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',
        ]);
    }

}