/**
 * @file index.ts
 * @description i18next bootstrap for the dashboard client. Loads the JSON locale
 * files for English (`en`) and Vietnamese (`vi`) lazily — only the active language
 * (and the `en` fallback) — wires browser language detection, and exports the
 * configured singleton consumed by `react-i18next` plus `i18nReady`, the promise
 * the entry point awaits before the first render.
 *
 * ## Namespaces
 * Translations are split by feature area (`dashboard`, `sessions`, `settings`,
 * etc.) so pages import only the keys they need via `useTranslation("ns")`.
 * `common` is the default namespace for shared labels and buttons.
 *
 * ## Detection order
 * 1. `localStorage` key `i18nextLng` (user override from Settings)
 * 2. `navigator.language` fallback
 *
 * Unknown regional variants (e.g. `en-US`) map to supported base languages via
 * `nonExplicitSupportedLngs`.
 *
 * `<html lang>` follows the resolved language on init and on every change.
 *
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */
/* =============================================================================
 * MODULE_GUIDE — extended in-file reference (comments only; safe to read, never executed)
 * =============================================================================
 * **Purpose:** Dashboard module consumed by the React client, MCP tools, or desktop shell depending on deployment mode.
 *
 * ## Design constraints
 * - Local-first: no telemetry leaves the machine unless the user configures webhooks.
 * - Fail-safe hooks path on the server must never block Claude Code; UI mirrors that
 *   philosophy by degrading gracefully (empty states, stale badges, reconnect loops).
 * - Destructive flows stay behind explicit confirmation modals and server-side gates.
 * - Internationalization: user-visible strings belong in i18n JSON, not literals here.
 *
 * ## Remote data & SSH
 * Remote Data Sources let operators aggregate multiple machines. SSH entries describe
 * how to reach a peer dashboard; the global data scope (`dataScope.ts`) narrows every
 * scoped GET via `?sources=`. Health checks and import history surface in Settings.
 *
 * ## Internal dependencies
 * - `./locales/<lng>/<ns>.json` (lazy, via `import.meta.glob`)
 *
 * ## Testing pointers
 * - Prefer colocated `__tests__` with Vitest + Testing Library for UI.
 * - Server contract changes require `npm run test:server` and OpenAPI sync.
 *
 * ## Related docs
 * - `ARCHITECTURE.md` — hooks → API → SQLite → WebSocket → UI pipeline.
 * - `docs/API.md` — REST reference.
 * - `skills/file-headers/` — mandatory `@author` header policy.
 * ============================================================================= */

import i18n, { type BackendModule, type ResourceKey } from "i18next";
import { initReactI18next } from "react-i18next";
import LanguageDetector from "i18next-browser-languagedetector";

// Every locale file is its own lazy chunk (vite.config.ts groups them into one
// chunk per language), so a page loads only the language it shows. i18next
// reads them through this inline backend: `init` fetches the detected language
// (plus the `en` fallback), and `changeLanguage` fetches a new one BEFORE it
// switches, so no raw key is ever painted.
const localeFiles = import.meta.glob<Record<string, unknown>>("./locales/*/*.json", {
  import: "default",
});
const lazyLocales: BackendModule = {
  type: "backend",
  init() {},
  read(lng, ns, cb) {
    const load = localeFiles[`./locales/${lng}/${ns}.json`];
    if (!load) return cb(null, {});
    load().then(
      (data) => cb(null, data as ResourceKey),
      (err) => cb(err, false)
    );
  },
};

/** Keep `<html lang>` on the active language, so a screen reader speaks the
 *  page with the right voice and the browser hyphenates/translates correctly.
 *  Registered before `init`, which fires the first `languageChanged`. */
export function syncDocumentLang(): void {
  if (typeof document === "undefined") return;
  document.documentElement.lang = i18n.resolvedLanguage || i18n.language || "en";
}
i18n.on("languageChanged", syncDocumentLang);

/** Resolves once the detected language's namespaces are loaded; `main.tsx`
 *  awaits it before the first render. */
export const i18nReady = i18n
  .use(lazyLocales)
  .use(LanguageDetector)
  .use(initReactI18next)
  .init({
    supportedLngs: ["en", "vi"],
    nonExplicitSupportedLngs: true,
    fallbackLng: "en",
    ns: [
      "common",
      "nav",
      "dashboard",
      "sessions",
      "activity",
      "analytics",
      "workflows",
      "settings",
      "kanban",
      "errors",
      "updates",
      "ccConfig",
      "codexConfig",
      "run",
      "alerts",
      "splash",
      "lanes",
      "users",
      "onboarding",
      "artifacts",
    ],
    defaultNS: "common",
    interpolation: { escapeValue: false },
    detection: {
      order: ["localStorage", "navigator"],
      caches: ["localStorage"],
      lookupLocalStorage: "i18nextLng",
    },
  });

syncDocumentLang();

/** Configured i18next instance — import side effects start {@link init}. */
export default i18n;