var dateUtils = (function (exports) {
  'use strict';

  function stripTime(timeValue) {
    return new Date(timeValue).setHours(0, 0, 0, 0);
  }

  function today() {
    return new Date().setHours(0, 0, 0, 0);
  }

  // Get the time value of the start of given date or year, month and day
  function dateValue(...args) {
    switch (args.length) {
      case 0:
        return today();
      case 1:
        return stripTime(args[0]);
    }

    // use setFullYear() to keep 2-digit year from being mapped to 1900-1999
    const newDate = new Date(0);
    newDate.setFullYear(...args);
    return newDate.setHours(0, 0, 0, 0);
  }

  function addDays(date, amount) {
    const newDate = new Date(date);
    return newDate.setDate(newDate.getDate() + amount);
  }

  function addWeeks(date, amount) {
    return addDays(date, amount * 7);
  }

  function addMonths(date, amount) {
    // If the day of the date is not in the new month, the last day of the new
    // month will be returned. e.g. Jan 31 + 1 month → Feb 28 (not Mar 03)
    const newDate = new Date(date);
    const monthsToSet = newDate.getMonth() + amount;
    let expectedMonth = monthsToSet % 12;
    if (expectedMonth < 0) {
      expectedMonth += 12;
    }

    const time = newDate.setMonth(monthsToSet);
    return newDate.getMonth() !== expectedMonth ? newDate.setDate(0) : time;
  }

  function addYears(date, amount) {
    // If the date is Feb 29 and the new year is not a leap year, Feb 28 of the
    // new year will be returned.
    const newDate = new Date(date);
    const expectedMonth = newDate.getMonth();
    const time = newDate.setFullYear(newDate.getFullYear() + amount);
    return expectedMonth === 1 && newDate.getMonth() === 2 ? newDate.setDate(0) : time;
  }

  // Calculate the distance bettwen 2 days of the week
  function dayDiff(day, from) {
    return (day - from + 7) % 7;
  }

  // Get the date of the specified day of the week of given base date
  function dayOfTheWeekOf(baseDate, dayOfWeek, weekStart = 0) {
    const baseDay = new Date(baseDate).getDay();
    return addDays(baseDate, dayDiff(dayOfWeek, weekStart) - dayDiff(baseDay, weekStart));
  }

  // Get the ISO week of a date
  function getWeek(date) {
    // start of ISO week is Monday
    const thuOfTheWeek = dayOfTheWeekOf(date, 4, 1);
    // 1st week == the week where the 4th of January is in
    const firstThu = dayOfTheWeekOf(new Date(thuOfTheWeek).setMonth(0, 4), 4, 1);
    return Math.round((thuOfTheWeek - firstThu) / 604800000) + 1;
  }

  // Get the start year of the period of years that includes given date
  // years: length of the year period
  function startOfYearPeriod(date, years) {
    /* @see https://en.wikipedia.org/wiki/Year_zero#ISO_8601 */
    const year = new Date(date).getFullYear();
    return Math.floor(year / years) * years;
  }

  exports.addDays = addDays;
  exports.addMonths = addMonths;
  exports.addWeeks = addWeeks;
  exports.addYears = addYears;
  exports.dateValue = dateValue;
  exports.dayOfTheWeekOf = dayOfTheWeekOf;
  exports.getWeek = getWeek;
  exports.startOfYearPeriod = startOfYearPeriod;
  exports.stripTime = stripTime;
  exports.today = today;

  Object.defineProperty(exports, '__esModule', { value: true });

  return exports;

}({}));