// 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::{AnyCalendar, IntoAnyCalendar};
use crate::error::{DateError, DateFromFieldsError};
use crate::options::DateFromFieldsOptions;
use crate::options::{DateAddOptions, DateDifferenceOptions};
use crate::types::{CyclicYear, EraYear, IsoWeekOfYear};
use crate::week::{RelativeUnit, WeekCalculator, WeekOf};
use crate::{types, Calendar, Iso};
#[cfg(feature = "alloc")]
use alloc::rc::Rc;
#[cfg(feature = "alloc")]
use alloc::sync::Arc;
use calendrical_calculations::rata_die::RataDie;
use core::fmt;
use core::ops::Deref;

/// Types that contain a calendar
///
/// This allows one to use [`Date`] with wrappers around calendars,
/// e.g. reference counted calendars.
pub trait AsCalendar {
    /// The calendar being wrapped
    type Calendar: Calendar;
    /// Obtain the inner calendar
    fn as_calendar(&self) -> &Self::Calendar;
}

impl<C: Calendar> AsCalendar for C {
    type Calendar = C;
    #[inline]
    fn as_calendar(&self) -> &Self {
        self
    }
}

#[cfg(feature = "alloc")]
/// ✨ *Enabled with the `alloc` Cargo feature.*
impl<C: AsCalendar> AsCalendar for Rc<C> {
    type Calendar = C::Calendar;
    #[inline]
    fn as_calendar(&self) -> &Self::Calendar {
        self.as_ref().as_calendar()
    }
}

#[cfg(feature = "alloc")]
/// ✨ *Enabled with the `alloc` Cargo feature.*
impl<C: AsCalendar> AsCalendar for Arc<C> {
    type Calendar = C::Calendar;
    #[inline]
    fn as_calendar(&self) -> &Self::Calendar {
        self.as_ref().as_calendar()
    }
}

/// This exists as a wrapper around `&'a T` so that
/// `Date<&'a C>` is possible for calendar `C`.
///
/// Unfortunately,
/// [`AsCalendar`] cannot be implemented on `&'a T` directly because
/// `&'a T` is `#[fundamental]` and the impl would clash with the one above with
/// `AsCalendar` for `C: Calendar`.
///
/// Use `Date<Ref<'a, C>>` where you would use `Date<&'a C>`
#[allow(clippy::exhaustive_structs)] // newtype
#[derive(PartialEq, Eq, Debug)]
pub struct Ref<'a, C>(pub &'a C);

impl<C> Copy for Ref<'_, C> {}

impl<C> Clone for Ref<'_, C> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<C: AsCalendar> AsCalendar for Ref<'_, C> {
    type Calendar = C::Calendar;
    #[inline]
    fn as_calendar(&self) -> &Self::Calendar {
        self.0.as_calendar()
    }
}

impl<C> Deref for Ref<'_, C> {
    type Target = C;
    fn deref(&self) -> &C {
        self.0
    }
}

/// A date for a given calendar.
///
/// **The primary definition of this type is in the [`icu_calendar`](https://docs.rs/icu_calendar) crate. Other ICU4X crates re-export it for convenience.**
///
/// This can work with wrappers around [`Calendar`] types,
/// e.g. `Rc<C>`, via the [`AsCalendar`] trait.
///
/// This can be constructed  constructed
/// from its fields via [`Self::try_new_from_codes()`], or can be constructed with one of the
/// `new_<calendar>_date()` per-calendar methods (and then freely converted between calendars).
///
/// ```rust
/// use icu::calendar::Date;
///
/// // Example: creation of ISO date from integers.
/// let date_iso = Date::try_new_iso(1970, 1, 2)
///     .expect("Failed to initialize ISO Date instance.");
///
/// assert_eq!(date_iso.era_year().year, 1970);
/// assert_eq!(date_iso.month().ordinal, 1);
/// assert_eq!(date_iso.day_of_month().0, 2);
/// ```
pub struct Date<A: AsCalendar> {
    pub(crate) inner: <A::Calendar as Calendar>::DateInner,
    pub(crate) calendar: A,
}

impl<A: AsCalendar> Date<A> {
    /// Construct a date from from era/month codes and fields, and some calendar representation
    ///
    /// The year is `extended_year` if no era is provided.
    ///
    /// This function will not accept year/extended_year values that are outside of the range `[-2²⁷, 2²⁷]`,
    /// regardless of the calendar, instead returning a [`DateError::Range`]. See [`Date::try_from_fields()`] for more
    /// information.
    #[inline]
    pub fn try_new_from_codes(
        era: Option<&str>,
        year: i32,
        month_code: types::MonthCode,
        day: u8,
        calendar: A,
    ) -> Result<Self, DateError> {
        let inner = calendar
            .as_calendar()
            .from_codes(era, year, month_code, day)?;
        Ok(Date { inner, calendar })
    }

    /// Construct a date from from a bag of fields.
    ///
    /// This function allows specifying the year as either extended year or era + era year,
    /// and the month as either ordinal or month code. It can constrain out-of-bounds values
    /// and fill in missing fields. See [`DateFromFieldsOptions`] for more information.
    ///
    /// This function will not accept year/extended_year values that are outside of the range `[-2²⁷, 2²⁷]`,
    /// regardless of the calendar, instead returning a [`DateFromFieldsError::Range`]. This allows us to to keep
    /// all operations on [`Date`]s infallible by staying clear of integer limits.
    /// Currently, calendar-specific `Date::try_new_calendarname()` constructors
    /// do not do this, and it is possible to obtain such extreme dates via calendar conversion or arithmetic,
    /// though [we may change that behavior in the future](https://github.com/unicode-org/icu4x/issues/7076).
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::calendar::cal::Gregorian;
    /// use icu::calendar::types::DateFields;
    /// use icu::calendar::Date;
    ///
    /// let mut fields = DateFields::default();
    /// fields.extended_year = Some(2000);
    /// fields.ordinal_month = Some(1);
    /// fields.day = Some(1);
    ///
    /// let d1 = Date::try_from_fields(fields, Default::default(), Gregorian)
    ///     .expect("Jan 1 in year 2000");
    ///
    /// let d2 = Date::try_new_gregorian(2000, 1, 1).unwrap();
    /// assert_eq!(d1, d2);
    /// ```
    ///
    /// See [`DateFromFieldsError`] for examples of error conditions.
    ///
    /// <div class="stab unstable">
    /// 🚧 This code is considered unstable; it may change at any time, in breaking or non-breaking ways,
    /// including in SemVer minor releases. Do not use this type unless you are prepared for things to occasionally break.
    ///
    /// Graduation tracking issue: [issue #7161](https://github.com/unicode-org/icu4x/issues/7161).
    /// </div>
    ///
    /// ✨ *Enabled with the `unstable` Cargo feature.*
    #[cfg(feature = "unstable")]
    #[inline]
    pub fn try_from_fields(
        fields: types::DateFields,
        options: DateFromFieldsOptions,
        calendar: A,
    ) -> Result<Self, DateFromFieldsError> {
        let inner = calendar.as_calendar().from_fields(fields, options)?;
        Ok(Date { inner, calendar })
    }

    /// Construct a date from a [`RataDie`] and some calendar representation
    #[inline]
    pub fn from_rata_die(rd: RataDie, calendar: A) -> Self {
        Date {
            inner: calendar.as_calendar().from_rata_die(rd),
            calendar,
        }
    }

    /// Convert the date to a [`RataDie`]
    #[inline]
    pub fn to_rata_die(&self) -> RataDie {
        self.calendar.as_calendar().to_rata_die(self.inner())
    }

    /// Construct a date from an ISO date and some calendar representation
    #[inline]
    pub fn new_from_iso(iso: Date<Iso>, calendar: A) -> Self {
        iso.to_calendar(calendar)
    }

    /// Convert the Date to an ISO Date
    #[inline]
    pub fn to_iso(&self) -> Date<Iso> {
        self.to_calendar(Iso)
    }

    /// Convert the Date to a date in a different calendar
    #[inline]
    pub fn to_calendar<A2: AsCalendar>(&self, calendar: A2) -> Date<A2> {
        let c1 = self.calendar.as_calendar();
        let c2 = calendar.as_calendar();
        let inner = if c1.has_cheap_iso_conversion() && c2.has_cheap_iso_conversion() {
            c2.from_iso(c1.to_iso(self.inner()))
        } else {
            c2.from_rata_die(c1.to_rata_die(self.inner()))
        };
        Date { inner, calendar }
    }

    /// The number of months in the year of this date
    #[inline]
    pub fn months_in_year(&self) -> u8 {
        self.calendar.as_calendar().months_in_year(self.inner())
    }

    /// The number of days in the year of this date
    #[inline]
    pub fn days_in_year(&self) -> u16 {
        self.calendar.as_calendar().days_in_year(self.inner())
    }

    /// The number of days in the month of this date
    #[inline]
    pub fn days_in_month(&self) -> u8 {
        self.calendar.as_calendar().days_in_month(self.inner())
    }

    /// The day of the week for this date
    #[inline]
    pub fn day_of_week(&self) -> types::Weekday {
        self.to_rata_die().into()
    }

    /// Add a `duration` to this date, mutating it
    ///
    /// <div class="stab unstable">
    /// 🚧 This code is considered unstable; it may change at any time, in breaking or non-breaking ways,
    /// including in SemVer minor releases. Do not use this type unless you are prepared for things to occasionally break.
    ///
    /// Graduation tracking issue: [issue #3964](https://github.com/unicode-org/icu4x/issues/3964).
    /// </div>
    ///
    /// ✨ *Enabled with the `unstable` Cargo feature.*
    #[cfg(feature = "unstable")]
    #[inline]
    pub fn try_add_with_options(
        &mut self,
        duration: types::DateDuration,
        options: DateAddOptions,
    ) -> Result<(), DateError> {
        let inner = self
            .calendar
            .as_calendar()
            .add(&self.inner, duration, options)?;
        self.inner = inner;
        Ok(())
    }

    /// Add a `duration` to this date, returning the new one
    ///
    /// <div class="stab unstable">
    /// 🚧 This code is considered unstable; it may change at any time, in breaking or non-breaking ways,
    /// including in SemVer minor releases. Do not use this type unless you are prepared for things to occasionally break.
    ///
    /// Graduation tracking issue: [issue #3964](https://github.com/unicode-org/icu4x/issues/3964).
    /// </div>
    ///
    /// ✨ *Enabled with the `unstable` Cargo feature.*
    #[cfg(feature = "unstable")]
    #[inline]
    pub fn try_added_with_options(
        mut self,
        duration: types::DateDuration,
        options: DateAddOptions,
    ) -> Result<Self, DateError> {
        self.try_add_with_options(duration, options)?;
        Ok(self)
    }

    /// Calculating the duration between `other - self`
    ///
    /// Although this returns a [`Result`], with most fixed calendars, this operation can't fail.
    /// In such cases, the error type is [`Infallible`], and the inner value can be safely
    /// unwrapped using [`Result::into_ok()`], which is available in nightly Rust as of this
    /// writing. In stable Rust, the value can be unwrapped using [pattern matching].
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::calendar::types::DateDuration;
    /// use icu::calendar::Date;
    ///
    /// let d1 = Date::try_new_iso(2020, 1, 1).unwrap();
    /// let d2 = Date::try_new_iso(2025, 10, 2).unwrap();
    /// let options = Default::default();
    ///
    /// // The value can be unwrapped with destructuring syntax:
    /// let Ok(duration) = d1.try_until_with_options(&d2, options);
    ///
    /// assert_eq!(duration, DateDuration::for_days(2101));
    /// ```
    ///
    /// [`Infallible`]: core::convert::Infallible
    /// [pattern matching]: https://doc.rust-lang.org/book/ch19-03-pattern-syntax.html
    ///
    /// <div class="stab unstable">
    /// 🚧 This code is considered unstable; it may change at any time, in breaking or non-breaking ways,
    /// including in SemVer minor releases. Do not use this type unless you are prepared for things to occasionally break.
    ///
    /// Graduation tracking issue: [issue #3964](https://github.com/unicode-org/icu4x/issues/3964).
    /// </div>
    ///
    /// ✨ *Enabled with the `unstable` Cargo feature.*
    #[cfg(feature = "unstable")]
    #[inline]
    pub fn try_until_with_options<B: AsCalendar<Calendar = A::Calendar>>(
        &self,
        other: &Date<B>,
        options: DateDifferenceOptions,
    ) -> Result<types::DateDuration, <A::Calendar as Calendar>::DifferenceError> {
        self.calendar
            .as_calendar()
            .until(self.inner(), other.inner(), options)
    }

    /// The calendar-specific year-info.
    ///
    /// This returns an enum, see [`Date::era_year()`] and [`Date::cyclic_year()`] which are available
    /// for concrete calendar types and return concrete types.
    #[inline]
    pub fn year(&self) -> types::YearInfo {
        self.calendar.as_calendar().year_info(&self.inner).into()
    }

    /// The "extended year".
    ///
    /// This year number can be used when you need a simple numeric representation
    /// of the year, and can be meaningfully compared with extended years from other
    /// eras or used in arithmetic.
    ///
    /// For calendars defined in Temporal, this will match the "arithmetic year"
    /// as defined in <https://tc39.es/proposal-intl-era-monthcode/>.
    /// This is typically anchored with year 1 as the year 1 of either the most modern or
    /// otherwise some "major" era for the calendar.
    ///
    /// See [`Self::year()`] for more information about the year.
    #[inline]
    pub fn extended_year(&self) -> i32 {
        self.year().extended_year()
    }

    /// Returns whether `self` is in a calendar-specific leap year
    #[inline]
    pub fn is_in_leap_year(&self) -> bool {
        self.calendar.as_calendar().is_in_leap_year(&self.inner)
    }

    /// The calendar-specific month represented by `self`
    #[inline]
    pub fn month(&self) -> types::MonthInfo {
        self.calendar.as_calendar().month(&self.inner)
    }

    /// The calendar-specific day-of-month represented by `self`
    #[inline]
    pub fn day_of_month(&self) -> types::DayOfMonth {
        self.calendar.as_calendar().day_of_month(&self.inner)
    }

    /// The calendar-specific day-of-month represented by `self`
    #[inline]
    pub fn day_of_year(&self) -> types::DayOfYear {
        self.calendar.as_calendar().day_of_year(&self.inner)
    }

    /// Construct a date from raw values for a given calendar. This does not check any
    /// invariants for the date and calendar, and should only be called by calendar implementations.
    ///
    /// Calling this outside of calendar implementations is sound, but calendar implementations are not
    /// expected to do anything sensible with such invalid dates.
    ///
    /// AnyCalendar *will* panic if AnyCalendar [`Date`] objects with mismatching
    /// date and calendar types are constructed
    #[inline]
    pub fn from_raw(inner: <A::Calendar as Calendar>::DateInner, calendar: A) -> Self {
        Self { inner, calendar }
    }

    /// Get the inner date implementation. Should not be called outside of calendar implementations
    #[inline]
    pub fn inner(&self) -> &<A::Calendar as Calendar>::DateInner {
        &self.inner
    }

    /// Get a reference to the contained calendar
    #[inline]
    pub fn calendar(&self) -> &A::Calendar {
        self.calendar.as_calendar()
    }

    /// Get a reference to the contained calendar wrapper
    ///
    /// (Useful in case the user wishes to e.g. clone an Rc)
    #[inline]
    pub fn calendar_wrapper(&self) -> &A {
        &self.calendar
    }
}

impl<A: AsCalendar<Calendar = C>, C: Calendar<Year = EraYear>> Date<A> {
    /// Returns information about the era for calendars using eras.
    pub fn era_year(&self) -> EraYear {
        self.calendar.as_calendar().year_info(self.inner())
    }
}

impl<A: AsCalendar<Calendar = C>, C: Calendar<Year = CyclicYear>> Date<A> {
    /// Returns information about the year cycle, for cyclic calendars.
    pub fn cyclic_year(&self) -> CyclicYear {
        self.calendar.as_calendar().year_info(self.inner())
    }
}

impl Date<Iso> {
    /// The ISO week of the year containing this date.
    ///
    /// # Examples
    ///
    /// ```
    /// use icu::calendar::types::IsoWeekOfYear;
    /// use icu::calendar::Date;
    ///
    /// let date = Date::try_new_iso(2022, 8, 26).unwrap();
    ///
    /// assert_eq!(
    ///     date.week_of_year(),
    ///     IsoWeekOfYear {
    ///         week_number: 34,
    ///         iso_year: 2022,
    ///     }
    /// );
    /// ```
    pub fn week_of_year(&self) -> IsoWeekOfYear {
        let week_of = WeekCalculator::ISO
            .week_of(
                365 + calendrical_calculations::gregorian::is_leap_year(self.inner.0.year - 1)
                    as u16,
                self.days_in_year(),
                self.day_of_year().0,
                self.day_of_week(),
            )
            .unwrap_or_else(|_| {
                // ISO calendar has more than 14 days per year
                debug_assert!(false);
                WeekOf {
                    week: 1,
                    unit: crate::week::RelativeUnit::Current,
                }
            });

        IsoWeekOfYear {
            week_number: week_of.week,
            iso_year: match week_of.unit {
                RelativeUnit::Current => self.inner.0.year,
                RelativeUnit::Next => self.inner.0.year + 1,
                RelativeUnit::Previous => self.inner.0.year - 1,
            },
        }
    }
}

impl<C: IntoAnyCalendar> Date<C> {
    /// Type-erase the date, converting it to a date for [`AnyCalendar`]
    pub fn to_any(self) -> Date<AnyCalendar> {
        Date::from_raw(
            self.calendar.date_to_any(&self.inner),
            self.calendar.to_any(),
        )
    }
}

impl<A: AsCalendar> Date<A> {
    /// Wrap the contained calendar type in `Rc<T>`, making it cheaper to clone.
    ///
    /// Useful when paired with [`Self::to_any()`] to obtain a `Date<Rc<AnyCalendar>>`
    ///
    /// ✨ *Enabled with the `alloc` Cargo feature.*
    #[cfg(feature = "alloc")]
    pub fn into_ref_counted(self) -> Date<Rc<A>> {
        Date::from_raw(self.inner, Rc::new(self.calendar))
    }

    /// Wrap the contained calendar type in `Arc<T>`, making it cheaper to clone in a thread-safe manner.
    ///
    /// Useful when paired with [`Self::to_any()`] to obtain a `Date<Arc<AnyCalendar>>`
    ///
    /// ✨ *Enabled with the `alloc` Cargo feature.*
    #[cfg(feature = "alloc")]
    pub fn into_atomic_ref_counted(self) -> Date<Arc<A>> {
        Date::from_raw(self.inner, Arc::new(self.calendar))
    }

    /// Wrap the calendar type in `Ref<T>`, making it cheaper to clone (by introducing a borrow)
    ///
    /// Useful for converting a `&Date<C>` into an equivalent `Date<D>` without cloning
    /// the calendar.
    pub fn as_borrowed(&self) -> Date<Ref<'_, A>> {
        Date::from_raw(self.inner, Ref(&self.calendar))
    }
}

impl<C, A, B> PartialEq<Date<B>> for Date<A>
where
    C: Calendar,
    A: AsCalendar<Calendar = C>,
    B: AsCalendar<Calendar = C>,
{
    fn eq(&self, other: &Date<B>) -> bool {
        self.inner.eq(&other.inner)
    }
}

impl<A: AsCalendar> Eq for Date<A> {}

impl<C, A, B> PartialOrd<Date<B>> for Date<A>
where
    C: Calendar,
    A: AsCalendar<Calendar = C>,
    B: AsCalendar<Calendar = C>,
{
    fn partial_cmp(&self, other: &Date<B>) -> Option<core::cmp::Ordering> {
        self.inner.partial_cmp(&other.inner)
    }
}

impl<C, A> Ord for Date<A>
where
    C: Calendar,
    C::DateInner: Ord,
    A: AsCalendar<Calendar = C>,
{
    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
        self.inner.cmp(&other.inner)
    }
}

impl<A: AsCalendar> fmt::Debug for Date<A> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        let month = self.month().ordinal;
        let day = self.day_of_month().0;
        let calendar = self.calendar.as_calendar().debug_name();
        match self.year() {
            types::YearInfo::Era(EraYear { year, era, .. }) => {
                write!(
                    f,
                    "Date({year}-{month}-{day}, {era} era, for calendar {calendar})"
                )
            }
            types::YearInfo::Cyclic(CyclicYear { year, related_iso }) => {
                write!(
                    f,
                    "Date({year}-{month}-{day}, ISO year {related_iso}, for calendar {calendar})"
                )
            }
        }
    }
}

impl<A: AsCalendar + Clone> Clone for Date<A> {
    fn clone(&self) -> Self {
        Self {
            inner: self.inner,
            calendar: self.calendar.clone(),
        }
    }
}

impl<A> Copy for Date<A> where A: AsCalendar + Copy {}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::Weekday;

    #[test]
    fn test_ord() {
        let dates_in_order = [
            Date::try_new_iso(-10, 1, 1).unwrap(),
            Date::try_new_iso(-10, 1, 2).unwrap(),
            Date::try_new_iso(-10, 2, 1).unwrap(),
            Date::try_new_iso(-1, 1, 1).unwrap(),
            Date::try_new_iso(-1, 1, 2).unwrap(),
            Date::try_new_iso(-1, 2, 1).unwrap(),
            Date::try_new_iso(0, 1, 1).unwrap(),
            Date::try_new_iso(0, 1, 2).unwrap(),
            Date::try_new_iso(0, 2, 1).unwrap(),
            Date::try_new_iso(1, 1, 1).unwrap(),
            Date::try_new_iso(1, 1, 2).unwrap(),
            Date::try_new_iso(1, 2, 1).unwrap(),
            Date::try_new_iso(10, 1, 1).unwrap(),
            Date::try_new_iso(10, 1, 2).unwrap(),
            Date::try_new_iso(10, 2, 1).unwrap(),
        ];
        for (i, i_date) in dates_in_order.iter().enumerate() {
            for (j, j_date) in dates_in_order.iter().enumerate() {
                let result1 = i_date.cmp(j_date);
                let result2 = j_date.cmp(i_date);
                assert_eq!(result1.reverse(), result2);
                assert_eq!(i.cmp(&j), i_date.cmp(j_date));
            }
        }
    }

    #[test]
    fn test_day_of_week() {
        // June 23, 2021 is a Wednesday
        assert_eq!(
            Date::try_new_iso(2021, 6, 23).unwrap().day_of_week(),
            Weekday::Wednesday,
        );
        // Feb 2, 1983 was a Wednesday
        assert_eq!(
            Date::try_new_iso(1983, 2, 2).unwrap().day_of_week(),
            Weekday::Wednesday,
        );
        // Jan 21, 2021 was a Tuesday
        assert_eq!(
            Date::try_new_iso(2020, 1, 21).unwrap().day_of_week(),
            Weekday::Tuesday,
        );
    }
}