git2-time-chrono-ext 0.2.0

use crate::Error;
use chrono::TimeZone;

/// An extension trait to convert `git2::Time` to `chrono::DateTime`.
/// # Examples
/// ```no_run
/// use git2_time_chrono_ext::Git2TimeChronoExt;
///
/// // Print `git2::Time` to `stdout`.
/// fn print_git2_time(time: git2::Time) {
///   println!("{}", time.to_local_date_time().unwrap());
/// }
///
/// // Convert `git2::Time` to `Stirng` in the specified format.
/// fn git2_time_to_string(time: git2::Time) -> String {
///   time.to_local_date_time().unwrap().format("%Y-%m-%d %H:%M").to_string()
/// }
/// ```
pub trait Git2TimeChronoExt {
    /// Convert [`git2::Time`] to [`chrono::DateTime<chrono::FixedOffset>`].
    ///
    /// This is useful when the original timezone in the [`git2::Time`] is needed.
    /// # Examples
    /// ```
    /// use git2_time_chrono_ext::Git2TimeChronoExt;
    ///
    /// // The Eastern Hemisphere time zone.
    /// let east_time = git2::Time::new(1745693791, 540);
    /// let east_datetime = east_time.to_date_time();
    /// assert!(east_datetime.is_ok());
    /// assert_eq!(east_datetime.unwrap().to_string(), "2025-04-27 03:56:31 +09:00");
    /// ```
    /// ```
    /// # use git2_time_chrono_ext::Git2TimeChronoExt;
    /// // The Western Hemisphere time zone.
    /// let west_time = git2::Time::new(1745196130, -420);
    /// let west_datetime = west_time.to_date_time();
    /// assert!(west_datetime.is_ok());
    /// assert_eq!(west_datetime.unwrap().to_string(), "2025-04-20 17:42:10 -07:00");
    /// ```
    fn to_date_time(&self) -> Result<chrono::DateTime<chrono::FixedOffset>, Error>;

    /// Convert [`git2::Time`] to [`chrono::DateTime`] in the specified time zone.
    /// # Examples
    /// ```
    /// use git2_time_chrono_ext::Git2TimeChronoExt;
    ///
    /// let time = git2::Time::new(1745196130, -420);
    /// let utc_datetime = time.to_date_time_in(&chrono::Utc);
    /// assert_eq!(utc_datetime.unwrap().to_string(), "2025-04-21 00:42:10 UTC");
    /// ```
    fn to_date_time_in<Tz: chrono::TimeZone>(&self, tz: &Tz)
    -> Result<chrono::DateTime<Tz>, Error>;

    /// Convert [`git2::Time`] to [`chrono::DateTime`] in the local time zone.
    /// This function is a shorthand of:
    /// ```
    /// # use git2_time_chrono_ext::Git2TimeChronoExt;
    /// # fn to_local(time: git2::Time) -> Result<chrono::DateTime<chrono::Local>, git2_time_chrono_ext::Error> {
    /// time.to_date_time_in(&chrono::Local)
    /// # }
    /// ```
    fn to_local_date_time(&self) -> Result<chrono::DateTime<chrono::Local>, Error>;
}

impl Git2TimeChronoExt for git2::Time {
    fn to_date_time(&self) -> Result<chrono::DateTime<chrono::FixedOffset>, Error> {
        let Some(tz) = chrono::FixedOffset::east_opt(self.offset_minutes() * 60) else {
            return Err(Error::InvalidTimeZone {
                offset_minutes: self.offset_minutes(),
            });
        };
        match tz.timestamp_opt(self.seconds(), 0) {
            chrono::MappedLocalTime::Single(datetime) => Ok(datetime),
            chrono::MappedLocalTime::Ambiguous(_, latest) => Ok(latest),
            chrono::MappedLocalTime::None => Err(Error::TimeNotMappable { time: *self }),
        }
    }

    fn to_date_time_in<Tz: chrono::TimeZone>(
        &self,
        tz: &Tz,
    ) -> Result<chrono::DateTime<Tz>, Error> {
        self.to_date_time()
            .map(|datetime| datetime.with_timezone(tz))
    }

    fn to_local_date_time(&self) -> Result<chrono::DateTime<chrono::Local>, Error> {
        self.to_date_time_in(&chrono::Local)
    }
}

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

    #[test]
    fn to_date_time_offset_invalid() {
        let time = git2::Time::new(0, 100_000);
        let result = time.to_date_time();
        assert!(result.is_err());
        let err = result.unwrap_err();
        assert!(matches!(
            err,
            Error::InvalidTimeZone {
                offset_minutes: 100_000
            }
        ));
    }
}