var parse = require('../parse/index.js')
var getISOWeek = require('../get_iso_week/index.js')

/**
 * @category ISO Week Helpers
 * @summary Set the ISO week to the given date.
 *
 * @description
 * Set the ISO week to the given date, saving the weekday number.
 *
 * ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
 *
 * @param {Date|String|Number} date - the date to be changed
 * @param {Number} isoWeek - the ISO week of the new date
 * @returns {Date} the new date with the ISO week setted
 *
 * @example
 * // Set the 53rd ISO week to 7 August 2004:
 * var result = setISOWeek(new Date(2004, 7, 7), 53)
 * //=> Sat Jan 01 2005 00:00:00
 */
function setISOWeek (dirtyDate, dirtyISOWeek) {
  var date = parse(dirtyDate)
  var isoWeek = Number(dirtyISOWeek)
  var diff = getISOWeek(date) - isoWeek
  date.setDate(date.getDate() - diff * 7)
  return date
}

module.exports = setISOWeek