//! Human-readable timestamp formatting for forum display.

use chrono::{DateTime, Utc};

/// Relative timestamp for thread listings: "just now", "3m ago", "2h ago", etc.
/// Falls back to "Jan 15" format for dates older than 7 days.
pub fn relative_timestamp(dt: DateTime<Utc>) -> String {
    let now = Utc::now();
    let delta = now.signed_duration_since(dt);

    if delta.num_seconds() < 60 {
        "just now".into()
    } else if delta.num_minutes() < 60 {
        format!("{}m ago", delta.num_minutes())
    } else if delta.num_hours() < 24 {
        format!("{}h ago", delta.num_hours())
    } else if delta.num_days() < 7 {
        format!("{}d ago", delta.num_days())
    } else {
        dt.format("%b %-d").to_string()
    }
}

/// Absolute timestamp for post display: "2026-03-13 10:30".
pub fn post_timestamp(dt: DateTime<Utc>) -> String {
    dt.format("%Y-%m-%d %H:%M").to_string()
}

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

    #[test]
    fn just_now() {
        let dt = Utc::now() - Duration::seconds(30);
        assert_eq!(relative_timestamp(dt), "just now");
    }

    #[test]
    fn minutes_ago() {
        let dt = Utc::now() - Duration::minutes(5);
        assert_eq!(relative_timestamp(dt), "5m ago");
    }

    #[test]
    fn hours_ago() {
        let dt = Utc::now() - Duration::hours(3);
        assert_eq!(relative_timestamp(dt), "3h ago");
    }

    #[test]
    fn days_ago() {
        let dt = Utc::now() - Duration::days(2);
        assert_eq!(relative_timestamp(dt), "2d ago");
    }

    #[test]
    fn older_than_week() {
        let dt = Utc::now() - Duration::days(10);
        let result = relative_timestamp(dt);
        // Should be in "Jan 15" format
        assert!(!result.contains("ago"), "expected date format, got: {result}");
    }

    #[test]
    fn post_timestamp_format() {
        let dt = chrono::NaiveDate::from_ymd_opt(2026, 3, 13)
            .unwrap()
            .and_hms_opt(10, 30, 0)
            .unwrap()
            .and_utc();
        assert_eq!(post_timestamp(dt), "2026-03-13 10:30");
    }

    #[test]
    fn boundary_59_seconds_is_just_now() {
        let dt = Utc::now() - Duration::seconds(59);
        assert_eq!(relative_timestamp(dt), "just now");
    }

    #[test]
    fn boundary_60_seconds_is_1m() {
        let dt = Utc::now() - Duration::seconds(60);
        assert_eq!(relative_timestamp(dt), "1m ago");
    }

    #[test]
    fn boundary_59_minutes_is_minutes() {
        let dt = Utc::now() - Duration::minutes(59);
        assert_eq!(relative_timestamp(dt), "59m ago");
    }

    #[test]
    fn boundary_60_minutes_is_1h() {
        let dt = Utc::now() - Duration::minutes(60);
        assert_eq!(relative_timestamp(dt), "1h ago");
    }

    #[test]
    fn boundary_23_hours_is_hours() {
        let dt = Utc::now() - Duration::hours(23);
        assert_eq!(relative_timestamp(dt), "23h ago");
    }

    #[test]
    fn boundary_24_hours_is_1d() {
        let dt = Utc::now() - Duration::hours(24);
        assert_eq!(relative_timestamp(dt), "1d ago");
    }

    #[test]
    fn boundary_6_days_is_days() {
        let dt = Utc::now() - Duration::days(6);
        assert_eq!(relative_timestamp(dt), "6d ago");
    }

    #[test]
    fn boundary_7_days_is_date() {
        let dt = Utc::now() - Duration::days(7);
        let result = relative_timestamp(dt);
        assert!(!result.contains("ago"), "expected date format, got: {result}");
    }

    #[test]
    fn post_timestamp_midnight() {
        let dt = chrono::NaiveDate::from_ymd_opt(2026, 1, 1)
            .unwrap()
            .and_hms_opt(0, 0, 0)
            .unwrap()
            .and_utc();
        assert_eq!(post_timestamp(dt), "2026-01-01 00:00");
    }

    #[test]
    fn zero_seconds_ago_is_just_now() {
        let dt = Utc::now();
        assert_eq!(relative_timestamp(dt), "just now");
    }
}