documenso/packages/lib/utils/i18n.ts

import type { ReadonlyRequestCookies } from 'next/dist/server/web/spec-extension/adapters/request-cookies';

import type { I18n } from '@lingui/core';

import { IS_APP_WEB, IS_APP_WEB_I18N_ENABLED } from '../constants/app';
import type { I18nLocaleData, SupportedLanguageCodes } from '../constants/i18n';
import { APP_I18N_OPTIONS } from '../constants/i18n';

export async function dynamicActivate(i18nInstance: I18n, locale: string) {
  const { messages } = await import(
    `../translations/${locale}/${IS_APP_WEB ? 'web' : 'marketing'}.js`
  );

  i18nInstance.loadAndActivate({ locale, messages });
}

const parseLanguageFromLocale = (locale: string): SupportedLanguageCodes | null => {
  const [language, _country] = locale.split('-');

  const foundSupportedLanguage = APP_I18N_OPTIONS.supportedLangs.find(
    (lang): lang is SupportedLanguageCodes => lang === language,
  );

  if (!foundSupportedLanguage) {
    return null;
  }

  return foundSupportedLanguage;
};

/**
 * Extract the language if supported from the cookies header.
 *
 * Returns `null` if not supported or not found.
 */
export const extractLocaleDataFromCookies = (
  cookies: ReadonlyRequestCookies,
): SupportedLanguageCodes | null => {
  const preferredLocale = cookies.get('i18n')?.value || '';

  const language = parseLanguageFromLocale(preferredLocale || '');

  if (!language) {
    return null;
  }

  return language;
};

/**
 * Extracts the language from the `accept-language` header.
 */
export const extractLocaleDataFromHeaders = (
  headers: Headers,
): { lang: SupportedLanguageCodes | null; locales: string[] } => {
  const headerLocales = (headers.get('accept-language') ?? '').split(',');

  const language = parseLanguageFromLocale(headerLocales[0]);

  return {
    lang: language,
    locales: [headerLocales[0]],
  };
};

type ExtractLocaleDataOptions = {
  headers: Headers;
  cookies: ReadonlyRequestCookies;
};

/**
 * Extract the supported language from the cookies, then header if not found.
 *
 * Will return the default fallback language if not found.
 */
export const extractLocaleData = ({
  headers,
  cookies,
}: ExtractLocaleDataOptions): I18nLocaleData => {
  let lang: SupportedLanguageCodes | null = extractLocaleDataFromCookies(cookies);

  const langHeader = extractLocaleDataFromHeaders(headers);

  if (!lang && langHeader?.lang) {
    lang = langHeader.lang;
  }

  // Override web app to be English.
  if (!IS_APP_WEB_I18N_ENABLED && IS_APP_WEB) {
    lang = 'en';
  }

  return {
    lang: lang || APP_I18N_OPTIONS.sourceLang,
    locales: langHeader.locales,
  };
};