import { NextRequest, NextResponse } from "next/server";
import { match as matchLocale } from "@formatjs/intl-localematcher";
import Negotiator from "negotiator";

const LOCALES = ["uz", "ru", "en"];
const DEFAULT_LOCALE = "uz";

type Locale = (typeof LOCALES)[number];

function getLocaleFromPathname(pathname: string): Locale | null {
  const firstSegment = pathname.split("/").filter(Boolean)[0];
  if (firstSegment && LOCALES.includes(firstSegment as Locale)) {
    return firstSegment as Locale;
  }
  return null;
}

function getLocaleFromCookie(request: NextRequest): Locale | null {
  const cookieLocale = request.cookies.get("NEXT_LOCALE")?.value;
  if (cookieLocale && LOCALES.includes(cookieLocale as Locale)) {
    return cookieLocale as Locale;
  }
  return null;
}

function getLocaleFromHeaders(request: NextRequest): Locale {
  const negotiatorHeaders: Record<string, string> = {};
  request.headers.forEach((value, key) => {
    negotiatorHeaders[key] = value;
  });

  const languages = new Negotiator({ headers: negotiatorHeaders }).languages();
  try {
    return matchLocale(languages, LOCALES as string[], DEFAULT_LOCALE) as Locale;
  } catch {
    return DEFAULT_LOCALE;
  }
}

export function middleware(request: NextRequest) {
  const { pathname, search } = request.nextUrl;

  // 1. If URL has a locale, pass it through with headers (+ sync cookie if needed)
  const localeFromPath = getLocaleFromPathname(pathname);
  const localeFromCookie = getLocaleFromCookie(request);
  const preferredLocale = localeFromPath ?? localeFromCookie ?? getLocaleFromHeaders(request);

  // 2. No locale in URL → redirect to preferred locale
  if (!localeFromPath) {
    const newUrl = new URL(`/${preferredLocale}${pathname}`, request.url);
    newUrl.search = search;
    return NextResponse.redirect(newUrl);
  }

  // 3. Build response with locale headers for server components
  const requestHeaders = new Headers(request.headers);
  requestHeaders.set("x-locale", localeFromPath);
  requestHeaders.set("x-pathname", pathname);

  const response = NextResponse.next({ request: { headers: requestHeaders } });

  // 4. Sync cookie if it differs from URL locale
  if (localeFromPath !== localeFromCookie) {
    response.cookies.set("NEXT_LOCALE", localeFromPath, {
      path: "/",
      maxAge: 31_536_000, // 1 year
      sameSite: "lax",
    });
  }

  return response;
}

export const config = {
  matcher: ["/((?!api|_next|_vercel|.*\\..*).*)"],
};