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

/**
 * @name subYears
 * @category Year Helpers
 * @summary Subtract the specified number of years from the given date.
 *
 * @description
 * Subtract the specified number of years from the given date.
 *
 * @param {Date|Number} date - the date to be changed
 * @param {Number} amount - the amount of 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 years subtracted
 * @throws {TypeError} 2 arguments required
 *
 * @example
 * // Subtract 5 years from 1 September 2014:
 * const result = subYears(new Date(2014, 8, 1), 5)
 * //=> Tue Sep 01 2009 00:00:00
 */
export default function subYears(
  dirtyDate: Date | number,
  dirtyAmount: number
): Date {
  requiredArgs(2, arguments)

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