class UriItem

class UriItem extends StringItem {
  
  /**
   * {@inheritdoc}
   */
  public static function defaultStorageSettings() {
    $storage_settings = parent::defaultStorageSettings();
    // is_ascii doesn't make sense for URIs.
    unset($storage_settings['is_ascii']);
    $storage_settings['max_length'] = 2048;
    return $storage_settings;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['value'] = DataDefinition::create('uri')->setLabel(t('URI value'))
      ->setSetting('case_sensitive', $field_definition->getSetting('case_sensitive'))
      ->setRequired(TRUE);
    return $properties;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function schema(FieldStorageDefinitionInterface $field_definition) {
    return [
      'columns' => [
        'value' => [
          'type' => 'varchar',
          'length' => (int) $field_definition->getSetting('max_length'),
          'binary' => $field_definition->getSetting('case_sensitive'),
        ],
      ],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    $value = $this->getValue();
    if (!isset($value['value']) || $value['value'] === '') {
      return TRUE;
    }
    return parent::isEmpty();
  }
  
  /**
   * {@inheritdoc}
   */
  public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
    $values = parent::generateSampleValue($field_definition);
    $suffix_length = $field_definition->getSetting('max_length') - 7;
    foreach ($values as $key => $value) {
      $values[$key] = 'http://' . mb_substr($value, 0, $suffix_length);
    }
    return $values;
  }

}