add set elements

backend/app/Element/CreateElementDto.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace App\Element;
+
+use App\Set\Set;
+
+class CreateElementDto
+{
+    public function __construct(
+        public Set $set,
+        public string $title,
+        public ?Element $parentElement,
+    ) {}
+}

backend/app/Element/Element.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace App\Element;
+
+use App\Set\Set;
+
+class Element
+{
+    public function __construct(
+        private int $id,
+        private string $title,
+        private Set $set,
+        private ?Element $parentElement,
+    ) {}
+
+    public function getId(): int
+    {
+        return $this->id;
+    }
+
+    public function getTitle(): string
+    {
+        return $this->title;
+    }
+
+    public function getSet(): Set
+    {
+        return $this->set;
+    }
+
+    public function getParentElement(): ?Element
+    {
+        return $this->parentElement;
+    }
+}

backend/app/Element/ElementModel.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace App\Element;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * @property int $id
+ * @property int $set_id
+ * @property string $title
+ * @property int|null $parent_element_id
+ *
+ * @method static Builder<static>|ElementModel newModelQuery()
+ * @method static Builder<static>|ElementModel newQuery()
+ * @method static Builder<static>|ElementModel query()
+ * @method static Builder<static>|ElementModel whereId($value)
+ * @method static Builder<static>|ElementModel whereParentElementId($value)
+ * @method static Builder<static>|ElementModel whereSetId($value)
+ * @method static Builder<static>|ElementModel whereTitle($value)
+ *
+ * @mixin \Eloquent
+ */
+class ElementModel extends Model
+{
+    protected $table = 'elements';
+
+    public $timestamps = false;
+
+    protected $fillable = [
+        'set_id',
+        'title',
+        'parent_element_id',
+    ];
+
+    protected $casts = [
+        'set_id' => 'integer',
+        'parent_element_id' => 'integer',
+    ];
+}

backend/app/Element/ElementRepository.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Element;
+
+interface ElementRepository
+{
+    public function create(CreateElementDto $dto): Element;
+
+    public function find(int $id): ?Element;
+
+    /**
+     * @return Element[]
+     */
+    public function findBySetId(int $id): array;
+}

backend/app/Element/EloquentElementRepository.php

@@ -0,0 +1,75 @@
+<?php
+
+namespace App\Element;
+
+use App\Set\SetRepository;
+use DomainException;
+
+class EloquentElementRepository implements ElementRepository
+{
+    public function __construct(private SetRepository $setRepo) {}
+
+    public function create(CreateElementDto $dto): Element
+    {
+        $model = ElementModel::create([
+            'set_id' => $dto->set->getId(),
+            'title' => $dto->title,
+            'parent_element_id' => $dto->parentElement?->getId(),
+        ]);
+
+        return new Element(
+            id: $model->id,
+            title: $dto->title,
+            set: $dto->set,
+            parentElement: $dto->parentElement,
+        );
+    }
+
+    public function find(int $id): ?Element
+    {
+        $model = ElementModel::find($id);
+
+        return $model === null ? null : $this->toDomain($model);
+    }
+
+    /**
+     * @return Element[]
+     */
+    public function findBySetId(int $id): array
+    {
+        $models = ElementModel::where('set_id', $id)->orderBy('id')->get();
+        $elements = [];
+        foreach ($models as $model) {
+            $elements[] = $this->toDomain($model);
+        }
+
+        return $elements;
+    }
+
+    private function toDomain(ElementModel $model): Element
+    {
+        $set = $this->setRepo->find($model->set_id);
+        if ($set === null) {
+            throw new DomainException(
+                "Set with id: {$model->set_id} doesnt exist"
+            );
+        }
+
+        $parentElement = null;
+        if ($model->parent_element_id !== null) {
+            $parentElement = $this->find($model->parent_element_id);
+            if ($parentElement === null) {
+                throw new DomainException(
+                    "Element with id: {$model->parent_element_id} doesnt exist"
+                );
+            }
+        }
+
+        return new Element(
+            id: $model->id,
+            title: $model->title,
+            set: $set,
+            parentElement: $parentElement,
+        );
+    }
+}

backend/app/Element/UseCases/CreateElement/CreateElement.php

@@ -0,0 +1,84 @@
+<?php
+
+namespace App\Element\UseCases\CreateElement;
+
+use App\Element\CreateElementDto;
+use App\Element\Element;
+use App\Element\ElementRepository;
+use App\Exceptions\BadRequestException;
+use App\Set\SetRepository;
+use DomainException;
+
+class CreateElement
+{
+    public function __construct(
+        private ElementRepository $elementRepo,
+        private SetRepository $setRepo,
+    ) {}
+
+    /**
+     * @throws BadRequestException
+     * @throws DomainException
+     */
+    public function execute(CreateElementRequest $request): Element
+    {
+        if ($request->setId === null) {
+            throw new BadRequestException('setId is required');
+        }
+        if ($request->title === null || $request->title === '') {
+            throw new BadRequestException('title is required');
+        }
+
+        $set = $this->setRepo->find($request->setId);
+        if ($set === null) {
+            throw new DomainException(
+                "Set with id: {$request->setId} doesnt exist"
+            );
+        }
+
+        if ($request->parentElementId === null) {
+            $this->validateNoRootElementExists($request->setId);
+
+            return $this->elementRepo->create(new CreateElementDto(
+                set: $set,
+                title: $request->title,
+                parentElement: null,
+            ));
+        }
+
+        $parentElement = $this->elementRepo->find(
+            $request->parentElementId
+        );
+        if ($parentElement === null) {
+            throw new DomainException(
+                "Element with id: {$request->parentElementId} doesnt exist"
+            );
+        }
+        if ($parentElement->getSet()->getId() !== $set->getId()) {
+            throw new DomainException(
+                'Parent element must belong to the same set'
+            );
+        }
+
+        return $this->elementRepo->create(new CreateElementDto(
+            set: $set,
+            title: $request->title,
+            parentElement: $parentElement,
+        ));
+    }
+
+    /**
+     * @throws DomainException
+     */
+    private function validateNoRootElementExists(int $setId): void
+    {
+        $elements = $this->elementRepo->findBySetId($setId);
+        foreach ($elements as $element) {
+            if ($element->getParentElement() === null) {
+                throw new DomainException(
+                    'A root element already exists for this set'
+                );
+            }
+        }
+    }
+}

backend/app/Element/UseCases/CreateElement/CreateElementRequest.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Element\UseCases\CreateElement;
+
+class CreateElementRequest
+{
+    public function __construct(
+        public ?int $setId,
+        public ?string $title,
+        public ?int $parentElementId,
+    ) {}
+}