class WorkspaceMergeForm

class WorkspaceMergeForm extends ConfirmFormBase implements ContainerInjectionInterface, WorkspaceSafeFormInterface {
  
  /**
   * The source workspace entity.
   *
   * @var \Drupal\workspaces\WorkspaceInterface
   */
  protected $sourceWorkspace;
  
  /**
   * The target workspace entity.
   *
   * @var \Drupal\workspaces\WorkspaceInterface
   */
  protected $targetWorkspace;
  
  /**
   * The workspace operation factory.
   *
   * @var \Drupal\workspaces\WorkspaceOperationFactory
   */
  protected $workspaceOperationFactory;
  
  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * Constructs a new WorkspaceMergeForm.
   *
   * @param \Drupal\workspaces\WorkspaceOperationFactory $workspace_operation_factory
   *   The workspace operation factory service.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   */
  public function __construct(WorkspaceOperationFactory $workspace_operation_factory, EntityTypeManagerInterface $entity_type_manager) {
    $this->workspaceOperationFactory = $workspace_operation_factory;
    $this->entityTypeManager = $entity_type_manager;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('workspaces.operation_factory'), $container->get('entity_type.manager'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'workspace_merge_form';
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state, ?WorkspaceInterface $source_workspace = NULL, ?WorkspaceInterface $target_workspace = NULL) {
    $this->sourceWorkspace = $source_workspace;
    $this->targetWorkspace = $target_workspace;
    $form = parent::buildForm($form, $form_state);
    $workspace_merger = $this->workspaceOperationFactory
      ->getMerger($this->sourceWorkspace, $this->targetWorkspace);
    $args = [
      '%source_label' => $this->sourceWorkspace
        ->label(),
      '%target_label' => $this->targetWorkspace
        ->label(),
    ];
    // List the changes that can be merged into the target.
    if ($source_rev_diff = $workspace_merger->getDifferringRevisionIdsOnSource()) {
      $total_count = $workspace_merger->getNumberOfChangesOnSource();
      $form['merge'] = [
        '#theme' => 'item_list',
        '#title' => $this->formatPlural($total_count, 'There is @count item that can be merged from %source_label to %target_label', 'There are @count items that can be merged from %source_label to %target_label', $args),
        '#items' => [],
        '#total_count' => $total_count,
      ];
      foreach ($source_rev_diff as $entity_type_id => $revision_difference) {
        $form['merge']['#items'][$entity_type_id] = $this->entityTypeManager
          ->getDefinition($entity_type_id)
          ->getCountLabel(count($revision_difference));
      }
    }
    // If there are no changes to merge, show an informational message.
    if (!isset($form['merge'])) {
      $form['description'] = [
        '#markup' => $this->t('There are no changes that can be merged from %source_label to %target_label.', $args),
      ];
      $form['actions']['submit']['#disabled'] = TRUE;
    }
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getQuestion() {
    return $this->t('Would you like to merge the contents of the %source_label workspace into %target_label?', [
      '%source_label' => $this->sourceWorkspace
        ->label(),
      '%target_label' => $this->targetWorkspace
        ->label(),
    ]);
  }
  
  /**
   * {@inheritdoc}
   */
  public function getDescription() {
    return $this->t('Merge workspace contents.');
  }
  
  /**
   * {@inheritdoc}
   */
  public function getCancelUrl() {
    return Url::fromRoute('entity.workspace.collection', [], [
      'query' => $this->getDestinationArray(),
    ]);
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $this->workspaceOperationFactory
      ->getMerger($this->sourceWorkspace, $this->targetWorkspace)
      ->merge();
    $this->messenger()
      ->addMessage($this->t('The contents of the %source_label workspace have been merged into %target_label.', [
      '%source_label' => $this->sourceWorkspace
        ->label(),
      '%target_label' => $this->targetWorkspace
        ->label(),
    ]));
  }

}