class BlockForm

class BlockForm extends EntityForm {
    
    /**
     * The block entity.
     *
     * @var \Drupal\block\BlockInterface
     */
    protected $entity;
    
    /**
     * The block storage.
     *
     * @var \Drupal\Core\Entity\EntityStorageInterface
     */
    protected $storage;
    
    /**
     * The condition plugin manager.
     *
     * @var \Drupal\Core\Condition\ConditionManager
     */
    protected $manager;
    
    /**
     * The language manager service.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $language;
    
    /**
     * The theme handler.
     *
     * @var \Drupal\Core\Extension\ThemeHandler
     */
    protected $themeHandler;
    
    /**
     * The context repository service.
     *
     * @var \Drupal\Core\Plugin\Context\ContextRepositoryInterface
     */
    protected $contextRepository;
    
    /**
     * The plugin form manager.
     *
     * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
     */
    protected $pluginFormFactory;
    
    /**
     * Constructs a BlockForm object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Executable\ExecutableManagerInterface $manager
     *   The ConditionManager for building the visibility UI.
     * @param \Drupal\Core\Plugin\Context\ContextRepositoryInterface $context_repository
     *   The lazy context repository service.
     * @param \Drupal\Core\Language\LanguageManagerInterface $language
     *   The language manager.
     * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
     *   The theme handler.
     * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $plugin_form_manager
     *   The plugin form manager.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, ExecutableManagerInterface $manager, ContextRepositoryInterface $context_repository, LanguageManagerInterface $language, ThemeHandlerInterface $theme_handler, PluginFormFactoryInterface $plugin_form_manager) {
        $this->storage = $entity_type_manager->getStorage('block');
        $this->manager = $manager;
        $this->contextRepository = $context_repository;
        $this->language = $language;
        $this->themeHandler = $theme_handler;
        $this->pluginFormFactory = $plugin_form_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('plugin.manager.condition'), $container->get('context.repository'), $container->get('language_manager'), $container->get('theme_handler'), $container->get('plugin_form.factory'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $entity = $this->entity;
        // Store the gathered contexts in the form state for other objects to use
        // during form building.
        $form_state->setTemporaryValue('gathered_contexts', $this->contextRepository
            ->getAvailableContexts());
        $form['#tree'] = TRUE;
        $form['settings'] = [];
        $subform_state = SubformState::createForSubform($form['settings'], $form, $form_state);
        $form['settings'] = $this->getPluginForm($entity->getPlugin())
            ->buildConfigurationForm($form['settings'], $subform_state);
        $form['visibility'] = $this->buildVisibilityInterface([], $form_state);
        // If creating a new block, calculate a safe default machine name.
        $form['id'] = [
            '#type' => 'machine_name',
            '#maxlength' => 64,
            '#description' => $this->t('A unique name for this block instance. Must be alpha-numeric and underscore separated.'),
            '#default_value' => !$entity->isNew() ? $entity->id() : $this->getUniqueMachineName($entity),
            '#machine_name' => [
                'exists' => '\\Drupal\\block\\Entity\\Block::load',
                'replace_pattern' => '[^a-z0-9_.]+',
                'source' => [
                    'settings',
                    'label',
                ],
            ],
            '#required' => TRUE,
            '#disabled' => !$entity->isNew(),
        ];
        // Theme settings.
        if ($theme = $entity->getTheme()) {
            $form['theme'] = [
                '#type' => 'value',
                '#value' => $theme,
            ];
        }
        else {
            $theme = $this->config('system.theme')
                ->get('default');
            $theme_options = [];
            foreach ($this->themeHandler
                ->listInfo() as $theme_name => $theme_info) {
                if (!empty($theme_info->status)) {
                    $theme_options[$theme_name] = $theme_info->info['name'];
                }
            }
            $form['theme'] = [
                '#type' => 'select',
                '#options' => $theme_options,
                '#title' => $this->t('Theme'),
                '#default_value' => $theme,
                '#ajax' => [
                    'callback' => '::themeSwitch',
                    'wrapper' => 'edit-block-region-wrapper',
                ],
            ];
        }
        // Hidden weight setting.
        $weight = $entity->isNew() ? $this->getRequest()->query
            ->get('weight', 0) : $entity->getWeight();
        $form['weight'] = [
            '#type' => 'hidden',
            '#default_value' => $weight,
        ];
        // Region settings.
        $entity_region = $entity->getRegion();
        $region = $entity->isNew() ? $this->getRequest()->query
            ->get('region', $entity_region) : $entity_region;
        $form['region'] = [
            '#type' => 'select',
            '#title' => $this->t('Region'),
            '#description' => $this->t('Select the region where this block should be displayed.'),
            '#default_value' => $region,
            '#required' => TRUE,
            '#options' => system_region_list($form_state->getValue('theme', $theme), REGIONS_VISIBLE),
            '#prefix' => '<div id="edit-block-region-wrapper">',
            '#suffix' => '</div>',
        ];
        $form['#attached']['library'][] = 'block/drupal.block.admin';
        return $form;
    }
    
    /**
     * Handles switching the available regions based on the selected theme.
     */
    public function themeSwitch($form, FormStateInterface $form_state) {
        return $form['region'];
    }
    
    /**
     * Helper function for building the visibility UI form.
     *
     * @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.
     *
     * @return array
     *   The form array with the visibility UI added in.
     */
    protected function buildVisibilityInterface(array $form, FormStateInterface $form_state) {
        $form['visibility_tabs'] = [
            '#type' => 'vertical_tabs',
            '#title' => $this->t('Visibility'),
            '#parents' => [
                'visibility_tabs',
            ],
            '#attached' => [
                'library' => [
                    'block/drupal.block',
                ],
            ],
        ];
        // @todo Allow list of conditions to be configured in
        //   https://www.drupal.org/node/2284687.
        $visibility = $this->entity
            ->getVisibility();
        $definitions = $this->manager
            ->getFilteredDefinitions('block_ui', $form_state->getTemporaryValue('gathered_contexts'), [
            'block' => $this->entity,
        ]);
        foreach ($definitions as $condition_id => $definition) {
            // Don't display the current theme condition.
            if ($condition_id == 'current_theme') {
                continue;
            }
            // Don't display the language condition until we have multiple languages.
            if ($condition_id == 'language' && !$this->language
                ->isMultilingual()) {
                continue;
            }
            // Don't display the deprecated node type condition unless it has existing
            // settings.
            // @todo Make this more generic in
            //   https://www.drupal.org/project/drupal/issues/2922451. Also remove
            //   the node_type specific logic below.
            if ($condition_id == 'node_type' && !isset($visibility[$condition_id])) {
                continue;
            }
            
            /** @var \Drupal\Core\Condition\ConditionInterface $condition */
            $condition = $this->manager
                ->createInstance($condition_id, $visibility[$condition_id] ?? []);
            $form_state->set([
                'conditions',
                $condition_id,
            ], $condition);
            $condition_form = $condition->buildConfigurationForm([], $form_state);
            $condition_form['#type'] = 'details';
            $condition_form['#title'] = $condition->getPluginDefinition()['label'];
            $condition_form['#group'] = 'visibility_tabs';
            $form[$condition_id] = $condition_form;
        }
        if (isset($form['node_type'])) {
            $form['node_type']['#title'] = $this->t('Content types (deprecated)');
            $form['node_type']['bundles']['#title'] = $this->t('Content types');
            $form['node_type']['negate']['#type'] = 'value';
            $form['node_type']['negate']['#title_display'] = 'invisible';
            $form['node_type']['negate']['#value'] = $form['node_type']['negate']['#default_value'];
        }
        if (isset($form['entity_bundle:node'])) {
            $form['entity_bundle:node']['negate']['#type'] = 'value';
            $form['entity_bundle:node']['negate']['#title_display'] = 'invisible';
            $form['entity_bundle:node']['negate']['#value'] = $form['entity_bundle:node']['negate']['#default_value'];
        }
        if (isset($form['user_role'])) {
            $form['user_role']['#title'] = $this->t('Roles');
            unset($form['user_role']['roles']['#description']);
            $form['user_role']['negate']['#type'] = 'value';
            $form['user_role']['negate']['#value'] = $form['user_role']['negate']['#default_value'];
        }
        if (isset($form['request_path'])) {
            $form['request_path']['#title'] = $this->t('Pages');
            $form['request_path']['negate']['#type'] = 'radios';
            $form['request_path']['negate']['#default_value'] = (int) $form['request_path']['negate']['#default_value'];
            $form['request_path']['negate']['#title_display'] = 'invisible';
            $form['request_path']['negate']['#options'] = [
                $this->t('Show for the listed pages'),
                $this->t('Hide for the listed pages'),
            ];
        }
        if (isset($form['language'])) {
            $form['language']['negate']['#type'] = 'value';
            $form['language']['negate']['#value'] = $form['language']['negate']['#default_value'];
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function actions(array $form, FormStateInterface $form_state) {
        $actions = parent::actions($form, $form_state);
        $actions['submit']['#value'] = $this->t('Save block');
        $actions['delete']['#title'] = $this->t('Remove block');
        return $actions;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        parent::validateForm($form, $form_state);
        $form_state->setValue('weight', (int) $form_state->getValue('weight'));
        // The Block Entity form puts all block plugin form elements in the
        // settings form element, so just pass that to the block for validation.
        $this->getPluginForm($this->entity
            ->getPlugin())
            ->validateConfigurationForm($form['settings'], SubformState::createForSubform($form['settings'], $form, $form_state));
        $this->validateVisibility($form, $form_state);
    }
    
    /**
     * Helper function to independently validate the visibility UI.
     *
     * @param array $form
     *   A nested array form elements comprising the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function validateVisibility(array $form, FormStateInterface $form_state) {
        // Validate visibility condition settings.
        foreach ($form_state->getValue('visibility') as $condition_id => $values) {
            // All condition plugins use 'negate' as a Boolean in their schema.
            // However, certain form elements may return it as 0/1. Cast here to
            // ensure the data is in the expected type.
            if (array_key_exists('negate', $values)) {
                $form_state->setValue([
                    'visibility',
                    $condition_id,
                    'negate',
                ], (bool) $values['negate']);
            }
            // Allow the condition to validate the form.
            $condition = $form_state->get([
                'conditions',
                $condition_id,
            ]);
            $condition->validateConfigurationForm($form['visibility'][$condition_id], SubformState::createForSubform($form['visibility'][$condition_id], $form, $form_state));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        parent::submitForm($form, $form_state);
        $entity = $this->entity;
        // The Block Entity form puts all block plugin form elements in the
        // settings form element, so just pass that to the block for submission.
        $sub_form_state = SubformState::createForSubform($form['settings'], $form, $form_state);
        // Call the plugin submit handler.
        $block = $entity->getPlugin();
        $this->getPluginForm($block)
            ->submitConfigurationForm($form, $sub_form_state);
        // If this block is context-aware, set the context mapping.
        if ($block instanceof ContextAwarePluginInterface && $block->getContextDefinitions()) {
            $context_mapping = $sub_form_state->getValue('context_mapping', []);
            $block->setContextMapping($context_mapping);
        }
        $this->submitVisibility($form, $form_state);
        // Save the settings of the plugin.
        $entity->save();
        $this->messenger()
            ->addStatus($this->t('The block configuration has been saved.'));
        $form_state->setRedirect('block.admin_display_theme', [
            'theme' => $form_state->getValue('theme'),
        ], [
            'query' => [
                'block-placement' => Html::getClass($this->entity
                    ->id()),
            ],
        ]);
    }
    
    /**
     * Helper function to independently submit the visibility UI.
     *
     * @param array $form
     *   A nested array form elements comprising the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function submitVisibility(array $form, FormStateInterface $form_state) {
        foreach ($form_state->getValue('visibility') as $condition_id => $values) {
            // Allow the condition to submit the form.
            $condition = $form_state->get([
                'conditions',
                $condition_id,
            ]);
            $condition->submitConfigurationForm($form['visibility'][$condition_id], SubformState::createForSubform($form['visibility'][$condition_id], $form, $form_state));
            $condition_configuration = $condition->getConfiguration();
            // Update the visibility conditions on the block.
            $this->entity
                ->getVisibilityConditions()
                ->addInstanceId($condition_id, $condition_configuration);
        }
    }
    
    /**
     * Generates a unique machine name for a block.
     *
     * @param \Drupal\block\BlockInterface $block
     *   The block entity.
     *
     * @return string
     *   Returns the unique name.
     */
    public function getUniqueMachineName(BlockInterface $block) {
        $suggestion = $block->getPlugin()
            ->getMachineNameSuggestion();
        // Get all the blocks which starts with the suggested machine name.
        $query = $this->storage
            ->getQuery();
        $query->condition('id', $suggestion, 'CONTAINS');
        $block_ids = $query->execute();
        $block_ids = array_map(function ($block_id) {
            $parts = explode('.', $block_id);
            return end($parts);
        }, $block_ids);
        // Iterate through potential IDs until we get a new one. E.g.
        // 'plugin', 'plugin_2', 'plugin_3', etc.
        $count = 1;
        $machine_default = $suggestion;
        while (in_array($machine_default, $block_ids)) {
            $machine_default = $suggestion . '_' . ++$count;
        }
        return $machine_default;
    }
    
    /**
     * Retrieves the plugin form for a given block and operation.
     *
     * @param \Drupal\Core\Block\BlockPluginInterface $block
     *   The block plugin.
     *
     * @return \Drupal\Core\Plugin\PluginFormInterface
     *   The plugin form for the block.
     */
    protected function getPluginForm(BlockPluginInterface $block) {
        if ($block instanceof PluginWithFormsInterface) {
            return $this->pluginFormFactory
                ->createInstance($block, 'configure');
        }
        return $block;
    }

}