interface IFuturesMarket {
  // all open/close orders are market right now (not limit)
  
  sclass OpenOrCloseOrder {
    settable S orderID; // optional
    
    settable HoldSide holdSide;
    settable double cryptoAmount;
    
    // Limit order if set. Otherwise market order.
    // Limit orders are good-until-cancel.
    settable double limitPrice = Double.NaN;
  }
  
  sclass OpenOrder extends OpenOrCloseOrder {
    settable double leverage = 1;
    settable bool isCross;
  }
  
  sclass CloseOrder extends OpenOrCloseOrder {
  }
  
  // throws exception if order failed
  void openPosition(OpenOrder order);
  
  // throws exception if order failed
  void closePosition(CloseOrder order);
  
  sclass SwappableImplementation is IFuturesMarket {
    public swappable void openPosition(OpenOrder order) {}
    public swappable void closePosition(CloseOrder order) {}
    public swappable double drift() { unimplemented(); }
    public FutureCoinParameters getCoinParameters() { unimplemented(); }
  }
  
  // Get current drift (sum of longs+shorts in crypto units)
  double drift();
  
  FutureCoinParameters getCoinParameters();
}