RPC Model

message Wallet {
  string username = 1;
  int64 balance = 2;
  int64 happened_at = 3; // unix time stamp
}

message Transaction {
  string username = 1;
  int64 amount = 2;
  int64 new_balance = 3;
  int64 tx_id 4; // it is generated by fund provider and unique among all transactions in fund provider
  int64 happened_at = 5; // unix time stamp
}

enum TransferLabel {
  TransferLabel_UNSPECIFIED = 0;
  TransferLabel_BET = 1;
  TransferLabel_PAYOUT = 2;
  TransferLabel_REFUND = 3;
  TransferLabel_P2P = 4;
  TransferLabel_TAX_PAYOUT = 5;
  TransferLabel_TAX_P2P = 6;
  TransferLabel_BUYIN = 7;
  TransferLabel_JACKPOT = 8;
  TransferLabel_LOTTERY = 9;
  // ....
}

message Transfer {
  string username = 1;
  int64 amount = 2;
  TransferLabel transfer_label = 3;
}