Draft: #3011202 add feeds integration

Closes #3011202

src/Feeds/Target/Metatag.php

+<?php
+
+namespace Drupal\metatag\Feeds\Target;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\feeds\FeedInterface;
+use Drupal\feeds\Plugin\Type\Target\FieldTargetBase;
+use Drupal\metatag\Feeds\MetatagFieldTargetDefinition;
+
+/**
+ * Provides a generic field target.
+ *
+ * @FeedsTarget(
+ *   id = "metatag",
+ *   field_types = {
+ *     "metatag"
+ *  }
+ * )
+ */
+class Metatag extends FieldTargetBase
+{
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static function prepareTarget(FieldDefinitionInterface $field_definition)
+  {
+
+    // Get metatag manager.
+    $metatag_manager = \Drupal::service('metatag.manager');
+
+    // Load basic tags.
+    // All tags are not manageable until https://www.drupal.org/project/feeds/issues/3173943 is resolved.
+
+    $metatag_basic = $metatag_manager->sortedGroupsWithTags()['basic']['tags'] ?? [];
+    $metatag_og = $metatag_manager->sortedGroupsWithTags()['open_graph']['tags'] ?? [];
+    $metatag_advanced = $metatag_manager->sortedGroupsWithTags()['advanced']['tags'] ?? [];
+
+    $metatag_tags = array_merge($metatag_basic, $metatag_og, $metatag_advanced);
+
+    // Create a field target definition.
+    // Can't use default FieldTargetDefinition because of https://www.drupal.org/project/feeds/issues/3173942.
+    $definition = MetatagFieldTargetDefinition::createFromFieldDefinition($field_definition);
+
+    // Loop over basic tags.
+    foreach ($metatag_tags as $tag_key => $tag_value) {
+      // Add tag as property
+      $definition->addProperty($tag_key, $tag_value['label'], $tag_value['label']);
+    }
+
+    return $definition;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTarget(FeedInterface $feed, EntityInterface $entity, $field_name, array $values)
+  {
+
+    if ($values = $this->prepareValues($values)) {
+      $entity_target = $this->getEntityTarget($feed, $entity);
+      if (!empty($entity_target)) {
+        $item_list = $entity_target->get($field_name);
+
+        // Append these values to the existing values.
+        $values = array_merge($item_list->getValue(), $values)[0];
+
+        // Serialize values
+        $values = serialize($values);
+
+        $item_list->setValue($values);
+      }
+    }
+  }
+
+}