TYPO3 ViewHelper to return domain of a given link - usefull eg. for conditions with domain names (“if link points to »twitter.com«, then…”)

DomainByLinkViewHelper.php

<?php
namespace Pixelbrackets\AcmeExtension\ViewHelpers;

use TYPO3\CMS\Fluid\Core\ViewHelper\AbstractViewHelper;

/**
 * Returns the domain of a given link
 *
 * = Examples =
 *
 * <code title="Default">
 * <p:domainByLink link="http://www.example.com/foo/bar" />
 * </code>
 * <output>
 * example.com
 * </output>
 *
 * <code title="Domain with Subdomain">
 * <p:domainByLink link="https://www.Example.com" showSubdomain="TRUE" />
 * </code>
 * <output>
 * www.example.com
 * </output>
 *
 * <code title="Inline notation">
 * {p:domainByLink(link: 'www2.example.co.uk')}
 * </code>
 * <output>
 * example.co.uk
 * </output>
 *
 */

class DomainByLinkViewHelper extends AbstractViewHelper {
	/**
	 * Get Domain
	 *
	 * @param string $link Link (e.g. example.com or https://example.com/foo/bar)
	 * @param boolean $showSubdomain Include subdomain in result (default FALSE)
	 * @return string
	 */
	public function render($link = NULL, $showSubdomain = FALSE) {
		if ($link === NULL) {
			$link = $this->renderChildren();
		}

		$parsedUrl = parse_url(strtolower(trim($link)));
		// fix for PHP < 5.4.7 if URL scheme is missing
		$domain = trim($parsedUrl['host'] ? $parsedUrl['host'] : array_shift(explode('/', $parsedUrl['path'], 2)));

		if($showSubdomain == FALSE) {
			preg_match('/[a-z0-9\-]{1,63}\.[a-z\.]{2,6}$/', $domain, $domainParts);
			$domain = $domainParts[0];
		}

		return $domain;
	}
}