1 files changed, 111 insertions, 0 deletions
diff --git a/packages/contract-wrappers/src/utils/exchange_transfer_simulator.ts b/packages/contract-wrappers/src/utils/exchange_transfer_simulator.ts
new file mode 100644
index 000000000..279f2a796
--- /dev/null
+++ b/packages/contract-wrappers/src/utils/exchange_transfer_simulator.ts
@@ -0,0 +1,111 @@
+import { ExchangeContractErrs } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+
+import { AbstractBalanceAndProxyAllowanceLazyStore } from '../abstract/abstract_balance_and_proxy_allowance_lazy_store';
+import { TradeSide, TransferType } from '../types';
+import { constants } from '../utils/constants';
+
+enum FailureReason {
+    Balance = 'balance',
+    ProxyAllowance = 'proxyAllowance',
+}
+
+const ERR_MSG_MAPPING = {
+    [FailureReason.Balance]: {
+        [TradeSide.Maker]: {
+            [TransferType.Trade]: ExchangeContractErrs.InsufficientMakerBalance,
+            [TransferType.Fee]: ExchangeContractErrs.InsufficientMakerFeeBalance,
+        },
+        [TradeSide.Taker]: {
+            [TransferType.Trade]: ExchangeContractErrs.InsufficientTakerBalance,
+            [TransferType.Fee]: ExchangeContractErrs.InsufficientTakerFeeBalance,
+        },
+    },
+    [FailureReason.ProxyAllowance]: {
+        [TradeSide.Maker]: {
+            [TransferType.Trade]: ExchangeContractErrs.InsufficientMakerAllowance,
+            [TransferType.Fee]: ExchangeContractErrs.InsufficientMakerFeeAllowance,
+        },
+        [TradeSide.Taker]: {
+            [TransferType.Trade]: ExchangeContractErrs.InsufficientTakerAllowance,
+            [TransferType.Fee]: ExchangeContractErrs.InsufficientTakerFeeAllowance,
+        },
+    },
+};
+
+export class ExchangeTransferSimulator {
+    private _store: AbstractBalanceAndProxyAllowanceLazyStore;
+    private static _throwValidationError(
+        failureReason: FailureReason,
+        tradeSide: TradeSide,
+        transferType: TransferType,
+    ): never {
+        const errMsg = ERR_MSG_MAPPING[failureReason][tradeSide][transferType];
+        throw new Error(errMsg);
+    }
+    constructor(store: AbstractBalanceAndProxyAllowanceLazyStore) {
+        this._store = store;
+    }
+    /**
+     * Simulates transferFrom call performed by a proxy
+     * @param  tokenAddress      Address of the token to be transferred
+     * @param  from              Owner of the transferred tokens
+     * @param  to                Recipient of the transferred tokens
+     * @param  amountInBaseUnits The amount of tokens being transferred
+     * @param  tradeSide         Is Maker/Taker transferring
+     * @param  transferType      Is it a fee payment or a value transfer
+     */
+    public async transferFromAsync(
+        tokenAddress: string,
+        from: string,
+        to: string,
+        amountInBaseUnits: BigNumber,
+        tradeSide: TradeSide,
+        transferType: TransferType,
+    ): Promise<void> {
+        // HACK: When simulating an open order (e.g taker is NULL_ADDRESS), we don't want to adjust balances/
+        // allowances for the taker. We do however, want to increase the balance of the maker since the maker
+        // might be relying on those funds to fill subsequent orders or pay the order's fees.
+        if (from === constants.NULL_ADDRESS && tradeSide === TradeSide.Taker) {
+            await this._increaseBalanceAsync(tokenAddress, to, amountInBaseUnits);
+            return;
+        }
+        const balance = await this._store.getBalanceAsync(tokenAddress, from);
+        const proxyAllowance = await this._store.getProxyAllowanceAsync(tokenAddress, from);
+        if (proxyAllowance.lessThan(amountInBaseUnits)) {
+            ExchangeTransferSimulator._throwValidationError(FailureReason.ProxyAllowance, tradeSide, transferType);
+        }
+        if (balance.lessThan(amountInBaseUnits)) {
+            ExchangeTransferSimulator._throwValidationError(FailureReason.Balance, tradeSide, transferType);
+        }
+        await this._decreaseProxyAllowanceAsync(tokenAddress, from, amountInBaseUnits);
+        await this._decreaseBalanceAsync(tokenAddress, from, amountInBaseUnits);
+        await this._increaseBalanceAsync(tokenAddress, to, amountInBaseUnits);
+    }
+    private async _decreaseProxyAllowanceAsync(
+        tokenAddress: string,
+        userAddress: string,
+        amountInBaseUnits: BigNumber,
+    ): Promise<void> {
+        const proxyAllowance = await this._store.getProxyAllowanceAsync(tokenAddress, userAddress);
+        if (!proxyAllowance.eq(constants.UNLIMITED_ALLOWANCE_IN_BASE_UNITS)) {
+            this._store.setProxyAllowance(tokenAddress, userAddress, proxyAllowance.minus(amountInBaseUnits));
+        }
+    }
+    private async _increaseBalanceAsync(
+        tokenAddress: string,
+        userAddress: string,
+        amountInBaseUnits: BigNumber,
+    ): Promise<void> {
+        const balance = await this._store.getBalanceAsync(tokenAddress, userAddress);
+        this._store.setBalance(tokenAddress, userAddress, balance.plus(amountInBaseUnits));
+    }
+    private async _decreaseBalanceAsync(
+        tokenAddress: string,
+        userAddress: string,
+        amountInBaseUnits: BigNumber,
+    ): Promise<void> {
+        const balance = await this._store.getBalanceAsync(tokenAddress, userAddress);
+        this._store.setBalance(tokenAddress, userAddress, balance.minus(amountInBaseUnits));
+    }
+}