add element persistence

backend/tests/Fakes/FakeElementRepository.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Element\CreateElementDto;
+use App\Element\Element;
+use App\Element\ElementRepository;
+
+class FakeElementRepository implements ElementRepository
+{
+    /**
+     * @var array<int, Element>
+     */
+    private array $elements = [];
+
+    public function create(CreateElementDto $dto): Element
+    {
+        $id = count($this->elements) + 1;
+        $element = new Element(
+            id: $id,
+            name: $dto->name,
+            kind: $dto->kind,
+            set: $dto->set,
+            parentElement: $dto->parentElement,
+            position: $this->nextPosition($dto),
+        );
+        $this->elements[$id] = $element;
+
+        return $this->copy($element);
+    }
+
+    public function find(int $id): ?Element
+    {
+        $element = $this->elements[$id] ?? null;
+
+        return $element === null ? null : $this->copy($element);
+    }
+
+    private function nextPosition(CreateElementDto $dto): int
+    {
+        $requestedParentId = $dto->parentElement?->getId();
+        $maximumPosition = 0;
+
+        foreach ($this->elements as $element) {
+            if ($element->getSet()->getId() !== $dto->set->getId()) {
+                continue;
+            }
+
+            $elementParentId = $element->getParentElement()?->getId();
+            if ($elementParentId !== $requestedParentId) {
+                continue;
+            }
+
+            $maximumPosition = max(
+                $maximumPosition,
+                $element->getPosition(),
+            );
+        }
+
+        return $maximumPosition + 1;
+    }
+
+    private function copy(Element $element): Element
+    {
+        $parentElement = $element->getParentElement();
+
+        return new Element(
+            id: $element->getId(),
+            name: $element->getName(),
+            kind: $element->getKind(),
+            set: $element->getSet(),
+            parentElement: $parentElement === null
+                ? null
+                : $this->copy($parentElement),
+            position: $element->getPosition(),
+        );
+    }
+}