import toDate from '../toDate/index.js'
import startOfISOWeek from '../startOfISOWeek/index.js'
import startOfISOWeekYear from '../startOfISOWeekYear/index.js'

var MILLISECONDS_IN_WEEK = 604800000

/**
 * @name getISOWeek
 * @category ISO Week Helpers
 * @summary Get the ISO week of the given date.
 *
 * @description
 * Get the ISO week of the given date.
 *
 * ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
 *
 *
 * ### 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|String|Number} date - the given date
 * @param {Options} [options] - the object with options. See [Options]{@link https://date-fns.org/docs/Options}
 * @param {0|1|2} [options.additionalDigits=2] - passed to `toDate`. See [toDate]{@link https://date-fns.org/docs/toDate}
 * @returns {Number} the ISO week
 * @throws {TypeError} 1 argument required
 * @throws {RangeError} `options.additionalDigits` must be 0, 1 or 2
 *
 * @example
 * // Which week of the ISO-week numbering year is 2 January 2005?
 * var result = getISOWeek(new Date(2005, 0, 2))
 * //=> 53
 */
export default function getISOWeek (dirtyDate, dirtyOptions) {
  if (arguments.length < 1) {
    throw new TypeError('1 argument required, but only ' + arguments.length + ' present')
  }

  var date = toDate(dirtyDate, dirtyOptions)
  var diff = startOfISOWeek(date, dirtyOptions).getTime() - startOfISOWeekYear(date, dirtyOptions).getTime()

  // Round the number of days to the nearest integer
  // because the number of milliseconds in a week is not constant
  // (e.g. it's different in the week of the daylight saving time clock shift)
  return Math.round(diff / MILLISECONDS_IN_WEEK) + 1
}
