feat: instant preview of edited email template

src/Config/EmailTextDefinition.php

@@ -28,4 +28,18 @@ readonly class EmailTextDefinition
     {
         return array_keys($this->placeholders);
     }
+
+    /**
+     * Placeholder values for the admin preview, where the placeholders stand in for
+     * themselves: no disposition is at hand there, and a visible [destination] tells an
+     * admin where a real value lands better than an invented one would.
+     *
+     * @return array<string, string>
+     */
+    public function getSamplePlaceholders(): array
+    {
+        $names = $this->getPlaceholderNames();
+
+        return array_combine($names, array_map(static fn (string $name): string => '['.$name.']', $names));
+    }
 }

src/Controller/Admin/System/EmailText/EditController.php

@@ -4,9 +4,9 @@ namespace App\Controller\Admin\System\EmailText;
 
 use App\Config\EmailTextCatalog;
 use App\Config\EmailTextKey;
+use App\Email\EmailTextRenderer;
 use App\Entity\EmailText;
 use App\Form\EmailTextType;
-use App\Htmx\HxRedirectResponse;
 use App\Repository\EmailTextRepository;
 use Doctrine\ORM\EntityManagerInterface;
 use Psr\Log\LoggerInterface;
@@ -21,6 +21,7 @@ class EditController extends AbstractController
     public function __construct(
         private readonly EmailTextCatalog $catalog,
         private readonly EmailTextRepository $emailTextRepository,
+        private readonly EmailTextRenderer $emailTextRenderer,
         private readonly EntityManagerInterface $entityManager,
         private readonly LoggerInterface $logger,
     ) {
@@ -46,7 +47,6 @@ class EditController extends AbstractController
 
         $form = $this->createForm(EmailTextType::class, $emailText, [
             'definition' => $definition,
-            'hx_post' => $request->getUri(),
         ]);
         $form->handleRequest($request);
 
@@ -63,12 +63,22 @@ class EditController extends AbstractController
                 'email_text_key' => $key->value,
             ]);
 
-            return new HxRedirectResponse($this->generateUrl('app_admin_system_email_text_index'));
+            return $this->redirectToRoute('app_admin_system_email_text_index');
         }
 
-        return $this->render('admin/system/email_text/modal_edit.html.twig', [
+        return $this->render('admin/system/email_text/edit.html.twig', [
             'form' => $form->createView(),
             'definition' => $definition,
+            'emailText' => $emailText,
+            // Filling the preview pane here saves the page a round trip on first paint;
+            // from then on the pane refreshes itself while the admin types.
+            'text' => $this->emailTextRenderer->renderValues(
+                $key,
+                $emailText->getSubject(),
+                $emailText->getHeadline(),
+                $emailText->getBody(),
+                $definition->getSamplePlaceholders()
+            ),
         ]);
     }
 }

src/Controller/Admin/System/EmailText/PreviewController.php

@@ -30,18 +30,9 @@ class PreviewController extends AbstractController
     {
         $definition = $this->catalog->get($key);
 
-        // The placeholders stand in for themselves: no disposition is at hand here, and a
-        // visible [destination] tells an admin where a real value lands better than an
-        // invented one would.
-        $placeholders = [];
-
-        foreach ($definition->getPlaceholderNames() as $name) {
-            $placeholders[$name] = '['.$name.']';
-        }
-
         return $this->render('admin/system/email_text/modal_preview.html.twig', [
             'definition' => $definition,
-            'text' => $this->emailTextRenderer->render($key, $placeholders),
+            'text' => $this->emailTextRenderer->render($key, $definition->getSamplePlaceholders()),
         ]);
     }
 }

src/Controller/Admin/System/EmailText/PreviewDraftController.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace App\Controller\Admin\System\EmailText;
+
+use App\Config\EmailTextCatalog;
+use App\Config\EmailTextKey;
+use App\Email\EmailTextRenderer;
+use App\Entity\EmailText;
+use App\Form\EmailTextType;
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Attribute\Route;
+use Symfony\Component\Security\Http\Attribute\IsGranted;
+
+class PreviewDraftController extends AbstractController
+{
+    public function __construct(
+        private readonly EmailTextCatalog $catalog,
+        private readonly EmailTextRenderer $emailTextRenderer,
+    ) {
+    }
+
+    /**
+     * Renders the fragment the edit page swaps in while an admin types, so the wording is
+     * checked before it is saved rather than after. Unlike PreviewController this reads
+     * the submitted values instead of the stored ones.
+     */
+    #[Route('/admin/system/email-text/preview-draft/{key}', name: 'app_admin_system_email_text_preview_draft', methods: ['POST'])]
+    #[IsGranted('ROLE_ADMIN')]
+    public function index(EmailTextKey $key, Request $request): Response
+    {
+        $definition = $this->catalog->get($key);
+
+        $form = $this->createForm(EmailTextType::class, new EmailText($key), [
+            'definition' => $definition,
+        ]);
+        $form->handleRequest($request);
+
+        /** @var EmailText $draft */
+        $draft = $form->getData();
+
+        // Deliberately rendered whether or not the form is valid: a text carrying a typo
+        // in a placeholder is exactly what an admin needs to see in the preview, and the
+        // field error is shown by the form itself when the text is saved.
+        return $this->render('admin/system/email_text/_preview.html.twig', [
+            'definition' => $definition,
+            'text' => $this->emailTextRenderer->renderValues(
+                $key,
+                $draft->getSubject(),
+                $draft->getHeadline(),
+                $draft->getBody(),
+                $definition->getSamplePlaceholders()
+            ),
+        ]);
+    }
+}

src/Email/EmailTextRenderer.php

@@ -43,9 +43,30 @@ class EmailTextRenderer
         $definition = $this->catalog->get($key);
         $emailText = $this->emailTextRepository->findByKey($key);
 
-        $subject = $emailText?->getSubject() ?: $definition->defaultSubject;
-        $headline = $emailText?->getHeadline() ?? $definition->defaultHeadline;
-        $body = $emailText?->getBody() ?: $definition->defaultBody;
+        return $this->renderValues(
+            $key,
+            $emailText?->getSubject() ?: $definition->defaultSubject,
+            $emailText?->getHeadline() ?? $definition->defaultHeadline,
+            $emailText?->getBody() ?: $definition->defaultBody,
+            $placeholders
+        );
+    }
+
+    /**
+     * Renders wording that is not (or not yet) the saved one - the admin preview shows
+     * what is currently in the form, which is the whole point of previewing before saving.
+     * The values come straight from a half-filled form, so all three may be null.
+     *
+     * @param array<string, string|int|null> $placeholders
+     */
+    public function renderValues(
+        EmailTextKey $key,
+        ?string $subject,
+        ?string $headline,
+        ?string $body,
+        array $placeholders,
+    ): RenderedEmailTextDto {
+        $definition = $this->catalog->get($key);
 
         // Two token maps from the same values: the subject of a mail is plain text, the
         // body is HTML. Escaping happens here, before substitution, so that neither the
@@ -63,9 +84,9 @@ class EmailTextRenderer
         }
 
         return new RenderedEmailTextDto(
-            strtr($subject, $plainTokens),
-            $this->prepare($headline, $htmlTokens),
-            $this->renderBody($body, $htmlTokens),
+            strtr($subject ?? '', $plainTokens),
+            $this->prepare($headline ?? '', $htmlTokens),
+            $this->renderBody($body ?? '', $htmlTokens),
         );
     }