1 files changed, 48 insertions, 0 deletions
diff --git a/packages/order-utils/src/rate_utils.ts b/packages/order-utils/src/rate_utils.ts
new file mode 100644
index 000000000..c9ca72c59
--- /dev/null
+++ b/packages/order-utils/src/rate_utils.ts
@@ -0,0 +1,48 @@
+import { schemas } from '@0xproject/json-schemas';
+import { Order } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+
+import { assert } from './assert';
+import { constants } from './constants';
+
+export const rateUtils = {
+    /**
+     * Takes an order and calculates the fee adjusted rate (takerAsset/makerAsset) by calculating how much takerAsset
+     * is required to cover the fees (feeRate * takerFee), adding the takerAssetAmount and dividing by makerAssetAmount
+     * @param   order       An object that conforms to the order interface
+     * @param   feeRate     The market rate of ZRX denominated in takerAssetAmount
+     *                      (ex. feeRate is 0.1 takerAsset/ZRX if it takes 1 unit of takerAsset to buy 10 ZRX)
+     *                      Defaults to 0
+     * @return  The rate (takerAsset/makerAsset) of the order adjusted for fees
+     */
+    getFeeAdjustedRateOfOrder(order: Order, feeRate: BigNumber = constants.ZERO_AMOUNT): BigNumber {
+        assert.doesConformToSchema('order', order, schemas.orderSchema);
+        assert.isBigNumber('feeRate', feeRate);
+        assert.assert(
+            feeRate.gte(constants.ZERO_AMOUNT),
+            `Expected feeRate: ${feeRate} to be greater than or equal to 0`,
+        );
+        const takerAssetAmountNeededToPayForFees = order.takerFee.mul(feeRate);
+        const totalTakerAssetAmount = takerAssetAmountNeededToPayForFees.plus(order.takerAssetAmount);
+        const rate = totalTakerAssetAmount.div(order.makerAssetAmount);
+        return rate;
+    },
+    /**
+     * Takes a fee order (makerAssetData corresponds to ZRX and takerAssetData corresponds to WETH) and calculates
+     * the fee adjusted rate (WETH/ZRX) by dividing the takerAssetAmount by the makerAmount minus the takerFee
+     * @param   feeOrder    An object that conforms to the order interface
+     * @return  The rate (WETH/ZRX) of the fee order adjusted for fees
+     */
+    getFeeAdjustedRateOfFeeOrder(feeOrder: Order): BigNumber {
+        assert.doesConformToSchema('feeOrder', feeOrder, schemas.orderSchema);
+        const zrxAmountAfterFees = feeOrder.makerAssetAmount.sub(feeOrder.takerFee);
+        assert.assert(
+            zrxAmountAfterFees.greaterThan(constants.ZERO_AMOUNT),
+            `Expected takerFee: ${JSON.stringify(feeOrder.takerFee)} to be less than makerAssetAmount: ${JSON.stringify(
+                feeOrder.makerAssetAmount,
+            )}`,
+        );
+        const rate = feeOrder.takerAssetAmount.div(zrxAmountAfterFees);
+        return rate;
+    },
+};