class FileUploadForm

class FileUploadForm extends AddFormBase {
    
    /**
     * The element info manager.
     *
     * @var \Drupal\Core\Render\ElementInfoManagerInterface
     */
    protected $elementInfo;
    
    /**
     * The renderer service.
     *
     * @var \Drupal\Core\Render\ElementInfoManagerInterface
     */
    protected $renderer;
    
    /**
     * The file system service.
     *
     * @var \Drupal\Core\File\FileSystemInterface
     */
    protected $fileSystem;
    
    /**
     * The file usage service.
     *
     * @var \Drupal\file\FileUsage\FileUsageInterface
     */
    protected $fileUsage;
    
    /**
     * The file repository service.
     *
     * @var \Drupal\file\FileRepositoryInterface
     */
    protected $fileRepository;
    
    /**
     * Constructs a new FileUploadForm.
     *
     * @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\Core\Render\ElementInfoManagerInterface $element_info
     *   The element info manager.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer service.
     * @param \Drupal\Core\File\FileSystemInterface $file_system
     *   The file system service.
     * @param \Drupal\media_library\OpenerResolverInterface $opener_resolver
     *   The opener resolver.
     * @param \Drupal\file\FileUsage\FileUsageInterface $file_usage
     *   The file usage service.
     * @param \Drupal\file\FileRepositoryInterface $file_repository
     *   The file repository service.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilder $library_ui_builder, ElementInfoManagerInterface $element_info, RendererInterface $renderer, FileSystemInterface $file_system, OpenerResolverInterface $opener_resolver, FileUsageInterface $file_usage, FileRepositoryInterface $file_repository) {
        parent::__construct($entity_type_manager, $library_ui_builder, $opener_resolver);
        $this->elementInfo = $element_info;
        $this->renderer = $renderer;
        $this->fileSystem = $file_system;
        $this->fileUsage = $file_usage;
        $this->fileRepository = $file_repository;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('media_library.ui_builder'), $container->get('element_info'), $container->get('renderer'), $container->get('file_system'), $container->get('media_library.opener_resolver'), $container->get('file.usage'), $container->get('file.repository'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return $this->getBaseFormId() . '_upload';
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getMediaType(FormStateInterface $form_state) {
        if ($this->mediaType) {
            return $this->mediaType;
        }
        $media_type = parent::getMediaType($form_state);
        // The file upload form only supports media types which use a file field as
        // a source field.
        $field_definition = $media_type->getSource()
            ->getSourceFieldDefinition($media_type);
        if (!is_a($field_definition->getClass(), FileFieldItemList::class, TRUE)) {
            throw new \InvalidArgumentException('Can only add media types which use a file field as a source field.');
        }
        return $media_type;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildInputElement(array $form, FormStateInterface $form_state) {
        // Create a file item to get the upload validators.
        $media_type = $this->getMediaType($form_state);
        $item = $this->createFileItem($media_type);
        
        /** @var \Drupal\media_library\MediaLibraryState $state */
        $state = $this->getMediaLibraryState($form_state);
        if (!$state->hasSlotsAvailable()) {
            return $form;
        }
        $slots = $state->getAvailableSlots();
        // Add a container to group the input elements for styling purposes.
        $form['container'] = [
            '#type' => 'container',
        ];
        $process = (array) $this->elementInfo
            ->getInfoProperty('managed_file', '#process', []);
        $form['container']['upload'] = [
            '#type' => 'managed_file',
            '#title' => $this->formatPlural($slots, 'Add file', 'Add files'),
            // @todo Move validation in https://www.drupal.org/node/2988215
'#process' => array_merge([
                '::validateUploadElement',
            ], $process, [
                '::processUploadElement',
            ]),
            '#upload_validators' => $item->getUploadValidators(),
            // Set multiple to true only if available slots is not exactly one
            // to ensure correct language (singular or plural) in UI
'#multiple' => $slots != 1 ? TRUE : FALSE,
            // Do not limit the number uploaded. There is validation based on the
            // number selected in the media library that prevents overages.
            // @see Drupal\media_library\Form\AddFormBase::updateLibrary()
'#cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED,
            '#remaining_slots' => $slots,
        ];
        $file_upload_help = [
            '#theme' => 'file_upload_help',
            '#upload_validators' => $form['container']['upload']['#upload_validators'],
            '#cardinality' => $slots,
        ];
        // The file upload help needs to be rendered since the description does not
        // accept render arrays. The FileWidget::formElement() method adds the file
        // upload help in the same way, so any theming improvements made to file
        // fields would also be applied to this upload field.
        // @see \Drupal\file\Plugin\Field\FieldWidget\FileWidget::formElement()
        $form['container']['upload']['#description'] = $this->renderer
            ->renderInIsolation($file_upload_help);
        return $form;
    }
    
    /**
     * Validates the upload element.
     *
     * @param array $element
     *   The upload element.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     *
     * @return array
     *   The processed upload element.
     */
    public function validateUploadElement(array $element, FormStateInterface $form_state) {
        if ($form_state::hasAnyErrors()) {
            // When an error occurs during uploading files, remove all files so the
            // user can re-upload the files.
            $element['#value'] = [];
        }
        $values = $form_state->getValue('upload', []);
        if (count($values['fids']) > $element['#cardinality'] && $element['#cardinality'] !== FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED) {
            $form_state->setError($element, $this->t('A maximum of @count files can be uploaded.', [
                '@count' => $element['#cardinality'],
            ]));
            $form_state->setValue('upload', []);
            $element['#value'] = [];
        }
        return $element;
    }
    
    /**
     * Processes an upload (managed_file) element.
     *
     * @param array $element
     *   The upload element.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     *
     * @return array
     *   The processed upload element.
     */
    public function processUploadElement(array $element, FormStateInterface $form_state) {
        $element['upload_button']['#submit'] = [
            '::uploadButtonSubmit',
        ];
        // Limit the validation errors to make sure
        // FormValidator::handleErrorsWithLimitedValidation doesn't remove the
        // current selection from the form state.
        // @see Drupal\Core\Form\FormValidator::handleErrorsWithLimitedValidation()
        $element['upload_button']['#limit_validation_errors'] = [
            [
                'upload',
            ],
            [
                'current_selection',
            ],
        ];
        $element['upload_button']['#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 $element;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildEntityFormElement(MediaInterface $media, array $form, FormStateInterface $form_state, $delta) {
        $element = parent::buildEntityFormElement($media, $form, $form_state, $delta);
        $source_field = $this->getSourceFieldName($media->bundle->entity);
        if (isset($element['fields'][$source_field])) {
            $element['fields'][$source_field]['widget'][0]['#process'][] = [
                static::class,
                'hideExtraSourceFieldComponents',
            ];
        }
        return $element;
    }
    
    /**
     * Processes an image or file source field element.
     *
     * @param array $element
     *   The entity form source field element.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current form state.
     * @param array $form
     *   The complete form.
     *
     * @return array
     *   The processed form element.
     */
    public static function hideExtraSourceFieldComponents($element, FormStateInterface $form_state, $form) {
        // Remove original button added by ManagedFile::processManagedFile().
        if (!empty($element['remove_button'])) {
            $element['remove_button']['#access'] = FALSE;
        }
        // Remove preview added by ImageWidget::process().
        if (!empty($element['preview'])) {
            $element['preview']['#access'] = FALSE;
        }
        $element['#title_display'] = 'none';
        $element['#description_display'] = 'none';
        // Remove the filename display.
        foreach ($element['#files'] as $file) {
            $element['file_' . $file->id()]['filename']['#access'] = FALSE;
        }
        return $element;
    }
    
    /**
     * Submit handler for the upload button, inside the managed_file element.
     *
     * @param array $form
     *   The form render array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     */
    public function uploadButtonSubmit(array $form, FormStateInterface $form_state) {
        $files = $this->entityTypeManager
            ->getStorage('file')
            ->loadMultiple($form_state->getValue('upload', []));
        $this->processInputValues($files, $form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function createMediaFromValue(MediaTypeInterface $media_type, EntityStorageInterface $media_storage, $source_field_name, $file) {
        if (!$file instanceof FileInterface) {
            throw new \InvalidArgumentException('Cannot create a media item without a file entity.');
        }
        // Create a file item to get the upload location.
        $item = $this->createFileItem($media_type);
        $upload_location = $item->getUploadLocation();
        if (!$this->fileSystem
            ->prepareDirectory($upload_location, FileSystemInterface::CREATE_DIRECTORY)) {
            throw new FileWriteException("The destination directory '{$upload_location}' is not writable");
        }
        $file = $this->fileRepository
            ->move($file, $upload_location);
        if (!$file) {
            throw new \RuntimeException("Unable to move file to '{$upload_location}'");
        }
        return parent::createMediaFromValue($media_type, $media_storage, $source_field_name, $file);
    }
    
    /**
     * Create a file field item.
     *
     * @param \Drupal\media\MediaTypeInterface $media_type
     *   The media type of the media item.
     *
     * @return \Drupal\file\Plugin\Field\FieldType\FileItem
     *   A created file item.
     */
    protected function createFileItem(MediaTypeInterface $media_type) {
        $field_definition = $media_type->getSource()
            ->getSourceFieldDefinition($media_type);
        $data_definition = FieldItemDataDefinition::create($field_definition);
        return new FileItem($data_definition);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function prepareMediaEntityForSave(MediaInterface $media) {
        
        /** @var \Drupal\file\FileInterface $file */
        $file = $media->get($this->getSourceFieldName($media->bundle->entity))->entity;
        $file->setPermanent();
        $file->save();
    }
    
    /**
     * Submit handler for the remove button.
     *
     * @param array $form
     *   The form render array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The form state.
     */
    public function removeButtonSubmit(array $form, FormStateInterface $form_state) {
        // Retrieve the delta of the media item from the parents of the remove
        // button.
        $triggering_element = $form_state->getTriggeringElement();
        $delta = array_slice($triggering_element['#array_parents'], -2, 1)[0];
        
        /** @var \Drupal\media\MediaInterface $removed_media */
        $removed_media = $form_state->get([
            'media',
            $delta,
        ]);
        $file = $removed_media->get($this->getSourceFieldName($removed_media->bundle->entity))->entity;
        if ($file instanceof FileInterface && empty($this->fileUsage
            ->listUsage($file))) {
            $file->delete();
        }
        parent::removeButtonSubmit($form, $form_state);
    }

}