public function createAction(
        string $production_slug,
        Request $request,
        TokenStorageInterface $token,
        AuthorizationCheckerInterface $auth
    ): Response {
        // Lookup the production by production_slug.
        $production_repo = $this->em->getRepository(Production::class);
        if (null === $production = $production_repo->findOneBy(['slug' => $production_slug])) {
            throw new NotFoundHttpException();
        }

        // Check permissions for this action.
        if (!$auth->isGranted('GROUP_ROLE_USER', $production)) {
            throw new AccessDeniedException();
        }

        // Get some basic information about the user.
        $user = $token->getToken()->getUser();

        // Create a new post.
        $post = new Post();
        $post->setActive(true);
        $post->setPinned(false);
        $post->setAuthor($user->getUsername());
        $post->addGroup($production);

        // This post is a reply.
        if ($request->query->has('reply-to')) {
            // Make sure the parent post is valid.
            $repo = $this->em->getRepository(Post::class);
            if (null === $parent = $repo->findOneBy(['id' => $request->query->get('reply-to')])) {
                throw new NotFoundHttpException();
            }

            // Must be a member of the same group.
            if (!$parent->getGroups()->contains($production)) {
                throw new AccessDeniedException();
            }

            // Parent must not be a child.
            if (null !== $parent->getParent()) {
                throw new AccessDeniedException();
            }
            $post->setParent($parent);

            // This is a reply, use the basic reply form.
            $form = $this->form->create(ReplyType::class, $post);
        } else {
            // This is a new post, use the post form.
            $form = $this->form->create(PostType::class, $post);
        }

        // Handle the form.
        $form->handleRequest($request);

        // Form is submitted and valid.
        if ($form->isSubmitted() && $form->isValid()) {
            // Persist the post.
            $this->em->persist($post);
            $this->em->flush();

            // Set success message and redirect.
            $this->session->getFlashBag()->add(
                'success',
                $this->translator->trans('post.created', [], BkstgNoticeBoardBundle::TRANSLATION_DOMAIN)
            );

            return new RedirectResponse($this->url_generator->generate(
                'bkstg_board_show',
                ['production_slug' => $production->getSlug()]
            ));
        }

        // Render the form.
        return new Response($this->templating->render('@BkstgNoticeBoard/Post/create.html.twig', [
            'form' => $form->createView(),
            'post' => $post,
            'production' => $production,
        ]));
    }