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) {
        $random = new Random();
        $max_length = $field_definition->getSetting('max_length');
        $min_length = min(10, $max_length);
        // The random value is generated multiple times to create a slight
        // preference towards values that are closer to the minimum length of the
        // string.
        $length = mt_rand($min_length, mt_rand($min_length, mt_rand($min_length, $max_length)));
        $values['value'] = $random->word($length);
        $suffix_length = $max_length - 7;
        foreach ($values as $key => $value) {
            $values[$key] = 'http://' . mb_substr($value, 0, $suffix_length);
        }
        return $values;
    }

}