import i18next, { ReactOptions, TFunction } from "i18next";
import LanguageDetector from "i18next-browser-languagedetector";
import HttpApi, { RequestCallback } from "i18next-http-backend";
import { initReactI18next } from "react-i18next";
import isDefined from "../Core/isDefined";

export interface I18nBackendOptions {
  /**
   *  A few overrides that would be useful from a TerriaMap. The
   *  i18next-http-backend library is still in its early stages, so the
   *  documentation is sparse - the types are a quick glean from upstream
   *  `i18next-http-backend` source
   *  */
  crossDomain?: boolean;
  loadPath?: string;
  parse?: (
    data: any,
    languages: string | [string],
    namespaces: string
  ) => { [key: string]: any };
  request?: (
    options: any,
    url: string,
    payload: any,
    callback: RequestCallback
  ) => void;
}

export interface I18nStartOptions {
  backend?: I18nBackendOptions;
  skipInit?: boolean; // skip initialising i18next. Used in CI
}

export interface LanguageConfiguration {
  enabled: boolean;
  debug: boolean;
  react: ReactOptions;
  languages: object;
  fallbackLanguage: string;
  changeLanguageOnStartWhen: string[];
  lookupCookie?: string;

  /** Base URL for override namespace translation files. If set, this makes up the base URL for translation override files. Should end in /
   *
   * For example, if `overridesBaseUrl = "test/path/"`, then the full path for translation override files will be `"test/path/{{lng}}.json"`
   **/
  overridesBaseUrl?: string;
}
const defaultLanguageConfiguration = {
  enabled: false,
  debug: false,
  react: {
    useSuspense: false
  },
  languages: {
    en: "english"
  },
  fallbackLanguage: "en",
  changeLanguageOnStartWhen: [
    "querystring",
    "localStorage",
    "navigator",
    "htmlTag"
  ],
  lookupCookie: "i18next"
};

class Internationalization {
  static initLanguage(
    languageConfiguration: LanguageConfiguration | undefined,
    /**
     * i18nOptions is explicitly a separate option from `languageConfiguration`,
     * as `languageConfiguration` can be serialised, but `i18nOptions` may have
     * some functions that are passed in from a TerriaMap
     */
    i18StartOptions: I18nStartOptions | undefined,
    terriajsResourcesBaseUrl: string
  ): Promise<TFunction> {
    const languageConfig = Object.assign(
      defaultLanguageConfiguration,
      languageConfiguration
    );
    /**
     * initialization of the language with i18next
     *
     * @param {Object} languageConfiguration configuration read from config.json
     * @param {Boolean} languageConfiguration.enabled is GUI language switching enabled
     * @param {Object} languageConfiguration.languages the languages to be used, example `{en: "english"}
     * @param {String} languageConfiguration.fallbackLanguage the language to be used on startup
     * @param {Array} languageConfiguration.changeLanguageOnStartWhen
     * @param {String} languageConfiguration.lookupCookie name of the cookie that handles i18n
     */

    return i18next
      .use(HttpApi)
      .use(LanguageDetector)
      .use(initReactI18next)
      .init({
        // use i18next-json-v3 as weblate still doesn't support v4
        compatibilityJSON: "v3",
        debug: languageConfig.debug,
        react: languageConfig.react,
        fallbackLng: languageConfig.fallbackLanguage,
        // whitelist: Object.keys(languageConfig.languages),
        // deprecated
        supportedLngs: Object.keys(languageConfig.languages),

        // to allow en-US when only en is on the whitelist - nonExplicitWhitelist must be set to true
        /**
         * for anyone else confused as I was, `nonExplicitSupportedLngs` &&
         * `load: "languageOnly"` seems functionally equivalent but perhaps this
         * will change in the future
         *
         * > also in my mind I conflated the config surrounding this a little
         * > bit with `load: "languageOnly"` - but upon looking at the source in
         * > i18next this confirms that they both intend to do similar things:
         *
         * https://github.com/i18next/i18next/blob/80a38100d21a7e7c1f9cb2acff5f709063027b9f/src/LanguageUtils.js#L78-L80
         *
         *  */
        nonExplicitSupportedLngs: true,

        // to not look into a folder like /locals/en-US/... when en-US is detected, use load: "languageOnly" to avoid using Country-Code in path
        load: "languageOnly",
        // send not translated keys to endpoint
        saveMissing: false,
        // allow loading of internal trnaslation files and backend files
        partialBundledLanguages: true,

        /*
          This setting adds a posibility for users to override translations using their own translation json file stored in
          `TerriaMap/wwwroot/languages/{{lng}}/languageOverrides.json`
          It will first look in defaultNS for translation and then check the fallbackNS
        */
        ns: ["translation", "languageOverrides"],
        defaultNS: "languageOverrides",
        fallbackNS: "translation",

        backend: Object.assign(
          {
            // Loads translation files from either a TerriaMap's languages assets or from TerriaJS' assets
            // Always load "translation" namespace from TerriaJS assets, and load "languageOverrides" namespace from the TerriaMap
            loadPath: function loadPath(
              [_lng]: string[],
              [namespace]: string[]
            ) {
              if (namespace === "translation")
                return `${terriajsResourcesBaseUrl}languages/{{lng}}/{{ns}}.json`;

              // Apply languageConfig.overridesBaseUrl to path for "languageOverrides" namespace if defined
              if (
                namespace === "languageOverrides" &&
                isDefined(languageConfig.overridesBaseUrl)
              ) {
                return `${languageConfig.overridesBaseUrl}{{lng}}.json`;
              }

              return "languages/{{lng}}/{{ns}}.json";
            },
            crossDomain: false
          },
          { ...i18StartOptions?.backend }
        ),

        detection: {
          // order and from where user language should be detected
          order: languageConfig.changeLanguageOnStartWhen,

          // keys or params to lookup language from
          lookupQuerystring: "lng",
          lookupCookie: languageConfig.lookupCookie,
          lookupLocalStorage: "i18nextLng",

          // cache user language on
          caches: ["localStorage"],
          excludeCacheFor: ["cimode"] // languages to not persist (cookie, localStorage)

          // optional expire and domain for set cookie
          // cookieMinutes: 10,
          // cookieDomain: "myDomain",
        },
        interpolation: {
          escapeValue: false // not needed for react as it escapes by default and not needed in node
        }
      });
  }
}

export default Internationalization;