/**
 * EnCoach i18n bootstrap.
 *
 * We keep the translation strings in TypeScript modules (one per locale) so
 * they go through type-checking and tree-shaking, and so non-translators
 * can't ship a broken JSON file that blocks the build.
 *
 * Language selection order (product decision: English is the default UI
 * language at startup; Arabic is opt-in via the language toggle):
 *   1. localStorage key ``encoach-lang`` (explicit user pick, persisted)
 *   2. ``en`` — fallback used on first visit, regardless of browser locale
 *
 * We intentionally do **not** read ``navigator.language`` anymore: an
 * Arabic-locale browser should still land on the English UI the first time
 * a user visits, because the QA team and the product manager both sign off
 * against the English baseline. Users that actively want Arabic flip the
 * toggle once and the preference is remembered from then on.
 *
 * RTL handling: whenever the active language switches to one of RTL_LANGS,
 * we flip ``document.documentElement.dir`` so Tailwind's RTL utilities +
 * Radix primitives pick up the change automatically.
 */

import i18n from "i18next";
import LanguageDetector from "i18next-browser-languagedetector";
import { initReactI18next } from "react-i18next";

import ar from "./locales/ar";
import en from "./locales/en";

const RTL_LANGS = new Set(["ar", "he", "fa", "ur"]);

export const SUPPORTED_LANGS = [
  { code: "en", label: "English" },
  { code: "ar", label: "العربية" },
] as const;

export type SupportedLang = (typeof SUPPORTED_LANGS)[number]["code"];

export const DEFAULT_LANG: SupportedLang = "en";

i18n
  .use(LanguageDetector)
  .use(initReactI18next)
  .init({
    resources: {
      en: { translation: en },
      ar: { translation: ar },
    },
    // Explicit default — english is the baseline UI language at startup.
    lng: DEFAULT_LANG,
    fallbackLng: DEFAULT_LANG,
    supportedLngs: SUPPORTED_LANGS.map((l) => l.code),
    interpolation: { escapeValue: false },
    detection: {
      // Only honour the user's saved pick. Navigator/htmlTag detection was
      // removed so Arabic-locale browsers don't silently boot the UI in
      // Arabic before the user has chosen.
      order: ["localStorage"],
      caches: ["localStorage"],
      lookupLocalStorage: "encoach-lang",
    },
    returnEmptyString: false,
  });

export function applyDirectionForLang(lang: string) {
  const base = lang.split("-")[0];
  const dir = RTL_LANGS.has(base) ? "rtl" : "ltr";
  if (typeof document !== "undefined") {
    document.documentElement.dir = dir;
    document.documentElement.lang = base;
  }
}

if (typeof window !== "undefined") {
  applyDirectionForLang(i18n.language || "en");
  i18n.on("languageChanged", applyDirectionForLang);
}

export default i18n;