class WorkflowTransitionDeleteForm

class WorkflowTransitionDeleteForm extends ConfirmFormBase {
    
    /**
     * The workflow entity the transition being deleted belongs to.
     *
     * @var \Drupal\workflows\WorkflowInterface
     */
    protected $workflow;
    
    /**
     * The workflow transition being deleted.
     *
     * @var \Drupal\workflows\TransitionInterface
     */
    protected $transition;
    
    /**
     * The transition being deleted.
     *
     * @var string
     */
    protected $transitionId;
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'workflow_transition_delete_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function getQuestion() {
        return $this->t('Are you sure you want to delete %transition from %workflow?', [
            '%transition' => $this->transition
                ->label(),
            '%workflow' => $this->workflow
                ->label(),
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCancelUrl() {
        return $this->workflow
            ->toUrl();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfirmText() {
        return $this->t('Delete');
    }
    
    /**
     * Form constructor.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param \Drupal\workflows\WorkflowInterface $workflow
     *   The workflow entity being edited.
     * @param string|null $workflow_transition
     *   The workflow transition being deleted.
     *
     * @return array
     *   The form structure.
     */
    public function buildForm(array $form, FormStateInterface $form_state, WorkflowInterface $workflow = NULL, $workflow_transition = NULL) {
        try {
            $this->transition = $workflow->getTypePlugin()
                ->getTransition($workflow_transition);
        } catch (\InvalidArgumentException $e) {
            throw new NotFoundHttpException();
        }
        $this->workflow = $workflow;
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->workflow
            ->getTypePlugin()
            ->deleteTransition($this->transition
            ->id());
        $this->workflow
            ->save();
        $this->messenger()
            ->addStatus($this->t('%transition transition deleted.', [
            '%transition' => $this->transition
                ->label(),
        ]));
        $form_state->setRedirectUrl($this->getCancelUrl());
    }

}