weseek__growi/apps/app/src/server/util/locale-utils.ts

import { Lang } from '@growi/core/dist/interfaces';
import type { IncomingHttpHeaders } from 'http';

import * as i18nextConfig from '^/config/i18next.config';

const ACCEPT_LANG_MAP = {
  en: Lang.en_US,
  ja: Lang.ja_JP,
  zh: Lang.zh_CN,
  fr: Lang.fr_FR,
  ko: Lang.ko_KR,
};

/**
 * It return the first language that matches ACCEPT_LANG_MAP keys from sorted accept languages array
 * @param sortedAcceptLanguagesArray
 */
const getPreferredLanguage = (sortedAcceptLanguagesArray: string[]): Lang => {
  for (const lang of sortedAcceptLanguagesArray) {
    const matchingLang = Object.keys(ACCEPT_LANG_MAP).find((key) =>
      lang.includes(key),
    );
    if (matchingLang) return ACCEPT_LANG_MAP[matchingLang];
  }
  return i18nextConfig.defaultLang;
};

/**
 * Detect locale from browser accept language
 * @param headers
 */
export const detectLocaleFromBrowserAcceptLanguage = (
  headers: IncomingHttpHeaders,
): Lang => {
  // 1. get the header accept-language
  // ex. "ja,ar-SA;q=0.8,en;q=0.6,en-CA;q=0.4,en-US;q=0.2"
  const acceptLanguages = headers['accept-language'];

  if (acceptLanguages == null) {
    return i18nextConfig.defaultLang;
  }

  // 1. trim blank spaces.
  // 2. separate by ,.
  // 3. if "lang;q=x", then { 'x', 'lang' } to add to the associative array.
  //    if "lang" has no weight x (";q=x"), add it with key = 1.
  // ex. {'1': 'ja','0.8': 'ar-SA','0.6': 'en','0.4': 'en-CA','0.2': 'en-US'}
  const acceptLanguagesDict = acceptLanguages
    .replace(/\s+/g, '')
    .split(',')
    .map((item) => item.split(/\s*;\s*q\s*=\s*/))
    .reduce((acc, [key, value = '1']) => {
      acc[value] = key;
      return acc;
    }, {});

  // 1. create an array of sorted languages in descending order.
  // ex. [ 'ja', 'ar-SA', 'en', 'en-CA', 'en-US' ]
  const sortedAcceptLanguagesArray = Object.keys(acceptLanguagesDict)
    .sort((x, y) => y.localeCompare(x))
    .map((item) => acceptLanguagesDict[item]);

  return getPreferredLanguage(sortedAcceptLanguagesArray);
};