import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";

const SUPPORTED_LOCALES = ["en", "de"] as const;

function getLocale(request: NextRequest): string {
  const acceptLang = request.headers.get("accept-language") ?? "";
  const preferred = acceptLang.split(",")[0]?.trim().slice(0, 2);
  if (preferred && SUPPORTED_LOCALES.includes(preferred as any)) return preferred;
  return "en";
}

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

  // API routes and static files pass through
  if (
    pathname.startsWith("/api/") ||
    pathname.includes(".") ||
    pathname.startsWith("/_next")
  ) {
    return NextResponse.next();
  }

  // Check if pathname already has a supported locale
  const hasLocale = SUPPORTED_LOCALES.some(
    (l) => pathname === `/${l}` || pathname.startsWith(`/${l}/`),
  );

  if (!hasLocale) {
    const locale = getLocale(request);
    const url = request.nextUrl.clone();
    url.pathname = `/${locale}${pathname === "/" ? "" : pathname}`;
    return NextResponse.redirect(url);
  }

  return NextResponse.next();
}

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