//! 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. Examples: "in 30d7h",
/// "in 3h12m", "in 47m", "12m 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();
    let sign = if secs >= 0 { "in " } else { " ago" };
    let body = dur_words(secs.abs());
    format!("{sign}{body}")
}

/// 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()
}

/// Compact duration. Starts with days when the span is at least one day.
fn dur_words(total: i64) -> String {
    let s = total.max(0);
    if s == 0 {
        return "<1m".to_string();
    }
    let days = s / 86_400;
    let rem = s % 86_400;
    if days > 0 {
        let hours = rem / 3_600;
        if hours > 0 {
            return format!("{days}d{hours}h");
        }
        return format!("{days}d");
    }
    let hours = s / 3_600;
    let mins = (s % 3_600) / 60;
    if hours > 0 {
        return format!("{hours}h{m}m", m = if mins > 0 { mins.to_string() } else { String::new() });
    }
    let mins = (s / 60).max(1);
    format!("{mins}m")
}

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