class DeleteEventForm

class DeleteEventForm extends ConfirmFormBase {
    
    /**
     * The Rules event manager.
     *
     * @var \Drupal\rules\Core\RulesEventManager
     */
    protected $eventManager;
    
    /**
     * The RulesUI handler of the currently active UI.
     *
     * @var \Drupal\rules\Ui\RulesUiHandlerInterface
     */
    protected $rulesUiHandler;
    
    /**
     * The Reaction Rule being modified.
     *
     * @var \Drupal\rules\Entity\ReactionRuleConfig
     */
    protected $reactionRule;
    
    /**
     * The ID of the event in the rule.
     *
     * @var string
     */
    protected $id;
    
    /**
     * Constructs a new event delete form.
     *
     * @param \Drupal\rules\Core\RulesEventManager $event_manager
     *   The Rules event plugin manager.
     */
    public function __construct(RulesEventManager $event_manager) {
        $this->eventManager = $event_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('plugin.manager.rules_event'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'rules_delete_event';
    }
    
    /**
     * 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\rules\Ui\RulesUiHandlerInterface $rules_ui_handler
     *   The RulesUI handler of the currently active UI.
     * @param \Drupal\rules\Entity\ReactionRuleConfig $rules_reaction_rule
     *   The rule config object this form is for.
     * @param string $id
     *   The ID of the event in the rule.
     *
     * @return array
     *   The form structure.
     */
    public function buildForm(array $form, FormStateInterface $form_state, RulesUiHandlerInterface $rules_ui_handler = NULL, ReactionRuleConfig $rules_reaction_rule = NULL, $id = NULL) {
        $this->rulesUiHandler = $rules_ui_handler;
        $this->reactionRule = $rules_reaction_rule;
        $this->id = $id;
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfirmText() {
        return $this->t('Delete');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getQuestion() {
        // Do not allow to delete an event if there's only one.
        if (count($this->reactionRule
            ->getEvents()) === 1) {
            throw new AccessDeniedHttpException('An event cannot be deleted if the reaction rule has only one.');
        }
        // Check of the event requested to be deleted, exists.
        if (!$this->reactionRule
            ->hasEvent($this->id)) {
            throw new NotFoundHttpException();
        }
        $event_definition = $this->eventManager
            ->getDefinition($this->id);
        return $this->t('Are you sure you want to delete the event %title from %rule?', [
            '%title' => $event_definition['label'],
            '%rule' => $this->rulesUiHandler
                ->getComponentLabel(),
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCancelUrl() {
        return $this->rulesUiHandler
            ->getBaseRouteUrl();
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->reactionRule
            ->removeEvent($this->id);
        $this->reactionRule
            ->save();
        $this->messenger()
            ->addMessage($this->t('Deleted event %label from %rule.', [
            '%label' => $this->eventManager
                ->getDefinition($this->id)['label'],
            '%rule' => $this->reactionRule
                ->label(),
        ]));
        $form_state->setRedirectUrl($this->getCancelUrl());
    }

}