middleware.ts

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

import { i18n } from '@/i18n/config';

import { match as matchLocale } from '@formatjs/intl-localematcher';
import Negotiator from 'negotiator';

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));

  // Use negotiator and intl-localematcher to get best locale
  const languages = new Negotiator({ headers: negotiatorHeaders }).languages();
  const locales: string[] = i18n.locales as unknown as string[];
  return matchLocale(languages, locales, i18n.defaultLocale);
}

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

  // 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 === '' ? '/' : pathname}`, request.url)
    );
  }
}

export const config = {
  // Matcher ignoring `/_next/` and `/api/`
  // matcher: ['/((?!api|_next/static|_next/image|favicon.ico).*)']
  // matcher: ['/((?!api|_next).*)']
  // 2023-8-28 update
  matcher: '/((?!api|static|.*\\..*|_next).*)'
};