add set layout api

backend/app/Set/UseCases/GetSetLayout/ElementLayoutNode.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Set\UseCases\GetSetLayout;
+
+use App\Element\Element;
+
+final readonly class ElementLayoutNode
+{
+    /**
+     * @param list<ElementLayoutNode> $children
+     */
+    public function __construct(
+        private Element $element,
+        private array $children,
+    ) {}
+
+    public function getElement(): Element
+    {
+        return $this->element;
+    }
+
+    /**
+     * @return list<ElementLayoutNode>
+     */
+    public function getChildren(): array
+    {
+        return $this->children;
+    }
+}

backend/app/Set/UseCases/GetSetLayout/GetSetLayout.php

@@ -0,0 +1,77 @@
+<?php
+
+namespace App\Set\UseCases\GetSetLayout;
+
+use App\Element\Element;
+use App\Element\ElementRepository;
+use App\Exceptions\NotFoundException;
+use App\Set\SetRepository;
+
+class GetSetLayout
+{
+    public function __construct(
+        private SetRepository $setRepository,
+        private ElementRepository $elementRepository,
+    ) {}
+
+    /**
+     * @throws NotFoundException
+     */
+    public function execute(int $setId): SetLayout
+    {
+        $set = $this->setRepository->find($setId);
+        if ($set === null) {
+            throw new NotFoundException('set not found');
+        }
+
+        $elementsByParentId = [];
+        foreach ($this->elementRepository->findBySet($set) as $element) {
+            $parentId = $element->getParentElement()?->getId() ?? 0;
+            $elementsByParentId[$parentId][] = $element;
+        }
+
+        foreach ($elementsByParentId as &$siblings) {
+            usort($siblings, function (
+                Element $first,
+                Element $second,
+            ): int {
+                $positionComparison = $first->getPosition()
+                    <=> $second->getPosition();
+                if ($positionComparison !== 0) {
+                    return $positionComparison;
+                }
+
+                return $first->getId() <=> $second->getId();
+            });
+        }
+        unset($siblings);
+
+        return new SetLayout(
+            set: $set,
+            elements: $this->buildNodes(0, $elementsByParentId),
+        );
+    }
+
+    /**
+     * @param array<int, list<Element>> $elementsByParentId
+     * @return list<ElementLayoutNode>
+     */
+    private function buildNodes(
+        int $parentId,
+        array $elementsByParentId,
+    ): array {
+        $nodes = [];
+
+        foreach ($elementsByParentId[$parentId] ?? [] as $element) {
+            $nodes[] = new ElementLayoutNode(
+                element: $element,
+                children: $this->buildNodes(
+                    $element->getId(),
+                    $elementsByParentId,
+                ),
+            );
+        }
+
+        return $nodes;
+    }
+}

backend/app/Set/UseCases/GetSetLayout/SetLayout.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Set\UseCases\GetSetLayout;
+
+use App\Set\Set;
+
+final readonly class SetLayout
+{
+    /**
+     * @param list<ElementLayoutNode> $elements
+     */
+    public function __construct(
+        private Set $set,
+        private array $elements,
+    ) {}
+
+    public function getSet(): Set
+    {
+        return $this->set;
+    }
+
+    /**
+     * @return list<ElementLayoutNode>
+     */
+    public function getElements(): array
+    {
+        return $this->elements;
+    }
+}