class WorkspaceMergeForm

class WorkspaceMergeForm extends ConfirmFormBase implements WorkspaceFormInterface, ContainerInjectionInterface {
    
    /**
     * 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' => \Drupal::destination()->getAsArray(),
        ]);
    }
    
    /**
     * {@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(),
        ]));
    }

}