import { toDate } from "./toDate.mjs";

/**
 * @name differenceInCalendarYears
 * @category Year Helpers
 * @summary Get the number of calendar years between the given dates.
 *
 * @description
 * Get the number of calendar years between the given dates.
 *
 * @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
 *
 * @param dateLeft - The later date
 * @param dateRight - The earlier date

 * @returns The number of calendar years
 *
 * @example
 * // How many calendar years are between 31 December 2013 and 11 February 2015?
 * const result = differenceInCalendarYears(
 *   new Date(2015, 1, 11),
 *   new Date(2013, 11, 31)
 * )
 * //=> 2
 */
export function differenceInCalendarYears(dateLeft, dateRight) {
  const _dateLeft = toDate(dateLeft);
  const _dateRight = toDate(dateRight);

  return _dateLeft.getFullYear() - _dateRight.getFullYear();
}

// Fallback for modularized imports:
export default differenceInCalendarYears;