tsk-bin 0.11.0

tsk — work with a clear context
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use std::time::{SystemTime, UNIX_EPOCH};

pub fn utc_now() -> String {
    let secs = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0);
    format_utc(secs)
}

pub fn format_utc(secs: u64) -> String {
    let days = (secs / 86_400) as i64;
    let rem = secs % 86_400;
    let (year, month, day) = civil_from_days(days);
    format!(
        "{:04}-{:02}-{:02}T{:02}:{:02}:{:02}Z",
        year,
        month,
        day,
        rem / 3600,
        (rem % 3600) / 60,
        rem % 60
    )
}

fn civil_from_days(days: i64) -> (i64, u64, u64) {
    let z = days + 719_468;
    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
    let doe = (z - era * 146_097) as u64;
    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
    let mp = (5 * doy + 2) / 153;
    let day = doy - (153 * mp + 2) / 5 + 1;
    let month = if mp < 10 { mp + 3 } else { mp - 9 };
    let year = yoe as i64 + era * 400 + if month <= 2 { 1 } else { 0 };
    (year, month, day)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn formats_the_epoch() {
        assert_eq!(format_utc(0), "1970-01-01T00:00:00Z");
    }

    #[test]
    fn formats_a_leap_day() {
        assert_eq!(format_utc(951_782_400), "2000-02-29T00:00:00Z");
    }

    #[test]
    fn formats_seconds_minutes_and_hours() {
        assert_eq!(format_utc(1_790_000_000), "2026-09-21T14:13:20Z");
        assert_eq!(format_utc(4_102_444_799), "2099-12-31T23:59:59Z");
    }

    #[test]
    fn utc_now_has_the_second_precision_shape() {
        let now = utc_now();
        assert_eq!(now.len(), 20);
        assert!(now.ends_with('Z'));
        assert_eq!(&now[10..11], "T");
    }
}