middleware.ts

import { NextRequest, NextResponse } from 'next/server'
import Negotiator from 'negotiator'
import { defaultLanguage, availableLanguages } from './i18n/settings'

const getNegotiatedLanguage = (
  headers: Negotiator.Headers,
): string | undefined => {
  return new Negotiator({ headers }).language([...availableLanguages])
}

export const config = {
  matcher: ['/((?!api|_next/static|_next/image|.*\\.png$).*)'],
}

export function middleware(request: NextRequest) {
  const headers = {
    'accept-language': request.headers.get('accept-language') ?? '',
  }
  const preferredLanguage = getNegotiatedLanguage(headers) || defaultLanguage
  const pathname = request.nextUrl.pathname
  const pathnameIsMissingLocale = availableLanguages.every(
    (lang) => !pathname.startsWith(`/${lang}/`) && pathname !== `/${lang}`,
  )

  if (pathnameIsMissingLocale) {
    if (preferredLanguage !== defaultLanguage) {
      return NextResponse.redirect(
        new URL(`/${preferredLanguage}${pathname}`, request.url),
      )
    } else {
      return NextResponse.rewrite(
        new URL(`/${defaultLanguage}${pathname}`, request.url),
      )
    }
  }

  return NextResponse.next()
}