1 files changed, 42 insertions, 0 deletions
diff --git a/src/contract_wrappers/token_wrapper.ts b/src/contract_wrappers/token_wrapper.ts
new file mode 100644
index 000000000..bd815554a
--- /dev/null
+++ b/src/contract_wrappers/token_wrapper.ts
@@ -0,0 +1,42 @@
+import * as _ from 'lodash';
+import * as BigNumber from 'bignumber.js';
+import {Web3Wrapper} from '../web3_wrapper';
+import {assert} from '../utils/assert';
+import {ContractWrapper} from './contract_wrapper';
+import * as TokenArtifacts from '../artifacts/Token.json';
+import {ERC20Contract} from '../types';
+
+export class TokenWrapper extends ContractWrapper {
+    private tokenContractsByAddress: {[address: string]: ERC20Contract};
+    constructor(web3Wrapper: Web3Wrapper) {
+        super(web3Wrapper);
+        this.tokenContractsByAddress = {};
+    }
+    public invalidateContractInstances() {
+        this.tokenContractsByAddress = {};
+    }
+    /**
+     * Returns an owner's ERC20 token balance
+     */
+    public async getBalanceAsync(tokenAddress: string, ownerAddress: string): Promise<BigNumber.BigNumber> {
+        assert.isETHAddressHex('ownerAddress', ownerAddress);
+        assert.isETHAddressHex('tokenAddress', tokenAddress);
+
+        const tokenContract = await this.getTokenContractAsync(tokenAddress);
+        let balance = await tokenContract.balanceOf.call(ownerAddress);
+        // The BigNumber instance returned by Web3 is of a much older version then our own, we therefore
+        // should always re-instantiate the returned BigNumber after retrieval.
+        balance = _.isUndefined(balance) ? new BigNumber(0) : new BigNumber(balance);
+        return balance;
+    }
+    private async getTokenContractAsync(tokenAddress: string): Promise<ERC20Contract> {
+        let tokenContract = this.tokenContractsByAddress[tokenAddress];
+        if (!_.isUndefined(tokenContract)) {
+            return tokenContract;
+        }
+        const contractInstance = await this.instantiateContractIfExistsAsync((TokenArtifacts as any), tokenAddress);
+        tokenContract = contractInstance as ERC20Contract;
+        this.tokenContractsByAddress[tokenAddress] = tokenContract;
+        return tokenContract;
+    }
+}