/**
  * Convert a rule string into a chain
  *
  * @param string $ruleString Chain Rules string format
  *
  * @return Chain
  */
 public function convert($ruleString)
 {
     $ruleSet = json_decode($ruleString);
     $this->_throwExceptionOnInvalidRuleSet($ruleSet);
     $rules = [];
     foreach ($ruleSet as $rule) {
         $ruleClass = $rule->rule;
         $settings = (array) $rule->settings;
         $this->_throwExceptionOnUnknownRuleClass($ruleClass);
         $rules[] = new $ruleClass($settings);
     }
     $chain = new Chain();
     $chain->setRules($rules);
     return $chain;
 }