import i18n from "i18next";
import { initReactI18next } from "react-i18next";
import { LS } from "../lib/storage";

// Endonyms (shown as-is regardless of the active language — the convention for language pickers).
export const LANGUAGES = [
  { code: "en", label: "English" },
  { code: "hu", label: "Magyar" },
] as const;
export type LangCode = (typeof LANGUAGES)[number]["code"];
const SUPPORTED = LANGUAGES.map((l) => l.code) as readonly string[];
const LANG_KEY = LS.lang;

// Auto-load every locale file (locales/<lang>/<area>.json) and merge each <area> under one
// `translation` namespace, so components use t("area.key") and adding an area needs no wiring.
const mods = import.meta.glob("./locales/*/*.json", { eager: true }) as Record<
  string,
  { default: Record<string, unknown> }
>;

const resources: Record<string, { translation: Record<string, unknown> }> = {};
for (const [path, mod] of Object.entries(mods)) {
  const m = path.match(/\/locales\/([a-z]{2})\/([a-zA-Z0-9_]+)\.json$/);
  if (!m) continue;
  const [, lang, area] = m;
  if (!lang || !area) continue; // both groups are required by the regex; satisfies the checker
  (resources[lang] ??= { translation: {} }).translation[area] = mod.default;
}

export function isSupported(code: string | null | undefined): code is LangCode {
  return !!code && SUPPORTED.includes(code);
}

// Initial language before the server preference is known: stored choice, else the browser
// language, else English. (After login, App adopts the server-persisted preference.)
function detectInitialLang(): LangCode {
  const stored = localStorage.getItem(LANG_KEY);
  if (isSupported(stored)) return stored;
  const nav = (navigator.language || "en").slice(0, 2).toLowerCase();
  return isSupported(nav) ? nav : "en";
}

const initial = detectInitialLang();
void i18n.use(initReactI18next).init({
  resources,
  lng: initial,
  fallbackLng: "en",
  interpolation: { escapeValue: false },
  returnNull: false,
});
document.documentElement.lang = initial;

export function setLanguage(code: LangCode): void {
  void i18n.changeLanguage(code);
  localStorage.setItem(LANG_KEY, code);
  document.documentElement.lang = code;
}

export default i18n;
