class FormWizardBase

abstract class FormWizardBase extends FormBase implements FormWizardInterface {
    
    /**
     * Tempstore Factory for keeping track of values in each step of the wizard.
     *
     * @var \Drupal\Core\TempStore\SharedTempStoreFactory
     */
    protected $tempstore;
    
    /**
     * The Form Builder.
     *
     * @var \Drupal\Core\Form\FormBuilderInterface
     */
    protected $builder;
    
    /**
     * The class resolver.
     *
     * @var \Drupal\Core\DependencyInjection\ClassResolverInterface
     */
    protected $classResolver;
    
    /**
     * The event dispatcher.
     *
     * @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
     */
    protected $dispatcher;
    
    /**
     * The shared temp store factory collection name.
     *
     * @var string
     */
    protected $tempstore_id;
    
    /**
     * The SharedTempStore key for our current wizard values.
     *
     * @var string|null
     */
    protected $machine_name;
    
    /**
     * The current active step of the wizard.
     *
     * @var string|null
     */
    protected $step;
    
    /**
     * Renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * @param \Drupal\Core\TempStore\SharedTempStoreFactory $tempstore
     *   Tempstore Factory for keeping track of values in each step of the
     *   wizard.
     * @param \Drupal\Core\Form\FormBuilderInterface $builder
     *   The Form Builder.
     * @param \Drupal\Core\DependencyInjection\ClassResolverInterface $class_resolver
     *   The class resolver.
     * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
     *   The event dispatcher.
     * @param $tempstore_id
     *   The shared temp store factory collection name.
     * @param null $machine_name
     *   The SharedTempStore key for our current wizard values.
     * @param null $step
     *   The current active step of the wizard.
     */
    public function __construct(SharedTempStoreFactory $tempstore, FormBuilderInterface $builder, ClassResolverInterface $class_resolver, EventDispatcherInterface $event_dispatcher, RouteMatchInterface $route_match, RendererInterface $renderer, $tempstore_id, $machine_name = NULL, $step = NULL) {
        $this->tempstore = $tempstore;
        $this->builder = $builder;
        $this->classResolver = $class_resolver;
        $this->dispatcher = $event_dispatcher;
        $this->routeMatch = $route_match;
        $this->renderer = $renderer;
        $this->tempstore_id = $tempstore_id;
        $this->machine_name = $machine_name;
        $this->step = $step;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getParameters() {
        return [
            'tempstore' => \Drupal::service('tempstore.shared'),
            'builder' => \Drupal::service('form_builder'),
            'class_resolver' => \Drupal::service('class_resolver'),
            'event_dispatcher' => \Drupal::service('event_dispatcher'),
            'renderer' => \Drupal::service('renderer'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function initValues() {
        $values = [];
        $event = new WizardEvent($this, $values);
        $this->dispatcher
            ->dispatch($event, FormWizardInterface::LOAD_VALUES);
        return $event->getValues();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTempstoreId() {
        return $this->tempstore_id;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTempstore() {
        $tempstore = $this->tempstore
            ->get($this->getTempstoreId());
        return $tempstore;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMachineName() {
        return $this->machine_name;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getStep($cached_values) {
        if (!$this->step) {
            $operations = $this->getOperations($cached_values);
            $steps = array_keys($operations);
            $this->step = reset($steps);
        }
        return $this->step;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getOperation($cached_values) {
        $operations = $this->getOperations($cached_values);
        $step = $this->getStep($cached_values);
        if (!empty($operations[$step])) {
            return $operations[$step];
        }
        throw new NotFoundHttpException();
    }
    
    /**
     * The translated text of the "Next" button's text.
     *
     * @return string
     */
    public function getNextOp() {
        return $this->t('Next');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getNextParameters($cached_values) {
        // Get the steps by key.
        $operations = $this->getOperations($cached_values);
        $steps = array_keys($operations);
        // Get the steps after the current step.
        $after = array_slice($operations, array_search($this->getStep($cached_values), $steps) + 1);
        // Get the steps after the current step by key.
        $after_keys = array_keys($after);
        $step = reset($after_keys);
        if (!$step) {
            $keys = array_keys($operations);
            $step = end($keys);
        }
        return [
            'machine_name' => $this->getMachineName(),
            'step' => $step,
            'js' => 'nojs',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPreviousParameters($cached_values) {
        $operations = $this->getOperations($cached_values);
        $step = $this->getStep($cached_values);
        // Get the steps by key.
        $steps = array_keys($operations);
        // Get the steps before the current step.
        $before = array_slice($operations, 0, array_search($step, $steps));
        // Get the steps before the current step by key.
        $before = array_keys($before);
        // Reverse the steps for easy access to the next step.
        $before_steps = array_reverse($before);
        $step = reset($before_steps);
        return [
            'machine_name' => $this->getMachineName(),
            'step' => $step,
            'js' => 'nojs',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        if (!$this->getMachineName() || !$this->getTempstore()
            ->get($this->getMachineName())) {
            $cached_values = $this->initValues();
        }
        else {
            $cached_values = $this->getTempstore()
                ->get($this->getMachineName());
        }
        $operation = $this->getOperation($cached_values);
        
        /** @var \Drupal\Core\Form\FormInterface $operation */
        $operation = $this->classResolver
            ->getInstanceFromDefinition($operation['form']);
        return $operation->getFormId();
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $cached_values = $form_state->getTemporaryValue('wizard');
        // Get the current form operation.
        $operation = $this->getOperation($cached_values);
        $form = $this->customizeForm($form, $form_state);
        
        /** @var \Drupal\Core\Form\FormInterface $formClass */
        $formClass = $this->classResolver
            ->getInstanceFromDefinition($operation['form']);
        // Pass include any custom values for this operation.
        if (!empty($operation['values'])) {
            $cached_values = array_merge($cached_values, $operation['values']);
            $form_state->setTemporaryValue('wizard', $cached_values);
        }
        // Build the form.
        $form = $formClass->buildForm($form, $form_state);
        if (isset($operation['title'])) {
            $form['#title'] = $operation['title'];
        }
        $form['actions'] = $this->actions($formClass, $form_state);
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        // Only perform this logic if we're moving to the next page. This prevents
        // the loss of cached values on ajax submissions.
        if ((string) $form_state->getValue('op') == (string) $this->getNextOp()) {
            $cached_values = $form_state->getTemporaryValue('wizard');
            if ($form_state->hasValue('label')) {
                $cached_values['label'] = $form_state->getValue('label');
            }
            if ($form_state->hasValue('id')) {
                $cached_values['id'] = $form_state->getValue('id');
            }
            if (is_null($this->machine_name) && !empty($cached_values['id'])) {
                $this->machine_name = $cached_values['id'];
            }
            $this->getTempstore()
                ->set($this->getMachineName(), $cached_values);
            $next_parameters = $this->getNextParameters($cached_values);
            if (!$form_state->get('ajax')) {
                $form_state->setRedirect($this->getRouteName(), $next_parameters);
            }
            else {
                // Switch steps for ajax forms.
                if (!empty($next_parameters['step'])) {
                    $this->step = $next_parameters['step'];
                }
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function populateCachedValues(array &$form, FormStateInterface $form_state) {
        $cached_values = $this->getTempstore()
            ->get($this->getMachineName());
        if (!$cached_values) {
            $cached_values = $form_state->getTemporaryValue('wizard');
            if (!$cached_values) {
                $cached_values = $this->initValues();
                $form_state->setTemporaryValue('wizard', $cached_values);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function previous(array &$form, FormStateInterface $form_state) {
        $cached_values = $form_state->getTemporaryValue('wizard');
        $prev_parameters = $this->getPreviousParameters($cached_values);
        // Redirect for non ajax forms.
        if (!$form_state->get('ajax')) {
            $form_state->setRedirect($this->getRouteName(), $prev_parameters);
        }
        else {
            // Switch step for ajax forms.
            if (!empty($prev_parameters['step'])) {
                $this->step = $prev_parameters['step'];
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function finish(array &$form, FormStateInterface $form_state) {
        $this->getTempstore()
            ->delete($this->getMachineName());
    }
    
    /**
     * Helper function for generating default form elements.
     *
     * @param array $form
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *
     * @return array
     */
    protected function customizeForm(array $form, FormStateInterface $form_state) {
        // Setup the step rendering theme element.
        $prefix = [
            '#theme' => [
                'ctools_wizard_trail',
            ],
            '#wizard' => $this,
            '#cached_values' => $form_state->getTemporaryValue('wizard'),
        ];
        $form['#prefix'] = $this->renderer
            ->render($prefix);
        return $form;
    }
    
    /**
     * Generates action elements for navigating between the operation steps.
     *
     * @param \Drupal\Core\Form\FormInterface $form_object
     *   The current operation form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current form state.
     *
     * @return array
     */
    protected function actions(FormInterface $form_object, FormStateInterface $form_state) {
        $cached_values = $form_state->getTemporaryValue('wizard');
        $operations = $this->getOperations($cached_values);
        $step = $this->getStep($cached_values);
        $operation = $operations[$step];
        $steps = array_keys($operations);
        // Slice to find the operations that occur before the current operation.
        $before = array_slice($operations, 0, array_search($step, $steps));
        // Slice to find the operations that occur after the current operation.
        $after = array_slice($operations, array_search($step, $steps) + 1);
        $actions = [
            '#type' => 'actions',
            'submit' => [
                '#type' => 'submit',
                '#value' => $this->t('Next'),
                '#button_type' => 'primary',
                '#validate' => [
                    '::populateCachedValues',
                    [
                        $form_object,
                        'validateForm',
                    ],
                ],
                '#submit' => [
                    [
                        $form_object,
                        'submitForm',
                    ],
                ],
            ],
        ];
        // Add any submit or validate functions for the step and the global ones.
        if (isset($operation['validate'])) {
            $actions['submit']['#validate'] = array_merge($actions['submit']['#validate'], $operation['validate']);
        }
        $actions['submit']['#validate'][] = '::validateForm';
        if (isset($operation['submit'])) {
            $actions['submit']['#submit'] = array_merge($actions['submit']['#submit'], $operation['submit']);
        }
        $actions['submit']['#submit'][] = '::submitForm';
        if ($form_state->get('ajax')) {
            // Ajax submissions need to submit to the current step, not "next".
            $parameters = $this->getNextParameters($cached_values);
            $parameters['step'] = $this->getStep($cached_values);
            $actions['submit']['#ajax'] = [
                'callback' => '::ajaxSubmit',
                'url' => Url::fromRoute($this->getRouteName(), $parameters),
                'options' => [
                    'query' => $this->getRequest()->query
                        ->all() + [
                        FormBuilderInterface::AJAX_FORM_REQUEST => TRUE,
                    ],
                ],
            ];
        }
        // If there are steps before this one, label the button "previous"
        // otherwise do not display a button.
        if ($before) {
            $actions['previous'] = [
                '#type' => 'submit',
                '#value' => $this->t('Previous'),
                '#validate' => [
                    [
                        $this,
                        'populateCachedValues',
                    ],
                ],
                '#submit' => [
                    [
                        $this,
                        'previous',
                    ],
                ],
                '#limit_validation_errors' => [],
                '#weight' => -10,
            ];
            if ($form_state->get('ajax')) {
                // Ajax submissions need to submit to the current step, not "previous".
                $parameters = $this->getPreviousParameters($cached_values);
                $parameters['step'] = $this->getStep($cached_values);
                $actions['previous']['#ajax'] = [
                    'callback' => '::ajaxPrevious',
                    'url' => Url::fromRoute($this->getRouteName(), $parameters),
                    'options' => [
                        'query' => $this->getRequest()->query
                            ->all() + [
                            FormBuilderInterface::AJAX_FORM_REQUEST => TRUE,
                        ],
                    ],
                ];
            }
        }
        // If there are not steps after this one, label the button "Finish".
        if (!$after) {
            $actions['submit']['#value'] = $this->t('Finish');
            $actions['submit']['#submit'][] = [
                $this,
                'finish',
            ];
            if ($form_state->get('ajax')) {
                $actions['submit']['#ajax']['callback'] = [
                    $this,
                    'ajaxFinish',
                ];
            }
        }
        return $actions;
    }
    public function ajaxSubmit(array $form, FormStateInterface $form_state) {
        $cached_values = $form_state->getTemporaryValue('wizard');
        $response = new AjaxResponse();
        $parameters = $this->getNextParameters($cached_values);
        $response->addCommand(new OpenModalWizardCommand($this, $this->getTempstoreId(), $parameters));
        return $response;
    }
    public function ajaxPrevious(array $form, FormStateInterface $form_state) {
        $cached_values = $form_state->getTemporaryValue('wizard');
        $response = new AjaxResponse();
        $parameters = $this->getPreviousParameters($cached_values);
        $response->addCommand(new OpenModalWizardCommand($this, $this->getTempstoreId(), $parameters));
        return $response;
    }
    public function ajaxFinish(array $form, FormStateInterface $form_state) {
        $response = new AjaxResponse();
        $response->addCommand(new CloseModalDialogCommand());
        return $response;
    }
    public function getRouteName() {
        return $this->routeMatch
            ->getRouteName();
    }

}