// This file is part of ICU4X.

//

// The contents of this file implement algorithms from Calendrical Calculations

// by Reingold & Dershowitz, Cambridge University Press, 4th edition (2018),

// which have been released as Lisp code at <https://github.com/EdReingold/calendar-code2/>

// under the Apache-2.0 license. Accordingly, this file is released under

// the Apache License, Version 2.0 which can be found at the calendrical_calculations

// package root or at http://www.apache.org/licenses/LICENSE-2.0.

use crate::helpers::{i64_to_i32, I32CastError, IntegerRoundings};

use crate::rata_die::RataDie;

/// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/main/calendar.l#L4720>

// Book states that the Persian epoch is the date: 3/19/622 and since the Persian Calendar has no year 0, the best choice was to use the Julian function.

const FIXED_PERSIAN_EPOCH: RataDie = crate::julian::fixed_from_julian(622, 3, 19);

// All these years are not leap, while they are considered leap by the 33-year

// rule. The year following each of them is leap, but it's considered non-leap

// by the 33-year rule. This table has been tested to match the modified

// astronomical algorithm based on the 52.5 degrees east meridian from 1178 AP

// (an arbitrary date before the Persian calendar was adopted in 1304 AP) to

// 3000 AP (an arbitrary date far into the future).

const NON_LEAP_CORRECTION: [i32; 78] = [

    1502, 1601, 1634, 1667, 1700, 1733, 1766, 1799, 1832, 1865, 1898, 1931, 1964, 1997, 2030, 2059,

    2063, 2096, 2129, 2158, 2162, 2191, 2195, 2224, 2228, 2257, 2261, 2290, 2294, 2323, 2327, 2356,

    2360, 2389, 2393, 2422, 2426, 2455, 2459, 2488, 2492, 2521, 2525, 2554, 2558, 2587, 2591, 2620,

    2624, 2653, 2657, 2686, 2690, 2719, 2723, 2748, 2752, 2756, 2781, 2785, 2789, 2818, 2822, 2847,

    2851, 2855, 2880, 2884, 2888, 2913, 2917, 2921, 2946, 2950, 2954, 2979, 2983, 2987,

];

const MIN_NON_LEAP_CORRECTION: i32 = NON_LEAP_CORRECTION[0];

/// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/main/calendar.l#L4803>

/// Not used, but kept for comparative purposes

pub fn fixed_from_arithmetic_persian(year: i32, month: u8, day: u8) -> RataDie {

    let p_year = i64::from(year);

    let month = i64::from(month);

    let day = i64::from(day);

    let y = if p_year > 0 {

        p_year - 474

    } else {

        p_year - 473

    };

    let year = y.rem_euclid(2820) + 474;

    RataDie::new(

        FIXED_PERSIAN_EPOCH.to_i64_date() - 1

            + 1029983 * y.div_euclid(2820)

            + 365 * (year - 1)

            + (31 * year - 5).div_euclid(128)

            + if month <= 7 {

                31 * (month - 1)

            } else {

                30 * (month - 1) + 6

            }

            + day,

    )

}

/// fixed_from_arithmetic_persian, modified to use the more correct 33-year rule

pub fn fixed_from_fast_persian(year: i32, month: u8, day: u8) -> RataDie {

    let p_year = i64::from(year);

    let month = i64::from(month);

    let day = i64::from(day);

    let mut new_year = FIXED_PERSIAN_EPOCH.to_i64_date() - 1

        + 365 * (p_year - 1)

        + (8 * p_year + 21).div_euclid(33);

    if year > MIN_NON_LEAP_CORRECTION && NON_LEAP_CORRECTION.binary_search(&(year - 1)).is_ok() {

        new_year -= 1;

    }

    RataDie::new(

        new_year - 1

            + if month <= 7 {

                31 * (month - 1)

            } else {

                30 * (month - 1) + 6

            }

            + day,

    )

}

/// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/main/calendar.l#L4857>

/// Not used, but kept for comparative purposes

pub fn arithmetic_persian_from_fixed(date: RataDie) -> Result<(i32, u8, u8), I32CastError> {

    let year = arithmetic_persian_year_from_fixed(date);

    let year = i64_to_i32(year)?;

    #[allow(clippy::unwrap_used)] // valid month,day

    let day_of_year = 1_i64 + (date - fixed_from_arithmetic_persian(year, 1, 1));

    #[allow(unstable_name_collisions)] // div_ceil is unstable and polyfilled

    let month = if day_of_year <= 186 {

        day_of_year.div_ceil(31) as u8

    } else {

        (day_of_year - 6).div_ceil(30) as u8

    };

    let day = (date - fixed_from_arithmetic_persian(year, month, 1) + 1) as u8;

    Ok((year, month, day))

}

/// arithmetic_persian_from_fixed, modified to use the 33-year rule method

pub fn fast_persian_from_fixed(date: RataDie) -> Result<(i32, u8, u8), I32CastError> {

    let year = fast_persian_year_from_fixed(date);

    let mut year = i64_to_i32(year)?;

    let mut day_of_year = 1_i64 + (date - fixed_from_fast_persian(year, 1, 1));

    if day_of_year == 366

        && year >= MIN_NON_LEAP_CORRECTION

        && NON_LEAP_CORRECTION.binary_search(&year).is_ok()

    {

        year += 1;

        day_of_year = 1;

    }

    #[allow(unstable_name_collisions)] // div_ceil is unstable and polyfilled

    let month = if day_of_year <= 186 {

        day_of_year.div_ceil(31) as u8

    } else {

        (day_of_year - 6).div_ceil(30) as u8

    };

    let day = (date - fixed_from_fast_persian(year, month, 1) + 1) as u8;

    Ok((year, month, day))

}

/// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/main/calendar.l#L4829>

/// Not used, but kept for comparative purposes

fn arithmetic_persian_year_from_fixed(date: RataDie) -> i64 {

    let d0 = date - fixed_from_arithmetic_persian(475, 1, 1);

    let n2820 = d0.div_euclid(1029983);

    let d1 = d0.rem_euclid(1029983);

    let y2820 = if d1 == 1029982 {

        2820

    } else {

        (128 * d1 + 46878).div_euclid(46751)

    };

    let year = 474 + n2820 * 2820 + y2820;

    if year > 0 {

        year

    } else {

        year - 1

    }

}

/// arithmetic_persian_year_from_fixed modified for the 33-year rule

fn fast_persian_year_from_fixed(date: RataDie) -> i64 {

    let days_since_epoch = date - FIXED_PERSIAN_EPOCH + 1;

    1 + (33 * days_since_epoch + 3).div_euclid(12053)

}

/// Lisp code reference: https://github.com/EdReingold/calendar-code2/blob/main/calendar.l#L4789

/// Not used, but kept for comparative purposes

#[allow(dead_code)]

fn is_arithmetic_leap_year(p_year: i32, _data: ()) -> bool {

    let mut p_year = p_year as i64;

    if 0 < p_year {

        p_year -= 474;

    } else {

        p_year -= 473;

    };

    let year = p_year.rem_euclid(2820) + 474;

    ((year + 38) * 31).rem_euclid(128) < 31

}

/// Calculated using the 33-year rule

pub fn is_leap_year(p_year: i32, _data: ()) -> bool {

    if p_year >= MIN_NON_LEAP_CORRECTION && NON_LEAP_CORRECTION.binary_search(&p_year).is_ok() {

        false

    } else if p_year > MIN_NON_LEAP_CORRECTION

        && NON_LEAP_CORRECTION.binary_search(&(p_year - 1)).is_ok()

    {

        true

    } else {

        let p_year = p_year as i64;

        (25 * p_year + 11).rem_euclid(33) < 8

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn test_persian_epoch() {

        let epoch = FIXED_PERSIAN_EPOCH.to_i64_date();

        // Iso year of Persian Epoch

        let epoch_year_from_fixed = crate::iso::iso_year_from_fixed(RataDie::new(epoch));

        // 622 is the correct ISO year for the Persian Epoch

        assert_eq!(epoch_year_from_fixed, 622);

    }

    // Persian New Year occurring in March of Gregorian year (g_year) to fixed date

    fn nowruz(g_year: i32) -> RataDie {

        let (y, _m, _d) = crate::iso::iso_from_fixed(FIXED_PERSIAN_EPOCH).unwrap();

        let persian_year = g_year - y + 1;

        let year = if persian_year <= 0 {

            persian_year - 1

        } else {

            persian_year

        };

        fixed_from_fast_persian(year, 1, 1)

    }

    #[test]

    fn test_nowruz() {

        // These values are used as test data in appendix C of the "Calendrical Calculations" book

        let nowruz_test_year_start = 2000;

        let nowruz_test_year_end = 2103;

        for year in nowruz_test_year_start..=nowruz_test_year_end {

            let two_thousand_eight_to_fixed = nowruz(year).to_i64_date();

            let iso_date = crate::iso::fixed_from_iso(year, 3, 21);

            let (persian_year, _m, _d) = fast_persian_from_fixed(iso_date).unwrap();

            assert_eq!(

                fast_persian_from_fixed(RataDie::new(two_thousand_eight_to_fixed))

                    .unwrap()

                    .0,

                persian_year

            );

        }

    }

}