import addISOWeekYears from '../addISOWeekYears/index'
import requiredArgs from '../_lib/requiredArgs/index'
import toInteger from '../_lib/toInteger/index'

/**
 * @name subISOWeekYears
 * @category ISO Week-Numbering Year Helpers
 * @summary Subtract the specified number of ISO week-numbering years from the given date.
 *
 * @description
 * Subtract the specified number of ISO week-numbering years from the given date.
 *
 * ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
 *
 * @param {Date|Number} date - the date to be changed
 * @param {Number} amount - the amount of ISO week-numbering years to be subtracted. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
 * @returns {Date} the new date with the ISO week-numbering years subtracted
 * @throws {TypeError} 2 arguments required
 *
 * @example
 * // Subtract 5 ISO week-numbering years from 1 September 2014:
 * const result = subISOWeekYears(new Date(2014, 8, 1), 5)
 * //=> Mon Aug 31 2009 00:00:00
 */
export default function subISOWeekYears(
  dirtyDate: Date | number,
  dirtyAmount: number
): Date {
  requiredArgs(2, arguments)

  const amount = toInteger(dirtyAmount)
  return addISOWeekYears(dirtyDate, -amount)
}