Metropolitan France Holidays

christianHolidays.ts

// Christian holidays utils
// base ressources
// https://gist.github.com/johndyer/0dffbdd98c2046f41180c051f378f343#gistcomment-3774086
// https://www.codeproject.com/Articles/10860/Calculating-Christian-Holidays by Jan Schreuder

import { addDays, format, subDays } from 'date-fns';

// https://gist.github.com/johndyer/0dffbdd98c2046f41180c051f378f343#gistcomment-3774086
// getEaster day for a given year
function getEaster(year: number) {
  const f = Math.floor,
    G = year % 19,
    C = f(year / 100),
    H = (C - f(C / 4) - f((8 * C + 13) / 25) + 19 * G + 15) % 30,
    I = H - f(H / 28) * (1 - f(29 / (H + 1)) * f((21 - G) / 11)),
    J = (year + f(year / 4) + I + 2 - C + f(C / 4)) % 7,
    L = I - J,
    month = 3 + f((L + 40) / 44),
    day = L + 28 - 31 * f(month / 4);
  return new Date(year, month - 1, day);
}

// Movable religious holidays relative to Easter

// 1 day after Easter
const getEasterMonday = (year: number) => addDays(getEaster(year), 1);

// Ascension Day is 39 days after Easter
const getAscensionDay = (year: number) => addDays(getEaster(year), 39);

// WhitMonday is 48 days after Easter monday (49 after whit sunday)
const getWhitMonday = (year: number) => addDays(addDays(getEasterMonday(year), 1), 48);

// Christ crucifixion is 2 days before Easter
const getGoodFriday = (year: number) => subDays(getEaster(year), 2);

// END movable holidays

const yearMonthDayFormat = 'yyyy-MM-dd';
/**
 * 
 * @param year 
 * @returns a dictionnary of holidays
 */
const getHolidays = (year: number): { [key: string]: string } => ({
  new_year_day: `${year}-01-01`,
  easter_monday: format(getEasterMonday(year), yearMonthDayFormat),
  labor_day: `${year}-05-01`,
  victory_1945: `${year}-05-08`,
  // local Alsace/Moselle holidays
  christ_crucifixion_friday: format(getGoodFriday(year), yearMonthDayFormat),
  ascension_day: format(getAscensionDay(year), yearMonthDayFormat),
  whit_monday: format(getWhitMonday(year), yearMonthDayFormat),
  national_day: `${year}-07-14`,
  assumption: `${year}-08-15`,
  all_saints: `${year}-11-01`,
  armistice_1918: `${year}-11-11`,
  christmas: `${year}-12-25`,
  // local Alsace/Moselle holidays
  christmas_second_day: `${year}-12-26`,
});

export { getHolidays };