index.ts

import { holidays as baseHolidays } from 'japanese-public-holidays';

export type HolidayInfo = {
  date: string;
  endDate: Date;
  name: string;
  startDate: Date;
};

export type HolidayMap = {
  [key: string]: {
    [key: string]: {
      [key: string]: HolidayInfo;
    };
  };
};

// NOTE: JST is UTC+9:00
const jstOffsetHour = 1000 * 60 * 60 * 9;

// NOTE: find backward is faster than find forward maybe
export const holidays = baseHolidays.reverse().map(function (holiday) {
  const { date, name } = holiday;

  const [year, month, day] = date.split('-').map(Number);

  if (year === undefined || month === undefined || day === undefined) {
    return {
      date,
      endDate: new Date(''),
      name,
      startDate: new Date('')
    };
  }

  const startDate = new Date(
    Date.UTC(year, month - 1, day, 0, 0, 0, 0) - jstOffsetHour
  );
  const endDate = new Date(
    Date.UTC(year, month - 1, day + 1, 0, 0, 0, 0) - jstOffsetHour - 1
  );

  return {
    date,
    endDate,
    name,
    startDate
  };
});

export const holidayMap: HolidayMap = holidays.reduce(function (
  result: HolidayMap,
  holiday
) {
  const { date } = holiday;
  const [year, month, day] = date.split('-');

  if (year === undefined || month === undefined || day === undefined) {
    return result;
  }

  const yearObject = ensureKey(result, year);
  const monthObject = ensureKey(yearObject, month);

  monthObject[day] = holiday;

  return result;
}, {});

/**
 * get holiday info
 *
 * @param date - target date
 * @returns return holiday info if date is holiday, otherwise return null
 */
export function getHolidayInfo(date: Date): HolidayInfo | null {
  if (!isDate(date)) {
    throw new TypeError('date must be a Date: ' + date);
  }

  const jstDate = new Date(date.getTime() + jstOffsetHour);

  const m = jstDate.getUTCMonth() + 1;
  const d = jstDate.getUTCDate();

  const year = String(jstDate.getUTCFullYear());
  const month = m < 10 ? `0${m}` : String(m);
  const day = d < 10 ? `0${d}` : String(d);

  const yearObject = ensureKey(holidayMap, year);
  const monthObject = ensureKey(yearObject, month);

  const result = monthObject[day];

  return result === undefined ? null : result;
}

/**
 * return true if date is holiday
 *
 * @param date - target date
 * @returns return true if date is holiday
 */
export function isHoliday(date: Date): boolean {
  if (!isDate(date)) {
    throw new TypeError('date must be a Date: ' + date);
  }

  return getHolidayInfo(date) !== null;
}

/** cache of Object.prototype.toString */
const toString = Object.prototype.toString;

/**
 * return true if date is Date instance
 *
 * @param value - target value
 * @returns return true if value is date
 */
function isDate(value: unknown): value is Date {
  return toString.call(value) === '[object Date]';
}

/**
 * for TS2532
 *
 * @param object - target object
 * @returns object
 */
function ensureKey<T>(object: Record<string, T | undefined>, key: string): T {
  if (!object[key]) {
    object[key] = {} as T;
  }

  return object[key]!;
}