8 files changed, 501 insertions, 0 deletions
diff --git a/packages/asset-buyer/src/constants.ts b/packages/asset-buyer/src/constants.ts
new file mode 100644
index 000000000..c0a1b090e
--- /dev/null
+++ b/packages/asset-buyer/src/constants.ts
@@ -0,0 +1,6 @@
+import { BigNumber } from '@0xproject/utils';
+
+export const constants = {
+    ZERO_AMOUNT: new BigNumber(0),
+    NULL_ADDRESS: '0x0000000000000000000000000000000000000000',
+};
diff --git a/packages/asset-buyer/src/forwarder_helper_factory.ts b/packages/asset-buyer/src/forwarder_helper_factory.ts
new file mode 100644
index 000000000..2b37ac98f
--- /dev/null
+++ b/packages/asset-buyer/src/forwarder_helper_factory.ts
@@ -0,0 +1,261 @@
+import { assert } from '@0xproject/assert';
+import { APIOrder, HttpClient, OrderbookResponse } from '@0xproject/connect';
+import { ContractWrappers, OrderAndTraderInfo, OrderStatus } from '@0xproject/contract-wrappers';
+import { schemas } from '@0xproject/json-schemas';
+import { assetDataUtils } from '@0xproject/order-utils';
+import { RemainingFillableCalculator } from '@0xproject/order-utils/lib/src/remaining_fillable_calculator';
+import { RPCSubprovider, Web3ProviderEngine } from '@0xproject/subproviders';
+import { SignedOrder } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+import * as _ from 'lodash';
+
+import { constants } from './constants';
+import { ForwarderHelperImpl, ForwarderHelperImplConfig } from './forwarder_helper_impl';
+import { ForwarderHelper, ForwarderHelperFactoryError } from './types';
+import { orderUtils } from './utils/order_utils';
+
+export const forwarderHelperFactory = {
+    /**
+     * Given an array of orders and an array of feeOrders, get a ForwarderHelper
+     * @param   orders      An array of objects conforming to SignedOrder. Each order should specify the same makerAssetData and takerAssetData
+     * @param   feeOrders   An array of objects conforming to SignedOrder. Each order should specify ZRX as makerAssetData WETH as takerAssetData
+     * @return  A ForwarderHelper, see type for definition
+     */
+    getForwarderHelperForOrders(orders: SignedOrder[], feeOrders: SignedOrder[] = []): ForwarderHelper {
+        assert.doesConformToSchema('orders', orders, schemas.signedOrdersSchema);
+        assert.doesConformToSchema('feeOrders', orders, schemas.signedOrdersSchema);
+        // TODO: Add assertion here for orders all having the same makerAsset and takerAsset
+        const config: ForwarderHelperImplConfig = {
+            orders,
+            feeOrders,
+        };
+        const helper = new ForwarderHelperImpl(config);
+        return helper;
+    },
+    /**
+     * Given a desired makerAsset and SRA url, get a ForwarderHelper
+     * @param   makerAssetData      An array of objects conforming to SignedOrder. Each order should specify the same makerAssetData and takerAssetData
+     * @param   sraUrl              A url pointing to an SRA v2 compliant endpoint.
+     * @param   rpcUrl              A url pointing to an ethereum node.
+     * @param   networkId           The ethereum networkId, defaults to 1 (mainnet).
+     * @return  A ForwarderHelper, see type for definition
+     */
+    async getForwarderHelperForMakerAssetDataAsync(
+        makerAssetData: string,
+        sraUrl: string,
+        rpcUrl?: string,
+        networkId: number = 1,
+    ): Promise<ForwarderHelper> {
+        assert.isHexString('makerAssetData', makerAssetData);
+        assert.isWebUri('sraUrl', sraUrl);
+        if (!_.isUndefined(rpcUrl)) {
+            assert.isWebUri('rpcUrl', rpcUrl);
+        }
+        assert.isNumber('networkId', networkId);
+        // create provider
+        const providerEngine = new Web3ProviderEngine();
+        if (!_.isUndefined(rpcUrl)) {
+            providerEngine.addProvider(new RPCSubprovider(rpcUrl));
+        }
+        providerEngine.start();
+        // create contract wrappers given provider and networkId
+        const contractWrappers = new ContractWrappers(providerEngine, { networkId });
+        // find ether token asset data
+        const etherTokenAddressIfExists = contractWrappers.etherToken.getContractAddressIfExists();
+        if (_.isUndefined(etherTokenAddressIfExists)) {
+            throw new Error(ForwarderHelperFactoryError.NoEtherTokenContractFound);
+        }
+        const etherTokenAssetData = assetDataUtils.encodeERC20AssetData(etherTokenAddressIfExists);
+        // find zrx token asset data
+        let zrxTokenAssetData: string;
+        try {
+            zrxTokenAssetData = contractWrappers.exchange.getZRXAssetData();
+        } catch (err) {
+            throw new Error(ForwarderHelperFactoryError.NoZrxTokenContractFound);
+        }
+        // get orderbooks for makerAsset/WETH and ZRX/WETH
+        const sraClient = new HttpClient(sraUrl);
+        const orderbookRequests = [
+            { baseAssetData: makerAssetData, quoteAssetData: etherTokenAssetData },
+            { baseAssetData: zrxTokenAssetData, quoteAssetData: etherTokenAssetData },
+        ];
+        const requestOpts = { networkId };
+        let makerAssetOrderbook: OrderbookResponse;
+        let zrxOrderbook: OrderbookResponse;
+        try {
+            [makerAssetOrderbook, zrxOrderbook] = await Promise.all(
+                _.map(orderbookRequests, request => sraClient.getOrderbookAsync(request, requestOpts)),
+            );
+        } catch (err) {
+            throw new Error(ForwarderHelperFactoryError.StandardRelayerApiError);
+        }
+        // validate orders and find remaining fillable from on chain state or sra api
+        let ordersAndRemainingFillableMakerAssetAmounts: OrdersAndRemainingFillableMakerAssetAmounts;
+        let feeOrdersAndRemainingFillableMakerAssetAmounts: OrdersAndRemainingFillableMakerAssetAmounts;
+        if (!_.isUndefined(rpcUrl)) {
+            // if we do have an rpc url, get on-chain orders and traders info via the OrderValidatorWrapper
+            const ordersFromSra = getOpenAsksFromOrderbook(makerAssetOrderbook);
+            const feeOrdersFromSra = getOpenAsksFromOrderbook(zrxOrderbook);
+            // TODO: try catch these requests and throw a more domain specific error
+            // TODO: optimization, reduce this to once RPC call buy combining orders into one array and then splitting up the response
+            const [makerAssetOrdersAndTradersInfo, feeOrdersAndTradersInfo] = await Promise.all(
+                _.map([ordersFromSra, feeOrdersFromSra], ordersToBeValidated => {
+                    const takerAddresses = _.map(ordersToBeValidated, () => constants.NULL_ADDRESS);
+                    return contractWrappers.orderValidator.getOrdersAndTradersInfoAsync(
+                        ordersToBeValidated,
+                        takerAddresses,
+                    );
+                }),
+            );
+            // take maker asset orders from SRA + on chain information and find the valid orders and remaining fillable maker asset amounts
+            ordersAndRemainingFillableMakerAssetAmounts = getValidOrdersAndRemainingFillableMakerAssetAmountsFromOnChain(
+                ordersFromSra,
+                makerAssetOrdersAndTradersInfo,
+                zrxTokenAssetData,
+            );
+            // take fee orders from SRA + on chain information and find the valid orders and remaining fillable maker asset amounts
+            feeOrdersAndRemainingFillableMakerAssetAmounts = getValidOrdersAndRemainingFillableMakerAssetAmountsFromOnChain(
+                feeOrdersFromSra,
+                feeOrdersAndTradersInfo,
+                zrxTokenAssetData,
+            );
+        } else {
+            // if we don't have an rpc url, assume all orders are valid and fallback to optional fill amounts from SRA
+            // if fill amounts are not available from the SRA, assume all orders are completely fillable
+            const apiOrdersFromSra = makerAssetOrderbook.asks.records;
+            const feeApiOrdersFromSra = zrxOrderbook.asks.records;
+            // take maker asset orders from SRA and the valid orders and remaining fillable maker asset amounts
+            ordersAndRemainingFillableMakerAssetAmounts = getValidOrdersAndRemainingFillableMakerAssetAmountsFromApi(
+                apiOrdersFromSra,
+            );
+            // take fee orders from SRA and find the valid orders and remaining fillable maker asset amounts
+            feeOrdersAndRemainingFillableMakerAssetAmounts = getValidOrdersAndRemainingFillableMakerAssetAmountsFromApi(
+                feeApiOrdersFromSra,
+            );
+        }
+        // compile final config
+        const config: ForwarderHelperImplConfig = {
+            orders: ordersAndRemainingFillableMakerAssetAmounts.orders,
+            feeOrders: feeOrdersAndRemainingFillableMakerAssetAmounts.orders,
+            remainingFillableMakerAssetAmounts:
+                ordersAndRemainingFillableMakerAssetAmounts.remainingFillableMakerAssetAmounts,
+            remainingFillableFeeAmounts:
+                feeOrdersAndRemainingFillableMakerAssetAmounts.remainingFillableMakerAssetAmounts,
+        };
+        const helper = new ForwarderHelperImpl(config);
+        return helper;
+    },
+};
+
+interface OrdersAndRemainingFillableMakerAssetAmounts {
+    orders: SignedOrder[];
+    remainingFillableMakerAssetAmounts: BigNumber[];
+}
+
+/**
+ * Given an array of APIOrder objects from a standard relayer api, return an array
+ * of fillable orders with their corresponding remainingFillableMakerAssetAmounts
+ */
+function getValidOrdersAndRemainingFillableMakerAssetAmountsFromApi(
+    apiOrders: APIOrder[],
+): OrdersAndRemainingFillableMakerAssetAmounts {
+    const result = _.reduce(
+        apiOrders,
+        (acc, apiOrder) => {
+            // get current accumulations
+            const { orders, remainingFillableMakerAssetAmounts } = acc;
+            // get order and metadata
+            const { order, metaData } = apiOrder;
+            // if the order is expired or not open, move on
+            if (orderUtils.isOrderExpired(order) || !orderUtils.isOpenOrder(order)) {
+                return acc;
+            }
+            // calculate remainingFillableMakerAssetAmount from api metadata, else assume order is completely fillable
+            const remainingFillableTakerAssetAmount = _.get(
+                metaData,
+                'remainingTakerAssetAmount',
+                order.takerAssetAmount,
+            );
+            const remainingFillableMakerAssetAmount = orderUtils.calculateRemainingMakerAssetAmount(
+                order,
+                remainingFillableTakerAssetAmount,
+            );
+            // if there is some amount of maker asset left to fill and add the order and remaining amount to the accumulations
+            // if there is not any maker asset left to fill, do not add
+            if (remainingFillableMakerAssetAmount.gt(constants.ZERO_AMOUNT)) {
+                return {
+                    orders: _.concat(orders, order),
+                    remainingFillableMakerAssetAmounts: _.concat(
+                        remainingFillableMakerAssetAmounts,
+                        remainingFillableMakerAssetAmount,
+                    ),
+                };
+            } else {
+                return acc;
+            }
+        },
+        { orders: [] as SignedOrder[], remainingFillableMakerAssetAmounts: [] as BigNumber[] },
+    );
+    return result;
+}
+
+/**
+ * Given an array of orders and corresponding on-chain infos, return a subset of the orders
+ * that are still fillable orders with their corresponding remainingFillableMakerAssetAmounts
+ */
+function getValidOrdersAndRemainingFillableMakerAssetAmountsFromOnChain(
+    inputOrders: SignedOrder[],
+    ordersAndTradersInfo: OrderAndTraderInfo[],
+    zrxAssetData: string,
+): OrdersAndRemainingFillableMakerAssetAmounts {
+    // iterate through the input orders and find the ones that are still fillable
+    // for the orders that are still fillable, calculate the remaining fillable maker asset amount
+    const result = _.reduce(
+        inputOrders,
+        (acc, order, index) => {
+            // get current accumulations
+            const { orders, remainingFillableMakerAssetAmounts } = acc;
+            // get corresponding on-chain state for the order
+            const { orderInfo, traderInfo } = ordersAndTradersInfo[index];
+            // if the order IS NOT fillable, do not add anything to the accumulations and continue iterating
+            if (orderInfo.orderStatus !== OrderStatus.FILLABLE) {
+                return acc;
+            }
+            // if the order IS fillable, add the order and calculate the remaining fillable amount
+            const transferrableAssetAmount = BigNumber.min([traderInfo.makerAllowance, traderInfo.makerBalance]);
+            const transferrableFeeAssetAmount = BigNumber.min([
+                traderInfo.makerZrxAllowance,
+                traderInfo.makerZrxBalance,
+            ]);
+            const remainingTakerAssetAmount = order.takerAssetAmount.minus(orderInfo.orderTakerAssetFilledAmount);
+            const remainingMakerAssetAmount = orderUtils.calculateRemainingMakerAssetAmount(
+                order,
+                remainingTakerAssetAmount,
+            );
+            const remainingFillableCalculator = new RemainingFillableCalculator(
+                order.makerFee,
+                order.makerAssetAmount,
+                order.makerAssetData === zrxAssetData,
+                transferrableAssetAmount,
+                transferrableFeeAssetAmount,
+                remainingMakerAssetAmount,
+            );
+            const remainingFillableAmount = remainingFillableCalculator.computeRemainingFillable();
+            return {
+                orders: _.concat(orders, order),
+                remainingFillableMakerAssetAmounts: _.concat(
+                    remainingFillableMakerAssetAmounts,
+                    remainingFillableAmount,
+                ),
+            };
+        },
+        { orders: [] as SignedOrder[], remainingFillableMakerAssetAmounts: [] as BigNumber[] },
+    );
+    return result;
+}
+
+function getOpenAsksFromOrderbook(orderbookResponse: OrderbookResponse): SignedOrder[] {
+    const asks = _.map(orderbookResponse.asks.records, apiOrder => apiOrder.order);
+    const result = _.filter(asks, ask => orderUtils.isOpenOrder(ask));
+    return result;
+}
diff --git a/packages/asset-buyer/src/forwarder_helper_impl.ts b/packages/asset-buyer/src/forwarder_helper_impl.ts
new file mode 100644
index 000000000..a90edb0bb
--- /dev/null
+++ b/packages/asset-buyer/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,
+        };
+    }
+}
diff --git a/packages/asset-buyer/src/globals.d.ts b/packages/asset-buyer/src/globals.d.ts
new file mode 100644
index 000000000..94e63a32d
--- /dev/null
+++ b/packages/asset-buyer/src/globals.d.ts
@@ -0,0 +1,6 @@
+declare module '*.json' {
+    const json: any;
+    /* tslint:disable */
+    export default json;
+    /* tslint:enable */
+}
diff --git a/packages/asset-buyer/src/index.ts b/packages/asset-buyer/src/index.ts
new file mode 100644
index 000000000..eb3a34bd5
--- /dev/null
+++ b/packages/asset-buyer/src/index.ts
@@ -0,0 +1,2 @@
+export { forwarderHelperFactory } from './forwarder_helper_factory';
+export { ForwarderHelper, ForwarderHelperError, MarketBuyOrdersInfoRequest, MarketBuyOrdersInfo } from './types';
diff --git a/packages/asset-buyer/src/types.ts b/packages/asset-buyer/src/types.ts
new file mode 100644
index 000000000..a7f02ff8d
--- /dev/null
+++ b/packages/asset-buyer/src/types.ts
@@ -0,0 +1,49 @@
+import { SignedOrder } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+
+export enum ForwarderHelperFactoryError {
+    NoEtherTokenContractFound = 'NO_ETHER_TOKEN_CONTRACT_FOUND',
+    NoZrxTokenContractFound = 'NO_ZRX_TOKEN_CONTRACT_FOUND',
+    StandardRelayerApiError = 'STANDARD_RELAYER_API_ERROR',
+}
+
+export interface ForwarderHelper {
+    /**
+     * Given a MarketBuyOrdersInfoRequest, returns a MarketBuyOrdersInfo containing all information relevant to fulfilling the request
+     * using the ForwarderContract marketBuyOrdersWithEth function.
+     * @param   request     An object that conforms to MarketBuyOrdersInfoRequest. See type definition for more information.
+     * @return  An object that conforms to MarketBuyOrdersInfo that satisfies the request. See type definition for more information.
+     */
+    getMarketBuyOrdersInfo: (request: MarketBuyOrdersInfoRequest) => MarketBuyOrdersInfo;
+}
+
+export enum ForwarderHelperError {
+    InsufficientMakerAssetLiquidity = 'INSUFFICIENT_MAKER_ASSET_LIQUIDITY',
+    InsufficientZrxLiquidity = 'INSUFFICIENT_ZRX_LIQUIDITY',
+}
+
+/**
+ * makerAssetFillAmount: The amount of makerAsset requesting to be filled
+ * feePercentage: Optional affiliate percentage amount factoring into eth amount calculations
+ */
+export interface MarketBuyOrdersInfoRequest {
+    makerAssetFillAmount: BigNumber;
+    feePercentage?: BigNumber;
+}
+
+/**
+ * makerAssetFillAmount: The amount of makerAsset requesting to be filled
+ * orders: An array of objects conforming to SignedOrder. These orders can be used to cover the requested makerAssetFillAmount plus slippage
+ * feeOrders: An array of objects conforming to SignedOrder. These orders can be used to cover the fees for the orders param above
+ * minEthAmount: Amount of eth in wei to send with the tx for the most optimistic case
+ * maxEthAmount: Amount of eth in wei to send with the tx for the worst case
+ * feePercentage: Affiliate fee percentage used to calculate the eth amounts above. Passed thru directly from the request
+ */
+export interface MarketBuyOrdersInfo {
+    makerAssetFillAmount: BigNumber;
+    orders: SignedOrder[];
+    feeOrders: SignedOrder[];
+    minEthAmount: BigNumber;
+    maxEthAmount: BigNumber;
+    feePercentage?: BigNumber;
+}
diff --git a/packages/asset-buyer/src/utils/forwarder_helper_impl_config_utils.ts b/packages/asset-buyer/src/utils/forwarder_helper_impl_config_utils.ts
new file mode 100644
index 000000000..253384f65
--- /dev/null
+++ b/packages/asset-buyer/src/utils/forwarder_helper_impl_config_utils.ts
@@ -0,0 +1,92 @@
+import { sortingUtils } from '@0xproject/order-utils';
+import { SignedOrder } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+import * as _ from 'lodash';
+
+import { ForwarderHelperImplConfig } from '../forwarder_helper_impl';
+
+interface SignedOrderWithAmount extends SignedOrder {
+    remainingFillAmount: BigNumber;
+}
+
+export const forwarderHelperImplConfigUtils = {
+    sortedConfig(config: ForwarderHelperImplConfig): ForwarderHelperImplConfig {
+        const { orders, feeOrders, remainingFillableMakerAssetAmounts, remainingFillableFeeAmounts } = config;
+        // TODO: provide a feeRate to the sorting function to more accurately sort based on the current market for ZRX tokens
+        const orderSorter = (ordersToSort: SignedOrder[]) => {
+            return sortingUtils.sortOrdersByFeeAdjustedRate(ordersToSort);
+        };
+        const sortOrdersResult = sortOrdersAndRemainingFillAmounts(
+            orderSorter,
+            orders,
+            remainingFillableMakerAssetAmounts,
+        );
+        const feeOrderSorter = (ordersToSort: SignedOrder[]) => {
+            return sortingUtils.sortFeeOrdersByFeeAdjustedRate(ordersToSort);
+        };
+        const sortFeeOrdersResult = sortOrdersAndRemainingFillAmounts(
+            feeOrderSorter,
+            feeOrders,
+            remainingFillableFeeAmounts,
+        );
+        return {
+            orders: sortOrdersResult.orders,
+            feeOrders: sortFeeOrdersResult.orders,
+            remainingFillableMakerAssetAmounts: sortOrdersResult.remainingFillAmounts,
+            remainingFillableFeeAmounts: sortFeeOrdersResult.remainingFillAmounts,
+        };
+    },
+};
+
+type OrderSorter = (orders: SignedOrder[]) => SignedOrder[];
+
+function sortOrdersAndRemainingFillAmounts(
+    orderSorter: OrderSorter,
+    orders: SignedOrder[],
+    remainingFillAmounts?: BigNumber[],
+): { orders: SignedOrder[]; remainingFillAmounts?: BigNumber[] } {
+    if (!_.isUndefined(remainingFillAmounts)) {
+        // Bundle orders together with their remainingFillAmounts so that we can sort them together
+        const orderWithAmounts = bundleSignedOrderWithAmounts(orders, remainingFillAmounts);
+        // Sort
+        const sortedOrderWithAmounts = orderSorter(orderWithAmounts) as SignedOrderWithAmount[];
+        // Unbundle after sorting
+        const unbundledSortedOrderWithAmounts = unbundleSignedOrderWithAmounts(sortedOrderWithAmounts);
+        return {
+            orders: unbundledSortedOrderWithAmounts.orders,
+            remainingFillAmounts: unbundledSortedOrderWithAmounts.amounts,
+        };
+    } else {
+        const sortedOrders = orderSorter(orders);
+        return {
+            orders: sortedOrders,
+        };
+    }
+}
+
+function bundleSignedOrderWithAmounts(orders: SignedOrder[], amounts: BigNumber[]): SignedOrderWithAmount[] {
+    const ordersAndAmounts = _.map(orders, (order, index) => {
+        return {
+            ...order,
+            remainingFillAmount: amounts[index],
+        };
+    });
+    return ordersAndAmounts;
+}
+
+function unbundleSignedOrderWithAmounts(
+    signedOrderWithAmounts: SignedOrderWithAmount[],
+): { orders: SignedOrder[]; amounts: BigNumber[] } {
+    const orders = _.map(signedOrderWithAmounts, order => {
+        const { remainingFillAmount, ...rest } = order;
+        return rest;
+    });
+    const amounts = _.map(signedOrderWithAmounts, order => {
+        const { remainingFillAmount } = order;
+        return remainingFillAmount;
+    });
+    return {
+        orders,
+        amounts,
+    };
+}
diff --git a/packages/asset-buyer/src/utils/order_utils.ts b/packages/asset-buyer/src/utils/order_utils.ts
new file mode 100644
index 000000000..bb0bdb80f
--- /dev/null
+++ b/packages/asset-buyer/src/utils/order_utils.ts
@@ -0,0 +1,21 @@
+import { SignedOrder } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+
+import { constants } from '../constants';
+
+export const orderUtils = {
+    isOrderExpired(order: SignedOrder): boolean {
+        const millisecondsInSecond = 1000;
+        const currentUnixTimestampSec = new BigNumber(Date.now() / millisecondsInSecond).round();
+        return order.expirationTimeSeconds.lessThan(currentUnixTimestampSec);
+    },
+    calculateRemainingMakerAssetAmount(order: SignedOrder, remainingTakerAssetAmount: BigNumber): BigNumber {
+        const result = remainingTakerAssetAmount.eq(0)
+            ? constants.ZERO_AMOUNT
+            : remainingTakerAssetAmount.times(order.makerAssetAmount).dividedToIntegerBy(order.takerAssetAmount);
+        return result;
+    },
+    isOpenOrder(order: SignedOrder): boolean {
+        return order.takerAddress === constants.NULL_ADDRESS;
+    },
+};