import { NextRequest, NextResponse } from 'next/server';
import acceptLanguage from 'accept-language';

const supportedLangs = ['en', 'zh-CN', 'zh-TW', 'ko', 'ja'];
const defaultLang = 'en';

acceptLanguage.languages(supportedLangs);

export const config = {
  matcher: [
    /*
     * Match all request paths except for the ones starting with:
     * - api (API routes)
     * - _next/static (static files)
     * - _next/image (image optimization files)
     * - favicon.ico (favicon file)
     * - sitemap.xml (sitemap file)
     * - robots.txt (robots file)
     */
    '/((?!api|_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)'
  ]
};

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

  // Check if there is any supported locale in the pathname
  const pathnameIsMissingLocale = supportedLangs.every(
    (locale) => !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`
  );

  // Redirect if there is no locale
  if (pathnameIsMissingLocale) {
    const locale = acceptLanguage.get(req.headers.get('Accept-Language')) || defaultLang;

    // e.g. incoming request is /products
    // The new URL is now /en/products
    return NextResponse.redirect(
      new URL(`/${locale}${pathname.startsWith('/') ? '' : '/'}${pathname}`, req.url)
    );
  }

  return NextResponse.next();
}