//! IANA timezone helpers backed by jiff's bundled tzdb, so results do not depend on the host.

use jiff::{Timestamp, tz::TimeZone};

use crate::error::{Error, Result};

/// Resolves an IANA name, falling back to UTC for anything unknown.
fn zone_or_utc(tz: &str) -> TimeZone {
    TimeZone::get(tz).unwrap_or(TimeZone::UTC)
}

/// Accepts only names known to the bundled tzdb, such as "Europe/Istanbul" or "UTC".
pub fn validate_timezone(name: &str) -> Result<()> {
    TimeZone::get(name)
        .map(|_| ())
        .map_err(|_| Error::Invalid(format!("timezone {name:?}")))
}

/// Every known IANA name, sorted and without duplicates, for the timezone `<select>`.
pub fn all_timezones() -> Vec<String> {
    let mut names: Vec<String> = jiff::tz::db()
        .available()
        .map(|name| name.to_string())
        .collect();
    names.sort();
    names.dedup();
    names
}

/// Absolute time for display, e.g. "2026-10-15 14:05 +03". Unknown zones fall back to UTC.
pub fn format_in_tz(unix: i64, tz: &str) -> String {
    let Ok(ts) = Timestamp::from_second(unix) else {
        return "invalid time".to_string();
    };
    let formatted = ts
        .to_zoned(zone_or_utc(tz))
        .strftime("%Y-%m-%d %H:%M %:z")
        .to_string();
    // Whole-hour offsets print as "+03" rather than "+03:00".
    match formatted.strip_suffix(":00") {
        Some(short) => short.to_string(),
        None => formatted,
    }
}

/// Local clock time with its offset, e.g. "14:05 (UTC+03:00)". Unknown zones fall back to UTC.
pub fn local_time_now(tz: &str, now_unix: i64) -> String {
    let Ok(ts) = Timestamp::from_second(now_unix) else {
        return "invalid time".to_string();
    };
    ts.to_zoned(zone_or_utc(tz))
        .strftime("%H:%M (UTC%:z)")
        .to_string()
}

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

    #[test]
    fn validates_known_and_unknown_names() {
        assert!(validate_timezone("Europe/Istanbul").is_ok());
        assert!(validate_timezone("UTC").is_ok());
        assert!(validate_timezone("Mars/Base").is_err());
        assert!(validate_timezone("").is_err());
    }

    #[test]
    fn formats_absolute_time_in_zone() {
        // 2026-10-15 11:05:00 UTC is 14:05 in Istanbul (UTC+03, no DST).
        let unix = 1_792_062_300;
        assert_eq!(
            format_in_tz(unix, "Europe/Istanbul"),
            "2026-10-15 14:05 +03"
        );
        assert_eq!(format_in_tz(unix, "Mars/Base"), "2026-10-15 11:05 +00");
    }

    #[test]
    fn local_time_shows_offset() {
        let unix = 1_792_062_300;
        assert_eq!(local_time_now("Europe/Istanbul", unix), "14:05 (UTC+03:00)");
        assert_eq!(local_time_now("UTC", unix), "11:05 (UTC+00:00)");
    }

    #[test]
    fn lists_timezones_sorted() {
        let zones = all_timezones();
        assert!(zones.iter().any(|z| z == "UTC"));
        assert!(zones.iter().any(|z| z == "America/New_York"));
        assert!(zones.windows(2).all(|w| w[0] < w[1]));
    }
}