class OEmbedForm

class OEmbedForm extends AddFormBase {
    
    /**
     * The oEmbed URL resolver service.
     *
     * @var \Drupal\media\OEmbed\UrlResolverInterface
     */
    protected $urlResolver;
    
    /**
     * The oEmbed resource fetcher service.
     *
     * @var \Drupal\media\OEmbed\ResourceFetcherInterface
     */
    protected $resourceFetcher;
    
    /**
     * Constructs a new OEmbedForm.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\media_library\MediaLibraryUiBuilder $library_ui_builder
     *   The media library UI builder.
     * @param \Drupal\media\OEmbed\UrlResolverInterface $url_resolver
     *   The oEmbed URL resolver service.
     * @param \Drupal\media\OEmbed\ResourceFetcherInterface $resource_fetcher
     *   The oEmbed resource fetcher service.
     * @param \Drupal\media_library\OpenerResolverInterface $opener_resolver
     *   The opener resolver.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilder $library_ui_builder, UrlResolverInterface $url_resolver, ResourceFetcherInterface $resource_fetcher, OpenerResolverInterface $opener_resolver = NULL) {
        parent::__construct($entity_type_manager, $library_ui_builder, $opener_resolver);
        $this->urlResolver = $url_resolver;
        $this->resourceFetcher = $resource_fetcher;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('media_library.ui_builder'), $container->get('media.oembed.url_resolver'), $container->get('media.oembed.resource_fetcher'), $container->get('media_library.opener_resolver'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return $this->getBaseFormId() . '_oembed';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getMediaType(FormStateInterface $form_state) {
        if ($this->mediaType) {
            return $this->mediaType;
        }
        $media_type = parent::getMediaType($form_state);
        if (!$media_type->getSource() instanceof OEmbedInterface) {
            throw new \InvalidArgumentException('Can only add media types which use an oEmbed source plugin.');
        }
        return $media_type;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildInputElement(array $form, FormStateInterface $form_state) {
        $media_type = $this->getMediaType($form_state);
        $providers = $media_type->getSource()
            ->getProviders();
        // Add a container to group the input elements for styling purposes.
        $form['container'] = [
            '#type' => 'container',
        ];
        $form['container']['url'] = [
            '#type' => 'url',
            '#title' => $this->t('Add @type via URL', [
                '@type' => $this->getMediaType($form_state)
                    ->label(),
            ]),
            '#description' => $this->t('Allowed providers: @providers.', [
                '@providers' => implode(', ', $providers),
            ]),
            '#required' => TRUE,
            '#attributes' => [
                'placeholder' => 'https://',
            ],
        ];
        $form['container']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Add'),
            '#button_type' => 'primary',
            '#validate' => [
                '::validateUrl',
            ],
            '#submit' => [
                '::addButtonSubmit',
            ],
            // @todo Move validation in https://www.drupal.org/node/2988215
'#ajax' => [
                'callback' => '::updateFormCallback',
                'wrapper' => 'media-library-wrapper',
                // Add a fixed URL to post the form since AJAX forms are automatically
                // posted to <current> instead of $form['#action'].
                // @todo Remove when https://www.drupal.org/project/drupal/issues/2504115
                //   is fixed.
'url' => Url::fromRoute('media_library.ui'),
                'options' => [
                    'query' => $this->getMediaLibraryState($form_state)
                        ->all() + [
                        FormBuilderInterface::AJAX_FORM_REQUEST => TRUE,
                    ],
                ],
            ],
        ];
        return $form;
    }
    
    /**
     * Validates the oEmbed URL.
     *
     * @param array $form
     *   The complete form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current form state.
     */
    public function validateUrl(array &$form, FormStateInterface $form_state) {
        $url = $form_state->getValue('url');
        if ($url) {
            try {
                $resource_url = $this->urlResolver
                    ->getResourceUrl($url);
                $this->resourceFetcher
                    ->fetchResource($resource_url);
            } catch (ResourceException $e) {
                $form_state->setErrorByName('url', $e->getMessage());
            }
        }
    }
    
    /**
     * Submit handler for the add button.
     *
     * @param array $form
     *   The form render array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     */
    public function addButtonSubmit(array $form, FormStateInterface $form_state) {
        $this->processInputValues([
            $form_state->getValue('url'),
        ], $form, $form_state);
    }

}