4 files changed, 180 insertions, 0 deletions
diff --git a/date-fns/src/formatISODuration/index.d.ts b/date-fns/src/formatISODuration/index.d.ts
new file mode 100644
index 0000000..dfbd333
--- /dev/null
+++ b/date-fns/src/formatISODuration/index.d.ts
@@ -0,0 +1,4 @@
+// This file is generated automatically by `scripts/build/typings.js`. Please, don't change it.
+
+import { formatISODuration } from 'date-fns'
+export default formatISODuration
diff --git a/date-fns/src/formatISODuration/index.js b/date-fns/src/formatISODuration/index.js
new file mode 100644
index 0000000..0702457
--- /dev/null
+++ b/date-fns/src/formatISODuration/index.js
@@ -0,0 +1,46 @@
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name formatISODuration
+ * @category Common Helpers
+ * @summary Format a duration object according as ISO 8601 duration string
+ *
+ * @description
+ * Format a duration object according to the ISO 8601 duration standard (https://www.digi.com/resources/documentation/digidocs/90001437-13/reference/r_iso_8601_duration_format.htm)
+ *
+ * @param {Duration} duration - the duration to format
+ *
+ * @returns {String} The ISO 8601 duration string
+ * @throws {TypeError} Requires 1 argument
+ * @throws {Error} Argument must be an object
+ *
+ * @example
+ * // Format the given duration as ISO 8601 string
+ * formatISODuration({
+ *   years: 39,
+ *   months: 2,
+ *   days: 20,
+ *   hours: 7,
+ *   minutes: 5,
+ *   seconds: 0
+ * })
+ * //=> 'P39Y2M20DT0H0M0S'
+ */
+
+export default function formatISODuration(duration) {
+  requiredArgs(1, arguments)
+
+  if (typeof duration !== 'object')
+    throw new Error('Duration must be an object')
+
+  const {
+    years = 0,
+    months = 0,
+    days = 0,
+    hours = 0,
+    minutes = 0,
+    seconds = 0
+  } = duration
+
+  return `P${years}Y${months}M${days}DT${hours}H${minutes}M${seconds}S`
+}
diff --git a/date-fns/src/formatISODuration/index.js.flow b/date-fns/src/formatISODuration/index.js.flow
new file mode 100644
index 0000000..3f8bb2c
--- /dev/null
+++ b/date-fns/src/formatISODuration/index.js.flow
@@ -0,0 +1,52 @@
+// @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: (duration: Duration) => string
diff --git a/date-fns/src/formatISODuration/test.js b/date-fns/src/formatISODuration/test.js
new file mode 100644
index 0000000..ecea358
--- /dev/null
+++ b/date-fns/src/formatISODuration/test.js
@@ -0,0 +1,78 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import formatISODuration from '.'
+import intervalToDuration from '../intervalToDuration'
+
+describe('formatISODuration', function() {
+  it('Everything returns correct duration for arbitrary dates', function() {
+    const start = new Date(1929, 0, 15, 12, 0, 0)
+    const end = new Date(1968, 3, 4, 19, 5, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P39Y2M20DT7H5M0S')
+  })
+  it('Everything returns P1Y1M1DT1H1M1S (1 of everything)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2021, 3, 2, 13, 1, 1)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P1Y1M1DT1H1M1S')
+  })
+  it('Returns P0Y0M0DT0H0M0S when the dates are the same', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2020, 2, 1, 12, 0, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P0Y0M0DT0H0M0S')
+  })
+  it('Seconds returns P0Y0M0DT0H0M1S (1 second)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2020, 2, 1, 12, 0, 1)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P0Y0M0DT0H0M1S')
+  })
+  it('Minutes returns P0Y0M0DT0H1M0S (1 minute)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2020, 2, 1, 12, 1, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P0Y0M0DT0H1M0S')
+  })
+  it('Hours returns P0Y0M0DT1H0M0S (1 hour)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2020, 2, 1, 13, 0, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P0Y0M0DT1H0M0S')
+  })
+  it('Days returns P0Y0M1DT0H0M0S (1 day)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2020, 2, 2, 12, 0, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P0Y0M1DT0H0M0S')
+  })
+  it('Months returns P0Y1M0DT0H0M0S (1 month)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2020, 3, 1, 12, 0, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P0Y1M0DT0H0M0S')
+  })
+  it('Years returns P1Y0M0DT0H0M1S (1 year)', function() {
+    const start = new Date(2020, 2, 1, 12, 0, 0)
+    const end = new Date(2021, 2, 1, 12, 0, 0)
+    const result = formatISODuration(intervalToDuration({ start, end }))
+
+    assert(result === 'P1Y0M0DT0H0M0S')
+  })
+
+  it('returns P0Y0M0DT0H0M0S when given an empty object', function() {
+    const result = formatISODuration({})
+
+    assert(result === 'P0Y0M0DT0H0M0S')
+  })
+})