// 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::any_calendar::AnyCalendarKind;

use crate::{types, CalendarError, Date, DateDuration, DateDurationUnit, Iso};

use core::fmt;

/// A calendar implementation

///

/// Only implementors of [`Calendar`] should care about these methods, in general users of

/// these calendars should use the methods on [`Date`] instead.

///

/// Individual [`Calendar`] implementations may have inherent utility methods

/// allowing for direct construction, etc.

///

/// For ICU4X 1.0, implementing this trait or calling methods directly is considered

/// unstable and prone to change, especially for `offset_date()` and `until()`.

pub trait Calendar {

    /// The internal type used to represent dates

    type DateInner: PartialEq + Eq + Clone + fmt::Debug;

    /// Construct a date from era/month codes and fields

    fn date_from_codes(

        &self,

        era: types::Era,

        year: i32,

        month_code: types::MonthCode,

        day: u8,

    ) -> Result<Self::DateInner, CalendarError>;

    /// Construct the date from an ISO date

    fn date_from_iso(&self, iso: Date<Iso>) -> Self::DateInner;

    /// Obtain an ISO date from this date

    fn date_to_iso(&self, date: &Self::DateInner) -> Date<Iso>;

    // fn validate_date(&self, e: Era, y: Year, m: MonthCode, d: Day) -> bool;

    // // similar validators for YearMonth, etc

    // fn is_leap<A: AsCalendar<Calendar = Self>>(&self, date: &Date<A>) -> bool;

    /// Count the number of months in a given year, specified by providing a date

    /// from that year

    fn months_in_year(&self, date: &Self::DateInner) -> u8;

    /// Count the number of days in a given year, specified by providing a date

    /// from that year

    fn days_in_year(&self, date: &Self::DateInner) -> u16;

    /// Count the number of days in a given month, specified by providing a date

    /// from that year/month

    fn days_in_month(&self, date: &Self::DateInner) -> u8;

    /// Calculate the day of the week and return it

    fn day_of_week(&self, date: &Self::DateInner) -> types::IsoWeekday {

        self.date_to_iso(date).day_of_week()

    }

Unexecuted instantiation: <icu_calendar::any_calendar::AnyCalendar as icu_calendar::calendar::Calendar>::day_of_week

Unexecuted instantiation: <icu_calendar::gregorian::Gregorian as icu_calendar::calendar::Calendar>::day_of_week

Unexecuted instantiation: <_ as icu_calendar::calendar::Calendar>::day_of_week

    // fn week_of_year(&self, date: &Self::DateInner) -> u8;

    #[doc(hidden)] // unstable

    /// Add `offset` to `date`

    fn offset_date(&self, date: &mut Self::DateInner, offset: DateDuration<Self>);

    #[doc(hidden)] // unstable

    /// Calculate `date2 - date` as a duration

    ///

    /// `calendar2` is the calendar object associated with `date2`. In case the specific calendar objects

    /// differ on data, the data for the first calendar is used, and `date2` may be converted if necessary.

    fn until(

        &self,

        date1: &Self::DateInner,

        date2: &Self::DateInner,

        calendar2: &Self,

        largest_unit: DateDurationUnit,

        smallest_unit: DateDurationUnit,

    ) -> DateDuration<Self>;

    /// Obtain a name for the calendar for debug printing

    fn debug_name(&self) -> &'static str;

    // fn since(&self, from: &Date<Self>, to: &Date<Self>) -> Duration<Self>, Error;

    /// The calendar-specific year represented by `date`

    fn year(&self, date: &Self::DateInner) -> types::FormattableYear;

    /// Calculate if a date is in a leap year

    fn is_in_leap_year(&self, date: &Self::DateInner) -> bool;

    /// The calendar-specific month represented by `date`

    fn month(&self, date: &Self::DateInner) -> types::FormattableMonth;

    /// The calendar-specific day-of-month represented by `date`

    fn day_of_month(&self, date: &Self::DateInner) -> types::DayOfMonth;

    /// Information of the day of the year

    fn day_of_year_info(&self, date: &Self::DateInner) -> types::DayOfYearInfo;

    /// The [`AnyCalendarKind`] corresponding to this calendar,

    /// if one exists. Implementors outside of `icu::calendar` should return `None`

    fn any_calendar_kind(&self) -> Option<AnyCalendarKind> {

        None

    }

}