// https://github.com/microsoft/TypeScript/blob/master/lib/lib.es2020.intl.d.ts

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declare namespace Intl {
  /**
   * [BCP 47 language tag](http://tools.ietf.org/html/rfc5646) definition.
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locales_argument).
   *
   * [Wikipedia](https://en.wikipedia.org/wiki/IETF_language_tag).
   */
  type BCP47LanguageTag = string;

  /**
   * Unit to use in the relative time internationalized message.
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/format#Parameters).
   *
   * [Specification](https://tc39.es/ecma402/#sec-singularrelativetimeunit).
   */
  type RelativeTimeFormatUnit =
    | 'year'
    | 'years'
    | 'quarter'
    | 'quarters'
    | 'month'
    | 'months'
    | 'week'
    | 'weeks'
    | 'day'
    | 'days'
    | 'hour'
    | 'hours'
    | 'minute'
    | 'minutes'
    | 'second'
    | 'seconds';

  /**
   * The locale matching algorithm to use.
   *
   * [MDN](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_negotiation).
   *
   * [Specification](https://tc39.es/ecma402/#sec-InitializeRelativeTimeFormat).
   */
  type RelativeTimeFormatLocaleMatcher = 'lookup' | 'best fit';

  /**
   * The format of output message.
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat#Parameters).
   *
   * [Specification](https://tc39.es/ecma402/#sec-InitializeRelativeTimeFormat).
   */
  type RelativeTimeFormatNumeric = 'always' | 'auto';

  /**
   * The length of the internationalized message.
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat#Parameters).
   *
   * [Specification](https://tc39.es/ecma402/#sec-InitializeRelativeTimeFormat).
   */
  type RelativeTimeFormatStyle = 'long' | 'short' | 'narrow';

  /**
   * An object with some or all of properties of `options` parameter
   * of `Intl.RelativeTimeFormat` constructor.
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat#Parameters).
   *
   * [Specification](https://tc39.es/ecma402/#sec-InitializeRelativeTimeFormat).
   */
  interface RelativeTimeFormatOptions {
    localeMatcher?: RelativeTimeFormatLocaleMatcher;
    numeric?: RelativeTimeFormatNumeric;
    style?: RelativeTimeFormatStyle;
  }

  /**
   * An object with properties reflecting the locale
   * and formatting options computed during initialization
   * of the `Intel.RelativeTimeFormat` object
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/resolvedOptions#Description).
   *
   * [Specification](https://tc39.es/ecma402/#table-relativetimeformat-resolvedoptions-properties)
   */
  interface ResolvedRelativeTimeFormatOptions {
    locale: BCP47LanguageTag;
    style: RelativeTimeFormatStyle;
    numeric: RelativeTimeFormatNumeric;
    numberingSystem: string;
  }

  /**
   * An object representing the relative time format in parts
   * that can be used for custom locale-aware formatting.
   *
   * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/formatToParts#Using_formatToParts).
   *
   * [Specification](https://tc39.es/ecma402/#sec-FormatRelativeTimeToParts).
   */
  interface RelativeTimeFormatPart {
    type: string;
    value: string;
    unit?: RelativeTimeFormatUnit;
  }

  interface RelativeTimeFormat {
    /**
     * Formats a value and a unit according to the locale
     * and formatting options of the given
     * [`Intl.RelativeTimeFormat`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/RelativeTimeFormat)
     * object.
     *
     * While this method automatically provides the correct plural forms,
     * the grammatical form is otherwise as neutral as possible.
     * It is the caller's responsibility to handle cut-off logic
     * such as deciding between displaying "in 7 days" or "in 1 week".
     * This API does not support relative dates involving compound units.
     * e.g "in 5 days and 4 hours".
     *
     * @param value -  Numeric value to use in the internationalized relative time message
     *
     * @param unit - [Unit](https://tc39.es/ecma402/#sec-singularrelativetimeunit)
     *  to use in the relative time internationalized message.
     *  Possible values are: `"year"`, `"quarter"`, `"month"`, `"week"`,
     *  `"day"`, `"hour"`, `"minute"`, `"second"`.
     *  Plural forms are also permitted.
     *
     * @throws `RangeError` if `unit` was given something other than `unit` possible values
     *
     * @returns Internationalized relative time message as string
     *
     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/format).
     *
     * [Specification](https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat.prototype.format).
     */
    format(value: number, unit: RelativeTimeFormatUnit): string;

    /**
     *  A version of the format method which it returns an array of objects
     *  which represent "parts" of the object,
     *  separating the formatted number into its constituent parts
     *  and separating it from other surrounding text.
     *  These objects have two properties:
     * `type` a NumberFormat formatToParts type, and `value`,
     *  which is the String which is the component of the output.
     *  If a "part" came from NumberFormat,
     *  it will have a unit property which indicates the `unit` being formatted;
     *  literals which are part of the larger frame will not have this property.
     *
     *  @param value - Numeric value to use in the internationalized relative time message
     *
     *  @param unit - [Unit](https://tc39.es/ecma402/#sec-singularrelativetimeunit)
     *   to use in the relative time internationalized message.
     *   Possible values are: `"year"`, `"quarter"`, `"month"`, `"week"`,
     *   `"day"`, `"hour"`, `"minute"`, `"second"`.
     *   Plural forms are also permitted.
     *
     *  @throws `RangeError` if `unit` was given something other than `unit` possible values
     *
     *  @returns Array of [FormatRelativeTimeToParts](https://tc39.es/ecma402/#sec-FormatRelativeTimeToParts)
     *
     *  [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/formatToParts).
     *
     *  [Specification](https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat.prototype.formatToParts).
     */
    formatToParts(value: number, unit: RelativeTimeFormatUnit): RelativeTimeFormatPart[];

    /**
     * Provides access to the locale and options computed during initialization of this `Intl.RelativeTimeFormat` object.
     *
     * @returns A new object with properties reflecting the locale
     *  and formatting options computed during initialization
     *  of the `Intel.RelativeTimeFormat` object.
     *
     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/resolvedOptions).
     *
     * [Specification](https://tc39.es/ecma402/#sec-intl.relativetimeformat.prototype.resolvedoptions)
     */
    resolvedOptions(): ResolvedRelativeTimeFormatOptions;
  }

  /**
   * The [`Intl.RelativeTimeFormat`](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/RelativeTimeFormat)
   * object is a constructor for objects that enable language-sensitive relative time formatting.
   *
   * Part of [Intl object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl)
   * namespace and the [ECMAScript Internationalization API](https://www.ecma-international.org/publications/standards/Ecma-402.htm).
   *
   * [Compatibility](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat#Browser_compatibility).
   *
   * [Polyfills](https://github.com/tc39/proposal-intl-relative-time#polyfills).
   */
  const RelativeTimeFormat: {
    /**
     * Constructor creates [Intl.RelativeTimeFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RelativeTimeFormat)
     * objects
     *
     * @param locales - A string with a [BCP 47 language tag](http://tools.ietf.org/html/rfc5646), or an array of such strings.
     *  For the general form and interpretation of the locales argument,
     *  see the [`Intl` page](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_identification_and_negotiation).
     *
     * @param options - An [object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat#Parameters)
     *  with some or all of options of the formatting.
     *  An object with some or all of the following properties:
     *  - `localeMatcher` - The locale matching algorithm to use.
     *    Possible values are `"lookup"` and `"best fit"`; the default is `"best fit"`.
     *    For information about this option, see [Intl page](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_negotiation).
     *  - `numeric` - The format of output message.
     *    Possible values are: `"always"` (default, e.g., `1 day ago`) or `"auto"` (e.g., `yesterday`).
     *    The `"auto"` value allows to not always have to use numeric values in the output.
     *  - `style` - The length of the internationalized message. Possible values are:
     *    `"long"` (default, e.g., in 1 month),
     *    `"short"` (e.g., in 1 mo.)
     *    or `"narrow"` (e.g., in 1 mo.). The narrow style could be similar to the short style for some locales.
     *
     * @returns [Intl.RelativeTimeFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RelativeTimeFormat) object.
     *
     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat).
     *
     * [Specification](https://tc39.es/ecma402/#sec-intl-relativetimeformat-constructor).
     */
    new (locales?: BCP47LanguageTag | BCP47LanguageTag[], options?: RelativeTimeFormatOptions): RelativeTimeFormat;

    /**
     * Returns an array containing those of the provided locales
     * that are supported in date and time formatting
     * without having to fall back to the runtime's default locale.
     *
     * @param locales - A string with a [BCP 47 language tag](http://tools.ietf.org/html/rfc5646), or an array of such strings.
     *  For the general form and interpretation of the locales argument,
     *  see the [`Intl` page](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_identification_and_negotiation).
     *
     * @param options - An [object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat#Parameters)
     *  with some or all of options of the formatting.
     *  An object with some or all of the following properties:
     *  - `localeMatcher` - The locale matching algorithm to use.
     *    Possible values are `"lookup"` and `"best fit"`; the default is `"best fit"`.
     *    For information about this option, see [Intl page](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_negotiation).
     *  - `numeric` - The format of output message.
     *    Possible values are: `"always"` (default, e.g., `1 day ago`) or `"auto"` (e.g., `yesterday`).
     *    The `"auto"` value allows to not always have to use numeric values in the output.
     *  - `style` - The length of the internationalized message. Possible values are:
     *    `"long"` (default, e.g., in 1 month),
     *    `"short"` (e.g., in 1 mo.)
     *    or `"narrow"` (e.g., in 1 mo.). The narrow style could be similar to the short style for some locales.
     *
     * @returns An array containing those of the provided locales
     *  that are supported in date and time formatting
     *  without having to fall back to the runtime's default locale.
     *
     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/supportedLocalesOf).
     *
     * [Specification](https://tc39.es/ecma402/#sec-Intl.RelativeTimeFormat.supportedLocalesOf).
     */
    supportedLocalesOf(
      locales: BCP47LanguageTag | BCP47LanguageTag[],
      options?: RelativeTimeFormatOptions
    ): BCP47LanguageTag[];
  };

  interface NumberFormatOptions {
    notation?: string;
    unit?: string;
    unitDisplay?: string;
  }

  interface ResolvedNumberFormatOptions {
    notation?: string;
    unit?: string;
    unitDisplay?: string;
  }
}