// 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::cal::coptic::CopticDateInner;
use crate::cal::Coptic;
use crate::calendar_arithmetic::{ArithmeticDate, DateFieldsResolver};
use crate::error::{
    DateError, DateFromFieldsError, EcmaReferenceYearError, MonthCodeError, UnknownEraError,
};
use crate::options::DateFromFieldsOptions;
use crate::options::{DateAddOptions, DateDifferenceOptions};
use crate::types::DateFields;
use crate::{types, Calendar, Date, RangeError};
use calendrical_calculations::rata_die::RataDie;
use tinystr::tinystr;

/// The Coptic year of the Amete Mihret epoch
const AMETE_MIHRET_OFFSET: i32 = -276;

/// The Coptic year of the Amete Alem epoch
const AMETE_ALEM_OFFSET: i32 = -5776;

/// Which era style the ethiopian calendar uses
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
#[non_exhaustive]
pub enum EthiopianEraStyle {
    /// Use the Anno Mundi era, anchored at the date of Creation, followed by the
    /// Incarnation era, anchored at the date of the Incarnation of Jesus
    AmeteMihret,
    /// Use the single Anno Mundi era, anchored at the date of Creation
    AmeteAlem,
}

/// The [Ethiopian Calendar](https://en.wikipedia.org/wiki/Ethiopian_calendar)
///
/// The Ethiopian calendar is a variant of the [`Coptic`] calendar. It differs
/// from the Coptic calendar by the names of the months as well as the era.
///
/// This implementation can be constructed in two modes: using the Amete Alem era
/// scheme, or the Amete Mihret era scheme (the default), see [`EthiopianEraStyle`]
/// for more info.
///
/// This implementation extends proleptically for dates before the calendar's creation.
///
/// This corresponds to the `"ethiopic"` and `"ethioaa"` [CLDR calendars](https://unicode.org/reports/tr35/#UnicodeCalendarIdentifier),
/// with `"ethiopic"` being for [`EthiopianEraStyle::AmeteMihret`]
///
/// # Era codes
///
/// This calendar always uses the `aa` era, where 1 Amete Alem is 5493 BCE. Dates before this era use negative years.
/// Dates before that use negative year numbers.
///
/// In the Amete Mihret scheme it uses the additional `am` era, 1 Amete Mihret is 9 CE.
///
/// # Months and days
///
/// The 13 months are called Mäskäräm (`M01`, 30 days), Ṭəqəmt (`M02`, 30 days),
/// Ḫədar (`M03`, 30 days), Taḫśaś (`M04`, 30 days), Ṭərr (`M05`, 30 days), Yäkatit (`M06`, 30 days),
/// Mägabit (`M07`, 30 days), Miyazya (`M08`, 30 days), Gənbo (`M09`, 30 days),
/// Säne (`M10`, 30 days), Ḥamle (`M11`, 30 days), Nähase (`M12`, 30 days), Ṗagʷəmen (`M13`, 5 days).
///
/// In leap years (years divisible by 4), Ṗagʷəmen gains a 6th day.
///
/// Standard years thus have 365 days, and leap years 366.
///
/// # Calendar drift
///
/// The Ethiopian calendar has the same year lengths and leap year rules as the [`Coptic`] and
/// [`Julian`](crate::cal::Julian) calendars, so it experiences the same drift of 1 day in ~128
/// years with respect to the seasons.
#[derive(Copy, Clone, Debug, Hash, Eq, PartialEq, PartialOrd, Ord)]
pub struct Ethiopian(EthiopianEraStyle);

impl Default for Ethiopian {
    fn default() -> Self {
        Self(EthiopianEraStyle::AmeteMihret)
    }
}

#[allow(missing_docs)] // not actually public
#[derive(Copy, Clone, Debug, Hash, Eq, PartialEq, PartialOrd, Ord)]
pub struct EthiopianDateInner(CopticDateInner);

impl DateFieldsResolver for Ethiopian {
    // Coptic year
    type YearInfo = i32;

    fn days_in_provided_month(year: Self::YearInfo, month: u8) -> u8 {
        Coptic::days_in_provided_month(year, month)
    }

    fn months_in_provided_year(year: Self::YearInfo) -> u8 {
        Coptic::months_in_provided_year(year)
    }

    #[inline]
    fn year_info_from_era(
        &self,
        era: &[u8],
        era_year: i32,
    ) -> Result<Self::YearInfo, UnknownEraError> {
        match (self.era_style(), era) {
            (EthiopianEraStyle::AmeteMihret, b"am") => Ok(era_year + AMETE_MIHRET_OFFSET),
            (_, b"aa") => Ok(era_year + AMETE_ALEM_OFFSET),
            (_, _) => Err(UnknownEraError),
        }
    }

    #[inline]
    fn year_info_from_extended(&self, extended_year: i32) -> Self::YearInfo {
        extended_year
            + if self.0 == EthiopianEraStyle::AmeteMihret {
                AMETE_MIHRET_OFFSET
            } else {
                AMETE_ALEM_OFFSET
            }
    }

    #[inline]
    fn reference_year_from_month_day(
        &self,
        month_code: types::ValidMonthCode,
        day: u8,
    ) -> Result<Self::YearInfo, EcmaReferenceYearError> {
        crate::cal::Coptic::reference_year_from_month_day(month_code, day)
    }

    #[inline]
    fn ordinal_month_from_code(
        &self,
        _year: &Self::YearInfo,
        month_code: types::ValidMonthCode,
        _options: DateFromFieldsOptions,
    ) -> Result<u8, MonthCodeError> {
        match month_code.to_tuple() {
            (month_number @ 1..=13, false) => Ok(month_number),
            _ => Err(MonthCodeError::NotInCalendar),
        }
    }
}

impl crate::cal::scaffold::UnstableSealed for Ethiopian {}
impl Calendar for Ethiopian {
    type DateInner = EthiopianDateInner;
    type Year = <Coptic as Calendar>::Year;
    type DifferenceError = <Coptic as Calendar>::DifferenceError;

    fn from_codes(
        &self,
        era: Option<&str>,
        year: i32,
        month_code: types::MonthCode,
        day: u8,
    ) -> Result<Self::DateInner, DateError> {
        ArithmeticDate::from_codes(era, year, month_code, day, self)
            .map(ArithmeticDate::cast)
            .map(CopticDateInner)
            .map(EthiopianDateInner)
    }

    #[cfg(feature = "unstable")]
    fn from_fields(
        &self,
        fields: DateFields,
        options: DateFromFieldsOptions,
    ) -> Result<Self::DateInner, DateFromFieldsError> {
        ArithmeticDate::from_fields(fields, options, self)
            .map(ArithmeticDate::cast)
            .map(CopticDateInner)
            .map(EthiopianDateInner)
    }

    fn from_rata_die(&self, rd: RataDie) -> Self::DateInner {
        EthiopianDateInner(Coptic.from_rata_die(rd))
    }

    fn to_rata_die(&self, date: &Self::DateInner) -> RataDie {
        Coptic.to_rata_die(&date.0)
    }

    fn has_cheap_iso_conversion(&self) -> bool {
        false
    }

    fn months_in_year(&self, date: &Self::DateInner) -> u8 {
        Coptic.months_in_year(&date.0)
    }

    fn days_in_year(&self, date: &Self::DateInner) -> u16 {
        Coptic.days_in_year(&date.0)
    }

    fn days_in_month(&self, date: &Self::DateInner) -> u8 {
        Coptic.days_in_month(&date.0)
    }

    #[cfg(feature = "unstable")]
    fn add(
        &self,
        date: &Self::DateInner,
        duration: types::DateDuration,
        options: DateAddOptions,
    ) -> Result<Self::DateInner, DateError> {
        Coptic
            .add(&date.0, duration, options)
            .map(EthiopianDateInner)
    }

    #[cfg(feature = "unstable")]
    fn until(
        &self,
        date1: &Self::DateInner,
        date2: &Self::DateInner,
        options: DateDifferenceOptions,
    ) -> Result<types::DateDuration, Self::DifferenceError> {
        Coptic.until(&date1.0, &date2.0, options)
    }

    fn year_info(&self, date: &Self::DateInner) -> Self::Year {
        let coptic_year = date.0 .0.year;
        let extended_year = if self.0 == EthiopianEraStyle::AmeteAlem {
            coptic_year - AMETE_ALEM_OFFSET
        } else {
            coptic_year - AMETE_MIHRET_OFFSET
        };

        if self.0 == EthiopianEraStyle::AmeteAlem || extended_year <= 0 {
            types::EraYear {
                era: tinystr!(16, "aa"),
                era_index: Some(0),
                year: coptic_year - AMETE_ALEM_OFFSET,
                extended_year,
                ambiguity: types::YearAmbiguity::CenturyRequired,
            }
        } else {
            types::EraYear {
                era: tinystr!(16, "am"),
                era_index: Some(1),
                year: coptic_year - AMETE_MIHRET_OFFSET,
                extended_year,
                ambiguity: types::YearAmbiguity::CenturyRequired,
            }
        }
    }

    fn is_in_leap_year(&self, date: &Self::DateInner) -> bool {
        Coptic.is_in_leap_year(&date.0)
    }

    fn month(&self, date: &Self::DateInner) -> types::MonthInfo {
        Coptic.month(&date.0)
    }

    fn day_of_month(&self, date: &Self::DateInner) -> types::DayOfMonth {
        Coptic.day_of_month(&date.0)
    }

    fn day_of_year(&self, date: &Self::DateInner) -> types::DayOfYear {
        Coptic.day_of_year(&date.0)
    }

    fn debug_name(&self) -> &'static str {
        "Ethiopian"
    }

    fn calendar_algorithm(&self) -> Option<crate::preferences::CalendarAlgorithm> {
        Some(crate::preferences::CalendarAlgorithm::Ethiopic)
    }
}

impl Ethiopian {
    /// Construct a new Ethiopian Calendar for the Amete Mihret era naming scheme
    pub const fn new() -> Self {
        Self(EthiopianEraStyle::AmeteMihret)
    }

    /// Construct a new Ethiopian Calendar with an explicit [`EthiopianEraStyle`].
    pub const fn new_with_era_style(era_style: EthiopianEraStyle) -> Self {
        Self(era_style)
    }

    /// Returns the [`EthiopianEraStyle`] used by this calendar.
    pub fn era_style(&self) -> EthiopianEraStyle {
        self.0
    }
}

impl Date<Ethiopian> {
    /// Construct new Ethiopian Date.
    ///
    /// ```rust
    /// use icu::calendar::cal::EthiopianEraStyle;
    /// use icu::calendar::Date;
    ///
    /// let date_ethiopian =
    ///     Date::try_new_ethiopian(EthiopianEraStyle::AmeteMihret, 2014, 8, 25)
    ///         .expect("Failed to initialize Ethopic Date instance.");
    ///
    /// assert_eq!(date_ethiopian.era_year().year, 2014);
    /// assert_eq!(date_ethiopian.month().ordinal, 8);
    /// assert_eq!(date_ethiopian.day_of_month().0, 25);
    /// ```
    pub fn try_new_ethiopian(
        era_style: EthiopianEraStyle,
        year: i32,
        month: u8,
        day: u8,
    ) -> Result<Date<Ethiopian>, RangeError> {
        let year = Ethiopian(era_style).year_info_from_extended(year);
        ArithmeticDate::try_from_ymd(year, month, day)
            .map(CopticDateInner)
            .map(EthiopianDateInner)
            .map(|inner| Date::from_raw(inner, Ethiopian(era_style)))
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_leap_year() {
        // 11th September 2023 in gregorian is 6/13/2015 in ethiopian
        let iso_date = Date::try_new_iso(2023, 9, 11).unwrap();
        let date_ethiopian = Date::new_from_iso(iso_date, Ethiopian::new());
        assert_eq!(date_ethiopian.extended_year(), 2015);
        assert_eq!(date_ethiopian.month().ordinal, 13);
        assert_eq!(date_ethiopian.day_of_month().0, 6);
    }

    #[test]
    fn test_iso_to_ethiopian_conversion_and_back() {
        let iso_date = Date::try_new_iso(1970, 1, 2).unwrap();
        let date_ethiopian = Date::new_from_iso(iso_date, Ethiopian::new());

        assert_eq!(date_ethiopian.extended_year(), 1962);
        assert_eq!(date_ethiopian.month().ordinal, 4);
        assert_eq!(date_ethiopian.day_of_month().0, 24);

        assert_eq!(
            date_ethiopian.to_iso(),
            Date::try_new_iso(1970, 1, 2).unwrap()
        );
    }

    #[test]
    fn test_iso_to_ethiopian_aa_conversion_and_back() {
        let iso_date = Date::try_new_iso(1970, 1, 2).unwrap();
        let date_ethiopian = Date::new_from_iso(iso_date, Ethiopian(EthiopianEraStyle::AmeteAlem));

        assert_eq!(date_ethiopian.extended_year(), 7462);
        assert_eq!(date_ethiopian.month().ordinal, 4);
        assert_eq!(date_ethiopian.day_of_month().0, 24);

        assert_eq!(
            date_ethiopian.to_iso(),
            Date::try_new_iso(1970, 1, 2).unwrap()
        );
    }

    #[test]
    fn test_roundtrip_negative() {
        // https://github.com/unicode-org/icu4x/issues/2254
        let iso_date = Date::try_new_iso(-1000, 3, 3).unwrap();
        let ethiopian = iso_date.to_calendar(Ethiopian::new());
        let recovered_iso = ethiopian.to_iso();
        assert_eq!(iso_date, recovered_iso);
    }

    #[test]
    fn extended_year() {
        assert_eq!(
            Date::new_from_iso(
                Date::try_new_iso(-5500 + 9, 1, 1).unwrap(),
                Ethiopian(EthiopianEraStyle::AmeteAlem)
            )
            .extended_year(),
            1
        );
        assert_eq!(
            Date::new_from_iso(
                Date::try_new_iso(9, 1, 1).unwrap(),
                Ethiopian(EthiopianEraStyle::AmeteAlem)
            )
            .extended_year(),
            5501
        );

        assert_eq!(
            Date::new_from_iso(
                Date::try_new_iso(-5500 + 9, 1, 1).unwrap(),
                Ethiopian(EthiopianEraStyle::AmeteMihret)
            )
            .extended_year(),
            -5499
        );
        assert_eq!(
            Date::new_from_iso(
                Date::try_new_iso(9, 1, 1).unwrap(),
                Ethiopian(EthiopianEraStyle::AmeteMihret)
            )
            .extended_year(),
            1
        );
    }
}