//! The [`UtcOffset`] struct and its associated `impl`s.

#[cfg(feature = "formatting")]
use alloc::string::String;
use core::cmp::Ordering;
use core::fmt;
use core::hash::{Hash, Hasher};
use core::mem::MaybeUninit;
use core::ops::Neg;
#[cfg(feature = "formatting")]
use std::io;

use deranged::{ri8, ri32, ru8};
use powerfmt::smart_display::{FormatterOptions, Metadata, SmartDisplay};

#[cfg(feature = "local-offset")]
use crate::OffsetDateTime;
use crate::error;
#[cfg(feature = "formatting")]
use crate::formatting::Formattable;
use crate::internal_macros::ensure_ranged;
use crate::num_fmt::{str_from_raw_parts, two_digits_zero_padded};
#[cfg(feature = "parsing")]
use crate::parsing::Parsable;
#[cfg(feature = "local-offset")]
use crate::sys::local_offset_at;
use crate::unit::*;

/// The type of the `hours` field of `UtcOffset`.
pub(crate) type Hours = ri8<-25, 25>;
/// The type of the `minutes` field of `UtcOffset`.
pub(crate) type Minutes =
    ri8<{ -(Minute::per_t::<i8>(Hour) - 1) }, { Minute::per_t::<i8>(Hour) - 1 }>;
/// The type of the `seconds` field of `UtcOffset`.
pub(crate) type Seconds =
    ri8<{ -(Second::per_t::<i8>(Minute) - 1) }, { Second::per_t::<i8>(Minute) - 1 }>;
/// The type capable of storing the range of whole seconds that a `UtcOffset` can encompass.
type WholeSeconds = ri32<
    {
        Hours::MIN.get() as i32 * Second::per_t::<i32>(Hour)
            + Minutes::MIN.get() as i32 * Second::per_t::<i32>(Minute)
            + Seconds::MIN.get() as i32
    },
    {
        Hours::MAX.get() as i32 * Second::per_t::<i32>(Hour)
            + Minutes::MAX.get() as i32 * Second::per_t::<i32>(Minute)
            + Seconds::MAX.get() as i32
    },
>;

/// An offset from UTC.
///
/// This struct can store values up to ±25:59:59. If you need support outside this range, please
/// file an issue with your use case.
// All three components _must_ have the same sign.
#[derive(Clone, Copy, Eq)]
#[cfg_attr(not(docsrs), repr(C))]
pub struct UtcOffset {
    // The order of this struct's fields matter. Do not reorder them.

    // Little endian version
    #[cfg(target_endian = "little")]
    seconds: Seconds,
    #[cfg(target_endian = "little")]
    minutes: Minutes,
    #[cfg(target_endian = "little")]
    hours: Hours,

    // Big endian version
    #[cfg(target_endian = "big")]
    hours: Hours,
    #[cfg(target_endian = "big")]
    minutes: Minutes,
    #[cfg(target_endian = "big")]
    seconds: Seconds,
}

impl Hash for UtcOffset {
    #[inline]
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        state.write_u32(self.as_u32_for_equality());
    }
}

impl PartialEq for UtcOffset {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        self.as_u32_for_equality().eq(&other.as_u32_for_equality())
    }
}

impl PartialOrd for UtcOffset {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for UtcOffset {
    #[inline]
    fn cmp(&self, other: &Self) -> Ordering {
        self.as_i32_for_comparison()
            .cmp(&other.as_i32_for_comparison())
    }
}

impl UtcOffset {
    /// Provide a representation of the `UtcOffset` as a `i32`. This value can be used for equality,
    /// and hashing. This value is not suitable for ordering; use `as_i32_for_comparison` instead.
    #[inline]
    pub(crate) const fn as_u32_for_equality(self) -> u32 {
        // Safety: Size and alignment are handled by the compiler. Both the source and destination
        // types are plain old data (POD) types.
        unsafe {
            if const { cfg!(target_endian = "little") } {
                core::mem::transmute::<[i8; 4], u32>([
                    self.seconds.get(),
                    self.minutes.get(),
                    self.hours.get(),
                    0,
                ])
            } else {
                core::mem::transmute::<[i8; 4], u32>([
                    self.hours.get(),
                    self.minutes.get(),
                    self.seconds.get(),
                    0,
                ])
            }
        }
    }

    /// Provide a representation of the `UtcOffset` as a `i32`. This value can be used for ordering.
    /// While it is suitable for equality, `as_u32_for_equality` is preferred for performance
    /// reasons.
    #[inline]
    const fn as_i32_for_comparison(self) -> i32 {
        (self.hours.get() as i32) << 16
            | (self.minutes.get() as i32) << 8
            | (self.seconds.get() as i32)
    }

    /// A `UtcOffset` that is UTC.
    ///
    /// ```rust
    /// # use time::UtcOffset;
    /// # use time_macros::offset;
    /// assert_eq!(UtcOffset::UTC, offset!(UTC));
    /// ```
    pub const UTC: Self = Self::from_whole_seconds_ranged(WholeSeconds::new_static::<0>());

    /// Create a `UtcOffset` representing an offset of the hours, minutes, and seconds provided, the
    /// validity of which must be guaranteed by the caller. All three parameters must have the same
    /// sign.
    ///
    /// # Safety
    ///
    /// - Hours must be in the range `-25..=25`.
    /// - Minutes must be in the range `-59..=59`.
    /// - Seconds must be in the range `-59..=59`.
    ///
    /// While the signs of the parameters are required to match to avoid bugs, this is not a safety
    /// invariant.
    #[doc(hidden)]
    #[inline]
    #[track_caller]
    pub const unsafe fn __from_hms_unchecked(hours: i8, minutes: i8, seconds: i8) -> Self {
        // Safety: The caller must uphold the safety invariants.
        unsafe {
            Self::from_hms_ranged_unchecked(
                Hours::new_unchecked(hours),
                Minutes::new_unchecked(minutes),
                Seconds::new_unchecked(seconds),
            )
        }
    }

    /// Create a `UtcOffset` representing an offset by the number of hours, minutes, and seconds
    /// provided.
    ///
    /// The sign of all three components should match. If they do not, all smaller components will
    /// have their signs flipped.
    ///
    /// ```rust
    /// # use time::UtcOffset;
    /// assert_eq!(UtcOffset::from_hms(1, 2, 3)?.as_hms(), (1, 2, 3));
    /// assert_eq!(UtcOffset::from_hms(1, -2, -3)?.as_hms(), (1, 2, 3));
    /// # Ok::<_, time::Error>(())
    /// ```
    #[inline]
    pub const fn from_hms(
        hours: i8,
        minutes: i8,
        seconds: i8,
    ) -> Result<Self, error::ComponentRange> {
        Ok(Self::from_hms_ranged(
            ensure_ranged!(Hours: hours("offset hour")),
            ensure_ranged!(Minutes: minutes("offset minute")),
            ensure_ranged!(Seconds: seconds("offset second")),
        ))
    }

    /// Create a `UtcOffset` representing an offset of the hours, minutes, and seconds provided. All
    /// three parameters must have the same sign.
    ///
    /// While the signs of the parameters are required to match, this is not a safety invariant.
    #[inline]
    #[track_caller]
    pub(crate) const fn from_hms_ranged_unchecked(
        hours: Hours,
        minutes: Minutes,
        seconds: Seconds,
    ) -> Self {
        if hours.get() < 0 {
            debug_assert!(minutes.get() <= 0);
            debug_assert!(seconds.get() <= 0);
        } else if hours.get() > 0 {
            debug_assert!(minutes.get() >= 0);
            debug_assert!(seconds.get() >= 0);
        }
        if minutes.get() < 0 {
            debug_assert!(seconds.get() <= 0);
        } else if minutes.get() > 0 {
            debug_assert!(seconds.get() >= 0);
        }

        Self {
            hours,
            minutes,
            seconds,
        }
    }

    /// Create a `UtcOffset` representing an offset by the number of hours, minutes, and seconds
    /// provided.
    ///
    /// The sign of all three components should match. If they do not, all smaller components will
    /// have their signs flipped.
    #[inline]
    pub(crate) const fn from_hms_ranged(
        hours: Hours,
        mut minutes: Minutes,
        mut seconds: Seconds,
    ) -> Self {
        if (hours.get() > 0 && minutes.get() < 0) || (hours.get() < 0 && minutes.get() > 0) {
            minutes = minutes.neg();
        }
        if (hours.get() > 0 && seconds.get() < 0)
            || (hours.get() < 0 && seconds.get() > 0)
            || (minutes.get() > 0 && seconds.get() < 0)
            || (minutes.get() < 0 && seconds.get() > 0)
        {
            seconds = seconds.neg();
        }

        Self {
            hours,
            minutes,
            seconds,
        }
    }

    /// Create a `UtcOffset` representing an offset by the number of seconds provided.
    ///
    /// ```rust
    /// # use time::UtcOffset;
    /// assert_eq!(UtcOffset::from_whole_seconds(3_723)?.as_hms(), (1, 2, 3));
    /// # Ok::<_, time::Error>(())
    /// ```
    #[inline]
    pub const fn from_whole_seconds(seconds: i32) -> Result<Self, error::ComponentRange> {
        Ok(Self::from_whole_seconds_ranged(
            ensure_ranged!(WholeSeconds: seconds),
        ))
    }

    /// Create a `UtcOffset` representing an offset by the number of seconds provided.
    // ignore because the function is crate-private
    /// ```rust,ignore
    /// # use time::UtcOffset;
    /// # use deranged::RangedI32;
    /// assert_eq!(
    ///     UtcOffset::from_whole_seconds_ranged(RangedI32::new_static::<3_723>()).as_hms(),
    ///     (1, 2, 3)
    /// );
    /// # Ok::<_, time::Error>(())
    /// ```
    #[inline]
    pub(crate) const fn from_whole_seconds_ranged(seconds: WholeSeconds) -> Self {
        // Safety: The type of `seconds` guarantees that all values are in range.
        unsafe {
            Self::__from_hms_unchecked(
                (seconds.get() / Second::per_t::<i32>(Hour)) as i8,
                ((seconds.get() % Second::per_t::<i32>(Hour)) / Minute::per_t::<i32>(Hour)) as i8,
                (seconds.get() % Second::per_t::<i32>(Minute)) as i8,
            )
        }
    }

    /// Obtain the UTC offset as its hours, minutes, and seconds. The sign of all three components
    /// will always match. A positive value indicates an offset to the east; a negative to the west.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert_eq!(offset!(+1:02:03).as_hms(), (1, 2, 3));
    /// assert_eq!(offset!(-1:02:03).as_hms(), (-1, -2, -3));
    /// ```
    #[inline]
    pub const fn as_hms(self) -> (i8, i8, i8) {
        (self.hours.get(), self.minutes.get(), self.seconds.get())
    }

    /// Obtain the UTC offset as its hours, minutes, and seconds. The sign of all three components
    /// will always match. A positive value indicates an offset to the east; a negative to the west.
    #[inline]
    #[cfg(any(feature = "formatting", feature = "quickcheck"))]
    pub(crate) const fn as_hms_ranged(self) -> (Hours, Minutes, Seconds) {
        (self.hours, self.minutes, self.seconds)
    }

    /// Obtain the number of whole hours the offset is from UTC. A positive value indicates an
    /// offset to the east; a negative to the west.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert_eq!(offset!(+1:02:03).whole_hours(), 1);
    /// assert_eq!(offset!(-1:02:03).whole_hours(), -1);
    /// ```
    #[inline]
    pub const fn whole_hours(self) -> i8 {
        self.hours.get()
    }

    /// Obtain the number of whole minutes the offset is from UTC. A positive value indicates an
    /// offset to the east; a negative to the west.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert_eq!(offset!(+1:02:03).whole_minutes(), 62);
    /// assert_eq!(offset!(-1:02:03).whole_minutes(), -62);
    /// ```
    #[inline]
    pub const fn whole_minutes(self) -> i16 {
        self.hours.get() as i16 * Minute::per_t::<i16>(Hour) + self.minutes.get() as i16
    }

    /// Obtain the number of minutes past the hour the offset is from UTC. A positive value
    /// indicates an offset to the east; a negative to the west.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert_eq!(offset!(+1:02:03).minutes_past_hour(), 2);
    /// assert_eq!(offset!(-1:02:03).minutes_past_hour(), -2);
    /// ```
    #[inline]
    pub const fn minutes_past_hour(self) -> i8 {
        self.minutes.get()
    }

    /// Obtain the number of whole seconds the offset is from UTC. A positive value indicates an
    /// offset to the east; a negative to the west.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert_eq!(offset!(+1:02:03).whole_seconds(), 3723);
    /// assert_eq!(offset!(-1:02:03).whole_seconds(), -3723);
    /// ```
    // This may be useful for anyone manually implementing arithmetic, as it
    // would let them construct a `Duration` directly.
    #[inline]
    pub const fn whole_seconds(self) -> i32 {
        self.hours.get() as i32 * Second::per_t::<i32>(Hour)
            + self.minutes.get() as i32 * Second::per_t::<i32>(Minute)
            + self.seconds.get() as i32
    }

    /// Obtain the number of seconds past the minute the offset is from UTC. A positive value
    /// indicates an offset to the east; a negative to the west.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert_eq!(offset!(+1:02:03).seconds_past_minute(), 3);
    /// assert_eq!(offset!(-1:02:03).seconds_past_minute(), -3);
    /// ```
    #[inline]
    pub const fn seconds_past_minute(self) -> i8 {
        self.seconds.get()
    }

    /// Check if the offset is exactly UTC.
    ///
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert!(!offset!(+1:02:03).is_utc());
    /// assert!(!offset!(-1:02:03).is_utc());
    /// assert!(offset!(UTC).is_utc());
    /// ```
    #[inline]
    pub const fn is_utc(self) -> bool {
        self.as_u32_for_equality() == Self::UTC.as_u32_for_equality()
    }

    /// Check if the offset is positive, or east of UTC.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert!(offset!(+1:02:03).is_positive());
    /// assert!(!offset!(-1:02:03).is_positive());
    /// assert!(!offset!(UTC).is_positive());
    /// ```
    #[inline]
    pub const fn is_positive(self) -> bool {
        self.as_i32_for_comparison() > Self::UTC.as_i32_for_comparison()
    }

    /// Check if the offset is negative, or west of UTC.
    ///
    /// ```rust
    /// # use time_macros::offset;
    /// assert!(!offset!(+1:02:03).is_negative());
    /// assert!(offset!(-1:02:03).is_negative());
    /// assert!(!offset!(UTC).is_negative());
    /// ```
    #[inline]
    pub const fn is_negative(self) -> bool {
        self.as_i32_for_comparison() < Self::UTC.as_i32_for_comparison()
    }

    /// Attempt to obtain the system's UTC offset at a known moment in time. If the offset cannot be
    /// determined, an error is returned.
    ///
    /// ```rust
    /// # use time::{UtcOffset, OffsetDateTime};
    /// let local_offset = UtcOffset::local_offset_at(OffsetDateTime::UNIX_EPOCH);
    /// # if false {
    /// assert!(local_offset.is_ok());
    /// # }
    /// ```
    #[cfg(feature = "local-offset")]
    #[inline]
    pub fn local_offset_at(datetime: OffsetDateTime) -> Result<Self, error::IndeterminateOffset> {
        local_offset_at(datetime).ok_or(error::IndeterminateOffset)
    }

    /// Attempt to obtain the system's current UTC offset. If the offset cannot be determined, an
    /// error is returned.
    ///
    /// ```rust
    /// # use time::UtcOffset;
    /// let local_offset = UtcOffset::current_local_offset();
    /// # if false {
    /// assert!(local_offset.is_ok());
    /// # }
    /// ```
    #[cfg(feature = "local-offset")]
    #[inline]
    pub fn current_local_offset() -> Result<Self, error::IndeterminateOffset> {
        let now = OffsetDateTime::now_utc();
        local_offset_at(now).ok_or(error::IndeterminateOffset)
    }
}

#[cfg(feature = "formatting")]
impl UtcOffset {
    /// Format the `UtcOffset` using the provided [format description](crate::format_description).
    #[inline]
    pub fn format_into(
        self,
        output: &mut (impl io::Write + ?Sized),
        format: &(impl Formattable + ?Sized),
    ) -> Result<usize, error::Format> {
        format.format_into(output, &self, &mut Default::default())
    }

    /// Format the `UtcOffset` using the provided [format description](crate::format_description).
    ///
    /// ```rust
    /// # use time::format_description;
    /// # use time_macros::offset;
    /// let format =
    ///     format_description::parse_borrowed::<3>("[offset_hour sign:mandatory]:[offset_minute]")?;
    /// assert_eq!(offset!(+1).format(&format)?, "+01:00");
    /// # Ok::<_, time::Error>(())
    /// ```
    #[inline]
    pub fn format(self, format: &(impl Formattable + ?Sized)) -> Result<String, error::Format> {
        format.format(&self, &mut Default::default())
    }
}

#[cfg(feature = "parsing")]
impl UtcOffset {
    /// Parse a `UtcOffset` from the input using the provided [format
    /// description](crate::format_description).
    ///
    /// ```rust
    /// # use time::UtcOffset;
    /// # use time_macros::{offset, format_description};
    /// let format = format_description!("[offset_hour]:[offset_minute]");
    /// assert_eq!(UtcOffset::parse("-03:42", &format)?, offset!(-3:42));
    /// # Ok::<_, time::Error>(())
    /// ```
    #[inline]
    pub fn parse(
        input: &str,
        description: &(impl Parsable + ?Sized),
    ) -> Result<Self, error::Parse> {
        description.parse_offset(input.as_bytes())
    }
}

mod private {
    /// Metadata for `UtcOffset`.
    #[non_exhaustive]
    #[derive(Debug, Clone, Copy)]
    pub struct UtcOffsetMetadata;
}
use private::UtcOffsetMetadata;

// This no longer needs special handling, as the format is fixed and doesn't require anything
// advanced. Trait impls can't be deprecated and the info is still useful for other types
// implementing `SmartDisplay`, so leave it as-is for now.
impl SmartDisplay for UtcOffset {
    type Metadata = UtcOffsetMetadata;

    #[inline]
    fn metadata(&self, _: FormatterOptions) -> Metadata<'_, Self> {
        Metadata::new(9, self, UtcOffsetMetadata)
    }

    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

impl UtcOffset {
    /// The maximum number of bytes that the `fmt_into_buffer` method will write, which is also used
    /// for the `Display` implementation.
    pub(crate) const DISPLAY_BUFFER_SIZE: usize = 9;

    /// Format the `UtcOffset` into the provided buffer, returning the number of bytes written.
    #[inline]
    pub(crate) const fn fmt_into_buffer(
        self,
        buf: &mut [MaybeUninit<u8>; Self::DISPLAY_BUFFER_SIZE],
    ) -> usize {
        let hours = self.hours.get().unsigned_abs();
        let minutes = self.minutes.get().unsigned_abs();
        let seconds = self.seconds.get().unsigned_abs();

        let sign = if self.is_negative() { b'-' } else { b'+' };
        buf[0] = MaybeUninit::new(sign);
        buf[3] = MaybeUninit::new(b':');
        buf[6] = MaybeUninit::new(b':');

        // Safety: `hours`, `minutes` and `seconds` are all less than 100. Both the source and
        // destination are valid for two bytes, aligned, and do not overlap.
        unsafe {
            two_digits_zero_padded(ru8::new_unchecked(hours))
                .as_ptr()
                .copy_to_nonoverlapping(buf.as_mut_ptr().add(1).cast(), 2);
            two_digits_zero_padded(ru8::new_unchecked(minutes))
                .as_ptr()
                .copy_to_nonoverlapping(buf.as_mut_ptr().add(4).cast(), 2);
            two_digits_zero_padded(ru8::new_unchecked(seconds))
                .as_ptr()
                .copy_to_nonoverlapping(buf.as_mut_ptr().add(7).cast(), 2);
        }

        // The number of bytes written does not vary; it is always 9.
        9
    }
}

impl fmt::Display for UtcOffset {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut buf = [MaybeUninit::uninit(); Self::DISPLAY_BUFFER_SIZE];
        let len = self.fmt_into_buffer(&mut buf);
        // Safety: All bytes up to `len` have been initialized with ASCII characters.
        let s = unsafe { str_from_raw_parts(buf.as_ptr().cast(), len) };
        f.pad(s)
    }
}

impl fmt::Debug for UtcOffset {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

impl Neg for UtcOffset {
    type Output = Self;

    #[inline]
    fn neg(self) -> Self::Output {
        Self::from_hms_ranged(self.hours.neg(), self.minutes.neg(), self.seconds.neg())
    }
}
