We would like you to implement a "good night" application to let users track when they go to bed and when they wake up. We require some restful APIs to achieve the following:
- Clock In operation, and return all clocked-in times, ordered by created time.
- Users can follow and unfollow other users.
- See the sleep records over the past week for their friends, ordered by the length of their sleep.
Please implement the model, DB migrations, and JSON API. You can assume that there are only two fields on the users: "id" and "name”. You do not need to implement any user registration API. You can use any gems you like.