class File

class File extends MediaSourceBase {
  
  /**
   * Key for "Name" metadata attribute.
   *
   * @var string
   */
  const METADATA_ATTRIBUTE_NAME = 'name';
  
  /**
   * Key for "MIME type" metadata attribute.
   *
   * @var string
   */
  const METADATA_ATTRIBUTE_MIME = 'mimetype';
  
  /**
   * Key for "File size" metadata attribute.
   *
   * @var string
   */
  const METADATA_ATTRIBUTE_SIZE = 'filesize';
  
  /**
   * {@inheritdoc}
   */
  public function getMetadataAttributes() {
    return [
      static::METADATA_ATTRIBUTE_NAME => $this->t('Name'),
      static::METADATA_ATTRIBUTE_MIME => $this->t('MIME type'),
      static::METADATA_ATTRIBUTE_SIZE => $this->t('File size'),
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function getMetadata(MediaInterface $media, $attribute_name) {
    /** @var \Drupal\file\FileInterface $file */
    $file = $media->get($this->configuration['source_field'])->entity;
    // If the source field is not required, it may be empty.
    if (!$file) {
      return parent::getMetadata($media, $attribute_name);
    }
    switch ($attribute_name) {
      case static::METADATA_ATTRIBUTE_NAME:
      case 'default_name':
        return $file->getFilename();
      case static::METADATA_ATTRIBUTE_MIME:
        return $file->getMimeType();
      case static::METADATA_ATTRIBUTE_SIZE:
        return $file->getSize();
      case 'thumbnail_uri':
        return $this->getThumbnail($file) ?: parent::getMetadata($media, $attribute_name);
      default:
        return parent::getMetadata($media, $attribute_name);
    }
  }
  
  /**
   * Gets the thumbnail image URI based on a file entity.
   *
   * @param \Drupal\file\FileInterface $file
   *   A file entity.
   *
   * @return string
   *   File URI of the thumbnail image or NULL if there is no specific icon.
   */
  protected function getThumbnail(FileInterface $file) {
    $icon_base = $this->configFactory
      ->get('media.settings')
      ->get('icon_base_uri');
    // We try to automatically use the most specific icon present in the
    // $icon_base directory, based on the MIME type. For instance, if an
    // icon file named "pdf.png" is present, it will be used if the file
    // matches this MIME type.
    $mimetype = $file->getMimeType();
    $mimetype = explode('/', $mimetype);
    $icon_names = [
      $mimetype[0] . '--' . $mimetype[1],
      $mimetype[1],
      $mimetype[0],
    ];
    foreach ($icon_names as $icon_name) {
      $thumbnail = $icon_base . '/' . $icon_name . '.png';
      if (is_file($thumbnail)) {
        return $thumbnail;
      }
    }
    return NULL;
  }
  
  /**
   * {@inheritdoc}
   */
  public function createSourceField(MediaTypeInterface $type) {
    return parent::createSourceField($type)->set('settings', [
      'file_extensions' => 'txt doc docx pdf',
    ]);
  }

}