use std::{
	time::{
		Duration,
		Instant,
		SystemTime,
	}
};

pub fn get_next_tick (interval_secs: u64, offset_secs: u64) -> Instant {
	let now_sys = SystemTime::now ();
	let now_mono = Instant::now ();
	
	let phase = get_phase (now_sys, interval_secs, offset_secs);
	now_mono.checked_add (Duration::from_millis (interval_secs * 1000 - u64::try_from (phase).unwrap ())).unwrap ()
}

fn get_phase (now: SystemTime, interval_secs: u64, offset_secs: u64) -> u64 {
	let ms_since_epoch = now.duration_since (SystemTime::UNIX_EPOCH).unwrap ().as_millis ();
	u64::try_from ((ms_since_epoch + u128::from (offset_secs) * 1000) % (u128::from (interval_secs) * 1000)).unwrap ()
}

#[cfg (test)]
mod test {
	use super::*;
	
	#[test]
	fn test () {
		let now = SystemTime::UNIX_EPOCH.checked_add (Duration::from_secs (1649201544)).unwrap ();
		
		assert_eq! (get_phase (now, 2225, 0), 394000);
		assert_eq! (get_phase (now, 2225, 30), 424000);
	}
}