1 files changed, 86 insertions, 0 deletions
diff --git a/packages/0x.js/src/order_watcher/remaining_fillable_calculator.ts b/packages/0x.js/src/order_watcher/remaining_fillable_calculator.ts
new file mode 100644
index 000000000..c77d4428c
--- /dev/null
+++ b/packages/0x.js/src/order_watcher/remaining_fillable_calculator.ts
@@ -0,0 +1,86 @@
+import {SignedOrder} from '../types';
+import {BigNumber} from 'bignumber.js';
+
+export class RemainingFillableCalculator {
+    private signedOrder: SignedOrder;
+    private isMakerTokenZRX: boolean;
+    // Transferrable Amount is the minimum of Approval and Balance
+    private transferrableMakerTokenAmount: BigNumber;
+    private transferrableMakerFeeTokenAmount: BigNumber;
+    private remainingMakerTokenAmount: BigNumber;
+    private remainingMakerFeeAmount: BigNumber;
+    constructor(signedOrder: SignedOrder,
+                isMakerTokenZRX: boolean,
+                transferrableMakerTokenAmount: BigNumber,
+                transferrableMakerFeeTokenAmount: BigNumber,
+                remainingMakerTokenAmount: BigNumber) {
+        this.signedOrder = signedOrder;
+        this.isMakerTokenZRX = isMakerTokenZRX;
+        this.transferrableMakerTokenAmount = transferrableMakerTokenAmount;
+        this.transferrableMakerFeeTokenAmount = transferrableMakerFeeTokenAmount;
+        this.remainingMakerTokenAmount = remainingMakerTokenAmount;
+        this.remainingMakerFeeAmount = remainingMakerTokenAmount.times(signedOrder.makerFee)
+                                                                .dividedToIntegerBy(signedOrder.makerTokenAmount);
+    }
+    public computeRemainingMakerFillable(): BigNumber {
+        if (this.hasSufficientFundsForFeeAndTransferAmount()) {
+            return this.remainingMakerTokenAmount;
+        }
+        if (this.signedOrder.makerFee.isZero()) {
+            return BigNumber.min(this.remainingMakerTokenAmount, this.transferrableMakerTokenAmount);
+        }
+        return this.calculatePartiallyFillableMakerTokenAmount();
+    }
+    public computeRemainingTakerFillable(): BigNumber {
+        return this.computeRemainingMakerFillable().times(this.signedOrder.takerTokenAmount)
+                                                   .dividedToIntegerBy(this.signedOrder.makerTokenAmount);
+    }
+    private hasSufficientFundsForFeeAndTransferAmount(): boolean {
+        if (this.isMakerTokenZRX) {
+            const totalZRXTransferAmountRequired = this.remainingMakerTokenAmount.plus(this.remainingMakerFeeAmount);
+            const hasSufficientFunds = this.transferrableMakerTokenAmount.greaterThanOrEqualTo(
+                                                                            totalZRXTransferAmountRequired);
+            return hasSufficientFunds;
+        } else {
+            const hasSufficientFundsForTransferAmount = this.transferrableMakerTokenAmount.greaterThanOrEqualTo(
+                                                            this.remainingMakerTokenAmount);
+            const hasSufficientFundsForFeeAmount = this.transferrableMakerFeeTokenAmount.greaterThanOrEqualTo(
+                                                       this.remainingMakerFeeAmount);
+            const hasSufficientFunds = hasSufficientFundsForTransferAmount && hasSufficientFundsForFeeAmount;
+            return hasSufficientFunds;
+        }
+    }
+    private calculatePartiallyFillableMakerTokenAmount(): BigNumber {
+        // Given an order for 200 wei for 2 ZRXwei fee, find 100 wei for 1 ZRXwei. Order ratio is then 100:1
+        const orderToFeeRatio = this.signedOrder.makerTokenAmount.dividedBy(this.signedOrder.makerFee);
+        // The number of times the maker can fill the order, if each fill only required the transfer of a single
+        // baseUnit of fee tokens.
+        // Given 2 ZRXwei, the maximum amount of times Maker can fill this order, in terms of fees, is 2
+        const fillableTimesInFeeTokenBaseUnits = BigNumber.min(this.transferrableMakerFeeTokenAmount,
+                                                               this.remainingMakerFeeAmount);
+        // The number of times the Maker can fill the order, given the Maker Token Balance
+        // Assuming a balance of 150 wei, and an orderToFeeRatio of 100:1, maker can fill this order 1 time.
+        let fillableTimesInMakerTokenUnits = this.transferrableMakerTokenAmount.dividedBy(orderToFeeRatio);
+        if (this.isMakerTokenZRX) {
+            // If ZRX is the maker token, the Fee and the Maker amount need to be removed from the same pool;
+            // 200 ZRXwei for 2ZRXwei fee can only be filled once (need 202 ZRXwei)
+            const totalZRXTokenPooled = this.transferrableMakerTokenAmount;
+            // The purchasing power here is less as the tokens are taken from the same Pool
+            // For every one number of fills, we have to take an extra ZRX out of the pool
+            fillableTimesInMakerTokenUnits = totalZRXTokenPooled.dividedBy(
+                                                                     orderToFeeRatio.plus(new BigNumber(1)));
+
+        }
+        // When Ratio is not fully divisible there can be remainders which cannot be represented, so they are floored.
+        // This can result in a RoundingError being thrown by the Exchange Contract.
+        const partiallyFillableMakerTokenAmount = fillableTimesInMakerTokenUnits
+                                                     .times(this.signedOrder.makerTokenAmount)
+                                                     .dividedToIntegerBy(this.signedOrder.makerFee);
+        const partiallyFillableFeeTokenAmount = fillableTimesInFeeTokenBaseUnits
+                                                     .times(this.signedOrder.makerTokenAmount)
+                                                     .dividedToIntegerBy(this.signedOrder.makerFee);
+        const partiallyFillableAmount = BigNumber.min(partiallyFillableMakerTokenAmount,
+                                                      partiallyFillableFeeTokenAmount);
+        return partiallyFillableAmount;
+    }
+}