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//! A crate for finding out dates of Czech public holidays.

use chrono::{Datelike, NaiveDate};
use computus;
use std::i32::MAX as I32_MAX;

/// Get dates of Czech public holidays in a given year.
pub fn holidays_in_year(y: i32) -> Vec<NaiveDate> {
    let mut hiy: Vec<NaiveDate> = vec![];
    for (sh_sy, sh_ty, sh_m, sh_d) in STATIC_HOLIDAYS {
        if y >= *sh_sy && y <= *sh_ty {
            hiy.push(NaiveDate::from_ymd(y, *sh_m, *sh_d));
        }
    }
    hiy.append(&mut get_easter_holidays(y));
    hiy.sort();
    hiy
}

/// Get dates of Czech public holidays within a given from-to date
/// range. The range is inclusive.
pub fn holidays_within(from: &NaiveDate, to: &NaiveDate) -> Vec<NaiveDate> {
    let mut hir = vec![];
    for y in from.year()..to.year() + 1 {
        hir.append(&mut holidays_in_year(y))
    }
    hir.retain(|holiday| holiday >= from && holiday <= to);
    hir
}

/// Query whether a given date is a Czech public holiday.
pub fn is_holiday(date: &NaiveDate) -> bool {
    is_static_holiday(date) || is_easter_holiday(date)
}

/// Query whether a given date (year, month, day) is a Czech public
/// holiday.
pub fn is_holiday_ymd(y: i32, m: u32, d: u32) -> bool {
    is_holiday(&NaiveDate::from_ymd(y, m, d))
}

// [(since_year, to_year, month, day), (since_year, to_year, month, day), ...]
const STATIC_HOLIDAYS: &'static [(i32, i32, u32, u32)] = &[
    (1951, I32_MAX, 1, 1),
    (1951, I32_MAX, 5, 1),
    (1992, I32_MAX, 5, 8),
    (1990, I32_MAX, 7, 5),
    (1990, I32_MAX, 7, 6),
    (2000, I32_MAX, 9, 28),
    (1988, I32_MAX, 10, 28),
    (2000, I32_MAX, 11, 17),
    (1990, I32_MAX, 12, 24),
    (1951, I32_MAX, 12, 25),
    (1951, I32_MAX, 12, 26),
    (1947, 1991, 5, 9),
];

fn is_static_holiday(date: &NaiveDate) -> bool {
    let (y, m, d) = (date.year(), date.month(), date.day());
    for (sh_sy, sh_ty, sh_m, sh_d) in STATIC_HOLIDAYS {
        if y >= *sh_sy && y <= *sh_ty && m == *sh_m && d == *sh_d {
            return true;
        }
    }
    false
}

fn is_easter_holiday(date: &NaiveDate) -> bool {
    get_easter_holidays(date.year()).contains(date)
}

fn get_easter_holidays(year: i32) -> Vec<NaiveDate> {
    vec![
        get_easter_holiday_friday(year),
        get_easter_holiday_monday(year),
    ]
    .into_iter()
    .filter(|opt| opt.is_some())
    .map(|opt| opt.expect("Date is None even though guarded by is_some filter"))
    .collect()
}

fn get_easter_holiday_monday(year: i32) -> Option<NaiveDate> {
    if year >= 1951 {
        get_easter_sunday(year).map(|es| es.succ())
    } else {
        None
    }
}

fn get_easter_holiday_friday(year: i32) -> Option<NaiveDate> {
    if year >= 2016 {
        get_easter_sunday(year).map(|es| es.pred().pred())
    } else {
        None
    }
}

fn get_easter_sunday(year: i32) -> Option<NaiveDate> {
    let easter_sunday = computus::gregorian(year);
    match easter_sunday {
        Ok(es) => Some(NaiveDate::from_ymd(es.year, es.month, es.day)),
        Err(_) => None,
    }
}

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

    #[test]
    fn test_is_holiday_ymd() {
        assert!(!is_holiday_ymd(1918, 10, 28));
        assert!(is_holiday_ymd(2018, 10, 28));

        assert!(!is_holiday_ymd(1999, 9, 28));
        assert!(is_holiday_ymd(2000, 9, 28));
        assert!(is_holiday_ymd(3000, 9, 28));

        assert!(is_holiday_ymd(2018, 4, 2));
        assert!(is_holiday_ymd(2018, 3, 30));

        assert!(is_holiday_ymd(2018, 4, 2));
        assert!(is_holiday_ymd(2018, 3, 30));

        assert!(is_holiday_ymd(2015, 4, 6));
        assert!(!is_holiday_ymd(2015, 4, 3));
    }

    #[test]
    fn test_holidays_within() {
        let from = NaiveDate::from_ymd(2015, 12, 1);
        let to = NaiveDate::from_ymd(2017, 4, 16);

        assert_eq!(
            holidays_within(&from, &to).as_slice(),
            &[
                NaiveDate::from_ymd(2015, 12, 24),
                NaiveDate::from_ymd(2015, 12, 25),
                NaiveDate::from_ymd(2015, 12, 26),
                NaiveDate::from_ymd(2016, 1, 1),
                NaiveDate::from_ymd(2016, 3, 25),
                NaiveDate::from_ymd(2016, 3, 28),
                NaiveDate::from_ymd(2016, 5, 1),
                NaiveDate::from_ymd(2016, 5, 8),
                NaiveDate::from_ymd(2016, 7, 5),
                NaiveDate::from_ymd(2016, 7, 6),
                NaiveDate::from_ymd(2016, 9, 28),
                NaiveDate::from_ymd(2016, 10, 28),
                NaiveDate::from_ymd(2016, 11, 17),
                NaiveDate::from_ymd(2016, 12, 24),
                NaiveDate::from_ymd(2016, 12, 25),
                NaiveDate::from_ymd(2016, 12, 26),
                NaiveDate::from_ymd(2017, 1, 1),
                NaiveDate::from_ymd(2017, 4, 14),
            ]
        );
    }
}