class ActionForm

class ActionForm implements ExpressionFormInterface {
    use ContextFormTrait;
    use StringTranslationTrait;
    use RulesUiHandlerTrait;
    
    /**
     * The action plugin manager.
     *
     * @var \Drupal\rules\Core\RulesActionManagerInterface
     */
    protected $actionManager;
    
    /**
     * The action expression that is edited in the form.
     *
     * @var \Drupal\rules\Engine\ActionExpressionInterface
     */
    protected $actionExpression;
    
    /**
     * Creates a new object of this class.
     */
    public function __construct(ActionExpressionInterface $action_expression, RulesActionManagerInterface $action_manager) {
        $this->actionManager = $action_manager;
        $this->actionExpression = $action_expression;
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $action_id = $form_state->get('action_id');
        $configuration = $this->actionExpression
            ->getConfiguration();
        if (empty($action_id) && !empty($configuration['action_id'])) {
            $action_id = $configuration['action_id'];
            $form_state->set('action_id', $action_id);
        }
        // Step 1 of the multistep form.
        if (!$action_id) {
            $action_definitions = $this->actionManager
                ->getGroupedDefinitions();
            $options = [];
            foreach ($action_definitions as $group => $definitions) {
                foreach ($definitions as $id => $definition) {
                    $options[$group][$id] = $definition['label'];
                }
            }
            $form['action_id'] = [
                '#type' => 'select',
                '#title' => $this->t('Action'),
                '#options' => $options,
                '#required' => TRUE,
            ];
            $form['continue'] = [
                '#type' => 'submit',
                '#value' => $this->t('Continue'),
                '#name' => 'continue',
                // Only validate the selected action in the first step.
'#limit_validation_errors' => [
                    [
                        'action_id',
                    ],
                ],
                '#submit' => [
                    static::class . '::submitFirstStep',
                ],
            ];
            return $form;
        }
        // Step 2 of the form.
        $action = $this->actionManager
            ->createInstance($action_id);
        $form['summary'] = [
            '#type' => 'details',
            '#title' => $this->t('Summary'),
        ];
        $form['summary']['description'] = [
            '#type' => 'container',
            '#plain_text' => $this->t('Action: @summary', [
                '@summary' => $action->summary(),
            ]),
            '#attributes' => [
                'class' => [
                    'form-item',
                ],
            ],
        ];
        $context_definitions = $action->getContextDefinitions();
        if (!empty($context_definitions)) {
            $form['context_definitions'] = [
                '#type' => 'details',
                '#title' => $this->t('Context variables'),
                '#open' => TRUE,
                '#tree' => TRUE,
            ];
            foreach ($context_definitions as $context_name => $context_definition) {
                $form = $this->buildContextForm($form, $form_state, $context_name, $context_definition, $configuration);
            }
        }
        $provides_definitions = $action->getProvidedContextDefinitions();
        if (!empty($provides_definitions)) {
            $form['provides'] = [
                '#type' => 'details',
                '#title' => $this->t('Provided variables'),
                '#description' => $this->t('You may change the name of any provided variables, but note that renaming already-utilized variables invalidates the existing uses.'),
                '#tree' => TRUE,
            ];
            foreach ($provides_definitions as $provides_name => $provides_definition) {
                $form = $this->buildProvidedContextForm($form, $form_state, $provides_name, $provides_definition, $configuration);
            }
        }
        $form['save'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save'),
            '#name' => 'save',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array $form, FormStateInterface $form_state) {
        // Only if there is an action selected already we can validate something.
        if ($form_state->get('action_id')) {
            // Invoke the submission handler which will setup the expression being
            // edited in the form. That way the expression is ready for other
            // validation handlers.
            $this->submitForm($form, $form_state);
        }
    }
    
    /**
     * Submit callback: save the selected action in the first step.
     */
    public static function submitFirstStep(array &$form, FormStateInterface $form_state) {
        $form_state->set('action_id', $form_state->getValue('action_id'));
        $form_state->setRebuild();
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $action_id = $form_state->get('action_id');
        // Nothing to do as long as the first step is not completed.
        if (!$action_id) {
            return;
        }
        $action_definition = $this->actionManager
            ->getDefinition($action_id);
        $context_config = $this->getContextConfigFromFormValues($form_state, $action_definition['context_definitions']);
        // Rename provided variables, if any.
        if ($provided_variables = $form_state->getValue('provides')) {
            foreach ($provided_variables as $provides_name => $provides_context) {
                // Do this only on rename.
                if ($provides_name !== $provides_context['name']) {
                    \Drupal::messenger()->addWarning("providing '" . $provides_name . "' as '" . $provides_context['name'] . "'");
                    $context_config->provideAs($provides_name, $provides_context['name']);
                }
            }
        }
        $configuration = $context_config->toArray();
        $configuration['action_id'] = $action_id;
        $this->actionExpression
            ->setConfiguration($configuration);
    }

}