Cache-Control header parser

parser.php

<?php

class Parser
{
    public function parse($string)
    {
        $this->string = trim($string);

        $directives = array();

        // handle empty string early so we don't need a separate start state
        if ($this->string == '') {
            return $directives;
        }

        state_directive:
        switch ($this->match(array('[a-z-]+'))) {
            case 0:
                $directive = $this->lastMatch;
                goto state_value;
                break;

            default:
                throw new Exception('expected DIRECTIVE');
                break;
        }

        state_value:
        switch ($this->match(array('="[^"]*"', '=([^",][^,]*)?'))) {
            case 0:
                $directives[$directive] = substr($this->lastMatch, 2, -1);
                goto state_separator;
                break;

            case 1:
                $directives[$directive] = rtrim(substr($this->lastMatch, 1));
                goto state_separator;
                break;

            default:
                $directives[$directive] = true;
                goto state_separator;
                break;
        }

        state_separator:
        switch ($this->match(array('\s*,\s*', '$'))) {
            case 0:
                goto state_directive;
                break;

            case 1:
                return $directives;
                break;

            default:
                throw new Exception('expected SEPARATOR or END');
                break;

        }
    }

    private function match($tokens)
    {
        foreach ($tokens as $i => $token) {
            if (preg_match('/^'.$token.'/', $this->string, $matches)) {
                $this->lastMatch = $matches[0];
                $this->string = substr($this->string, strlen($matches[0]));
                return $i;
            }
        }
        return -1;
    }
}

$parser = new Parser();
print_r($parser->parse('no-store, private=test, no-cache="a,b,c"'));