class TextItemBase

abstract class TextItemBase extends FieldItemBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultFieldSettings() {
        return [
            'allowed_formats' => [],
        ] + parent::defaultFieldSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
        $element = parent::fieldSettingsForm($form, $form_state);
        $settings = $this->getSettings();
        $element['allowed_formats'] = [
            '#type' => 'checkboxes',
            '#title' => $this->t('Allowed text formats'),
            '#options' => $this->get('format')
                ->getPossibleOptions(),
            '#default_value' => !empty($settings['allowed_formats']) ? $settings['allowed_formats'] : [],
            '#description' => $this->t('Select the allowed text formats. If no formats are selected, all available text formats will be displayed to the user.'),
            '#element_validate' => [
                [
                    static::class,
                    'validateAllowedFormats',
                ],
            ],
        ];
        return $element;
    }
    
    /**
     * Render API callback: Processes the allowed formats value.
     *
     * Ensure the element's value is an indexed array of selected format IDs.
     * This function is assigned as an #element_validate callback.
     *
     * @see static::fieldSettingsForm()
     */
    public static function validateAllowedFormats(array &$element, FormStateInterface $form_state) {
        $value = array_values(array_filter($form_state->getValue($element['#parents'])));
        $form_state->setValueForElement($element, $value);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function calculateDependencies(FieldDefinitionInterface $field_definition) {
        // Add explicitly allowed formats as config dependencies.
        $format_dependencies = [];
        $dependencies = parent::calculateDependencies($field_definition);
        if (!is_null($field_definition->getSetting('allowed_formats'))) {
            $format_dependencies = array_map(function (string $format_id) {
                return 'filter.format.' . $format_id;
            }, $field_definition->getSetting('allowed_formats'));
        }
        $config = $dependencies['config'] ?? [];
        $dependencies['config'] = array_merge($config, $format_dependencies);
        return $dependencies;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
        $properties['value'] = DataDefinition::create('string')->setLabel(t('Text'))
            ->setRequired(TRUE);
        $properties['format'] = DataDefinition::create('filter_format')->setLabel(t('Text format'))
            ->setSetting('allowed_formats', $field_definition->getSetting('allowed_formats'));
        $properties['processed'] = DataDefinition::create('string')->setLabel(t('Processed text'))
            ->setDescription(t('The text with the text format applied.'))
            ->setComputed(TRUE)
            ->setClass('\\Drupal\\text\\TextProcessed')
            ->setSetting('text source', 'value')
            ->setInternal(FALSE);
        return $properties;
    }
    
    /**
     * {@inheritdoc}
     */
    public function applyDefaultValue($notify = TRUE) {
        // @todo Add in the filter default format here.
        $this->setValue([
            'format' => NULL,
        ], $notify);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isEmpty() {
        $value = $this->get('value')
            ->getValue();
        return $value === NULL || $value === '';
    }
    
    /**
     * {@inheritdoc}
     */
    public function onChange($property_name, $notify = TRUE) {
        // Unset processed properties that are affected by the change.
        foreach ($this->definition
            ->getPropertyDefinitions() as $property => $definition) {
            if ($definition->getClass() == '\\Drupal\\text\\TextProcessed') {
                if ($property_name == 'format' || $definition->getSetting('text source') == $property_name) {
                    $this->writePropertyValue($property, NULL);
                }
            }
        }
        parent::onChange($property_name, $notify);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
        $random = new Random();
        $settings = $field_definition->getSettings();
        if (empty($settings['max_length'])) {
            // Textarea handling
            $value = $random->paragraphs();
        }
        else {
            // Textfield handling.
            $max = ceil($settings['max_length'] / 3);
            $value = substr($random->sentences(mt_rand(1, $max), FALSE), 0, $settings['max_length']);
        }
        $values = [
            'value' => $value,
            'summary' => $value,
            'format' => filter_fallback_format(),
        ];
        return $values;
    }

}