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    // This is a part of Chrono.
    // See README.md and LICENSE.txt for details.

    //! The time zone which has a fixed offset from UTC.

    use core::fmt;
    use core::ops::{Add, Sub};
    use oldtime::Duration as OldDuration;

    use super::{LocalResult, Offset, TimeZone};
    use div::div_mod_floor;
    use naive::{NaiveDate, NaiveDateTime, NaiveTime};
    use DateTime;
    use Timelike;

    /// The time zone with fixed offset, from UTC-23:59:59 to UTC+23:59:59.
    ///
    /// Using the [`TimeZone`](./trait.TimeZone.html) methods
    /// on a `FixedOffset` struct is the preferred way to construct
    /// `DateTime<FixedOffset>` instances. See the [`east`](#method.east) and
    /// [`west`](#method.west) methods for examples.
    #[derive(PartialEq, Eq, Hash, Copy, Clone)]
    pub struct FixedOffset {
        local_minus_utc: i32,
    }

    impl FixedOffset {
        /// Makes a new `FixedOffset` for the Eastern Hemisphere with given timezone difference.
        /// The negative `secs` means the Western Hemisphere.
        ///
        /// Panics on the out-of-bound `secs`.
        ///
        /// # Example
        ///
        /// ~~~~
        /// use chrono::{FixedOffset, TimeZone};
        /// let hour = 3600;
        /// let datetime = FixedOffset::east(5 * hour).ymd(2016, 11, 08)
        ///                                           .and_hms(0, 0, 0);
        /// assert_eq!(&datetime.to_rfc3339(), "2016-11-08T00:00:00+05:00")
        /// ~~~~
        pub fn east(secs: i32) -> FixedOffset {
            FixedOffset::east_opt(secs).expect("FixedOffset::east out of bounds")
        }

        /// Makes a new `FixedOffset` for the Eastern Hemisphere with given timezone difference.
        /// The negative `secs` means the Western Hemisphere.
        ///
        /// Returns `None` on the out-of-bound `secs`.
        pub fn east_opt(secs: i32) -> Option<FixedOffset> {
            if -86_400 < secs && secs < 86_400 {
                Some(FixedOffset { local_minus_utc: secs })
            } else {
                None
            }
        }

        /// Makes a new `FixedOffset` for the Western Hemisphere with given timezone difference.
        /// The negative `secs` means the Eastern Hemisphere.
        ///
        /// Panics on the out-of-bound `secs`.
        ///
        /// # Example
        ///
        /// ~~~~
        /// use chrono::{FixedOffset, TimeZone};
        /// let hour = 3600;
        /// let datetime = FixedOffset::west(5 * hour).ymd(2016, 11, 08)
        ///                                           .and_hms(0, 0, 0);
        /// assert_eq!(&datetime.to_rfc3339(), "2016-11-08T00:00:00-05:00")
        /// ~~~~
        pub fn west(secs: i32) -> FixedOffset {
            FixedOffset::west_opt(secs).expect("FixedOffset::west out of bounds")
        }

        /// Makes a new `FixedOffset` for the Western Hemisphere with given timezone difference.
        /// The negative `secs` means the Eastern Hemisphere.
        ///
        /// Returns `None` on the out-of-bound `secs`.
        pub fn west_opt(secs: i32) -> Option<FixedOffset> {
            if -86_400 < secs && secs < 86_400 {
                Some(FixedOffset { local_minus_utc: -secs })
            } else {
                None
            }
        }

        /// Returns the number of seconds to add to convert from UTC to the local time.
        #[inline]
        pub fn local_minus_utc(&self) -> i32 {
            self.local_minus_utc
        }

        /// Returns the number of seconds to add to convert from the local time to UTC.
        #[inline]
        pub fn utc_minus_local(&self) -> i32 {
            -self.local_minus_utc
        }
    }

    impl TimeZone for FixedOffset {
        type Offset = FixedOffset;

        fn from_offset(offset: &FixedOffset) -> FixedOffset {
            *offset
        }

        fn offset_from_local_date(&self, _local: &NaiveDate) -> LocalResult<FixedOffset> {
            LocalResult::Single(*self)
        }
        fn offset_from_local_datetime(&self, _local: &NaiveDateTime) -> LocalResult<FixedOffset> {
            LocalResult::Single(*self)
        }

        fn offset_from_utc_date(&self, _utc: &NaiveDate) -> FixedOffset {
            *self
        }
        fn offset_from_utc_datetime(&self, _utc: &NaiveDateTime) -> FixedOffset {
            *self
        }
    }

    impl Offset for FixedOffset {
        fn fix(&self) -> FixedOffset {
            *self
        }
    }

    impl fmt::Debug for FixedOffset {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            let offset = self.local_minus_utc;
            let (sign, offset) = if offset < 0 { ('-', -offset) } else { ('+', offset) };
            let (mins, sec) = div_mod_floor(offset, 60);
            let (hour, min) = div_mod_floor(mins, 60);
            if sec == 0 {
                write!(f, "{}{:02}:{:02}", sign, hour, min)
            } else {
                write!(f, "{}{:02}:{:02}:{:02}", sign, hour, min, sec)
            }
        }
    }

    impl fmt::Display for FixedOffset {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Debug::fmt(self, f)
        }
    }

    // addition or subtraction of FixedOffset to/from Timelike values is the same as
    // adding or subtracting the offset's local_minus_utc value
    // but keep keeps the leap second information.
    // this should be implemented more efficiently, but for the time being, this is generic right now.

    fn add_with_leapsecond<T>(lhs: &T, rhs: i32) -> T
    where
        T: Timelike + Add<OldDuration, Output = T>,
    {
        // extract and temporarily remove the fractional part and later recover it
        let nanos = lhs.nanosecond();
        let lhs = lhs.with_nanosecond(0).unwrap();
        (lhs + OldDuration::seconds(i64::from(rhs))).with_nanosecond(nanos).unwrap()
    }

    impl Add<FixedOffset> for NaiveTime {
        type Output = NaiveTime;

        #[inline]
        fn add(self, rhs: FixedOffset) -> NaiveTime {
            add_with_leapsecond(&self, rhs.local_minus_utc)
        }
    }

    impl Sub<FixedOffset> for NaiveTime {
        type Output = NaiveTime;

        #[inline]
        fn sub(self, rhs: FixedOffset) -> NaiveTime {
            add_with_leapsecond(&self, -rhs.local_minus_utc)
        }
    }

    impl Add<FixedOffset> for NaiveDateTime {
        type Output = NaiveDateTime;

        #[inline]
        fn add(self, rhs: FixedOffset) -> NaiveDateTime {
            add_with_leapsecond(&self, rhs.local_minus_utc)
        }
    }

    impl Sub<FixedOffset> for NaiveDateTime {
        type Output = NaiveDateTime;

        #[inline]
        fn sub(self, rhs: FixedOffset) -> NaiveDateTime {
            add_with_leapsecond(&self, -rhs.local_minus_utc)
        }
    }

    impl<Tz: TimeZone> Add<FixedOffset> for DateTime<Tz> {
        type Output = DateTime<Tz>;

        #[inline]
        fn add(self, rhs: FixedOffset) -> DateTime<Tz> {
            add_with_leapsecond(&self, rhs.local_minus_utc)
        }
    }

    impl<Tz: TimeZone> Sub<FixedOffset> for DateTime<Tz> {
        type Output = DateTime<Tz>;

        #[inline]
        fn sub(self, rhs: FixedOffset) -> DateTime<Tz> {
            add_with_leapsecond(&self, -rhs.local_minus_utc)
        }
    }

    #[cfg(test)]
    mod tests {
        use super::FixedOffset;
        use offset::TimeZone;

        #[test]
        fn test_date_extreme_offset() {
            // starting from 0.3 we don't have an offset exceeding one day.
            // this makes everything easier!
            assert_eq!(
                format!("{:?}", FixedOffset::east(86399).ymd(2012, 2, 29)),
                "2012-02-29+23:59:59".to_string()
            );
            assert_eq!(
                format!("{:?}", FixedOffset::east(86399).ymd(2012, 2, 29).and_hms(5, 6, 7)),
                "2012-02-29T05:06:07+23:59:59".to_string()
            );
            assert_eq!(
                format!("{:?}", FixedOffset::west(86399).ymd(2012, 3, 4)),
                "2012-03-04-23:59:59".to_string()
            );
            assert_eq!(
                format!("{:?}", FixedOffset::west(86399).ymd(2012, 3, 4).and_hms(5, 6, 7)),
                "2012-03-04T05:06:07-23:59:59".to_string()
            );
        }
    }