add get element use case

backend/app/Element/UseCases/GetElement/GetElement.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace App\Element\UseCases\GetElement;
+
+use App\Element\Element;
+use App\Element\ElementRepository;
+use App\Exceptions\BadRequestException;
+use App\Exceptions\NotFoundException;
+
+class GetElement
+{
+    public function __construct(private ElementRepository $elementRepository)
+    {
+    }
+
+    /**
+     * @throws BadRequestException
+     * @throws NotFoundException
+     */
+    public function execute(GetElementRequest $request): Element
+    {
+        if ($request->id === null) {
+            throw new BadRequestException('id is required');
+        }
+
+        $element = $this->elementRepository->find($request->id);
+        if ($element === null) {
+            throw new NotFoundException('Element not found');
+        }
+
+        return $element;
+    }
+}

backend/app/Element/UseCases/GetElement/GetElementRequest.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace App\Element\UseCases\GetElement;
+
+class GetElementRequest
+{
+    public function __construct(public ?int $id)
+    {
+    }
+}

backend/app/Exceptions/NotFoundException.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace App\Exceptions;
+
+use DomainException;
+
+class NotFoundException extends DomainException
+{
+}