NextJS middleware using getViewportFromUserAgent

next-middleware.js

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

  // public static stuff
  if (pathname.startsWith('/images') || pathname.startsWith('/fonts')) {
    return undefined;
  }

  // api/static/client routes NextJS stuff
  if (pathname.includes('.') || pathname.startsWith('/api')) {
    return undefined;
  }

  // prevent making internal stuff external
  if (pathname.startsWith('/internal')) {
    return new Response(null, { status: 404 });
  }

  const hostname = req.headers.get('host');
  const countryCode = getCountryCode(hostname);
  const defaultLanguage = 'nl';

  const viewport = getViewportFromUserAgent(req.headers.get('user-agent'));

  // We are on NL website, uses nl-NL internally only!
  if (countryCode === 'nl') {
    if (pathname.startsWith('/nl')) {
      return new Response(null, { status: 404 });
    }

    return NextResponse.rewrite(`/internal/${viewport}/nl-NL${pathname}`);
  }
}