PHP function to extract URLs from post text.

class.Post.php

    /**
     * Extract URLs from post text.
     * Find syntactically correct URLs such as http://foobar.com/data.php and some plausible URL fragments, e.g.
     * bit.ly/asb12 www.google.com, and fix URL fragments to be valid URLs.
     * Only return valid URLs
     * Regex pattern based on http://daringfireball.net/2010/07/improved_regex_for_matching_urls
     * with a modification in the third group to ensure that https?:/// (third slash) doesn't match.
     * @param string $post_text
     * @return array $matches
     */
    public static function extractURLs($post_text) {
        $url_pattern = '(?i)\b'.
        '((?:https?://|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}/)'.
        '(?:[^\s()<>/][^\s()<>]*|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+'.
        '(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:\'".,<>?¬´¬ª‚Äú‚Äù‚Äò‚Äô,”]))';
        preg_match_all('#'.$url_pattern.'#', $post_text, $matches);
        $corrected_urls = array_map( 'Link::addMissingHttp', $matches[0]);
        return array_filter($corrected_urls,'Utils::validateURL');
    }