PHP class for parsing html and get links

DomHelper

<?php

class helper {

	//---------------------------------------------------------------------------

	public function __construct() {

	}

	//---------------------------------------------------------------------------
	
	public function getLinks($html, $parent) {

		$ret = array();


		$dom = new domDocument;
		@$dom -> loadHTML($html);

		$dom -> preserveWhiteSpace = false;


		$links = $dom -> getElementsByTagName('a');

		foreach ($links as $tag) {
			$u = $tag -> getAttribute('href');

			$u = $this -> checkIfIntern($u, $parent);
			$bool = $this -> isValidURL($u);
			$ext = $this -> checkExtension($u);

			switch ($ext) {

				case 'gif' :
				case 'png' :
				case 'jpg' :
				case 'jpeg' :
					break;

				case 'js' :
				case 'css' :
				case 'pdf' :
					break;

				default :
					if ($bool != false && !empty($u))
						$ret[] = $u;
			}

		}

		return $ret;
	}

	//---------------------------------------------------------------------------

	public function isValidURL($url) {

		$pattern = "/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i";

		if (preg_match($pattern, $url))
			return true;
		else
			return false;
	}

	//---------------------------------------------------------------------------

	public function checkExtension($url) {

		$get = strtok($url, '?');
		$ext = pathinfo($get, PATHINFO_EXTENSION);
		return strtolower($ext);
	}

	//---------------------------------------------------------------------------

	public function checkIfIntern($url, $parent) {

		if (substr($url, 0, 1) == '/') {

			$foo = parse_url($parent);
			$baseurl = $foo['scheme'] . '://' . $foo['host'] . '/';

			$url = str_replace('//', '/', $baseurl . $url);
			$url = str_replace('http:/', 'http://', $url);
			return $url;
		}

		$url_domain = $this -> GetDomain($url);
		$parent_domain = $this -> GetDomain($parent);

		if ($url_domain == $parent_domain)
			return $url;

		return false;

	}

	//---------------------------------------------------------------------------

	public function GetDomain($domainb) {

		preg_match('@^(?:http://)?([^/]+)@i', $domainb, $host);
		preg_match('/[^.]+\.[^.]+$/', $host[1], $matches);
		return $matches[0];

	}

	//---------------------------------------------------------------------------


}