import differenceInDays from '../differenceInDays/index'
import requiredArgs from '../_lib/requiredArgs/index'

/**
 * @name differenceInWeeks
 * @category Week Helpers
 * @summary Get the number of full weeks between the given dates.
 *
 * @description
 * Get the number of full weeks between two dates. Fractional weeks are
 * truncated towards zero.
 *
 * One "full week" is the distance between a local time in one day to the same
 * local time 7 days earlier or later. A full week can sometimes be less than
 * or more than 7*24 hours if a daylight savings change happens between two dates.
 *
 * To ignore DST and only measure exact 7*24-hour periods, use this instead:
 * `Math.floor(differenceInHours(dateLeft, dateRight)/(7*24))|0`.
 *
 *
 * ### v2.0.0 breaking changes:
 *
 * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
 *
 * @param {Date|Number} dateLeft - the later date
 * @param {Date|Number} dateRight - the earlier date
 * @returns {Number} the number of full weeks
 * @throws {TypeError} 2 arguments required
 *
 * @example
 * // How many full weeks are between 5 July 2014 and 20 July 2014?
 * const result = differenceInWeeks(new Date(2014, 6, 20), new Date(2014, 6, 5))
 * //=> 2
 *
 * // How many full weeks are between
 * // 1 March 2020 0:00 and 6 June 2020 0:00 ?
 * // Note: because local time is used, the
 * // result will always be 8 weeks (54 days),
 * // even if DST starts and the period has
 * // only 54*24-1 hours.
 * const result = differenceInWeeks(
 *   new Date(2020, 5, 1),
 *   new Date(2020, 2, 6)
 * )
 * //=> 8
 */
export default function differenceInWeeks(
  dirtyDateLeft: Date | number,
  dirtyDateRight: Date | number
): number {
  requiredArgs(2, arguments)

  const diff = differenceInDays(dirtyDateLeft, dirtyDateRight) / 7
  return diff > 0 ? Math.floor(diff) : Math.ceil(diff)
}
