add set elements

backend/app/Set/UseCases/CreateSet/CreateSet.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace App\Set\UseCases\CreateSet;
+
+use App\Element\CreateElementDto;
+use App\Element\ElementRepository;
+use App\Exceptions\BadRequestException;
+use App\Set\CreateSetDto;
+use App\Set\Set;
+use App\Set\SetRepository;
+
+class CreateSet
+{
+    public function __construct(
+        private SetRepository $setRepo,
+        private ElementRepository $elementRepo,
+    ) {}
+
+    /**
+     * @throws BadRequestException
+     */
+    public function execute(CreateSetRequest $request): Set
+    {
+        if ($request->name === null || $request->name === '') {
+            throw new BadRequestException('name is required');
+        }
+
+        $set = $this->setRepo->create(new CreateSetDto(
+            name: $request->name,
+        ));
+
+        $this->elementRepo->create(new CreateElementDto(
+            set: $set,
+            title: $set->getName(),
+            parentElement: null,
+        ));
+
+        return $set;
+    }
+}

backend/app/Set/UseCases/CreateSet/CreateSetRequest.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace App\Set\UseCases\CreateSet;
+
+class CreateSetRequest
+{
+    public function __construct(
+        public ?string $name,
+    ) {}
+}