//! Human time strings from ISO 8601 UTC timestamps.
//!
//! Used by the pretty renderer for "resets in 3h12m" and "in 47m". Parses are
//! lenient. A parse failure returns the raw string unchanged.

use chrono::{DateTime, Utc};

/// Relative phrasing of a future or past timestamp. Example: "in 3h12m" or
/// "47m ago". Falls back to the input on parse failure.
pub fn relative(iso: &str) -> String {
    let Some(t) = parse(iso) else {
        return iso.to_string();
    };
    let now = Utc::now();
    let d = t.signed_duration_since(now);
    let secs = d.num_seconds();

    if secs.abs() < 60 {
        if secs >= 0 {
            "in <1m".to_string()
        } else {
            "<1m ago".to_string()
        }
    } else {
        let h = secs / 3600;
        let m = (secs % 3600) / 60;
        let core = match (h.abs() > 0, m != 0) {
            (true, true) => format!("{}h{}m", h.abs(), m.abs()),
            (true, false) => format!("{}h", h.abs()),
            (false, _) => format!("{}m", m.abs()),
        };
        if secs >= 0 {
            format!("in {core}")
        } else {
            format!("{core} ago")
        }
    }
}

/// Absolute UTC string like "2025-08-31 17:00 UTC".
pub fn absolute(iso: &str) -> String {
    let Some(t) = parse(iso) else {
        return iso.to_string();
    };
    t.format("%Y-%m-%d %H:%M UTC").to_string()
}

fn parse(iso: &str) -> Option<DateTime<Utc>> {
    DateTime::parse_from_rfc3339(iso)
        .ok()
        .map(|dt| dt.with_timezone(&Utc))
}