// This Source Code Form is subject to the terms of the Mozilla Public

// License, v. 2.0. If a copy of the MPL was not distributed with this

// file, You can obtain one at https://mozilla.org/MPL/2.0/.

use crate::calendar::gregorian::Gregorian;

use crate::calendar::prelude::CommonDate;

use crate::calendar::prelude::HasLeapYears;

use crate::calendar::prelude::Perennial;

use crate::calendar::prelude::Quarter;

use crate::calendar::prelude::ToFromCommonDate;

use crate::calendar::AllowYearZero;

use crate::calendar::CalendarMoment;

use crate::calendar::HasIntercalaryDays;

use crate::calendar::OrdinalDate;

use crate::calendar::ToFromOrdinalDate;

use crate::common::error::CalendarError;

use crate::common::math::TermNum;

use crate::day_count::BoundedDayCount;

use crate::day_count::CalculatedBounds;

use crate::day_count::Epoch;

use crate::day_count::Fixed;

use crate::day_count::FromFixed;

use crate::day_count::ToFixed;

#[allow(unused_imports)] //FromPrimitive is needed for derive

use num_traits::FromPrimitive;

use std::num::NonZero;

const FRENCH_EPOCH_GREGORIAN: CommonDate = CommonDate {

    year: 1792,

    month: 9,

    day: 22,

};

const NON_MONTH: u8 = 13;

/// Represents a month in the French Revolutionary Calendar

///

/// Note that the Sansculottides at the end of the French Revolutionary calendar

/// year have no month and thus are not represented by FrenchRevMonth. When representing

/// an arbitrary day in the French Revolutionary calendar, use an `Option<FrenchRevMonth>`

/// for the the month field.

#[derive(Debug, PartialEq, PartialOrd, Clone, Copy, FromPrimitive, ToPrimitive)]

pub enum FrenchRevMonth {

    Vendemiaire = 1,

    Brumaire,

    Frimaire,

    Nivose,

    Pluviose,

    Ventose,

    Germinal,

    Floreal,

    Prairial,

    Messidor,

    Thermidor,

    Fructidor,

}

/// Represents a weekday in the French Revolutionary Calendar

///

/// The calendar reforms during the French Revolution included the creation of

/// a ten-day week. The name of each day is based on the numeric position in the week.

///

/// Note that the Sansculottides at the end of the French Revolutionary calendar

/// year do not have a weekday.

#[derive(Debug, PartialEq, PartialOrd, Clone, Copy, FromPrimitive, ToPrimitive)]

pub enum FrenchRevWeekday {

    Primidi = 1,

    Duodi,

    Tridi,

    Quartidi,

    Quintidi,

    Sextidi,

    Septidi,

    Octidi,

    Nonidi,

    Decadi,

}

/// Represents an epagomenal day at the end of the French Revolutionary calendar year

#[derive(Debug, PartialEq, PartialOrd, Clone, Copy, FromPrimitive, ToPrimitive)]

pub enum Sansculottide {

    Vertu = 1,

    Genie,

    Travail,

    Opinion,

    Recompense,

    Revolution,

}

/// Represents a date in the algorithmic approximation of the French Revolutionary calendar

/// (ie. French Republican calendar)

///

/// The calendar actually implemented during the French First Republic relied on astronomical

/// observations to determine whether a given year was a leap year. **FrenchRevArith does not

/// read astronomical data nor approximate such data - instead it relies on algorithmic

/// rules to determine the start of new years, similar to those used by the Gregorian calendar**.

///

/// The leap year rule is determined by the parameter L.

/// * L = false: According to this rule, any year which is a multiple of 4 is a leap year

///    unless it is a multiple of 100. Any year which is a multiple of 100 is not a leap year

///    unless it is a multiple of 400. Any year which is a multiple of 400 is a leap year

///    unless it is a multiple of 4000. For example, years 4, 8, and 12 are leap years.

/// * L = true: This approximation is exactly the same as the one used where L = false, except

///    that an offset of 1 is added to the year before starting the calculation. For example,

///    years 3, 7 and 11 are leap years.

///

/// The approximation where L = false was proposed by Gilbert Romme, who directed the creation

/// of the calendar. It is commonly used by other software approximating the French Revolutionary

/// calendar. However, it was never used by any French government -

/// the calendar actually used during the French First Republic used astronomical observations

/// to determine leap years, and contradicted Romme's approximations. The official leap years

/// during the Revolution were years 3, 7, and 11 whereas the leap years produced by Romme's

/// approximation are years 4, 8, and 12.

///

/// The approximation where L = true ensures that leap years are consistent with the French

/// government for the years where the Revolutionary calendar was officially used. This is a

/// rather crude approximation which is not astronomically accurate outside those particular

/// years.

///

/// The value of L should be determined by the caller's use case:

/// * for consistency with other software using Romme's approximation: L = false

/// * for consistency with Romme's wishes: L = false

/// * for consistency with historical dates during the French First Republic: L = true

/// * for consistency with historical dates during the Paris Commune: L = true

/// * for consistency with how the calendar was "originally intended" to work for

///   time periods not mentioned above: **not supported**

///

/// The final use case in the list above is not currently supported by this library.

/// Implementing that feature requires calculating the date of the autumnal equinox

/// at the Paris Observatory. If a future version of this library implements such

/// astronomical calculations, those calculations will not be provided by FrenchRevArith.

/// Instead, such calculations shall be provided by a new struct with a new name.

///

/// ## Further reading

/// + [Wikipedia](https://en.wikipedia.org/wiki/French_Republican_calendar)

/// + [Guanzhong "quantum" Chen](https://quantum5.ca/2022/03/09/art-of-time-keeping-part-4-french-republican-calendar/)

#[derive(Debug, PartialEq, PartialOrd, Clone, Copy)]

pub struct FrenchRevArith<const L: bool>(CommonDate);

impl<const L: bool> AllowYearZero for FrenchRevArith<L> {}

impl<const L: bool> ToFromOrdinalDate for FrenchRevArith<L> {

    fn valid_ordinal(ord: OrdinalDate) -> Result<(), CalendarError> {

        let correction = if Self::is_leap(ord.year) { 
1620
 } else { 
01.94k
 };

        if ord.day_of_year > 0 && 
ord.day_of_year <= (365 + correction)2.04k
 {

            Ok(())

        } else {

            Err(CalendarError::InvalidDayOfYear)

        }

    }

    fn ordinal_from_fixed(fixed_date: Fixed) -> OrdinalDate {

        //LISTING 17.10 (*Calendrical Calculations: The Ultimate Edition* by Reingold & Dershowitz.)

        //This does not include the month and day terms

        let date = fixed_date.get_day_i();

        let epoch = Self::epoch().get_day_i();

        let approx = ((4000 * (date - epoch + 2)).div_euclid(1460969) + 1) as i32;

        let approx_start = Self(CommonDate::new(approx, 1, 1)).to_fixed().get_day_i();

        let year = if date < approx_start {

            approx - 1

        } else {

            approx

        };

        let year_start = Self(CommonDate::new(year, 1, 1)).to_fixed().get_day_i();

        let doy = (date - year_start + 1) as u16;

        OrdinalDate {

            year: year,

            day_of_year: doy,

        }

    }

    fn to_ordinal(self) -> OrdinalDate {

        //LISTING 17.9 (*Calendrical Calculations: The Ultimate Edition* by Reingold & Dershowitz.)

        //This is only the terms relying on month and day.

        let offset_m = 30 * ((self.0.month as u16) - 1);

        let offset_d = self.0.day as u16;

        OrdinalDate {

            year: self.0.year,

            day_of_year: offset_m + offset_d,

        }

    }

    fn from_ordinal_unchecked(ord: OrdinalDate) -> Self {

        //LISTING 17.10 (*Calendrical Calculations: The Ultimate Edition* by Reingold & Dershowitz.)

        //This is only the terms relying on month and day.

        //This is modified to use ordinal days instead of days from epoch.

        let month = (1 + (ord.day_of_year - 1).div_euclid(30)) as u8;

        let month_start = Self(CommonDate::new(ord.year, month, 1)).to_ordinal();

        let day = (1 + ord.day_of_year - month_start.day_of_year) as u8;

        FrenchRevArith(CommonDate::new(ord.year, month, day))

    }

}

impl<const L: bool> FrenchRevArith<L> {

    /// Returns L

    pub fn is_adjusted(self) -> bool {

        L

    }

}

impl<const L: bool> HasIntercalaryDays<Sansculottide> for FrenchRevArith<L> {

    fn complementary(self) -> Option<Sansculottide> {

        if self.0.month == NON_MONTH {

            Sansculottide::from_u8(self.0.day)

        } else {

            None

        }

    }

    fn complementary_count(f_year: i32) -> u8 {

        if FrenchRevArith::<L>::is_leap(f_year) {

            6

        } else {

            5

        }

    }

}

impl<const L: bool> Perennial<FrenchRevMonth, FrenchRevWeekday> for FrenchRevArith<L> {

    fn weekday(self) -> Option<FrenchRevWeekday> {

        if self.0.month == NON_MONTH {

            None

        } else {

            FrenchRevWeekday::from_i64((self.0.day as i64).adjusted_remainder(10))

        }

    }

    fn days_per_week() -> u8 {

        10

    }

    fn weeks_per_month() -> u8 {

        3

    }

}

impl<const L: bool> HasLeapYears for FrenchRevArith<L> {

    fn is_leap(year: i32) -> bool {

        //LISTING 17.8 (*Calendrical Calculations: The Ultimate Edition* by Reingold & Dershowitz.)

        //Modified to use L

        let f_year = if L { 
year + 19.69k
 } else { 
year11.0k
 };

        let m4 = f_year.modulus(4);

        let m400 = f_year.modulus(400);

        let m4000 = f_year.modulus(4000);

        m4 == 0 && (
m400 != 1006.67k
 && 
m400 != 2006.57k
 && 
m400 != 3006.49k
) && 
m4000 != 06.44k

    }

}

impl<const L: bool> CalculatedBounds for FrenchRevArith<L> {}

impl<const L: bool> Epoch for FrenchRevArith<L> {

    fn epoch() -> Fixed {

        Gregorian::try_from_common_date(FRENCH_EPOCH_GREGORIAN)

            .expect("Epoch known to be valid")

            .to_fixed()

    }

}

impl<const L: bool> FromFixed for FrenchRevArith<L> {

    fn from_fixed(fixed_date: Fixed) -> FrenchRevArith<L> {

        //LISTING 17.10 (*Calendrical Calculations: The Ultimate Edition* by Reingold & Dershowitz.)

        //Split compared to original

        let ord = Self::ordinal_from_fixed(fixed_date);

        Self::from_ordinal_unchecked(ord)

    }

}

impl<const L: bool> ToFixed for FrenchRevArith<L> {

    fn to_fixed(self) -> Fixed {

        //LISTING 17.9 (*Calendrical Calculations: The Ultimate Edition* by Reingold & Dershowitz.)

        //Split compared to original: terms relying on month and day are processed in to_ordinal

        let year = self.0.year as i64;

        let y_adj = if L { 
136.8k
 } else { 
036.8k
 };

        let offset_e = Self::epoch().get_day_i() - 1;

        let offset_y = 365 * (year - 1);

        let offset_leap = (year + y_adj - 1).div_euclid(4) - (year + y_adj - 1).div_euclid(100)

            + (year + y_adj - 1).div_euclid(400)

            - (year + y_adj - 1).div_euclid(4000);

        let ord = self.to_ordinal().day_of_year as i64;

        Fixed::cast_new(offset_e + offset_y + offset_leap + ord)

    }

}

impl<const L: bool> ToFromCommonDate<FrenchRevMonth> for FrenchRevArith<L> {

    fn to_common_date(self) -> CommonDate {

        self.0

    }

    fn from_common_date_unchecked(date: CommonDate) -> Self {

        debug_assert!(Self::valid_ymd(date).is_ok());

        Self(date)

    }

    fn valid_ymd(date: CommonDate) -> Result<(), CalendarError> {

        if date.month < 1 || 
date.month > NON_MONTH46.0k
 {

            Err(CalendarError::InvalidMonth)

        } else if date.day < 1 {

            Err(CalendarError::InvalidDay)

        } else if date.month < NON_MONTH && 
date.day > 3028.6k
 {

            Err(CalendarError::InvalidDay)

        } else if date.month == NON_MONTH

            && date.day > FrenchRevArith::<L>::complementary_count(date.year)

        {

            Err(CalendarError::InvalidDay)

        } else {

            Ok(())

        }

    }

    fn year_end_date(year: i32) -> CommonDate {

        CommonDate::new(

            year,

            NON_MONTH,

            FrenchRevArith::<L>::complementary_count(year),

        )

    }

}

impl<const L: bool> Quarter for FrenchRevArith<L> {

    fn quarter(self) -> NonZero<u8> {

        let m = self.to_common_date().month;

        if m == NON_MONTH {

            NonZero::new(4 as u8).expect("4 != 0")

        } else {

            NonZero::new(((m - 1) / 3) + 1).expect("(m-1)/3 > -1")

        }

    }

}

/// Represents a date *and time* in the algorithmic approximation of the French Revolutionary Calendar

pub type FrenchRevArithMoment<const L: bool> = CalendarMoment<FrenchRevArith<L>>;

#[cfg(test)]

mod tests {

    use super::*;

    use proptest::proptest;

    #[test]

    fn leaps() {

        assert!(FrenchRevArith::<true>::is_leap(3));

        assert!(FrenchRevArith::<true>::is_leap(7));

        assert!(FrenchRevArith::<true>::is_leap(11));

        assert!(FrenchRevArith::<false>::is_leap(4));

        assert!(FrenchRevArith::<false>::is_leap(8));

        assert!(FrenchRevArith::<false>::is_leap(12));

    }

    #[test]

    fn revolutionary_events() {

        // https://en.wikipedia.org/wiki/Glossary_of_the_French_Revolution#Events_commonly_known_by_their_Revolutionary_dates

        // 13 Vendémiaire and 18 Brumaire can be mangled when L = false

        let event_list = [

            (

                CommonDate::new(2, FrenchRevMonth::Prairial as u8, 22),

                CommonDate::new(2, FrenchRevMonth::Prairial as u8, 22),

                CommonDate::new(1794, 6, 10),

            ),

            (

                CommonDate::new(2, FrenchRevMonth::Thermidor as u8, 9),

                CommonDate::new(2, FrenchRevMonth::Thermidor as u8, 9),

                CommonDate::new(1794, 7, 27),

            ),

            (

                CommonDate::new(4, FrenchRevMonth::Vendemiaire as u8, 13),

                CommonDate::new(4, FrenchRevMonth::Vendemiaire as u8, 13 + 1), //Supposed to be 13

                CommonDate::new(1795, 10, 5),

            ),

            (

                CommonDate::new(5, FrenchRevMonth::Fructidor as u8, 18),

                CommonDate::new(5, FrenchRevMonth::Fructidor as u8, 18),

                CommonDate::new(1797, 9, 4),

            ),

            (

                CommonDate::new(6, FrenchRevMonth::Floreal as u8, 22),

                CommonDate::new(6, FrenchRevMonth::Floreal as u8, 22),

                CommonDate::new(1798, 5, 11),

            ),

            (

                CommonDate::new(7, FrenchRevMonth::Prairial as u8, 30),

                CommonDate::new(7, FrenchRevMonth::Prairial as u8, 30),

                CommonDate::new(1799, 6, 18),

            ),

            (

                CommonDate::new(8, FrenchRevMonth::Brumaire as u8, 18),

                CommonDate::new(8, FrenchRevMonth::Brumaire as u8, 18 + 1), //Supposed to be 18

                CommonDate::new(1799, 11, 9),

            ),

            // Paris Commune

            (

                CommonDate::new(79, FrenchRevMonth::Floreal as u8, 16),

                CommonDate::new(79, FrenchRevMonth::Floreal as u8, 16),

                CommonDate::new(1871, 5, 6),

            ),

        ];

        for 
pair8
 in event_list {

            let df0 = FrenchRevArith::<true>::try_from_common_date(pair.0)

                .unwrap()

                .to_fixed();

            let df1 = FrenchRevArith::<false>::try_from_common_date(pair.1)

                .unwrap()

                .to_fixed();

            let dg = Gregorian::try_from_common_date(pair.2).unwrap().to_fixed();

            assert_eq!(df0, dg);

            assert_eq!(df1, dg);

        }

    }

    proptest! {

        #[test]

        fn align_to_gregorian(year in 0..100) {

            // https://en.wikipedia.org/wiki/French_Republican_calendar

            // > Autumn:

            // >     Vendémiaire (...), starting 22, 23, or 24 September

            // >     Brumaire (...), starting 22, 23, or 24 October

            // >     Frimaire (...), starting 21, 22, or 23 November

            // > Winter:

            // >     Nivôse (...), starting 21, 22, or 23 December

            // >     Pluviôse (...), starting 20, 21, or 22 January

            // >     Ventôse (...), starting 19, 20, or 21 February

            // > Spring:

            // >     Germinal (...), starting 21 or 22 March

            // >     Floréal (...), starting 20 or 21 April

            // >     Prairial (...), starting 20 or 21 May

            // > Summer:

            // >     Messidor (...), starting 19 or 20 June

            // >     Thermidor (...), starting 19 or 20 July; ...

            // >     Fructidor (...), starting 18 or 19 August

            // Not clear how long this property is supposed to hold, given

            // the differing leap year rule. There can be off by one errors

            // if L is false.

            let d_list = [

                ( CommonDate{ year, month: 1, day: 1 }, 9, 22, 24),

                ( CommonDate{ year, month: 2, day: 1 }, 10, 22, 24),

                ( CommonDate{ year, month: 3, day: 1 }, 11, 21, 23),

                ( CommonDate{ year, month: 4, day: 1 }, 12, 21, 23),

                ( CommonDate{ year, month: 5, day: 1 }, 1, 20, 22),

                ( CommonDate{ year, month: 6, day: 1 }, 2, 19, 21),

                ( CommonDate{ year, month: 7, day: 1 }, 3, 21, 22),

                ( CommonDate{ year, month: 8, day: 1 }, 4, 20, 21),

                ( CommonDate{ year, month: 9, day: 1 }, 5, 20, 21),

                ( CommonDate{ year, month: 10, day: 1 }, 6, 19, 20),

                ( CommonDate{ year, month: 11, day: 1 }, 7, 19, 20),

                ( CommonDate{ year, month: 12, day: 1 }, 8, 18, 19),

            ];

            for item in d_list {

                let r0 = FrenchRevArith::<true>::try_from_common_date(item.0).unwrap();

                let f0 = r0.to_fixed();

                let r1 = FrenchRevArith::<false>::try_from_common_date(item.0).unwrap();

                let f1 = r1.to_fixed();

                let g = Gregorian::from_fixed(f0);

                let gc = g.to_common_date();

                assert_eq!(gc.month, item.1);

                assert!(item.2 <= gc.day && item.3 >= gc.day);

                assert!((f1.get_day_i() - f0.get_day_i()).abs() < 2);

            }

        }

    }

}