public function addJob($job = []) {
        if(!isset($job['msg']))
            throw new RuntimeException('Job without a message');

        if(!isset($job['schedule']))
            throw new RuntimeException('Job without a CRON expression');

        if(!isset($job['function']))
            throw new RuntimeException('Job without a function');

        if($this->isDue($job['schedule']))
            $this->jobs[] = $job;
    }