class UserNameItem

class UserNameItem extends StringItem {
    
    /**
     * {@inheritdoc}
     */
    public function isEmpty() {
        $value = $this->get('value')
            ->getValue();
        // Take into account that the name of the anonymous user is an empty string.
        if ($this->getEntity()
            ->isAnonymous()) {
            return $value === NULL;
        }
        return $value === NULL || $value === '';
    }
    
    /**
     * {@inheritdoc}
     */
    public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
        $random = new Random();
        $max_length = min(UserInterface::USERNAME_MAX_LENGTH, $field_definition->getSetting('max_length'));
        // Generate a list of words, which can be used to generate a string.
        $words = explode(' ', $random->sentences(8));
        // Begin with a username that is either 2 or 3 words.
        $count = mt_rand(2, 3);
        // Capitalize the words used in usernames 50% of the time.
        $words = mt_rand(0, 1) ? array_map('ucfirst', $words) : $words;
        // Username is a single long word 50% of the time. In the case of a single
        // long word, sometimes the generated username may also contain periods in
        // the middle of the username.
        $separator = ' ';
        if (mt_rand(0, 1)) {
            $separator = '';
            $count = mt_rand(2, 8);
            // The username will start with a capital letter 50% of the time.
            $words = mt_rand(0, 1) ? array_map('strtolower', $words) : $words;
        }
        $string = implode($separator, array_splice($words, 0, $count));
        // Normalize the string to not be longer than the maximum length, and to not
        // end with a space or a period.
        $values['value'] = rtrim(mb_substr($string, 0, $max_length), ' .');
        return $values;
    }

}