//! Times as people read them: relative ("3 hours ago") with the absolute
//! form for a tooltip.

use time::format_description::well_known::Rfc3339;
use time::OffsetDateTime;

/// `just now`, `5 minutes ago`, `3 days ago`, `2 years ago`.
pub fn ago(when_ms: u64, now_ms: u64) -> String {
    if when_ms == 0 {
        return "unknown".into();
    }
    if when_ms > now_ms {
        return "in the future".into();
    }
    let s = (now_ms - when_ms) / 1000;
    let (n, unit) = if s < 45 {
        return "just now".into();
    } else if s < 90 {
        (1, "minute")
    } else if s < 3600 {
        (s / 60, "minute")
    } else if s < 86_400 {
        (s / 3600, "hour")
    } else if s < 86_400 * 30 {
        (s / 86_400, "day")
    } else if s < 86_400 * 365 {
        (s / (86_400 * 30), "month")
    } else {
        (s / (86_400 * 365), "year")
    };
    format!("{n} {unit}{} ago", if n == 1 { "" } else { "s" })
}

/// `2026-09-27 17:02 UTC`.
pub fn absolute(when_ms: u64) -> String {
    match OffsetDateTime::from_unix_timestamp((when_ms / 1000) as i64) {
        Ok(t) => {
            let f = time::macros::format_description!("[year]-[month]-[day] [hour]:[minute] UTC");
            t.format(&f).unwrap_or_default()
        }
        Err(_) => String::new(),
    }
}

/// `21 Oct 2026`, the UTC day.
pub fn day(when_ms: u64) -> String {
    match OffsetDateTime::from_unix_timestamp((when_ms / 1000) as i64) {
        Ok(t) => {
            let f = time::macros::format_description!("[day padding:none] [month repr:short] [year]");
            t.format(&f).unwrap_or_default()
        }
        Err(_) => String::new(),
    }
}

pub fn rfc3339(when_ms: u64) -> String {
    OffsetDateTime::from_unix_timestamp((when_ms / 1000) as i64).ok().and_then(|t| t.format(&Rfc3339).ok()).unwrap_or_default()
}

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

    #[test]
    fn days() {
        assert_eq!(day(1_792_540_800_000), "21 Oct 2026");
    }

    #[test]
    fn relative() {
        let now = 1_800_000_000_000;
        assert_eq!(ago(now - 10_000, now), "just now");
        assert_eq!(ago(now - 60_000, now), "1 minute ago");
        assert_eq!(ago(now - 5 * 60_000, now), "5 minutes ago");
        assert_eq!(ago(now - 3 * 3_600_000, now), "3 hours ago");
        assert_eq!(ago(now - 2 * 86_400_000, now), "2 days ago");
        assert_eq!(ago(now - 400 * 86_400_000, now), "1 year ago");
        assert_eq!(ago(0, now), "unknown");
        assert_eq!(absolute(1_758_990_120_000), "2025-09-27 16:22 UTC");
    }
}