https://medium.com/geogo-in/state-machines-in-rails-5-45259a4f42da 文章
https://peterswj.github.io/2017/09/10/%E6%88%91%E7%9C%BC%E7%9D%9B%E9%87%8C%E7%9A%84%E6%9C%89%E9%99%90%E7%8A%B6%E6%80%81%E6%9C%BA/