Bring back trading to fiatBalance

lib/trader.js

@@ -116,7 +116,21 @@ Trader.prototype.fiatBalance = function (transferSatoshis, tradeFiat) {
   //                      [ $ ] = [ $ ]
   var fiatTransferBalance = ((adjustedTransferBalance / SATOSHI_FACTOR) * rate) / lowBalanceMargin;
 
-  return fiatTransferBalance;
+  // If this server is also configured to trade received fiat for Bitcoins,
+  // we also need to calculate if we have enough funds on our trade exchange.
+  if (balance.tradeBalance === null) return fiatTransferBalance;
+  var tradeBalance = balance.tradeBalance;
+
+  // We need to secure `tradeFiat` (amount of fiat in this transaction) and
+  // enough fiat to cover our trading queue (trades aren't executed immediately).
+  var adjustedFiat = tradeFiat + this.tradeQueueFiatBalance(rate);
+
+  // So we subtract `adjustedFiat` from `tradeBalance` and again, apply
+  // `lowBalanceMargin`.
+  var fiatTradeBalance = (tradeBalance - adjustedFiat) / lowBalanceMargin;
+
+  // And we return the smallest number.
+  return Math.min(fiatTransferBalance, fiatTradeBalance);
 };
 
 Trader.prototype.sendBitcoins = function (deviceFingerprint, tx, cb) {