import 'server-only'
import { fileId, fileRepository } from '@/entities/file'
import { blob, db } from '@/shared/api'
import { currentVisitor } from '@/shared/lib/visitor-session'

function notFound(): Response {
  return new Response('not found', { status: 404 })
}

/**
 * The bytes of one attachment, for the visitor who attached it. The platform's
 * blob URL needs the deployment token, which the browser does not have, so the
 * app downloads server-side and streams the bytes back. Anything that is not
 * the visitor's own attachment answers 404, never 403.
 */
export async function downloadAttachment(id: string): Promise<Response> {
  const parsed = fileId.safeParse(id)
  if (!parsed.success) return notFound()
  const visitor = await currentVisitor()
  if (!visitor) return notFound()
  const file = await fileRepository(db()).get(parsed.data, visitor)
  if (!file) return notFound()
  const upstream = await blob().download(file.url)
  if (!upstream.body) return notFound()
  return new Response(upstream.body, {
    headers: {
      'content-type': file.contentType,
      // RFC 5987: the name is percent-encoded, so quotes and CR/LF cannot inject.
      'content-disposition': `attachment; filename*=UTF-8''${encodeURIComponent(file.name)}`,
    },
  })
}

/** `GET /files/<id>`: the route handler the app router re-exports. */
export async function GET(_request: Request, context: { params: Promise<{ id: string }> }): Promise<Response> {
  return downloadAttachment((await context.params).id)
}