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

const COOKIE = 'admin_token'

/** Constant-time string comparison to prevent timing attacks */
function safeEqual(a: string, b: string): boolean {
  if (a.length !== b.length) return false
  let diff = 0
  for (let i = 0; i < a.length; i++) {
    diff |= a.charCodeAt(i) ^ b.charCodeAt(i)
  }
  return diff === 0
}

/**
 * Derive a session token from the admin password using SHA-256.
 * The raw password is never stored in the cookie.
 */
async function deriveSessionToken(password: string): Promise<string> {
  const data = new TextEncoder().encode(`admin-session-v1:${password}`)
  const hash = await crypto.subtle.digest('SHA-256', data)
  return Array.from(new Uint8Array(hash))
    .map((b) => b.toString(16).padStart(2, '0'))
    .join('')
}

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

  if (pathname === '/shop/admin/login' || pathname === '/api/admin/login') {
    return NextResponse.next()
  }

  if (pathname.startsWith('/shop/admin') || pathname.startsWith('/api/admin')) {
    const token    = request.cookies.get(COOKIE)?.value
    const password = process.env.ADMIN_PASSWORD

    if (!password || !token) {
      if (pathname.startsWith('/api/')) {
        return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
      }
      return NextResponse.redirect(new URL('/shop/admin/login', request.url))
    }

    const expected = await deriveSessionToken(password)
    if (!safeEqual(token, expected)) {
      if (pathname.startsWith('/api/')) {
        return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
      }
      return NextResponse.redirect(new URL('/shop/admin/login', request.url))
    }
  }

  return NextResponse.next()
}

export const config = {
  matcher: ['/shop/admin/:path*', '/api/admin/:path*'],
}