silverstripe-dms/code/DMSShortcodeHandler.php

<?php
/**
 * Handles replacing `dms_document_link` shortcodes with links to the actual
 * document.
 */
class DMSShortcodeHandler {

	public static function handle(
		$arguments, $content, ShortcodeParser $parser, $tag, array $extra = array()
	) {
		if(!empty($arguments['id'])) {
			$document = DMSDocument::get()->byID($arguments['id']);

			if($document && !$document->isHidden()) {
				if($content) {
					return sprintf(
						'<a href="%s">%s</a>', $document->Link(), $parser->parse($content)
					);
				} else {
					if(isset($extra['element'])) {
						$extra['element']->setAttribute('data-ext', $document->getExtension());
						$extra['element']->setAttribute('data-size', $document->getFileSizeFormatted());
					}

					return $document->Link();
				}
			}
		}

		$error = ErrorPage::get()->filter('ErrorCode', '404')->First();

		if($error) {
			return $error->Link();
		}

		return '';
	}

}