add child creation

backend/app/Controllers/ElementController.php

@@ -3,6 +3,8 @@
 namespace App\Controllers;
 
 use App\Element\Element;
+use App\Element\UseCases\CreateChildElement\CreateChildElement;
+use App\Element\UseCases\CreateChildElement\CreateChildElementRequest;
 use App\Element\UseCases\GetElement\GetElement;
 use App\Element\UseCases\GetElement\GetElementRequest;
 use App\Element\UseCases\UpdateElement\UpdateElement;
@@ -18,6 +20,7 @@ class ElementController
 {
     public function __construct(
         private GetElement $getElement,
+        private CreateChildElement $createChildElement,
         private UpdateElement $updateElement,
         private FileUploader $fileUploader,
     ) {
@@ -55,6 +58,30 @@ class ElementController
         ], 200);
     }
 
+    public function createChild(Request $request, ?int $parentId): JsonResponse
+    {
+        try {
+            $element = $this->createChildElement->execute(
+                new CreateChildElementRequest(
+                    parentElementId: $parentId,
+                    title: $this->stringInput($request, 'title'),
+                )
+            );
+        } catch (BadRequestException $exception) {
+            return new JsonResponse([
+                'error' => $exception->getMessage(),
+            ], 400);
+        } catch (NotFoundException $exception) {
+            return new JsonResponse([
+                'error' => $exception->getMessage(),
+            ], 404);
+        }
+
+        return new JsonResponse([
+            'element' => $this->buildElementPayload($element),
+        ], 201);
+    }
+
     public function update(Request $request): JsonResponse
     {
         $file = $this->uploadedFileInput($request, 'file');

backend/app/Element/UseCases/CreateChildElement/CreateChildElement.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace App\Element\UseCases\CreateChildElement;
+
+use App\Element\CreateElementDto;
+use App\Element\Element;
+use App\Element\ElementRepository;
+use App\Exceptions\BadRequestException;
+use App\Exceptions\NotFoundException;
+
+class CreateChildElement
+{
+    public function __construct(private ElementRepository $elementRepository)
+    {
+    }
+
+    /**
+     * @throws BadRequestException
+     * @throws NotFoundException
+     */
+    public function execute(CreateChildElementRequest $request): Element
+    {
+        if ($request->parentElementId === null) {
+            throw new BadRequestException('parentElementId is required');
+        }
+
+        if ($request->title === null || $request->title === '') {
+            throw new BadRequestException('title is required');
+        }
+
+        $parentElement = $this->elementRepository->find(
+            $request->parentElementId
+        );
+        if ($parentElement === null) {
+            throw new NotFoundException('Parent element not found');
+        }
+
+        return $this->elementRepository->create(new CreateElementDto(
+            set: $parentElement->getSet(),
+            title: $request->title,
+            description: '',
+            iconImageUrl: null,
+            richText: '',
+            shortPdfPath: null,
+            longPdfPath: null,
+            youtubeUrl: null,
+            parentElement: $parentElement,
+        ));
+    }
+}

backend/app/Element/UseCases/CreateChildElement/CreateChildElementRequest.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Element\UseCases\CreateChildElement;
+
+class CreateChildElementRequest
+{
+    public function __construct(
+        public ?int $parentElementId,
+        public ?string $title,
+    ) {
+    }
+}