Added support for product attribute value entity

Closes #3481957

src/Plugin/SingleContentSyncBaseFieldsProcessor/CommerceProductAttributeValue.php

+<?php
+
+namespace Drupal\commerce_sync\Plugin\SingleContentSyncBaseFieldsProcessor;
+
+use Drupal\commerce_product\Entity\ProductAttributeValueInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Entity\FieldableEntityInterface;
+use Drupal\Core\Messenger\MessengerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\single_content_sync\ContentExporterInterface;
+use Drupal\single_content_sync\SingleContentSyncBaseFieldsProcessorPluginBase;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Implementation for commerce product variation base fields processor plugin.
+ *
+ * @SingleContentSyncBaseFieldsProcessor(
+ *   id = "commerce_product_attribute_value",
+ *   label = @Translation("Commerce Product Attribute Value"),
+ *   entity_type = "commerce_product_attribute_value",
+ * )
+ */
+class CommerceProductAttributeValue extends SingleContentSyncBaseFieldsProcessorPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The content exporter.
+   *
+   * @var \Drupal\single_content_sync\ContentExporterInterface
+   */
+  protected ContentExporterInterface $exporter;
+
+  /**
+   * The messenger service.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected MessengerInterface $messenger;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected EntityTypeManagerInterface $entityTypeManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, MessengerInterface $messenger, EntityTypeManagerInterface $entity_type_manager) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+
+    $this->messenger = $messenger;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('messenger'),
+      $container->get('entity_type.manager'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function exportBaseValues(FieldableEntityInterface $entity): array {
+    assert($entity instanceof ProductAttributeValueInterface);
+
+    $base_fields = [
+      'attribute' => $entity->getAttribute()->toArray(),
+      'name' => $entity->getName(),
+      'weight' => $entity->getWeight(),
+    ];
+
+    return $base_fields;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function mapBaseFieldsValues(array $values, FieldableEntityInterface $entity): array {
+    assert($entity instanceof ProductAttributeValueInterface);
+
+    $base_fields = [
+      'name' => $values['name'],
+      'weight' => $values['weight'],
+    ];
+
+    if (!empty($values['attribute'])) {
+      $storage = $this->entityTypeManager->getStorage('commerce_product_attribute');
+      $attribute = $storage->load($values['attribute']['id']);
+      if ($attribute) {
+        $base_fields['attribute'] = $attribute->id();
+      }
+      else {
+        $this->messenger->addError(t('Attribute type @type does not exist.', ['@type' => $values['attribute']['id']]));
+      }
+    }
+
+    return $base_fields;
+  }
+
+}