        self.expiration = Some(time);
    }

    /// Cancels the timer.
    /// After cancellation, a timer will no longer report as expired.
    #[inline]
    pub fn cancel(&mut self) {
        self.expiration = None;
    }

    /// Returns true if the timer has expired
    #[inline]
    pub fn is_expired(&self, current_time: Timestamp) -> bool {
        match self.expiration {
            Some(timeout) => timeout.has_elapsed(current_time),
            _ => false,
        }
    }

    /// Returns true if the timer is armed
    #[inline]
    pub fn is_armed(&self) -> bool {
        self.expiration.is_some()
    }

    /// Notifies the timer of the current time.
    /// If the timer's expiration occurs before the current time, it will be cancelled.
    /// The method returns whether the timer was expired and had been
    /// cancelled.
    #[inline]
    pub fn poll_expiration(&mut self, current_time: Timestamp) -> Poll<()> {
        if self.is_expired(current_time) {
            self.cancel();
            Poll::Ready(())
        } else {
            Poll::Pending
        }
    }
}

impl From<Option<Timestamp>> for Timer {
    #[inline]
    fn from(expiration: Option<Timestamp>) -> Self {
        Self { expiration }
    }
}

/// Returned when a `Query` wants to end a timer query
#[derive(Clone, Copy, Debug, Default)]
pub struct QueryBreak;

/// The return type of a `timers` call
pub type Result<T = (), E = QueryBreak> = core::result::Result<T, E>;

/// A trait for a components that owns at least one timer
pub trait Provider {
    /// Notifies the query of any timers owned by the provider
    ///
    /// The provider should also delegate to subcomponents that own timers as well.
    fn timers<Q: Query>(&self, query: &mut Q) -> Result;

    /// Returns the next `Timestamp` at which the earliest timer is armed in the provider
    #[inline]
    fn next_expiration(&self) -> Option<Timestamp> {
        let mut timeout: Option<Timestamp> = None;
        let _ = self.timers(&mut timeout);
        timeout
    }

    /// Returns `true` if there are any timers armed
    #[inline]
    fn is_armed(&self) -> bool {
        let mut is_armed = IsArmed::default();
        let _ = self.timers(&mut is_armed);
        is_armed.0
    }

    /// Counts the number of armed timers in the provider
    #[inline]
    fn armed_timer_count(&self) -> usize {
        let mut count = ArmedCount::default();
        let _ = self.timers(&mut count);
        count.0
    }

    /// Iterates over each timer in the provider and calls the provided function
    #[inline]
    fn for_each_timer<F: FnMut(&Timer) -> Result>(&self, f: F) {
        let mut for_each = ForEach(f);
        let _ = self.timers(&mut for_each);
    }
}

impl Provider for Timer {
    #[inline]
    fn timers<Q: Query>(&self, query: &mut Q) -> Result {
        query.on_timer(self)
    }
}

impl<T: Provider> Provider for &T {
    #[inline]
    fn timers<Q: Query>(&self, query: &mut Q) -> Result {
        (**self).timers(query)
    }
}

impl<T: Provider> Provider for &mut T {
    #[inline]
    fn timers<Q: Query>(&self, query: &mut Q) -> Result {
        (**self).timers(query)
    }
}

/// Implement Provider for a 2-element tuple to make it easy to do joins
impl<A: Provider, B: Provider> Provider for (A, B) {
    #[inline]
    fn timers<Q: Query>(&self, query: &mut Q) -> Result {
        self.0.timers(query)?;
        self.1.timers(query)?;
        Ok(())
    }
}

impl<T: Provider> Provider for Option<T> {
    #[inline]
    fn timers<Q: Query>(&self, query: &mut Q) -> Result {
        if let Some(t) = self.as_ref() {
            t.timers(query)?;
        }
        Ok(())
    }
}

/// A query to be executed against a provider
pub trait Query {
    /// Called for each timer owned by the provider
    fn on_timer(&mut self, timer: &Timer) -> Result;
}

/// Implement Query for `Option<Timestamp>` to make it easy to get the earliest armed timestamp
impl Query for Option<Timestamp> {
    #[inline]
    fn on_timer(&mut self, timer: &Timer) -> Result {
        match (self, timer.expiration) {
            // Take the minimum of the two timers
            (Some(a), Some(b)) => *a = (*a).min(b),
            // We don't have a time yet so just assign the expiration of the other
            (a @ None, b) => *a = b,
            // do nothing for everything else
            _ => {}
        }
        Ok(())
    }
}

/// Counts all of the armed timers
#[derive(Debug, Default)]
pub struct ArmedCount(pub usize);

impl Query for ArmedCount {
    #[inline]
    fn on_timer(&mut self, timer: &Timer) -> Result {
        if timer.is_armed() {
            self.0 += 1;
        }
        Ok(())
    }
}

/// Returns `true` if any of the timers are armed
#[derive(Debug, Default)]
pub struct IsArmed(pub bool);

impl Query for IsArmed {
    #[inline]
    fn on_timer(&mut self, timer: &Timer) -> Result {
        if timer.is_armed() {
            self.0 = true;
            return Err(QueryBreak);
        }
        Ok(())
    }
}

/// Iterates over each timer in the provider and calls a function
#[derive(Debug, Default)]
pub struct ForEach<F: FnMut(&Timer) -> Result>(F);

impl<F: FnMut(&Timer) -> Result> Query for ForEach<F> {
    #[inline]
    fn on_timer(&mut self, timer: &Timer) -> Result {
        (self.0)(timer)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::time::clock::{Clock, NoopClock};
    use core::time::Duration;

    #[test]
    fn is_armed_test() {
        let now = NoopClock.get_time();
        let mut timer = Timer::default();

        assert!(!timer.is_armed());

        timer.set(now);
        assert!(timer.is_armed());

        timer.cancel();
        assert!(!timer.is_armed());
    }

    #[test]
    fn is_expired_test() {
        let mut now = NoopClock.get_time();
        let mut timer = Timer::default();

        assert!(!timer.is_expired(now));

        timer.set(now + Duration::from_millis(100));

        now += Duration::from_millis(99);
        assert!(!timer.is_expired(now));

        assert!(
            timer.is_expired(now + Duration::from_micros(1)),
            "if a timer is less than 1ms in the future is should expire"
        );

        now += Duration::from_millis(1);
        assert!(timer.is_expired(now));

        timer.cancel();
        assert!(!timer.is_expired(now));
    }

    #[test]
    fn poll_expiration_test() {
        let mut now = NoopClock.get_time();
        let mut timer = Timer::default();

        timer.set(now + Duration::from_millis(100));

        assert!(!timer.poll_expiration(now).is_ready());
        assert!(timer.is_armed());

        now += Duration::from_millis(100);

        assert!(timer.poll_expiration(now).is_ready());
        assert!(!timer.is_armed());
    }
}