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

const SHARED_LANGUAGE_COOKIE = 'rentaldrivego-language'
const MARKETPLACE_LANGUAGE_COOKIE = 'marketplace-language'


function rejectInternalSubrequest(request: NextRequest): NextResponse | null {
  if (!request.headers.has('x-middleware-subrequest')) return null
  return new NextResponse('Unsupported internal request header', { status: 400 })
}

function isValidLanguage(val: string | null | undefined): val is 'en' | 'fr' | 'ar' {
  return val === 'en' || val === 'fr' || val === 'ar'
}

function detectFromAcceptLanguage(header: string | null): 'en' | 'fr' | 'ar' {
  if (!header) return 'en'
  for (const entry of header.split(',')) {
    const code = entry.split(';')[0].trim().split('-')[0].toLowerCase()
    if (code === 'ar' || code === 'fr' || code === 'en') return code as 'en' | 'fr' | 'ar'
  }
  return 'en'
}

export function middleware(request: NextRequest) {
  const rejected = rejectInternalSubrequest(request)
  if (rejected) return rejected

  const sharedLang = request.cookies.get(SHARED_LANGUAGE_COOKIE)?.value

  // Already has the canonical language cookie — no action needed
  if (isValidLanguage(sharedLang)) return NextResponse.next()

  const legacyLang = request.cookies.get(MARKETPLACE_LANGUAGE_COOKIE)?.value
  const resolved: 'en' | 'fr' | 'ar' = isValidLanguage(legacyLang)
    ? legacyLang
    : detectFromAcceptLanguage(request.headers.get('accept-language'))

  // Inject the resolved language into the request cookie header so that
  // getMarketplaceLanguage() (which calls cookies()) sees the correct value
  // even on this very first render — before the browser has stored the cookie.
  const requestHeaders = new Headers(request.headers)
  const existing = request.headers.get('cookie') ?? ''
  const injected = `${SHARED_LANGUAGE_COOKIE}=${resolved}`
  requestHeaders.set('cookie', existing ? `${existing}; ${injected}` : injected)

  const response = NextResponse.next({ request: { headers: requestHeaders } })

  // Persist in the browser for future requests
  response.cookies.set(SHARED_LANGUAGE_COOKIE, resolved, {
    maxAge: 365 * 24 * 60 * 60,
    path: '/',
    sameSite: 'lax',
  })

  return response
}

export const config = {
  matcher: [
    '/((?!_next/static|_next/image|favicon\\.ico|.*\\.(?:png|ico|jpg|jpeg|svg|webp)$).*)',
  ],
}