#![forbid(unsafe_code)]

use std::sync::OnceLock;
use std::time::{Duration, Instant};

static CAPTURE_ORIGIN: OnceLock<Instant> = OnceLock::new();

fn origin() -> Instant {
    *CAPTURE_ORIGIN.get_or_init(Instant::now)
}

/// Return the shared live-capture timestamp for upstream camera/mic packets.
///
/// Inputs: none.
/// Outputs: microseconds elapsed since the relay child first stamped live media.
/// Why: camera and microphone capture pipelines run independently, so they need
/// one explicit common origin before the server can keep them on the same live
/// call timeline.
#[must_use]
pub fn capture_pts_us() -> u64 {
    origin().elapsed().as_micros().min(u64::MAX as u128) as u64
}

/// Measure how old one shared capture timestamp is right now.
///
/// Inputs: a packet timestamp previously produced by `capture_pts_us`.
/// Outputs: the elapsed age as a `Duration`.
/// Why: upstream freshness telemetry should use the same shared live clock as
/// packet timestamps so queue-age calculations stay honest.
#[must_use]
pub fn packet_age(pts_us: u64) -> Duration {
    Duration::from_micros(capture_pts_us().saturating_sub(pts_us))
}

#[cfg(test)]
mod tests {
    use super::{capture_pts_us, packet_age};
    use std::time::Duration;

    #[test]
    fn capture_pts_us_monotonically_advances() {
        let first = capture_pts_us();
        std::thread::sleep(Duration::from_millis(2));
        let second = capture_pts_us();
        assert!(second >= first);
    }

    #[test]
    fn packet_age_is_small_for_recent_packets() {
        let pts = capture_pts_us();
        std::thread::sleep(Duration::from_millis(2));
        let age = packet_age(pts);
        assert!(age >= Duration::from_millis(1));
        assert!(age < Duration::from_secs(1));
    }
}