import { getDefaultOptions } from "./_lib/defaultOptions.js";
import { toDate } from "./toDate.js";

/**
 * The {@link startOfWeek} function options.
 */

/**
 * @name startOfWeek
 * @category Week Helpers
 * @summary Return the start of a week for the given date.
 *
 * @description
 * Return the start of a week for the given date.
 * The result will be in the local timezone.
 *
 * @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).
 * @typeParam ResultDate - The result `Date` type, it is the type returned from the context function if it is passed, or inferred from the arguments.
 *
 * @param date - The original date
 * @param options - An object with options
 *
 * @returns The start of a week
 *
 * @example
 * // The start of a week for 2 September 2014 11:55:00:
 * const result = startOfWeek(new Date(2014, 8, 2, 11, 55, 0))
 * //=> Sun Aug 31 2014 00:00:00
 *
 * @example
 * // If the week starts on Monday, the start of the week for 2 September 2014 11:55:00:
 * const result = startOfWeek(new Date(2014, 8, 2, 11, 55, 0), { weekStartsOn: 1 })
 * //=> Mon Sep 01 2014 00:00:00
 */
export function startOfWeek(date, options) {
  const defaultOptions = getDefaultOptions();
  const weekStartsOn =
    options?.weekStartsOn ??
    options?.locale?.options?.weekStartsOn ??
    defaultOptions.weekStartsOn ??
    defaultOptions.locale?.options?.weekStartsOn ??
    0;

  const _date = toDate(date, options?.in);
  const day = _date.getDay();
  const diff = (day < weekStartsOn ? 7 : 0) + day - weekStartsOn;

  _date.setDate(_date.getDate() - diff);
  _date.setHours(0, 0, 0, 0);
  return _date;
}

// Fallback for modularized imports:
export default startOfWeek;