1 files changed, 88 insertions, 0 deletions
diff --git a/packages/0x.js/src/utils/exchange_transfer_simulator.ts b/packages/0x.js/src/utils/exchange_transfer_simulator.ts
new file mode 100644
index 000000000..308ef06db
--- /dev/null
+++ b/packages/0x.js/src/utils/exchange_transfer_simulator.ts
@@ -0,0 +1,88 @@
+import * as _ from 'lodash';
+import BigNumber from 'bignumber.js';
+import {ExchangeContractErrs, TradeSide, TransferType, BlockParamLiteral} from '../types';
+import {TokenWrapper} from '../contract_wrappers/token_wrapper';
+import {BalanceAndProxyAllowanceLazyStore} from '../stores/balance_proxy_allowance_lazy_store';
+
+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: BalanceAndProxyAllowanceLazyStore;
+    private UNLIMITED_ALLOWANCE_IN_BASE_UNITS: BigNumber;
+    constructor(token: TokenWrapper) {
+        this.store = new BalanceAndProxyAllowanceLazyStore(token);
+        this.UNLIMITED_ALLOWANCE_IN_BASE_UNITS = token.UNLIMITED_ALLOWANCE_IN_BASE_UNITS;
+    }
+    /**
+     * 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> {
+        const balance = await this.store.getBalanceAsync(tokenAddress, from);
+        const proxyAllowance = await this.store.getProxyAllowanceAsync(tokenAddress, from);
+        if (proxyAllowance.lessThan(amountInBaseUnits)) {
+            this.throwValidationError(FailureReason.ProxyAllowance, tradeSide, transferType);
+        }
+        if (balance.lessThan(amountInBaseUnits)) {
+            this.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(this.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));
+    }
+    private throwValidationError(failureReason: FailureReason, tradeSide: TradeSide,
+                                 transferType: TransferType): Promise<never> {
+        const errMsg = ERR_MSG_MAPPING[failureReason][tradeSide][transferType];
+        throw new Error(errMsg);
+    }
+}