//! Minimal UTC timestamp/duration formatting, without a `chrono`/`time`
//! dependency. Timestamps are stored as Unix seconds (`i64`) everywhere in
//! profile/instance state; this module only turns them into text for
//! `status`/`list` output.

use std::time::{SystemTime, UNIX_EPOCH};

pub fn now() -> i64 {
    SystemTime::now().duration_since(UNIX_EPOCH).map(|d| d.as_secs() as i64).unwrap_or(0)
}

/// `YYYY-MM-DD HH:MM:SS UTC`, via Howard Hinnant's civil-from-days algorithm
/// (public domain, http://howardhinnant.github.io/date_algorithms.html) -
/// avoids pulling in a whole calendar/timezone crate for what's otherwise a
/// handful of integer operations.
pub fn fmt_timestamp(unix_secs: i64) -> String
{
    let days        = unix_secs.div_euclid(86_400);
    let secs_of_day = unix_secs.rem_euclid(86_400);
    let (h, m, s)   = (secs_of_day / 3600, (secs_of_day / 60) % 60, secs_of_day % 60);

    let z   = days + 719_468;
    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;

    let doe = (z - era * 146_097) as i64;                            // [0, 146096]
    let yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365; // [0, 399]

    let y = yoe + era * 400;

    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100); // [0, 365]
    let mp  = (5 * doy + 2) / 153;                     // [0, 11]
    let d   = doy - (153 * mp + 2) / 5 + 1;            // [1, 31]
    let m_num = if mp < 10 { mp + 3 } else { mp - 9 }; // [1, 12]

    let y = if m_num <= 2 { y + 1 } else { y };

    format!("{y:04}-{m_num:02}-{d:02} {h:02}:{m:02}:{s:02} UTC")
}

/// Compact `1d 02h 03m 04s`-style duration, dropping leading zero units.
pub fn fmt_duration(secs: i64) -> String
{
    let secs     = secs.max(0);
    let (d, rem) = (secs / 86_400, secs % 86_400);
    let (h, rem) = (rem / 3600, rem % 3600);
    let (m, s)   = (rem / 60, rem % 60);

    match (d, h, m) {
        (d, _, _) if d > 0 => format!("{d}d {h:02}h {m:02}m {s:02}s"),
        (_, h, _) if h > 0 => format!("{h}h {m:02}m {s:02}s"),
        (_, _, m) if m > 0 => format!("{m}m {s:02}s"),
        _                  => format!("{s}s"),
    }
}

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

    #[test]
    fn formats_known_epoch() {
        assert_eq!(fmt_timestamp(0), "1970-01-01 00:00:00 UTC");
        assert_eq!(fmt_timestamp(1_700_000_000), "2023-11-14 22:13:20 UTC");
    }

    #[test]
    fn formats_durations() {
        assert_eq!(fmt_duration(5), "5s");
        assert_eq!(fmt_duration(65), "1m 05s");
        assert_eq!(fmt_duration(3665), "1h 01m 05s");
        assert_eq!(fmt_duration(90_065), "1d 01h 01m 05s");
    }
}