5 files changed, 310 insertions, 0 deletions
diff --git a/date-fns/src/differenceInCalendarWeeks/benchmark.js b/date-fns/src/differenceInCalendarWeeks/benchmark.js
new file mode 100644
index 0000000..d014aee
--- /dev/null
+++ b/date-fns/src/differenceInCalendarWeeks/benchmark.js
@@ -0,0 +1,16 @@
+// @flow
+/* eslint-env mocha */
+/* global suite, benchmark */
+
+import differenceInCalendarWeeks from '.'
+
+suite('differenceInCalendarWeeks', function () {
+  benchmark('date-fns', function () {
+    return differenceInCalendarWeeks(this.dateA, this.dateB)
+  })
+}, {
+  setup: function () {
+    this.dateA = new Date()
+    this.dateB = new Date(this.dateA.getTime() + 604800000)
+  }
+})
diff --git a/date-fns/src/differenceInCalendarWeeks/index.d.ts b/date-fns/src/differenceInCalendarWeeks/index.d.ts
new file mode 100644
index 0000000..c370dd6
--- /dev/null
+++ b/date-fns/src/differenceInCalendarWeeks/index.d.ts
@@ -0,0 +1,4 @@
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { differenceInCalendarWeeks } from 'date-fns'
+export default differenceInCalendarWeeks
diff --git a/date-fns/src/differenceInCalendarWeeks/index.js.flow b/date-fns/src/differenceInCalendarWeeks/index.js.flow
new file mode 100644
index 0000000..e4968a9
--- /dev/null
+++ b/date-fns/src/differenceInCalendarWeeks/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: (
+  dateLeft: Date | number,
+  dateRight: Date | number,
+  options?: {
+    locale?: Locale,
+    weekStartsOn?: 0 | 1 | 2 | 3 | 4 | 5 | 6,
+  }
+) => number
diff --git a/date-fns/src/differenceInCalendarWeeks/index.ts b/date-fns/src/differenceInCalendarWeeks/index.ts
new file mode 100644
index 0000000..da15cb7
--- /dev/null
+++ b/date-fns/src/differenceInCalendarWeeks/index.ts
@@ -0,0 +1,67 @@
+import startOfWeek from '../startOfWeek/index'
+import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+import { LocaleOptions, WeekStartOptions } from '../types'
+
+const MILLISECONDS_IN_WEEK = 604800000
+
+/**
+ * @name differenceInCalendarWeeks
+ * @category Week Helpers
+ * @summary Get the number of calendar weeks between the given dates.
+ *
+ * @description
+ * Get the number of calendar weeks between the given dates.
+ *
+ * ### 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} dateLeft - the later date
+ * @param {Date|Number} dateRight - the earlier 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 {Number} the number of calendar weeks
+ * @throws {TypeError} 2 arguments required
+ * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
+ *
+ * @example
+ * // How many calendar weeks are between 5 July 2014 and 20 July 2014?
+ * const result = differenceInCalendarWeeks(
+ *   new Date(2014, 6, 20),
+ *   new Date(2014, 6, 5)
+ * )
+ * //=> 3
+ *
+ * @example
+ * // If the week starts on Monday,
+ * // how many calendar weeks are between 5 July 2014 and 20 July 2014?
+ * const result = differenceInCalendarWeeks(
+ *   new Date(2014, 6, 20),
+ *   new Date(2014, 6, 5),
+ *   { weekStartsOn: 1 }
+ * )
+ * //=> 2
+ */
+export default function differenceInCalendarWeeks(
+  dirtyDateLeft: Date | number,
+  dirtyDateRight: Date | number,
+  dirtyOptions?: LocaleOptions & WeekStartOptions
+): number {
+  requiredArgs(2, arguments)
+
+  const startOfWeekLeft = startOfWeek(dirtyDateLeft, dirtyOptions)
+  const startOfWeekRight = startOfWeek(dirtyDateRight, dirtyOptions)
+
+  const timestampLeft =
+    startOfWeekLeft.getTime() - getTimezoneOffsetInMilliseconds(startOfWeekLeft)
+  const timestampRight =
+    startOfWeekRight.getTime() -
+    getTimezoneOffsetInMilliseconds(startOfWeekRight)
+
+  // Round the number of days to the nearest integer
+  // because the number of milliseconds in a week is not constant
+  // (e.g. it's different in the week of the daylight saving time clock shift)
+  return Math.round((timestampLeft - timestampRight) / MILLISECONDS_IN_WEEK)
+}
diff --git a/date-fns/src/differenceInCalendarWeeks/test.ts b/date-fns/src/differenceInCalendarWeeks/test.ts
new file mode 100644
index 0000000..8a1f6e2
--- /dev/null
+++ b/date-fns/src/differenceInCalendarWeeks/test.ts
@@ -0,0 +1,164 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import differenceInCalendarWeeks from '.'
+
+describe('differenceInCalendarWeeks', function () {
+  it('returns the number of calendar weeks between the given dates', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 6 /* Jul */, 8, 18, 0),
+      new Date(2014, 5 /* Jun */, 29, 6, 0)
+    )
+    assert(result === 1)
+  })
+
+  it('allows to specify which day is the first day of the week', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 6 /* Jul */, 8, 18, 0),
+      new Date(2014, 5 /* Jun */, 29, 6, 0),
+      { weekStartsOn: 1 }
+    )
+    assert(result === 2)
+  })
+
+  it('allows to specify which day is the first day of the week in locale', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 6 /* Jul */, 8, 18, 0),
+      new Date(2014, 5 /* Jun */, 29, 6, 0),
+      {
+        // @ts-expect-error
+        locale: {
+          options: { weekStartsOn: 1 },
+        },
+      }
+    )
+    assert(result === 2)
+  })
+
+  it('`options.weekStartsOn` overwrites the first day of the week specified in locale', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 6 /* Jul */, 8, 18, 0),
+      new Date(2014, 5 /* Jun */, 29, 6, 0),
+      {
+        weekStartsOn: 1,
+        // @ts-expect-error
+        locale: {
+          options: { weekStartsOn: 0 },
+        },
+      }
+    )
+    assert(result === 2)
+  })
+
+  it('returns a positive number if the time value of the second date is smaller', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 6 /* Jul */, 8, 18, 0),
+      new Date(2014, 5 /* Jun */, 29, 6, 0),
+      // @ts-expect-error
+      { weekStartsOn: '1' }
+    )
+    assert(result === 2)
+  })
+
+  it('returns a negative number if the time value of the first date is smaller', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 5 /* Jun */, 29, 6, 0),
+      new Date(2014, 6 /* Jul */, 8, 18, 0)
+    )
+    assert(result === -1)
+  })
+
+  it('accepts timestamps', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2014, 6 /* Jul */, 12).getTime(),
+      new Date(2014, 6 /* Jul */, 2).getTime()
+    )
+    assert(result === 1)
+  })
+
+  describe('edge cases', function () {
+    it('the difference is less than a week, but the given dates are in different calendar weeks', function () {
+      const result = differenceInCalendarWeeks(
+        new Date(2014, 6 /* Jul */, 6),
+        new Date(2014, 6 /* Jul */, 5)
+      )
+      assert(result === 1)
+    })
+
+    it('the same for the swapped dates', function () {
+      const result = differenceInCalendarWeeks(
+        new Date(2014, 6 /* Jul */, 5),
+        new Date(2014, 6 /* Jul */, 6)
+      )
+      assert(result === -1)
+    })
+
+    it('the days of weeks of the given dates are the same', function () {
+      const result = differenceInCalendarWeeks(
+        new Date(2014, 6 /* Jul */, 9),
+        new Date(2014, 6 /* Jul */, 2)
+      )
+      assert(result === 1)
+    })
+
+    it('the given dates are the same', function () {
+      const result = differenceInCalendarWeeks(
+        new Date(2014, 8 /* Sep */, 5, 0, 0),
+        new Date(2014, 8 /* Sep */, 5, 0, 0)
+      )
+      assert(result === 0)
+    })
+
+    it('does not return -0 when the given dates are the same', () => {
+      function isNegativeZero(x: number): boolean {
+        return x === 0 && 1 / x < 0
+      }
+
+      const result = differenceInCalendarWeeks(
+        new Date(2014, 8 /* Sep */, 5, 0, 0),
+        new Date(2014, 8 /* Sep */, 5, 0, 0)
+      )
+
+      const resultIsNegative = isNegativeZero(result)
+      assert(resultIsNegative === false)
+    })
+  })
+
+  it('returns NaN if the first date is `Invalid Date`', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(NaN),
+      new Date(2017, 0 /* Jan */, 1)
+    )
+    assert(isNaN(result))
+  })
+
+  it('returns NaN if the second date is `Invalid Date`', function () {
+    const result = differenceInCalendarWeeks(
+      new Date(2017, 0 /* Jan */, 1),
+      new Date(NaN)
+    )
+    assert(isNaN(result))
+  })
+
+  it('returns NaN if the both dates are `Invalid Date`', function () {
+    const result = differenceInCalendarWeeks(new Date(NaN), new Date(NaN))
+    assert(isNaN(result))
+  })
+
+  it('throws `RangeError` if `options.weekStartsOn` is not convertable to 0, 1, ..., 6 or undefined', function () {
+    // @ts-expect-error
+    const block = differenceInCalendarWeeks.bind(
+      null,
+      new Date(2014, 6 /* Jul */, 8, 18, 0),
+      new Date(2014, 5 /* Jun */, 29, 6, 0),
+      { weekStartsOn: NaN }
+    )
+    assert.throws(block, RangeError)
+  })
+
+  it('throws TypeError exception if passed less than 2 arguments', function () {
+    assert.throws(differenceInCalendarWeeks.bind(null), TypeError)
+    assert.throws(differenceInCalendarWeeks.bind(null, 1), TypeError)
+  })
+})