Modification of Drupal [Content Sync](https://www.drupal.org/project/content_sync) module. It replace the single item export tab. On which it is heavily based. When an an entity is selected, it can be exported as a tar file. Along with the entity's dependencies and attached medias saved as files (not base64) with extensions. Entity type and bund…

ContentSingleExportForm.php

/*
* Modification of Drupal [Content Sync](https://www.drupal.org/project/content_sync) module. 
* It replace the single item export tab. On which it is heavily based. When an an entity is 
* selected, it can be exported as a tar file. Along with the entity's dependencies and attached 
* medias saved as files (not base64) with extensions. Entity type and bundle/sub-type are 
* hardcoded and are set to "node" and "poi_collection". Quick and dirty but does the job.
*/

<?php

namespace Drupal\content_sync\Form;

use Drupal\content_sync\ContentSyncManagerInterface;
use Drupal\content_sync\Exporter\ContentExporterInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\Core\Entity\EntityTypeBundleInfo;
use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Entity\ContentEntityType;
use Symfony\Component\DependencyInjection\ContainerInterface;



/**
 * Provides a form for exporting a single content file.
 */
class ContentSingleExportForm extends FormBase {

  use ContentExportTrait;

  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * The entity bundle manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeBundleInfo
   */
  protected $entityBundleManager;

  /**
   * @var \Drupal\content_sync\Exporter\ContentExporterInterface
   */
  protected $contentExporter;

  /**
   * @var \Drupal\content_sync\ContentSyncManagerInterface
   */
  protected $contentSyncManager;

  /**
   * Constructs a new ContentSingleExportForm.
   *
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *
   * @param \Drupal\Core\Entity\EntityTypeBundleInfo $entity_bundle_manager
   *
   * @param \Drupal\content_sync\Exporter\ContentExporterInterface $content_exporter
   */
  public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityTypeBundleInfo $entity_bundle_manager, ContentExporterInterface $content_exporter, ContentSyncManagerInterface $content_sync_manager) {
    $this->entityTypeManager = $entity_type_manager;
    $this->entityBundleManager = $entity_bundle_manager;
    $this->contentExporter = $content_exporter;
    $this->contentSyncManager = $content_sync_manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('entity_type.manager'),
      $container->get('entity_type.bundle.info'),
      $container->get('content_sync.exporter'),
      $container->get('content_sync.manager')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'config_single_export_form';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state, $content_type = 'node', $content_name = NULL, $content_entity = NULL) {

    $default_type = 'node';
    $default_name = 'poi_collection';

    // Auto-complete field for the content entity
    if($default_type && $default_name){
      $form['content_entity'] = [
        '#title' => $this->t('Content Entity'),
        '#type' => 'entity_autocomplete',
        '#target_type' => $default_type,
        '#selection_handler' => 'default',
        '#selection_settings' => [
          'target_bundles' => [$default_name],
        ],
        '#ajax' => [
          'callback' => '::updateExport',
          'wrapper' => 'edit-export-wrapper',
            'event' => 'autocompleteclose',
        ],
      ];
      // Autocomplete doesn't support target bundles parameter on bundle-less entities.
      $target_type = \Drupal::entityManager()->getDefinition($default_type);
      $target_type_bundles = $target_type->getBundleEntityType();
      if(is_null($target_type_bundles)){
        unset($form['content_entity']['#selection_settings']);
      }
    }

    $form['export'] = [
      '#title' => $this->t('Here is your configuration:'),
      '#type' => 'textarea',
      '#rows' => 5,
      '#prefix' => '<div id="edit-export-wrapper">',
      '#suffix' => '</div>',
    ];

    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Export'),
    ];

    return $form;
  }

  /**
   * Handles switching the content type selector.
   */
  protected function findContent($content_type) {
    $names = [
      '' => $this->t('- Select -'),
    ];
    // For a given entity type, load all entities.
    if ($content_type) {
      $entity_storage = $this->entityBundleManager->getBundleInfo($content_type);
      foreach ($entity_storage as $entityKey => $entity) {
        $entity_id = $entityKey;
        if ($label = $entity['label']) {
          $names[$entity_id] = new TranslatableMarkup('@label (@id)', ['@label' => $label, '@id' => $entity_id]);
        }
        else {
          $names[$entity_id] = $entity_id;
        }
      }
    }
    return $names;
  }

  /**
   * Handles switching the export textarea.
   */
  public function updateExport($form, FormStateInterface $form_state) {
    // Get submitted values
    // $entity_type = $form_state->getValue('content_type');
    $entity_id = $form_state->getValue('content_entity');

    $entity_type = 'node';
    // $entity_id = 'poi_collection';

    // DB entity to YAML
    $entity = $this->entityTypeManager->getStorage($entity_type)->load($entity_id);

    // Generate the YAML file.
    $serializer_context = [];
    $language = \Drupal::languageManager()->getCurrentLanguage()->getId();
    $entity = $entity->getTranslation($language);
    $exported_entity = $this->contentExporter->exportEntity($entity, $serializer_context);

    // Create the name
    $name = $entity_type . "." . $entity->bundle() . "." . $entity->uuid();

    // Return form values
    $form['export']['#value'] = $exported_entity;
    $form['export']['#description'] = $this->t('Filename: %name', ['%name' => $name . '.yml']);
    return $form['export'];
  }

  public function snapshot() {
    //Set batch operations by entity type/bundle
    $entities_list = [];
    $entity_type_definitions = $this->entityTypeManager->getDefinitions();
    foreach ($entity_type_definitions as $entity_type => $definition) {
      $reflection = new \ReflectionClass($definition->getClass());
      if ($reflection->implementsInterface(ContentEntityInterface::class)) {
        $entities = $this->entityTypeManager->getStorage($entity_type)
                                            ->getQuery()
                                            ->execute();
        foreach ($entities as $entity_id) {
          $entities_list[] = [
            'entity_type' => $entity_type,
            'entity_id' => $entity_id,
          ];
        }
      }
    }
    if (!empty($entities_list)) {
      $serializer_context['export_type'] = 'snapshot';
      $batch = $this->generateExportBatch($entities_list, $serializer_context);
      batch_set($batch);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    // drupal_set_message(t('The form has been submitted.'));
    // Delete the content tar file in case an older version exist.
    file_unmanaged_delete($this->getTempFile());
    $entities_list = [];
    $entity_type = 'node';
    $entity_id = $form_state->getValue('content_entity');
    $entities_list[] = [
      'entity_type' => $entity_type,
      'entity_id' => $entity_id,
    ];
    if (!empty($entities_list)) {
      $serializer_context['export_type'] = 'tar';
      $serializer_context['include_files'] = 'folder';
      $serializer_context['include_dependencies'] = true;
      $batch = $this->generateExportBatch($entities_list, $serializer_context);
      batch_set($batch);
    }
  }

  /**
   * @{@inheritdoc}
   */
  protected function getEntityTypeManager() {
    return $this->entityTypeManager;
  }

  /**
   * @{@inheritdoc}
   */
  protected function getContentExporter() {
    return $this->contentExporter;
  }

  /**
   * @{@inheritdoc}
   */
  protected function getExportLogger() {
    return $this->logger('content_sync');
  }
}