// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::error::InvalidOffsetError;
use core::str::FromStr;

/// An offset from Coordinated Universal Time (UTC)
#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
pub struct UtcOffset(i32);

impl UtcOffset {
    /// Attempt to create a [`UtcOffset`] from a seconds input.
    ///
    /// Returns [`InvalidOffsetError`] if the seconds are out of bounds.
    pub fn try_from_seconds(seconds: i32) -> Result<Self, InvalidOffsetError> {
        if seconds.unsigned_abs() > 18 * 60 * 60 {
            Err(InvalidOffsetError)
        } else {
            Ok(Self(seconds))
        }
    }

    /// Creates a [`UtcOffset`] from eighths of an hour.
    ///
    /// This is chosen because eighths of an hour cover all current time zones
    /// and all values of i8 are within range of this type.
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::timezone::UtcOffset;
    ///
    /// assert_eq!(
    ///     UtcOffset::try_from_str("-0600").unwrap(),
    ///     UtcOffset::from_eighths_of_hour(-6 * 8),
    /// );
    /// ```
    pub const fn from_eighths_of_hour(eighths_of_hour: i8) -> Self {
        Self(eighths_of_hour as i32 * 450)
    }

    /// Creates a [`UtcOffset`] of zero.
    pub const fn zero() -> Self {
        Self(0)
    }

    /// Parse a [`UtcOffset`] from bytes.
    ///
    /// The offset must range from UTC-12 to UTC+14.
    ///
    /// The string must be an ISO-8601 time zone designator:
    /// e.g. Z
    /// e.g. +05
    /// e.g. +0500
    /// e.g. +05:00
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::timezone::UtcOffset;
    ///
    /// let offset0: UtcOffset = UtcOffset::try_from_str("Z").unwrap();
    /// let offset1: UtcOffset = UtcOffset::try_from_str("+05").unwrap();
    /// let offset2: UtcOffset = UtcOffset::try_from_str("+0500").unwrap();
    /// let offset3: UtcOffset = UtcOffset::try_from_str("-05:00").unwrap();
    ///
    /// let offset_err0 =
    ///     UtcOffset::try_from_str("0500").expect_err("Invalid input");
    /// let offset_err1 =
    ///     UtcOffset::try_from_str("+05000").expect_err("Invalid input");
    ///
    /// assert_eq!(offset0.to_seconds(), 0);
    /// assert_eq!(offset1.to_seconds(), 18000);
    /// assert_eq!(offset2.to_seconds(), 18000);
    /// assert_eq!(offset3.to_seconds(), -18000);
    /// ```
    #[inline]
    pub fn try_from_str(s: &str) -> Result<Self, InvalidOffsetError> {
        Self::try_from_utf8(s.as_bytes())
    }

    /// See [`Self::try_from_str`]
    pub fn try_from_utf8(mut code_units: &[u8]) -> Result<Self, InvalidOffsetError> {
        fn try_get_time_component([tens, ones]: [u8; 2]) -> Option<i32> {
            Some(((tens as char).to_digit(10)? * 10 + (ones as char).to_digit(10)?) as i32)
        }

        let offset_sign = match code_units {
            [b'+', rest @ ..] => {
                code_units = rest;
                1
            }
            [b'-', rest @ ..] => {
                code_units = rest;
                -1
            }
            // Unicode minus ("\u{2212}" == [226, 136, 146])
            [226, 136, 146, rest @ ..] => {
                code_units = rest;
                -1
            }
            [b'Z'] => return Ok(Self(0)),
            _ => return Err(InvalidOffsetError),
        };

        let hours = match code_units {
            &[h1, h2, ..] => try_get_time_component([h1, h2]),
            _ => None,
        }
        .ok_or(InvalidOffsetError)?;

        let minutes = match code_units {
            /* ±hh */
            &[_, _] => Some(0),
            /* ±hhmm, ±hh:mm */
            &[_, _, m1, m2] | &[_, _, b':', m1, m2] => {
                try_get_time_component([m1, m2]).filter(|&m| m < 60)
            }
            _ => None,
        }
        .ok_or(InvalidOffsetError)?;

        Self::try_from_seconds(offset_sign * (hours * 60 + minutes) * 60)
    }

    /// Create a [`UtcOffset`] from a seconds input without checking bounds.
    #[inline]
    pub fn from_seconds_unchecked(seconds: i32) -> Self {
        Self(seconds)
    }

    /// Returns the raw offset value in seconds.
    pub fn to_seconds(self) -> i32 {
        self.0
    }

    /// Returns the raw offset value in eights of an hour (7.5 minute units).
    pub fn to_eighths_of_hour(self) -> i8 {
        (self.0 / 450) as i8
    }

    /// Whether the [`UtcOffset`] is non-negative.
    pub fn is_non_negative(self) -> bool {
        self.0 >= 0
    }

    /// Whether the [`UtcOffset`] is zero.
    pub fn is_zero(self) -> bool {
        self.0 == 0
    }

    /// Returns the hours part of if the [`UtcOffset`]
    pub fn hours_part(self) -> i32 {
        self.0 / 3600
    }

    /// Returns the minutes part of if the [`UtcOffset`].
    pub fn minutes_part(self) -> u32 {
        (self.0 % 3600 / 60).unsigned_abs()
    }

    /// Returns the seconds part of if the [`UtcOffset`].
    pub fn seconds_part(self) -> u32 {
        (self.0 % 60).unsigned_abs()
    }
}

impl FromStr for UtcOffset {
    type Err = InvalidOffsetError;

    #[inline]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::try_from_str(s)
    }
}

/// A time zone variant, representing the currently observed relative offset.
///
/// The semantics vary from time zone to time zone and could represent concepts
/// such as Standard time, Daylight time, Summer time, or Ramadan time.
#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
#[zerovec::make_ule(ZoneVariantULE)]
#[repr(u8)]
#[cfg_attr(feature = "datagen", derive(serde::Serialize, databake::Bake))]
#[cfg_attr(feature = "datagen", databake(path = icu_timezone))]
#[cfg_attr(feature = "serde", derive(serde::Deserialize))]
#[non_exhaustive]
pub enum ZoneVariant {
    /// The variant corresponding to `"standard"` in CLDR.
    ///
    /// The semantics vary from time zone to time zone. The time zone display
    /// name of this variant may or may not be called "Standard Time".
    Standard = 0,
    /// The variant corresponding to `"daylight"` in CLDR.
    ///
    /// The semantics vary from time zone to time zone. The time zone display
    /// name of this variant may or may not be called "Daylight Time".
    Daylight = 1,
}