// 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::fmt;
use oldtime::Duration as OldDuration;

use div::div_mod_floor;
use naive::date::NaiveDate;
use naive::datetime::NaiveDateTime;
use super::{TimeZone, Offset, LocalResult};

/// The time zone with fixed offset, from UTC-23:59:59 to UTC+23:59:59.
///
/// Using the [`TimeZone`](../../../chrono/offset/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
        }
    }
}

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 local_minus_utc(&self) -> OldDuration { OldDuration::seconds(self.local_minus_utc as i64) }
}

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) }
}