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

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

/// 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(Copy, Clone, PartialEq, Eq)]
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 -86400 < secs && secs < 86400 {
            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 -86400 < secs && secs < 86400 {
            Some(FixedOffset { local_minus_utc: -secs })
        } else {
            None
        }
    }

    /// Returns the number of seconds to add to convert from UTC to the local time.
    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.
    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 same to
// 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(rhs as i64)).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 offset::TimeZone;
    use super::FixedOffset;

    #[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());
    }
}