Regex Flickr Parser

$regexstr = '~
# Match Flickr link and embed code
(?:<a [^>]*href=")?		# If a tag match up to first quote of src
(?:				# Group Flickr url
	https?:\/\/		# Either http or https
	(?:[\w]+\.)*		# Optional subdomains
	(?:               		# Group host alternatives.
		flic\.kr     	# Either flic.kr
	        	| flickr\.com	# or flickr.com 
	)			# End Host Group
	(?:\/photos)?		# Optional video sub directory
	\/[^\/]+\/		# Slash and stuff before Id
	([0-9a-zA-Z]+)	# $1: PHOTO_ID is numeric
	[^\s]*			# Not a space
)				# End group
"?				# Match end quote if part of src
(?:.*></a>)?			# Match the end of the a tag
~ix';

function ParseForFlickr($string){
	$regexstr = <<REGEX FROM ABOVE>>;
 
	require_once('phpFlickr.php');
	$f = new phpFlickr("<<Flickr API Key>>");
 
	preg_match_all($regexstr, $string, $matches, PREG_SET_ORDER);
 
	//Loop results		
	foreach ($matches as $val) {	
		//If short code decode it     
		if (strpos($val[0], "flic.kr") !== false) {
			$val[1] = $this->flickrDecode($val[1]);
		} 
 
		//make flickr api call with photo id
		$pinfo = $f->photos_getSizes($val[1]);
		//Array 3 is the medium 500 size
		$imgstr = ' <p><img class="upostimg" src="'.$pinfo[3]['source'].'" /></p> ';
		$string = str_replace($val[0],$imgstr,$string);
	}
	return $string;
}
 
function flickrDecode($num){
	$alphabet = "123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";
 
	$decoded = 0;
	$multi = 1;
	while (strlen($num) > 0) {
		$digit = $num[strlen($num)-1];
		$decoded += $multi * strpos($alphabet, $digit);
		$multi = $multi * strlen($alphabet);
		$num = substr($num, 0, -1);
	}
 
	return $decoded;
}