import { cookies } from "next/headers";
import { getRequestConfig } from "next-intl/server";

// i18n WITHOUT routing: the locale is chosen by a `NEXT_LOCALE` cookie (set by
// the language switcher) rather than a URL segment, so every existing route and
// the access-guard middleware keep working unchanged. English is the fallback.
export const SUPPORTED_LOCALES = ["en", "it", "nl", "de", "fr", "es"] as const;
export type AppLocale = (typeof SUPPORTED_LOCALES)[number];
export const DEFAULT_LOCALE: AppLocale = "en";

export function isSupportedLocale(value: string | undefined): value is AppLocale {
  return !!value && (SUPPORTED_LOCALES as readonly string[]).includes(value);
}

export default getRequestConfig(async () => {
  const store = await cookies();
  const cookieLocale = store.get("NEXT_LOCALE")?.value;
  const locale: AppLocale = isSupportedLocale(cookieLocale) ? cookieLocale : DEFAULT_LOCALE;

  // Safe: `locale` is validated against SUPPORTED_LOCALES above (only en/it/nl/de/fr/es).
  const messages = (await import(`../messages/${locale}.json`)).default;
  // English is the source of truth; fall back to it for any key missing from a
  // translation so the UI never shows a raw key path.
  const fallback =
    locale === DEFAULT_LOCALE
      ? messages
      : (await import(`../messages/${DEFAULT_LOCALE}.json`)).default;

  return {
    locale,
    messages,
    // Never throw on a missing message — use the English value, or a humanised
    // key as a last resort.
    getMessageFallback({ key }: { key: string }) {
      const fromEnglish = key
        .split(".")
        .reduce<unknown>((o, k) => (o && typeof o === "object" ? (o as Record<string, unknown>)[k] : undefined), fallback);
      if (typeof fromEnglish === "string") return fromEnglish;
      const seg = key.split(".").pop() ?? key;
      return seg.replace(/[._-]/g, " ").replace(/\b\w/g, (c) => c.toUpperCase());
    },
    onError() {
      // Swallow MISSING_MESSAGE etc. — getMessageFallback already degrades.
    },
  };
});