class FieldRdfaTestBase

abstract class FieldRdfaTestBase extends FieldKernelTestBase {
    use RdfParsingTrait;
    
    /**
     * The machine name of the field type to test.
     *
     * @var string
     */
    protected $fieldType;
    
    /**
     * The name of the field to create for testing.
     *
     * @var string
     */
    protected $fieldName = 'field_test';
    
    /**
     * The URI to identify the entity.
     *
     * @var string
     */
    protected $uri = 'http://ex.com';
    
    /**
     * The entity to render for testing.
     *
     * @var \Drupal\Core\Entity\ContentEntityBase
     */
    protected $entity;
    
    /**
     * TRUE if verbose debugging is enabled.
     *
     * @var bool
     */
    protected $debug = FALSE;
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    protected static $modules = [
        'rdf',
    ];
    
    /**
     * @var string
     */
    protected $testValue;
    
    /**
     * Helper function to test the formatter's RDFa.
     *
     * @param array $formatter
     *   An associative array describing the formatter to test and its settings
     *   containing:
     *   - type: The machine name of the field formatter to test.
     *   - settings: The settings of the field formatter to test.
     * @param string $property
     *   The property that should be found.
     * @param array $expected_rdf_value
     *   An associative array describing the expected value of the property
     *   containing:
     *   - value: The actual value of the string or URI.
     *   - type: The type of RDF value, e.g. 'literal' for a string, or 'uri'.
     *   Defaults to 'literal'.
     *   - datatype: (optional) The datatype of the value (e.g. xsd:dateTime).
     */
    protected function assertFormatterRdfa($formatter, $property, $expected_rdf_value) {
        $expected_rdf_value += [
            'type' => 'literal',
        ];
        // The field formatter will be rendered inside the entity. Set the field
        // formatter in the entity display options before rendering the entity.
        \Drupal::service('entity_display.repository')->getViewDisplay('entity_test', 'entity_test')
            ->setComponent($this->fieldName, $formatter)
            ->save();
        $build = \Drupal::entityTypeManager()->getViewBuilder($this->entity
            ->getEntityTypeId())
            ->view($this->entity, 'default');
        $output = \Drupal::service('renderer')->renderRoot($build);
        $this->setRawContent($output);
        $this->assertTrue($this->hasRdfProperty($output, $this->uri, $this->uri, $property, $expected_rdf_value), "Formatter {$formatter['type']} exposes data correctly for {$this->fieldType} fields.");
    }
    
    /**
     * Creates the field for testing.
     *
     * @param array $field_settings
     *   (optional) An array of field settings.
     */
    protected function createTestField($field_settings = []) {
        FieldStorageConfig::create([
            'field_name' => $this->fieldName,
            'entity_type' => 'entity_test',
            'type' => $this->fieldType,
        ])
            ->save();
        FieldConfig::create([
            'entity_type' => 'entity_test',
            'field_name' => $this->fieldName,
            'bundle' => 'entity_test',
            'settings' => $field_settings,
        ])
            ->save();
    }
    
    /**
     * Gets the absolute URI of an entity.
     *
     * @param \Drupal\Core\Entity\ContentEntityBase $entity
     *   The entity for which to generate the URI.
     *
     * @return string
     *   The absolute URI.
     */
    protected function getAbsoluteUri($entity) {
        return $entity->toUrl('canonical', [
            'absolute' => TRUE,
        ])
            ->toString();
    }
    
    /**
     * Parses a content and return the html element.
     *
     * @param string $content
     *   The html to parse.
     *
     * @return array
     *   An array containing simplexml objects.
     */
    protected function parseContent($content) {
        $htmlDom = new \DOMDocument();
        @$htmlDom->loadHTML('<?xml encoding="UTF-8">' . $content);
        $elements = simplexml_import_dom($htmlDom);
        return $elements;
    }
    
    /**
     * Performs an xpath search on a certain content.
     *
     * The search is relative to the root element of the $content variable.
     *
     * @param string $content
     *   The html to parse.
     * @param string $xpath
     *   The xpath string to use in the search.
     * @param array $arguments
     *   Some arguments for the xpath.
     *
     * @return array|false
     *   The return value of the xpath search. For details on the xpath string
     *   format and return values see the SimpleXML documentation,
     *   http://php.net/manual/function.simplexml-element-xpath.php.
     */
    protected function xpathContent($content, $xpath, array $arguments = []) {
        if ($elements = $this->parseContent($content)) {
            $xpath = $this->buildXPathQuery($xpath, $arguments);
            $result = $elements->xpath($xpath);
            // Some combinations of PHP / libxml versions return an empty array
            // instead of the documented FALSE. Forcefully convert any falsish values
            // to an empty array to allow foreach(...) constructions.
            return $result ? $result : [];
        }
        else {
            return FALSE;
        }
    }

}