4 files changed, 236 insertions, 0 deletions
diff --git a/date-fns/src/getWeekYear/index.d.ts b/date-fns/src/getWeekYear/index.d.ts
new file mode 100644
index 0000000..c8fc528
--- /dev/null
+++ b/date-fns/src/getWeekYear/index.d.ts
@@ -0,0 +1,4 @@
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { getWeekYear } from 'date-fns'
+export default getWeekYear
diff --git a/date-fns/src/getWeekYear/index.js.flow b/date-fns/src/getWeekYear/index.js.flow
new file mode 100644
index 0000000..2c948ae
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+++ b/date-fns/src/getWeekYear/index.js.flow
@@ -0,0 +1,59 @@
+// @flow
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+export type Interval = {
+  start: Date | number,
+  end: Date | number,
+}
+
+export type Locale = {
+  code?: string,
+  formatDistance?: (...args: Array<any>) => any,
+  formatRelative?: (...args: Array<any>) => any,
+  localize?: {
+    ordinalNumber: (...args: Array<any>) => any,
+    era: (...args: Array<any>) => any,
+    quarter: (...args: Array<any>) => any,
+    month: (...args: Array<any>) => any,
+    day: (...args: Array<any>) => any,
+    dayPeriod: (...args: Array<any>) => any,
+  },
+  formatLong?: {
+    date: (...args: Array<any>) => any,
+    time: (...args: Array<any>) => any,
+    dateTime: (...args: Array<any>) => any,
+  },
+  match?: {
+    ordinalNumber: (...args: Array<any>) => any,
+    era: (...args: Array<any>) => any,
+    quarter: (...args: Array<any>) => any,
+    month: (...args: Array<any>) => any,
+    day: (...args: Array<any>) => any,
+    dayPeriod: (...args: Array<any>) => any,
+  },
+  options?: {
+    weekStartsOn?: 0 | 1 | 2 | 3 | 4 | 5 | 6,
+    firstWeekContainsDate?: 1 | 2 | 3 | 4 | 5 | 6 | 7,
+  },
+}
+
+export type Duration = {
+  years?: number,
+  months?: number,
+  weeks?: number,
+  days?: number,
+  hours?: number,
+  minutes?: number,
+  seconds?: number,
+}
+
+export type Day = 0 | 1 | 2 | 3 | 4 | 5 | 6
+
+declare module.exports: (
+  date: Date | number,
+  options?: {
+    locale?: Locale,
+    weekStartsOn?: 0 | 1 | 2 | 3 | 4 | 5 | 6,
+    firstWeekContainsDate?: 1 | 2 | 3 | 4 | 5 | 6 | 7,
+  }
+) => number
diff --git a/date-fns/src/getWeekYear/index.ts b/date-fns/src/getWeekYear/index.ts
new file mode 100644
index 0000000..649b8d1
--- /dev/null
+++ b/date-fns/src/getWeekYear/index.ts
@@ -0,0 +1,98 @@
+import startOfWeek from '../startOfWeek/index'
+import toDate from '../toDate/index'
+import toInteger from '../_lib/toInteger/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+import {
+  WeekStartOptions,
+  LocaleOptions,
+  FirstWeekContainsDateOptions,
+} from '../types'
+
+/**
+ * @name getWeekYear
+ * @category Week-Numbering Year Helpers
+ * @summary Get the local week-numbering year of the given date.
+ *
+ * @description
+ * Get the local week-numbering year of the given date.
+ * 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 given 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 {Number} the local 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
+ * // Which week numbering year is 26 December 2004 with the default settings?
+ * const result = getWeekYear(new Date(2004, 11, 26))
+ * //=> 2005
+ *
+ * @example
+ * // Which week numbering year is 26 December 2004 if week starts on Saturday?
+ * const result = getWeekYear(new Date(2004, 11, 26), { weekStartsOn: 6 })
+ * //=> 2004
+ *
+ * @example
+ * // Which week numbering year is 26 December 2004 if the first week contains 4 January?
+ * const result = getWeekYear(new Date(2004, 11, 26), { firstWeekContainsDate: 4 })
+ * //=> 2004
+ */
+export default function getWeekYear(
+  dirtyDate: Date | number,
+  options?: LocaleOptions & WeekStartOptions & FirstWeekContainsDateOptions
+): number {
+  requiredArgs(1, arguments)
+
+  const date = toDate(dirtyDate)
+  const year = date.getFullYear()
+
+  const localeFirstWeekContainsDate =
+    options?.locale?.options?.firstWeekContainsDate
+  const defaultFirstWeekContainsDate =
+    localeFirstWeekContainsDate == null
+      ? 1
+      : toInteger(localeFirstWeekContainsDate)
+  const firstWeekContainsDate =
+    options?.firstWeekContainsDate == null
+      ? defaultFirstWeekContainsDate
+      : toInteger(options.firstWeekContainsDate)
+
+  // Test if weekStartsOn is between 1 and 7 _and_ is not NaN
+  if (!(firstWeekContainsDate >= 1 && firstWeekContainsDate <= 7)) {
+    throw new RangeError(
+      'firstWeekContainsDate must be between 1 and 7 inclusively'
+    )
+  }
+
+  const firstWeekOfNextYear = new Date(0)
+  firstWeekOfNextYear.setFullYear(year + 1, 0, firstWeekContainsDate)
+  firstWeekOfNextYear.setHours(0, 0, 0, 0)
+  const startOfNextYear = startOfWeek(firstWeekOfNextYear, options)
+
+  const firstWeekOfThisYear = new Date(0)
+  firstWeekOfThisYear.setFullYear(year, 0, firstWeekContainsDate)
+  firstWeekOfThisYear.setHours(0, 0, 0, 0)
+  const startOfThisYear = startOfWeek(firstWeekOfThisYear, options)
+
+  if (date.getTime() >= startOfNextYear.getTime()) {
+    return year + 1
+  } else if (date.getTime() >= startOfThisYear.getTime()) {
+    return year
+  } else {
+    return year - 1
+  }
+}
diff --git a/date-fns/src/getWeekYear/test.ts b/date-fns/src/getWeekYear/test.ts
new file mode 100644
index 0000000..0f8bf54
--- /dev/null
+++ b/date-fns/src/getWeekYear/test.ts
@@ -0,0 +1,75 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'assert'
+import getWeekYear from '.'
+
+describe('getWeekYear', () => {
+  it('returns the local week-numbering year of the given date', () => {
+    const result = getWeekYear(new Date(2004, 11 /* Dec */, 26))
+    assert(result === 2005)
+  })
+
+  it('accepts a timestamp', () => {
+    const result = getWeekYear(new Date(2000, 11 /* Dec */, 30).getTime())
+    assert(result === 2000)
+  })
+
+  it('handles dates before 100 AD', () => {
+    const initialDate = new Date(0)
+    initialDate.setFullYear(7, 11 /* Dec */, 31)
+    initialDate.setHours(0, 0, 0, 0)
+    const result = getWeekYear(initialDate)
+    assert(result === 8)
+  })
+
+  it('returns NaN if the given date is invalid', () => {
+    const result = getWeekYear(new Date(NaN))
+    assert(isNaN(result))
+  })
+
+  it('allows to specify `weekStartsOn` and `firstWeekContainsDate` in locale', () => {
+    const date = new Date(2004, 11 /* Dec */, 26)
+    const result = getWeekYear(date, {
+      // @ts-expect-error
+      locale: {
+        options: { weekStartsOn: 1, firstWeekContainsDate: 4 },
+      },
+    })
+    assert(result === 2004)
+  })
+
+  it('`options.weekStartsOn` overwrites the first day of the week specified in locale', () => {
+    const date = new Date(2004, 11 /* Dec */, 26)
+    const result = getWeekYear(date, {
+      weekStartsOn: 1,
+      firstWeekContainsDate: 4,
+      // @ts-expect-error
+      locale: {
+        options: { weekStartsOn: 0, firstWeekContainsDate: 1 },
+      },
+    })
+    assert(result === 2004)
+  })
+
+  it('throws `RangeError` if `options.weekStartsOn` is not convertable to 0, 1, ..., 6 or undefined', () => {
+    // @ts-expect-error
+    const block = getWeekYear.bind(null, new Date(2007, 11 /* Dec */, 31), {
+      weekStartsOn: NaN,
+    })
+    assert.throws(block, RangeError)
+  })
+
+  it('throws `RangeError` if `options.firstWeekContainsDate` is not convertable to 1, 2, ..., 7 or undefined', () => {
+    // @ts-expect-error
+    const block = getWeekYear.bind(null, new Date(2007, 11 /* Dec */, 31), {
+      firstWeekContainsDate: NaN,
+    })
+    assert.throws(block, RangeError)
+  })
+
+  it('throws TypeError exception if passed less than 1 argument', () => {
+    // @ts-expect-error
+    assert.throws(getWeekYear.bind(null), TypeError)
+  })
+})