use std::cmp::PartialEq;
use std::time::{Duration, Instant};
#[derive(Debug)]
struct Event<T> {
    item: T,
    time: Instant,
}
pub enum State<T> {
    Ready(T),
    Wait(Duration),
    Empty,
}
pub struct Debouncer<T> {
    delay: Duration,
    events: Vec<Event<T>>,
}
impl<T: PartialEq + std::fmt::Debug> Debouncer<T> {
    pub fn new(delay: Duration) -> Debouncer<T> {
        Debouncer {
            delay,
            events: vec![],
        }
    }
    pub fn new_events<I: Iterator<Item = T>>(&mut self, mut items: I) {
        let time = Instant::now();
        let cutoff = time - self.delay;
        while let Some(item) = items.next() {
            self.events.retain(|e| e.time < cutoff || e.item != item);
            self.events.push(Event { item, time });
        }
    }
    pub fn get(&mut self) -> State<T> {
        let time = Instant::now();
        let cutoff = time - self.delay;
        match self.events.get(0) {
            None => State::Empty,
            Some(e) if e.time > cutoff => State::Wait(e.time - cutoff),
            Some(_) => State::Ready(self.events.remove(0).item),
        }
    }
}