1 files changed, 64 insertions, 0 deletions
diff --git a/packages/forwarder-helper/src/forwarder_helper_impl.ts b/packages/forwarder-helper/src/forwarder_helper_impl.ts
new file mode 100644
index 000000000..a90edb0bb
--- /dev/null
+++ b/packages/forwarder-helper/src/forwarder_helper_impl.ts
@@ -0,0 +1,64 @@
+import { marketUtils } from '@0xproject/order-utils';
+import { SignedOrder } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+import * as _ from 'lodash';
+
+import { constants } from './constants';
+import { ForwarderHelper, ForwarderHelperError, MarketBuyOrdersInfo, MarketBuyOrdersInfoRequest } from './types';
+import { forwarderHelperImplConfigUtils } from './utils/forwarder_helper_impl_config_utils';
+
+const SLIPPAGE_PERCENTAGE = new BigNumber(0.2); // 20% slippage protection, possibly move this into request interface
+
+export interface ForwarderHelperImplConfig {
+    orders: SignedOrder[];
+    feeOrders: SignedOrder[];
+    remainingFillableMakerAssetAmounts?: BigNumber[];
+    remainingFillableFeeAmounts?: BigNumber[];
+}
+
+export class ForwarderHelperImpl implements ForwarderHelper {
+    public readonly config: ForwarderHelperImplConfig;
+    constructor(config: ForwarderHelperImplConfig) {
+        this.config = forwarderHelperImplConfigUtils.sortedConfig(config);
+    }
+    public getMarketBuyOrdersInfo(request: MarketBuyOrdersInfoRequest): MarketBuyOrdersInfo {
+        const { makerAssetFillAmount, feePercentage } = request;
+        const { orders, feeOrders, remainingFillableMakerAssetAmounts, remainingFillableFeeAmounts } = this.config;
+        // TODO: make the slippage percentage customizable
+        const slippageBufferAmount = makerAssetFillAmount.mul(SLIPPAGE_PERCENTAGE).round();
+        const { resultOrders, remainingFillAmount } = marketUtils.findOrdersThatCoverMakerAssetFillAmount(
+            orders,
+            makerAssetFillAmount,
+            {
+                remainingFillableMakerAssetAmounts,
+                slippageBufferAmount,
+            },
+        );
+        if (remainingFillAmount.gt(constants.ZERO_AMOUNT)) {
+            throw new Error(ForwarderHelperError.InsufficientMakerAssetLiquidity);
+        }
+        // TODO: update this logic to find the minimum amount of feeOrders to cover the worst case as opposed to
+        // finding order that cover all fees, this will help with estimating ETH and minimizing gas usage
+        const { resultFeeOrders, remainingFeeAmount } = marketUtils.findFeeOrdersThatCoverFeesForTargetOrders(
+            resultOrders,
+            feeOrders,
+            {
+                remainingFillableMakerAssetAmounts,
+                remainingFillableFeeAmounts,
+            },
+        );
+        if (remainingFeeAmount.gt(constants.ZERO_AMOUNT)) {
+            throw new Error(ForwarderHelperError.InsufficientZrxLiquidity);
+        }
+        // TODO: calculate min and max eth usage
+        // TODO: optimize orders call data
+        return {
+            makerAssetFillAmount,
+            orders: resultOrders,
+            feeOrders: resultFeeOrders,
+            minEthAmount: constants.ZERO_AMOUNT,
+            maxEthAmount: constants.ZERO_AMOUNT,
+            feePercentage,
+        };
+    }
+}