import { LocaleOptions, WeekStartOptions } from '../types'
import toDate from '../toDate/index'
import toInteger from '../_lib/toInteger/index'
import requiredArgs from '../_lib/requiredArgs/index'

/**
 * @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.
 *
 * ### v2.0.0 breaking changes:
 *
 * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
 *
 * @param {Date|Number} date - the original date
 * @param {Object} [options] - an object with options.
 * @param {Locale} [options.locale=defaultLocale] - the locale object. See [Locale]{@link https://date-fns.org/docs/Locale}
 * @param {0|1|2|3|4|5|6} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
 * @returns {Date} the start of a week
 * @throws {TypeError} 1 argument required
 * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
 *
 * @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 default function startOfWeek(
  dirtyDate: Date | number,
  dirtyOptions?: LocaleOptions & WeekStartOptions
): Date {
  requiredArgs(1, arguments)

  const options = dirtyOptions || {}
  const locale = options.locale
  const localeWeekStartsOn =
    locale && locale.options && locale.options.weekStartsOn
  const defaultWeekStartsOn =
    localeWeekStartsOn == null ? 0 : toInteger(localeWeekStartsOn)
  const weekStartsOn =
    options.weekStartsOn == null
      ? defaultWeekStartsOn
      : toInteger(options.weekStartsOn)

  // Test if weekStartsOn is between 0 and 6 _and_ is not NaN
  if (!(weekStartsOn >= 0 && weekStartsOn <= 6)) {
    throw new RangeError('weekStartsOn must be between 0 and 6 inclusively')
  }

  const date = toDate(dirtyDate)
  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
}
