class EmailItem

class EmailItem extends FieldItemBase {
  
  /**
   * {@inheritdoc}
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['value'] = DataDefinition::create('email')->setLabel(new TranslatableMarkup('Email'))
      ->setRequired(TRUE);
    return $properties;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function schema(FieldStorageDefinitionInterface $field_definition) {
    return [
      'columns' => [
        'value' => [
          'type' => 'varchar',
          'length' => Email::EMAIL_MAX_LENGTH,
        ],
      ],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function getConstraints() {
    $constraint_manager = \Drupal::typedDataManager()->getValidationConstraintManager();
    $constraints = parent::getConstraints();
    $constraints[] = $constraint_manager->create('ComplexData', [
      'value' => [
        'Length' => [
          'max' => Email::EMAIL_MAX_LENGTH,
          'maxMessage' => $this->t('%name: the email address can not be longer than @max characters.', [
            '%name' => $this->getFieldDefinition()
              ->getLabel(),
            '@max' => Email::EMAIL_MAX_LENGTH,
          ]),
        ],
      ],
    ]);
    return $constraints;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
    $random = new Random();
    $values['value'] = $random->name() . '@example.com';
    return $values;
  }
  
  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    return $this->value === NULL || $this->value === '';
  }

}