class FieldStorageAddForm

class FieldStorageAddForm extends FormBase {
    
    /**
     * The name of the entity type.
     *
     * @var string
     */
    protected $entityTypeId;
    
    /**
     * The entity bundle.
     *
     * @var string
     */
    protected $bundle;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The entity field manager.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected $entityFieldManager;
    
    /**
     * The entity display repository.
     *
     * @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface
     */
    protected $entityDisplayRepository;
    
    /**
     * The field type plugin manager.
     *
     * @var \Drupal\Core\Field\FieldTypePluginManagerInterface
     */
    protected $fieldTypePluginManager;
    
    /**
     * The configuration factory.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * Constructs a new FieldStorageAddForm object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Field\FieldTypePluginManagerInterface $field_type_plugin_manager
     *   The field type plugin manager.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The configuration factory.
     * @param \Drupal\Core\Entity\EntityFieldManagerInterface|null $entity_field_manager
     *   (optional) The entity field manager.
     * @param \Drupal\Core\Entity\EntityDisplayRepositoryInterface $entity_display_repository
     *   (optional) The entity display repository.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, FieldTypePluginManagerInterface $field_type_plugin_manager, ConfigFactoryInterface $config_factory, EntityFieldManagerInterface $entity_field_manager = NULL, EntityDisplayRepositoryInterface $entity_display_repository = NULL) {
        $this->entityTypeManager = $entity_type_manager;
        $this->fieldTypePluginManager = $field_type_plugin_manager;
        $this->configFactory = $config_factory;
        $this->entityFieldManager = $entity_field_manager;
        $this->entityDisplayRepository = $entity_display_repository;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'field_ui_field_storage_add_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('plugin.manager.field.field_type'), $container->get('config.factory'), $container->get('entity_field.manager'), $container->get('entity_display.repository'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, $entity_type_id = NULL, $bundle = NULL) {
        if (!$form_state->get('entity_type_id')) {
            $form_state->set('entity_type_id', $entity_type_id);
        }
        if (!$form_state->get('bundle')) {
            $form_state->set('bundle', $bundle);
        }
        $this->entityTypeId = $form_state->get('entity_type_id');
        $this->bundle = $form_state->get('bundle');
        // Gather valid field types.
        $field_type_options = [];
        foreach ($this->fieldTypePluginManager
            ->getGroupedDefinitions($this->fieldTypePluginManager
            ->getUiDefinitions()) as $category => $field_types) {
            foreach ($field_types as $name => $field_type) {
                $field_type_options[$category][$name] = $field_type['label'];
            }
        }
        $form['add'] = [
            '#type' => 'container',
            '#attributes' => [
                'class' => [
                    'form--inline',
                    'clearfix',
                ],
            ],
        ];
        $form['add']['new_storage_type'] = [
            '#type' => 'select',
            '#title' => $this->t('Add a new field'),
            '#options' => $field_type_options,
            '#empty_option' => $this->t('- Select a field type -'),
        ];
        // Re-use existing field.
        if ($existing_field_storage_options = $this->getExistingFieldStorageOptions()) {
            $form['add']['separator'] = [
                '#type' => 'item',
                '#markup' => $this->t('or'),
            ];
            $form['add']['existing_storage_name'] = [
                '#type' => 'select',
                '#title' => $this->t('Re-use an existing field'),
                '#options' => $existing_field_storage_options,
                '#empty_option' => $this->t('- Select an existing field -'),
            ];
            $form['#attached']['drupalSettings']['existingFieldLabels'] = $this->getExistingFieldLabels(array_keys($existing_field_storage_options));
        }
        else {
            // Provide a placeholder form element to simplify the validation code.
            $form['add']['existing_storage_name'] = [
                '#type' => 'value',
                '#value' => FALSE,
            ];
        }
        // Field label and field_name.
        $form['new_storage_wrapper'] = [
            '#type' => 'container',
            '#states' => [
                '!visible' => [
                    ':input[name="new_storage_type"]' => [
                        'value' => '',
                    ],
                ],
            ],
        ];
        $form['new_storage_wrapper']['label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Label'),
            '#size' => 15,
        ];
        $field_prefix = $this->config('field_ui.settings')
            ->get('field_prefix');
        $form['new_storage_wrapper']['field_name'] = [
            '#type' => 'machine_name',
            '#field_prefix' => $field_prefix,
            '#size' => 15,
            '#description' => $this->t('A unique machine-readable name containing letters, numbers, and underscores.'),
            // Calculate characters depending on the length of the field prefix
            // setting. Maximum length is 32.
'#maxlength' => FieldStorageConfig::NAME_MAX_LENGTH - strlen($field_prefix),
            '#machine_name' => [
                'source' => [
                    'new_storage_wrapper',
                    'label',
                ],
                'exists' => [
                    $this,
                    'fieldNameExists',
                ],
            ],
            '#required' => FALSE,
        ];
        // Provide a separate label element for the "Re-use existing field" case
        // and place it outside the $form['add'] wrapper because those elements
        // are displayed inline.
        if ($existing_field_storage_options) {
            $form['existing_storage_label'] = [
                '#type' => 'textfield',
                '#title' => $this->t('Label'),
                '#size' => 15,
                '#states' => [
                    '!visible' => [
                        ':input[name="existing_storage_name"]' => [
                            'value' => '',
                        ],
                    ],
                ],
            ];
        }
        // Place the 'translatable' property as an explicit value so that contrib
        // modules can form_alter() the value for newly created fields. By default
        // we create field storage as translatable so it will be possible to enable
        // translation at field level.
        $form['translatable'] = [
            '#type' => 'value',
            '#value' => TRUE,
        ];
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save and continue'),
            '#button_type' => 'primary',
        ];
        $form['#attached']['library'][] = 'field_ui/drupal.field_ui';
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        // Missing field type.
        if (!$form_state->getValue('new_storage_type') && !$form_state->getValue('existing_storage_name')) {
            $form_state->setErrorByName('new_storage_type', $this->t('You need to select a field type or an existing field.'));
        }
        elseif ($form_state->getValue('new_storage_type') && $form_state->getValue('existing_storage_name')) {
            $form_state->setErrorByName('new_storage_type', $this->t('Adding a new field and re-using an existing field at the same time is not allowed.'));
            return;
        }
        $this->validateAddNew($form, $form_state);
        $this->validateAddExisting($form, $form_state);
    }
    
    /**
     * Validates the 'add new field' case.
     *
     * @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.
     *
     * @see \Drupal\field_ui\Form\FieldStorageAddForm::validateForm()
     */
    protected function validateAddNew(array $form, FormStateInterface $form_state) {
        // Validate if any information was provided in the 'add new field' case.
        if ($form_state->getValue('new_storage_type')) {
            // Missing label.
            if (!$form_state->getValue('label')) {
                $form_state->setErrorByName('label', $this->t('Add new field: you need to provide a label.'));
            }
            // Missing field name.
            if (!$form_state->getValue('field_name')) {
                $form_state->setErrorByName('field_name', $this->t('Add new field: you need to provide a machine name for the field.'));
            }
            else {
                $field_name = $form_state->getValue('field_name');
                // Add the field prefix.
                $field_name = $this->configFactory
                    ->get('field_ui.settings')
                    ->get('field_prefix') . $field_name;
                $form_state->setValueForElement($form['new_storage_wrapper']['field_name'], $field_name);
            }
        }
    }
    
    /**
     * Validates the 're-use existing field' case.
     *
     * @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.
     *
     * @see \Drupal\field_ui\Form\FieldStorageAddForm::validateForm()
     */
    protected function validateAddExisting(array $form, FormStateInterface $form_state) {
        if ($form_state->getValue('existing_storage_name')) {
            // Missing label.
            if (!$form_state->getValue('existing_storage_label')) {
                $form_state->setErrorByName('existing_storage_label', $this->t('Re-use existing field: you need to provide a label.'));
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $error = FALSE;
        $values = $form_state->getValues();
        $destinations = [];
        $entity_type = $this->entityTypeManager
            ->getDefinition($this->entityTypeId);
        // Create new field.
        if ($values['new_storage_type']) {
            $field_storage_values = [
                'field_name' => $values['field_name'],
                'entity_type' => $this->entityTypeId,
                'type' => $values['new_storage_type'],
                'translatable' => $values['translatable'],
            ];
            $field_values = [
                'field_name' => $values['field_name'],
                'entity_type' => $this->entityTypeId,
                'bundle' => $this->bundle,
                'label' => $values['label'],
                // Field translatability should be explicitly enabled by the users.
'translatable' => FALSE,
            ];
            $widget_id = $formatter_id = NULL;
            $widget_settings = $formatter_settings = [];
            // Check if we're dealing with a preconfigured field.
            if (strpos($field_storage_values['type'], 'field_ui:') !== FALSE) {
                [
                    ,
                    $field_type,
                    $option_key,
                ] = explode(':', $field_storage_values['type'], 3);
                $field_storage_values['type'] = $field_type;
                $field_definition = $this->fieldTypePluginManager
                    ->getDefinition($field_type);
                $options = $this->fieldTypePluginManager
                    ->getPreconfiguredOptions($field_definition['id']);
                $field_options = $options[$option_key];
                // Merge in preconfigured field storage options.
                if (isset($field_options['field_storage_config'])) {
                    foreach ([
                        'cardinality',
                        'settings',
                    ] as $key) {
                        if (isset($field_options['field_storage_config'][$key])) {
                            $field_storage_values[$key] = $field_options['field_storage_config'][$key];
                        }
                    }
                }
                // Merge in preconfigured field options.
                if (isset($field_options['field_config'])) {
                    foreach ([
                        'required',
                        'settings',
                    ] as $key) {
                        if (isset($field_options['field_config'][$key])) {
                            $field_values[$key] = $field_options['field_config'][$key];
                        }
                    }
                }
                $widget_id = $field_options['entity_form_display']['type'] ?? NULL;
                $widget_settings = $field_options['entity_form_display']['settings'] ?? [];
                $formatter_id = $field_options['entity_view_display']['type'] ?? NULL;
                $formatter_settings = $field_options['entity_view_display']['settings'] ?? [];
            }
            // Create the field storage and field.
            try {
                $this->entityTypeManager
                    ->getStorage('field_storage_config')
                    ->create($field_storage_values)
                    ->save();
                $field = $this->entityTypeManager
                    ->getStorage('field_config')
                    ->create($field_values);
                $field->save();
                $this->configureEntityFormDisplay($values['field_name'], $widget_id, $widget_settings);
                $this->configureEntityViewDisplay($values['field_name'], $formatter_id, $formatter_settings);
                // Always show the field settings step, as the cardinality needs to be
                // configured for new fields.
                $route_parameters = [
                    'field_config' => $field->id(),
                ] + FieldUI::getRouteBundleParameter($entity_type, $this->bundle);
                $destinations[] = [
                    'route_name' => "entity.field_config.{$this->entityTypeId}_storage_edit_form",
                    'route_parameters' => $route_parameters,
                ];
                $destinations[] = [
                    'route_name' => "entity.field_config.{$this->entityTypeId}_field_edit_form",
                    'route_parameters' => $route_parameters,
                ];
                $destinations[] = [
                    'route_name' => "entity.{$this->entityTypeId}.field_ui_fields",
                    'route_parameters' => $route_parameters,
                ];
                // Store new field information for any additional submit handlers.
                $form_state->set([
                    'fields_added',
                    '_add_new_field',
                ], $values['field_name']);
            } catch (\Exception $e) {
                $error = TRUE;
                $this->messenger()
                    ->addError($this->t('There was a problem creating field %label: @message', [
                    '%label' => $values['label'],
                    '@message' => $e->getMessage(),
                ]));
            }
        }
        // Re-use existing field.
        if ($values['existing_storage_name']) {
            $field_name = $values['existing_storage_name'];
            try {
                $field = $this->entityTypeManager
                    ->getStorage('field_config')
                    ->create([
                    'field_name' => $field_name,
                    'entity_type' => $this->entityTypeId,
                    'bundle' => $this->bundle,
                    'label' => $values['existing_storage_label'],
                ]);
                $field->save();
                $this->configureEntityFormDisplay($field_name);
                $this->configureEntityViewDisplay($field_name);
                $route_parameters = [
                    'field_config' => $field->id(),
                ] + FieldUI::getRouteBundleParameter($entity_type, $this->bundle);
                $destinations[] = [
                    'route_name' => "entity.field_config.{$this->entityTypeId}_field_edit_form",
                    'route_parameters' => $route_parameters,
                ];
                $destinations[] = [
                    'route_name' => "entity.{$this->entityTypeId}.field_ui_fields",
                    'route_parameters' => $route_parameters,
                ];
                // Store new field information for any additional submit handlers.
                $form_state->set([
                    'fields_added',
                    '_add_existing_field',
                ], $field_name);
            } catch (\Exception $e) {
                $error = TRUE;
                $this->messenger()
                    ->addError($this->t('There was a problem creating field %label: @message', [
                    '%label' => $values['label'],
                    '@message' => $e->getMessage(),
                ]));
            }
        }
        if ($destinations) {
            $destination = $this->getDestinationArray();
            $destinations[] = $destination['destination'];
            $form_state->setRedirectUrl(FieldUI::getNextDestination($destinations, $form_state));
        }
        elseif (!$error) {
            $this->messenger()
                ->addStatus($this->t('Your settings have been saved.'));
        }
    }
    
    /**
     * Configures the field for the default form mode.
     *
     * @param string $field_name
     *   The field name.
     * @param string|null $widget_id
     *   (optional) The plugin ID of the widget. Defaults to NULL.
     * @param array $widget_settings
     *   (optional) An array of widget settings. Defaults to an empty array.
     */
    protected function configureEntityFormDisplay($field_name, $widget_id = NULL, array $widget_settings = []) {
        $options = [];
        if ($widget_id) {
            $options['type'] = $widget_id;
            if (!empty($widget_settings)) {
                $options['settings'] = $widget_settings;
            }
        }
        // Make sure the field is displayed in the 'default' form mode (using
        // default widget and settings). It stays hidden for other form modes
        // until it is explicitly configured.
        $this->entityDisplayRepository
            ->getFormDisplay($this->entityTypeId, $this->bundle, 'default')
            ->setComponent($field_name, $options)
            ->save();
    }
    
    /**
     * Configures the field for the default view mode.
     *
     * @param string $field_name
     *   The field name.
     * @param string|null $formatter_id
     *   (optional) The plugin ID of the formatter. Defaults to NULL.
     * @param array $formatter_settings
     *   (optional) An array of formatter settings. Defaults to an empty array.
     */
    protected function configureEntityViewDisplay($field_name, $formatter_id = NULL, array $formatter_settings = []) {
        $options = [];
        if ($formatter_id) {
            $options['type'] = $formatter_id;
            if (!empty($formatter_settings)) {
                $options['settings'] = $formatter_settings;
            }
        }
        // Make sure the field is displayed in the 'default' view mode (using
        // default formatter and settings). It stays hidden for other view
        // modes until it is explicitly configured.
        $this->entityDisplayRepository
            ->getViewDisplay($this->entityTypeId, $this->bundle)
            ->setComponent($field_name, $options)
            ->save();
    }
    
    /**
     * Returns an array of existing field storages that can be added to a bundle.
     *
     * @return array
     *   An array of existing field storages keyed by name.
     */
    protected function getExistingFieldStorageOptions() {
        $options = [];
        // Load the field_storages and build the list of options.
        $field_types = $this->fieldTypePluginManager
            ->getDefinitions();
        foreach ($this->entityFieldManager
            ->getFieldStorageDefinitions($this->entityTypeId) as $field_name => $field_storage) {
            // Do not show:
            // - non-configurable field storages,
            // - locked field storages,
            // - field storages that should not be added via user interface,
            // - field storages that already have a field in the bundle.
            $field_type = $field_storage->getType();
            if ($field_storage instanceof FieldStorageConfigInterface && !$field_storage->isLocked() && empty($field_types[$field_type]['no_ui']) && !in_array($this->bundle, $field_storage->getBundles(), TRUE)) {
                $options[$field_name] = $this->t('@type: @field', [
                    '@type' => $field_types[$field_type]['label'],
                    '@field' => $field_name,
                ]);
            }
        }
        asort($options);
        return $options;
    }
    
    /**
     * Gets the human-readable labels for the given field storage names.
     *
     * Since not all field storages are required to have a field, we can only
     * provide the field labels on a best-effort basis (e.g. the label of a field
     * storage without any field attached to a bundle will be the field name).
     *
     * @param array $field_names
     *   An array of field names.
     *
     * @return array
     *   An array of field labels keyed by field name.
     */
    protected function getExistingFieldLabels(array $field_names) {
        // Get all the fields corresponding to the given field storage names and
        // this entity type.
        $field_ids = $this->entityTypeManager
            ->getStorage('field_config')
            ->getQuery()
            ->condition('entity_type', $this->entityTypeId)
            ->condition('field_name', $field_names)
            ->execute();
        $fields = $this->entityTypeManager
            ->getStorage('field_config')
            ->loadMultiple($field_ids);
        // Go through all the fields and use the label of the first encounter.
        $labels = [];
        foreach ($fields as $field) {
            if (!isset($labels[$field->getName()])) {
                $labels[$field->getName()] = $field->label();
            }
        }
        // For field storages without any fields attached to a bundle, the default
        // label is the field name.
        $labels += array_combine($field_names, $field_names);
        return $labels;
    }
    
    /**
     * Checks if a field machine name is taken.
     *
     * @param string $value
     *   The machine name, not prefixed.
     * @param array $element
     *   An array containing the structure of the 'field_name' element.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @return bool
     *   Whether or not the field machine name is taken.
     */
    public function fieldNameExists($value, $element, FormStateInterface $form_state) {
        // Don't validate the case when an existing field has been selected.
        if ($form_state->getValue('existing_storage_name')) {
            return FALSE;
        }
        // Add the field prefix.
        $field_name = $this->configFactory
            ->get('field_ui.settings')
            ->get('field_prefix') . $value;
        $field_storage_definitions = $this->entityFieldManager
            ->getFieldStorageDefinitions($this->entityTypeId);
        return isset($field_storage_definitions[$field_name]);
    }

}