middleware.ts

import NextAuth from 'next-auth';
import { authConfig } from './auth.config';
import { match as matchLocale } from '@formatjs/intl-localematcher';
import Negotiator from 'negotiator';
import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';
import { i18n } from './i18n-config';

function getLocale(request: NextRequest): string | undefined {
  // Negotiator expects plain object so we need to transform headers
  const negotiatorHeaders: Record<string, string> = {};
  request.headers.forEach((value, key) => (negotiatorHeaders[key] = value));

  // @ts-ignore locales are readonly
  const locales: string[] = i18n.locales;

  // Use negotiator and intl-localematcher to get best locale
  let languages = new Negotiator({ headers: negotiatorHeaders }).languages(
    locales,
  );

  const locale = matchLocale(languages, locales, i18n.defaultLocale);

  return locale;
}

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

  // // `/_next/` and `/api/` are ignored by the watcher, but we need to ignore files in `public` manually.
  // // If you have one
  if (
    [
      '/manifest.json',
      '/favicon.ico',
      // Your other files in `public`
    ].includes(pathname)
  ) {
    return;
  }

  if (request.nextUrl.pathname.endsWith(".mp3")) {
    return NextResponse.next();
  }

  // Check if there is any supported locale in the pathname
  const pathnameIsMissingLocale = i18n.locales.every(
    (locale) =>
      !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`,
  );

  // Redirect if there is no locale
  if (pathnameIsMissingLocale) {
    const locale = getLocale(request);

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

export default NextAuth(authConfig).auth;

export const config = {
  // https://nextjs.org/docs/app/building-your-application/routing/middleware#matcher
  matcher: ['/((?!api|_next/static|_next/image|.*\\.png$).*)'],
};