add element siblings

backend/app/Controllers/ElementController.php

@@ -46,18 +46,15 @@ class ElementController
         }
 
         $element = $result->getElement();
-        $childElements = [];
-        foreach ($result->getChildElements() as $childElement) {
-            $childElements[] = [
-                'id' => $childElement->getId(),
-                'title' => $childElement->getTitle(),
-                'description' => $childElement->getDescription(),
-            ];
-        }
 
         return new JsonResponse([
-            'childElements' => $childElements,
+            'childElements' => $this->buildElementSummaryPayloads(
+                $result->getChildElements(),
+            ),
             'element' => $this->buildElementPayload($element),
+            'siblingElements' => $this->buildElementSummaryPayloads(
+                $result->getSiblingElements(),
+            ),
         ], 200);
     }
 
@@ -253,6 +250,28 @@ class ElementController
         ];
     }
 
+    /**
+     * @param Element[] $elements
+     * @return array<int, array{
+     *     id: int,
+     *     title: string,
+     *     description: string,
+     * }>
+     */
+    private function buildElementSummaryPayloads(array $elements): array
+    {
+        $payloads = [];
+        foreach ($elements as $element) {
+            $payloads[] = [
+                'id' => $element->getId(),
+                'title' => $element->getTitle(),
+                'description' => $element->getDescription(),
+            ];
+        }
+
+        return $payloads;
+    }
+
     private function storageUrl(?string $path, string $folderPrefix): ?string
     {
         if ($path === null) {

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

@@ -27,10 +27,19 @@ class GetElement
             throw new NotFoundException('Element not found');
         }
 
+        $parentElement = $element->getParentElement();
+        if ($parentElement === null) {
+            $siblingElements = [$element];
+        } else {
+            $siblingElements = $this->elementRepository
+                ->findByParentElement($parentElement);
+        }
+
         return new GetElementResult(
             element: $element,
             childElements: $this->elementRepository
                 ->findByParentElement($element),
+            siblingElements: $siblingElements,
         );
     }
 }

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

@@ -8,10 +8,12 @@ class GetElementResult
 {
     /**
      * @param Element[] $childElements
+     * @param Element[] $siblingElements
      */
     public function __construct(
         private Element $element,
         private array $childElements,
+        private array $siblingElements,
     ) {
     }
 
@@ -27,4 +29,12 @@ class GetElementResult
     {
         return $this->childElements;
     }
+
+    /**
+     * @return Element[]
+     */
+    public function getSiblingElements(): array
+    {
+        return $this->siblingElements;
+    }
 }