1 files changed, 56 insertions, 12 deletions
diff --git a/packages/asset-buyer/src/utils/order_utils.ts b/packages/asset-buyer/src/utils/order_utils.ts
index ff47eb7c5..1cc2cf95f 100644
--- a/packages/asset-buyer/src/utils/order_utils.ts
+++ b/packages/asset-buyer/src/utils/order_utils.ts
@@ -12,19 +12,63 @@ export const orderUtils = {
         const currentUnixTimestampSec = new BigNumber(Date.now() / millisecondsInSecond).round();
         return order.expirationTimeSeconds.lessThan(currentUnixTimestampSec.plus(secondsFromNow));
     },
-    calculateRemainingMakerAssetAmount(order: SignedOrder, remainingTakerAssetAmount: BigNumber): BigNumber {
-        if (remainingTakerAssetAmount.eq(0)) {
-            return constants.ZERO_AMOUNT;
-        }
-        return remainingTakerAssetAmount.times(order.makerAssetAmount).dividedToIntegerBy(order.takerAssetAmount);
-    },
-    calculateRemainingTakerAssetAmount(order: SignedOrder, remainingMakerAssetAmount: BigNumber): BigNumber {
-        if (remainingMakerAssetAmount.eq(0)) {
-            return constants.ZERO_AMOUNT;
-        }
-        return remainingMakerAssetAmount.times(order.takerAssetAmount).dividedToIntegerBy(order.makerAssetAmount);
-    },
     isOpenOrder(order: SignedOrder): boolean {
         return order.takerAddress === constants.NULL_ADDRESS;
     },
+    // given a remaining amount of takerAsset, calculate how much makerAsset is available
+    getRemainingMakerAmount(order: SignedOrder, remainingTakerAmount: BigNumber): BigNumber {
+        const remainingMakerAmount = remainingTakerAmount
+            .times(order.makerAssetAmount)
+            .div(order.takerAssetAmount)
+            .floor();
+        return remainingMakerAmount;
+    },
+    // given a desired amount of makerAsset, calculate how much takerAsset is required to fill that amount
+    getTakerFillAmount(order: SignedOrder, makerFillAmount: BigNumber): BigNumber {
+        // Round up because exchange rate favors Maker
+        const takerFillAmount = makerFillAmount
+            .mul(order.takerAssetAmount)
+            .div(order.makerAssetAmount)
+            .ceil();
+        return takerFillAmount;
+    },
+    // given a desired amount of takerAsset to fill, calculate how much fee is required by the taker to fill that amount
+    getTakerFeeAmount(order: SignedOrder, takerFillAmount: BigNumber): BigNumber {
+        // Round down because Taker fee rate favors Taker
+        const takerFeeAmount = takerFillAmount
+            .mul(order.takerFee)
+            .div(order.takerAssetAmount)
+            .floor();
+        return takerFeeAmount;
+    },
+    // given a desired amount of takerAsset to fill, calculate how much makerAsset will be filled
+    getMakerFillAmount(order: SignedOrder, takerFillAmount: BigNumber): BigNumber {
+        // Round down because exchange rate favors Maker
+        const makerFillAmount = takerFillAmount
+            .mul(order.makerAssetAmount)
+            .div(order.takerAssetAmount)
+            .floor();
+        return makerFillAmount;
+    },
+    // given a desired amount of makerAsset, calculate how much fee is required by the maker to fill that amount
+    getMakerFeeAmount(order: SignedOrder, makerFillAmount: BigNumber): BigNumber {
+        // Round down because Maker fee rate favors Maker
+        const makerFeeAmount = makerFillAmount
+            .mul(order.makerFee)
+            .div(order.makerAssetAmount)
+            .floor();
+        return makerFeeAmount;
+    },
+    // given a desired amount of ZRX from a fee order, calculate how much takerAsset is required to fill that amount
+    // also calculate how much ZRX needs to be bought in order fill the desired amount + takerFee
+    getTakerFillAmountForFeeOrder(order: SignedOrder, makerFillAmount: BigNumber): [BigNumber, BigNumber] {
+        // For each unit of TakerAsset we buy (MakerAsset - TakerFee)
+        const adjustedTakerFillAmount = makerFillAmount
+            .mul(order.takerAssetAmount)
+            .div(order.makerAssetAmount.sub(order.takerFee))
+            .ceil();
+        // The amount that we buy will be greater than makerFillAmount, since we buy some amount for fees.
+        const adjustedMakerFillAmount = orderUtils.getMakerFillAmount(order, adjustedTakerFillAmount);
+        return [adjustedTakerFillAmount, adjustedMakerFillAmount];
+    },
 };