Function to generate an async stream that yields an event every second

create_countdown_timer.rs

fn create_countdown_stream(duration: Duration) -> impl Stream<Item = Event, Error = io::Error> {
    let start = Instant::now();
    Interval::new(start, Duration::from_secs(1))
        .map(move |now| {
            Event::Countdown(
                // Include the remaining seconds in the event, but value should never below zero
                duration
                    .checked_sub(now.duration_since(start))
                    .map_or(0, |rem| rem.as_secs()),
            )
        })
        .map_err(|err| io::Error::new(io::ErrorKind::Other, err))
}