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+import getWeekYear from '../getWeekYear/index'
+import startOfWeek from '../startOfWeek/index'
+import toInteger from '../_lib/toInteger/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name startOfWeekYear
+ * @category Week-Numbering Year Helpers
+ * @summary Return the start of a local week-numbering year for the given date.
+ *
+ * @description
+ * Return the start of a local week-numbering year.
+ * The exact calculation depends on the values of
+ * `options.weekStartsOn` (which is the index of the first day of the week)
+ * and `options.firstWeekContainsDate` (which is the day of January, which is always in
+ * the first week of the week-numbering year)
+ *
+ * Week numbering: https://en.wikipedia.org/wiki/Week#Week_numbering
+ *
+ * ### 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)
+ * @param {1|2|3|4|5|6|7} [options.firstWeekContainsDate=1] - the day of January, which is always in the first week of the year
+ * @returns {Date} the start of a week-numbering year
+ * @throws {TypeError} 1 argument required
+ * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
+ * @throws {RangeError} `options.firstWeekContainsDate` must be between 1 and 7
+ *
+ * @example
+ * // The start of an a week-numbering year for 2 July 2005 with default settings:
+ * var result = startOfWeekYear(new Date(2005, 6, 2))
+ * //=> Sun Dec 26 2004 00:00:00
+ *
+ * @example
+ * // The start of a week-numbering year for 2 July 2005
+ * // if Monday is the first day of week
+ * // and 4 January is always in the first week of the year:
+ * var result = startOfWeekYear(new Date(2005, 6, 2), {
+ *   weekStartsOn: 1,
+ *   firstWeekContainsDate: 4
+ * })
+ * //=> Mon Jan 03 2005 00:00:00
+ */
+export default function startOfWeekYear(dirtyDate, dirtyOptions) {
+  requiredArgs(1, arguments)
+
+  var options = dirtyOptions || {}
+  var locale = options.locale
+  var localeFirstWeekContainsDate =
+    locale && locale.options && locale.options.firstWeekContainsDate
+  var defaultFirstWeekContainsDate =
+    localeFirstWeekContainsDate == null
+      ? 1
+      : toInteger(localeFirstWeekContainsDate)
+  var firstWeekContainsDate =
+    options.firstWeekContainsDate == null
+      ? defaultFirstWeekContainsDate
+      : toInteger(options.firstWeekContainsDate)
+
+  var year = getWeekYear(dirtyDate, dirtyOptions)
+  var firstWeek = new Date(0)
+  firstWeek.setFullYear(year, 0, firstWeekContainsDate)
+  firstWeek.setHours(0, 0, 0, 0)
+  var date = startOfWeek(firstWeek, dirtyOptions)
+  return date
+}