/*
 * Copyright 2020 Adobe. All rights reserved.
 * This file is licensed to you under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under
 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

// https://en.wikipedia.org/wiki/Right-to-left
const RTL_SCRIPTS = new Set(['Arab', 'Syrc', 'Samr', 'Mand', 'Thaa', 'Mend', 'Nkoo', 'Adlm', 'Rohg', 'Hebr']);
const RTL_LANGS = new Set(['ae', 'ar', 'arc', 'bcc', 'bqi', 'ckb', 'dv', 'fa', 'glk', 'he', 'ku', 'mzn', 'nqo', 'pnb', 'ps', 'sd', 'ug', 'ur', 'yi']);

/**
 * Determines if a locale is read right to left using [Intl.Locale]{@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Locale}.
 */
export function isRTL(localeString: string): boolean {
  // If the Intl.Locale API is available, use it to get the locale's text direction.
  if (Intl.Locale) {
    let locale = new Intl.Locale(localeString).maximize();

    // Use the text info object to get the direction if possible.
    // @ts-ignore - this was implemented as a property by some browsers before it was standardized as a function.
    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Locale/getTextInfo
    let textInfo = typeof locale.getTextInfo === 'function' ? locale.getTextInfo() : locale.textInfo;
    if (textInfo) {
      return textInfo.direction === 'rtl';
    }

    // Fallback: guess using the script.
    // This is more accurate than guessing by language, since languages can be written in multiple scripts.
    if (locale.script) {
      return RTL_SCRIPTS.has(locale.script);
    }
  }

  // If not, just guess by the language (first part of the locale)
  let lang = localeString.split('-')[0];
  return RTL_LANGS.has(lang);
}