public function hash(
        string $directive = 'script-src',
        string $script = '',
        string $algorithm = 'sha384'
    ): self {
        $ruleKeys = \array_keys($this->policies);
        if (\in_array($directive, $ruleKeys)) {
            $this->policies[$directive]['hashes'] []= [
                $algorithm => Base64::encode(
                    \hash($algorithm, $script, true)
                )
            ];
        }
        return $this;
    }