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

//! The UTC (Coordinated Universal Time) time zone.

use std::fmt;
use oldtime;

use naive::{NaiveDate, NaiveDateTime};
use {Date, DateTime};
use super::{TimeZone, Offset, LocalResult, FixedOffset};

/// The UTC time zone. This is the most efficient time zone when you don't need the local time.
/// It is also used as an offset (which is also a dummy type).
///
/// Using the [`TimeZone`](../../../chrono/offset/trait.TimeZone.html) methods
/// on the UTC struct is the preferred way to construct `DateTime<UTC>`
/// instances.
///
/// # Example
///
/// ~~~~
/// use chrono::{DateTime, TimeZone, NaiveDateTime, UTC};
///
/// let dt = DateTime::<UTC>::from_utc(NaiveDateTime::from_timestamp(61, 0), UTC);
///
/// assert_eq!(UTC.timestamp(61, 0), dt);
/// assert_eq!(UTC.ymd(1970, 1, 1).and_hms(0, 1, 1), dt);
/// ~~~~
#[derive(Copy, Clone, PartialEq, Eq)]
pub struct UTC;

impl UTC {
    /// Returns a `Date` which corresponds to the current date.
    pub fn today() -> Date<UTC> { UTC::now().date() }

    /// Returns a `DateTime` which corresponds to the current date.
    pub fn now() -> DateTime<UTC> {
        let spec = oldtime::get_time();
        let naive = NaiveDateTime::from_timestamp(spec.sec, spec.nsec as u32);
        DateTime::from_utc(naive, UTC)
    }
}

impl TimeZone for UTC {
    type Offset = UTC;

    fn from_offset(_state: &UTC) -> UTC { UTC }

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

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

impl Offset for UTC {
    fn fix(&self) -> FixedOffset { FixedOffset::east(0) }
}

impl fmt::Debug for UTC {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "Z") }
}

impl fmt::Display for UTC {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "UTC") }
}