The application on Android, on the functionality of one to one "currency exchanger". That is, the user exposes a request to exchange their $ 100 for 1000 "chips" at the rate of 1:10. The first buyer claims the purchase of $ 30. The second wants to take $ 20. The fourth is still $ 40. Here the second one refuses to repurchase his $ 20, and the first one raises his request to $ 60. Moreover, in the account of EVERY user, you need to write current applications - how many you exchanged yourself, how many you wanted to redeem other applications, etc.
I plan to do all this on the basis of FireBase, so I just stumbled, what fields to do in the database? What, under each responding user to do their own fields?