timerwheel 0.1.0

// Copyright © 2026-present The Timerwheel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::cmp::Reverse;
use std::collections::BinaryHeap;

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub(crate) struct BucketOffer {
    pub(crate) expiration_ms: u64,
    pub(crate) bucket_index: usize,
}

#[derive(Debug, Default)]
pub(crate) struct DelayQueue {
    offers: BinaryHeap<Reverse<BucketOffer>>,
}

impl DelayQueue {
    pub(crate) fn offer(&mut self, offer: BucketOffer) {
        self.offers.push(Reverse(offer));
    }

    pub(crate) fn peek(&self) -> Option<BucketOffer> {
        self.offers.peek().map(|Reverse(offer)| *offer)
    }

    pub(crate) fn poll(&mut self) -> Option<BucketOffer> {
        self.offers.pop().map(|Reverse(offer)| offer)
    }
}

#[cfg(test)]
mod tests {
    use super::{BucketOffer, DelayQueue};

    #[test]
    fn delay_queue_orders_by_expiration() {
        let mut queue = DelayQueue::default();

        queue.offer(BucketOffer {
            expiration_ms: 20,
            bucket_index: 2,
        });
        queue.offer(BucketOffer {
            expiration_ms: 10,
            bucket_index: 1,
        });

        assert_eq!(queue.poll().expect("first").expiration_ms, 10);
        assert_eq!(queue.poll().expect("second").expiration_ms, 20);
    }
}