Split a string by commas which are not inside potentially nested parentheses

Two days ago I started working on a code parser and I'm stuck.

How can I split a string by commas that are not inside brackets? Let me show you what I mean.

I have this string to parse:

one, two, three, (four, (five, six), (ten)), seven

I would like to get this result:

array(
 "one"; 
 "two"; 
 "three"; 
 "(four, (five, six), (ten))"; 
 "seven"
)

but instead I get:

array(
  "one"; 
  "two"; 
  "three"; 
  "(four"; 
  "(five"; 
  "six)"; 
  "(ten))";
  "seven"
)

How can I do this in PHP RegEx.

You can do that easier:

preg_match_all('/[^(,\s]+|\([^)]+\)/', $str, $matches)

But it would be better if you use a real parser. Maybe something like this:

$str = 'one, two, three, (four, (five, six), (ten)), seven';
$buffer = '';
$stack = array();
$depth = 0;
$len = strlen($str);
for ($i=0; $i<$len; $i++) {
    $char = $str[$i];
    switch ($char) {
    case '(':
        $depth++;
        break;
    case ',':
        if (!$depth) {
            if ($buffer !== '') {
                $stack[] = $buffer;
                $buffer = '';
            }
            continue 2;
        }
        break;
    case ' ':
        if (!$depth) {
            continue 2;
        }
        break;
    case ')':
        if ($depth) {
            $depth--;
        } else {
            $stack[] = $buffer.$char;
            $buffer = '';
            continue 2;
        }
        break;
    }
    $buffer .= $char;
}
if ($buffer !== '') {
    $stack[] = $buffer;
}
var_dump($stack);