Allow users to specify the contracts backend in abi-gen

18 files changed, 169 insertions, 70 deletions

diff --git a/packages/0x.js/contract_templates/contract.handlebars b/packages/0x.js/contract_templates/contract.handlebars
index 33699b8a7..2954145a7 100644
--- a/packages/0x.js/contract_templates/contract.handlebars
+++ b/packages/0x.js/contract_templates/contract.handlebars
@@ -6,6 +6,9 @@
 // tslint:disable-next-line:no-unused-variable
 import { TxData, TxDataPayable } from '@0xproject/types';
 import { BigNumber, classUtils, promisify } from '@0xproject/utils';
+import { Web3Wrapper } from '@0xproject/web3-wrapper';
+import * as ethersContracts from 'ethers-contracts';
+import * as _ from 'lodash';
 import * as Web3 from 'web3';
 
 import {BaseContract} from './base_contract';
@@ -28,6 +31,7 @@ export enum {{contractName}}Events {
 {{/each}}
 {{/if}}
 
+// tslint:disable:no-parameter-reassignment
 export class {{contractName}}Contract extends BaseContract {
 {{#each methods}}
     {{#this.constant}}
@@ -37,8 +41,8 @@ export class {{contractName}}Contract extends BaseContract {
     {{> tx contractName=../contractName}}
     {{/this.constant}}
 {{/each}}
-    constructor(web3ContractInstance: Web3.ContractInstance, defaults: Partial<TxData>) {
-        super(web3ContractInstance, defaults);
-        classUtils.bindAll(this, ['_web3ContractInstance', '_defaults']);
+    constructor(web3Wrapper: Web3Wrapper, abi: Web3.ContractAbi, address: string) {
+        super(web3Wrapper, abi, address);
+        classUtils.bindAll(this, ['_ethersInterface', '_address', '_abi', '_web3Wrapper']);
     }
 } // tslint:disable:max-file-line-count
diff --git a/packages/0x.js/contract_templates/partials/call.handlebars b/packages/0x.js/contract_templates/partials/call.handlebars
index 0475136f0..c533712b7 100644
--- a/packages/0x.js/contract_templates/partials/call.handlebars
+++ b/packages/0x.js/contract_templates/partials/call.handlebars
@@ -4,12 +4,20 @@ public {{this.name}} = {
         defaultBlock?: Web3.BlockParam,
     ): Promise<{{> return_type outputs=outputs}}> {
         const self = this as {{contractName}}Contract;
-        const result = await promisify<{{> return_type outputs=outputs}}>(
-            self._web3ContractInstance.{{this.name}}.call,
-            self._web3ContractInstance,
-        )(
+        const inputAbi = _.find(this._abi, {name: '{{this.name}}'}).inputs;
+        [{{> params inputs=inputs}}] = BaseContract._transformABIData(inputAbi, [{{> params inputs=inputs}}], BaseContract._bigNumberToString.bind(this));
+        const callDescription = self._ethersInterface.functions.{{this.name}}(
             {{> params inputs=inputs}}
-        );
-        return result;
+        ) as ethersContracts.CallDescription;
+        const callData = await self._applyDefaultsToTxDataAsync(
+            {
+                data: callDescription.data,
+            }
+        )
+        const rawCallResult = await self._web3Wrapper.callAsync(callData);
+        let resultArray = callDescription.parse(rawCallResult);
+        const outputAbi = _.find(this._abi, {name: '{{this.name}}'}).outputs;
+        resultArray = BaseContract._transformABIData(outputAbi, resultArray, BaseContract._lowercaseAddress.bind(this));
+        return resultArray{{#singleReturnValue}}[0]{{/singleReturnValue}};
     },
 };
diff --git a/packages/0x.js/contract_templates/partials/tx.handlebars b/packages/0x.js/contract_templates/partials/tx.handlebars
index 9df83266a..aae9aa404 100644
--- a/packages/0x.js/contract_templates/partials/tx.handlebars
+++ b/packages/0x.js/contract_templates/partials/tx.handlebars
@@ -9,19 +9,22 @@ public {{this.name}} = {
     {{/this.payable}}
     ): Promise<string> {
         const self = this as {{contractName}}Contract;
+        const inputAbi = _.find(this._abi, {name: '{{this.name}}'}).inputs;
+        [{{> params inputs=inputs}}] = BaseContract._transformABIData(inputAbi, [{{> params inputs=inputs}}], BaseContract._bigNumberToString.bind(this));
+        const data = this._ethersInterface.functions.{{this.name}}(
+            {{> params inputs=inputs}}
+        ).data
         const txDataWithDefaults = await self._applyDefaultsToTxDataAsync(
-            txData,
+            {
+                ...txData,
+                data,
+            },
             self.{{this.name}}.estimateGasAsync.bind(
                 self,
                 {{> params inputs=inputs}}
             ),
         );
-        const txHash = await promisify<string>(
-            self._web3ContractInstance.{{this.name}}, self._web3ContractInstance,
-        )(
-            {{> params inputs=inputs}}
-            txDataWithDefaults,
-        );
+        const txHash = await this._web3Wrapper.sendTransactionAsync(txDataWithDefaults);
         return txHash;
     },
     async estimateGasAsync(
@@ -29,15 +32,16 @@ public {{this.name}} = {
         txData: TxData = {},
     ): Promise<number> {
         const self = this as {{contractName}}Contract;
-        const txDataWithDefaults = await self._applyDefaultsToTxDataAsync(
-            txData,
-        );
-        const gas = await promisify<number>(
-            self._web3ContractInstance.{{this.name}}.estimateGas, self._web3ContractInstance,
-        )(
+        const data = this._ethersInterface.functions.{{this.name}}(
             {{> params inputs=inputs}}
-            txDataWithDefaults,
+        ).data
+        const txDataWithDefaults = await self._applyDefaultsToTxDataAsync(
+            {
+                ...txData,
+                data,
+            }
         );
+        const gas = await this._web3Wrapper.estimateGasAsync(txDataWithDefaults);
         return gas;
     },
     getABIEncodedTransactionData(
@@ -45,7 +49,9 @@ public {{this.name}} = {
         txData: TxData = {},
     ): string {
         const self = this as {{contractName}}Contract;
-        const abiEncodedTransactionData = self._web3ContractInstance.{{this.name}}.getData();
+        const abiEncodedTransactionData = this._ethersInterface.functions.{{this.name}}(
+            {{> params inputs=inputs}}
+        ).data
         return abiEncodedTransactionData;
     },
 };
diff --git a/packages/0x.js/package.json b/packages/0x.js/package.json
index 4fb0eb6ac..6a0a84cfc 100644
--- a/packages/0x.js/package.json
+++ b/packages/0x.js/package.json
@@ -17,7 +17,7 @@
         "build": "run-p build:umd:prod build:commonjs; exit 0;",
         "docs:json": "typedoc --excludePrivate --excludeExternals --target ES5 --json $JSON_FILE_PATH $PROJECT_DIR",
         "upload_docs_json": "aws s3 cp generated_docs/index.json $S3_URL --profile 0xproject --grants read=uri=http://acs.amazonaws.com/groups/global/AllUsers --content-type application/json",
-        "generate_contract_wrappers": "node ../abi-gen/lib/index.js --abis 'src/artifacts/@(Exchange|Token|TokenTransferProxy|EtherToken|TokenRegistry|DummyToken).json' --template contract_templates/contract.handlebars --partials 'contract_templates/partials/**/*.handlebars' --output src/contract_wrappers/generated",
+        "generate_contract_wrappers": "node ../abi-gen/lib/index.js --abis 'src/artifacts/@(Exchange|Token|TokenTransferProxy|EtherToken|TokenRegistry|DummyToken).json' --template contract_templates/contract.handlebars --partials 'contract_templates/partials/**/*.handlebars' --output src/contract_wrappers/generated && prettier --write 'src/contract_wrappers/generated/**.ts'",
         "lint": "tslint --project . 'src/**/*.ts' 'test/**/*.ts'",
         "test:circleci": "run-s test:coverage report_test_coverage",
         "test": "run-s clean test:commonjs",
@@ -91,6 +91,7 @@
         "ethereumjs-abi": "^0.6.4",
         "ethereumjs-blockstream": "^2.0.6",
         "ethereumjs-util": "^5.1.1",
+        "ethers-contracts": "^2.2.1",
         "js-sha3": "^0.7.0",
         "lodash": "^4.17.4",
         "uuid": "^3.1.0",
diff --git a/packages/0x.js/src/contract_wrappers/contract_wrapper.ts b/packages/0x.js/src/contract_wrappers/contract_wrapper.ts
index b313273b5..ad7727de5 100644
--- a/packages/0x.js/src/contract_wrappers/contract_wrapper.ts
+++ b/packages/0x.js/src/contract_wrappers/contract_wrapper.ts
@@ -108,10 +108,10 @@ export class ContractWrapper {
         const logWithDecodedArgs = this._abiDecoder.tryToDecodeLogOrNoop(log);
         return logWithDecodedArgs;
     }
-    protected async _instantiateContractIfExistsAsync(
+    protected async _getContractAbiAndAddressFromArtifactsAsync(
         artifact: Artifact,
         addressIfExists?: string,
-    ): Promise<Web3.ContractInstance> {
+    ): Promise<[Web3.ContractAbi, string]> {
         let contractAddress: string;
         if (_.isUndefined(addressIfExists)) {
             if (_.isUndefined(artifact.networks[this._networkId])) {
@@ -125,8 +125,8 @@ export class ContractWrapper {
         if (!doesContractExist) {
             throw new Error(CONTRACT_NAME_TO_NOT_FOUND_ERROR[artifact.contract_name]);
         }
-        const contractInstance = this._web3Wrapper.getContractInstance(artifact.abi, contractAddress);
-        return contractInstance;
+        const abiAndAddress: [Web3.ContractAbi, string] = [artifact.abi, contractAddress];
+        return abiAndAddress;
     }
     protected _getContractAddress(artifact: Artifact, addressIfExists?: string): string {
         if (_.isUndefined(addressIfExists)) {
diff --git a/packages/0x.js/src/contract_wrappers/ether_token_wrapper.ts b/packages/0x.js/src/contract_wrappers/ether_token_wrapper.ts
index 4807eff33..42f8213a2 100644
--- a/packages/0x.js/src/contract_wrappers/ether_token_wrapper.ts
+++ b/packages/0x.js/src/contract_wrappers/ether_token_wrapper.ts
@@ -187,11 +187,11 @@ export class EtherTokenWrapper extends ContractWrapper {
         if (!_.isUndefined(etherTokenContract)) {
             return etherTokenContract;
         }
-        const web3ContractInstance = await this._instantiateContractIfExistsAsync(
+        const [abi, address] = await this._getContractAbiAndAddressFromArtifactsAsync(
             artifacts.EtherTokenArtifact,
             etherTokenAddress,
         );
-        const contractInstance = new EtherTokenContract(web3ContractInstance, this._web3Wrapper.getContractDefaults());
+        const contractInstance = new EtherTokenContract(this._web3Wrapper, abi, address);
         etherTokenContract = contractInstance;
         this._etherTokenContractsByAddress[etherTokenAddress] = etherTokenContract;
         return etherTokenContract;
diff --git a/packages/0x.js/src/contract_wrappers/exchange_wrapper.ts b/packages/0x.js/src/contract_wrappers/exchange_wrapper.ts
index 6bafc84c1..e0f6bd539 100644
--- a/packages/0x.js/src/contract_wrappers/exchange_wrapper.ts
+++ b/packages/0x.js/src/contract_wrappers/exchange_wrapper.ts
@@ -858,7 +858,7 @@ export class ExchangeWrapper extends ContractWrapper {
         });
         if (!_.isUndefined(errLog)) {
             const logArgs = (errLog as LogWithDecodedArgs<LogErrorContractEventArgs>).args;
-            const errCode = logArgs.errorId.toNumber();
+            const errCode = logArgs.errorId;
             const errMessage = this._exchangeContractErrCodesToMsg[errCode];
             throw new Error(errMessage);
         }
@@ -906,11 +906,11 @@ export class ExchangeWrapper extends ContractWrapper {
         if (!_.isUndefined(this._exchangeContractIfExists)) {
             return this._exchangeContractIfExists;
         }
-        const web3ContractInstance = await this._instantiateContractIfExistsAsync(
+        const [abi, address] = await this._getContractAbiAndAddressFromArtifactsAsync(
             artifacts.ExchangeArtifact,
             this._contractAddressIfExists,
         );
-        const contractInstance = new ExchangeContract(web3ContractInstance, this._web3Wrapper.getContractDefaults());
+        const contractInstance = new ExchangeContract(this._web3Wrapper, abi, address);
         this._exchangeContractIfExists = contractInstance;
         return this._exchangeContractIfExists;
     }
diff --git a/packages/0x.js/src/contract_wrappers/generated/base_contract.ts b/packages/0x.js/src/contract_wrappers/generated/base_contract.ts
index d8fac7eea..a62c785bc 100644
--- a/packages/0x.js/src/contract_wrappers/generated/base_contract.ts
+++ b/packages/0x.js/src/contract_wrappers/generated/base_contract.ts
@@ -1,11 +1,45 @@
-import {TxData, TxDataPayable} from '@0xproject/types';
+import { TxData, TxDataPayable } from '@0xproject/types';
+import { Web3Wrapper } from '@0xproject/web3-wrapper';
+import * as ethersContracts from 'ethers-contracts';
 import * as _ from 'lodash';
 import * as Web3 from 'web3';
 
 export class BaseContract {
-    protected _web3ContractInstance: Web3.ContractInstance;
-    protected _defaults: Partial<TxData>;
-    protected async _applyDefaultsToTxDataAsync<T extends TxData|TxDataPayable>(
+    protected _ethersInterface: ethersContracts.Interface;
+    protected _web3Wrapper: Web3Wrapper;
+    protected _abi: Web3.ContractAbi;
+    protected _address: string;
+    protected static _transformABIData(
+        abis: Web3.DataItem[],
+        values: any[],
+        transformation: (type: string, value: any) => any,
+    ): any {
+        return _.map(values, (value: any, i: number) =>
+            BaseContract._transformTypedData(abis[i].type, value, transformation),
+        );
+    }
+    protected static _lowercaseAddress(type: string, value: string): string {
+        return type === 'address' ? value.toLowerCase() : value;
+    }
+    protected static _bigNumberToString(type: string, value: string): string {
+        return _.isObject(value) && (value as any).isBigNumber ? value.toString() : value;
+    }
+    private static _transformTypedData(
+        type: string,
+        values: any,
+        transformation: (type: string, value: any) => any,
+    ): any {
+        const trailingArrayRegex = /\[\d*\]$/;
+        if (type.match(trailingArrayRegex)) {
+            const arrayItemType = type.replace(trailingArrayRegex, '');
+            return _.map(values, (value: any, i: number) =>
+                this._transformTypedData(arrayItemType, value, transformation),
+            );
+        } else {
+            return transformation(type, values);
+        }
+    }
+    protected async _applyDefaultsToTxDataAsync<T extends Partial<TxData | TxDataPayable>>(
         txData: T,
         estimateGasAsync?: (txData: T) => Promise<number>,
     ): Promise<TxData> {
@@ -15,7 +49,8 @@ export class BaseContract {
         // 3. Gas estimate calculation + safety margin
         const removeUndefinedProperties = _.pickBy;
         const txDataWithDefaults = {
-            ...removeUndefinedProperties(this._defaults),
+            to: this._address,
+            ...removeUndefinedProperties(this._web3Wrapper.getContractDefaults()),
             ...removeUndefinedProperties(txData as any),
             // HACK: TS can't prove that T is spreadable.
             // Awaiting https://github.com/Microsoft/TypeScript/pull/13288 to be merged
@@ -26,8 +61,10 @@ export class BaseContract {
         }
         return txDataWithDefaults;
     }
-    constructor(web3ContractInstance: Web3.ContractInstance, defaults: Partial<TxData>) {
-        this._web3ContractInstance = web3ContractInstance;
-        this._defaults = defaults;
+    constructor(web3Wrapper: Web3Wrapper, abi: Web3.ContractAbi, address: string) {
+        this._web3Wrapper = web3Wrapper;
+        this._abi = abi;
+        this._address = address;
+        this._ethersInterface = new ethersContracts.Interface(abi);
     }
 }
diff --git a/packages/0x.js/src/contract_wrappers/token_registry_wrapper.ts b/packages/0x.js/src/contract_wrappers/token_registry_wrapper.ts
index f0ae5f33c..e1806c6f2 100644
--- a/packages/0x.js/src/contract_wrappers/token_registry_wrapper.ts
+++ b/packages/0x.js/src/contract_wrappers/token_registry_wrapper.ts
@@ -23,7 +23,7 @@ export class TokenRegistryWrapper extends ContractWrapper {
             address: metadata[0],
             name: metadata[1],
             symbol: metadata[2],
-            decimals: metadata[3].toNumber(),
+            decimals: metadata[3],
         };
         return token;
     }
@@ -50,7 +50,8 @@ export class TokenRegistryWrapper extends ContractWrapper {
     public async getTokenAddressesAsync(): Promise<string[]> {
         const tokenRegistryContract = await this._getTokenRegistryContractAsync();
         const addresses = await tokenRegistryContract.getTokenAddresses.callAsync();
-        return addresses;
+        const lowerCaseAddresses = _.map(addresses, address => address.toLowerCase());
+        return lowerCaseAddresses;
     }
     /**
      * Retrieves a token by address currently listed in the Token Registry smart contract
@@ -116,14 +117,11 @@ export class TokenRegistryWrapper extends ContractWrapper {
         if (!_.isUndefined(this._tokenRegistryContractIfExists)) {
             return this._tokenRegistryContractIfExists;
         }
-        const web3ContractInstance = await this._instantiateContractIfExistsAsync(
+        const [abi, address] = await this._getContractAbiAndAddressFromArtifactsAsync(
             artifacts.TokenRegistryArtifact,
             this._contractAddressIfExists,
         );
-        const contractInstance = new TokenRegistryContract(
-            web3ContractInstance,
-            this._web3Wrapper.getContractDefaults(),
-        );
+        const contractInstance = new TokenRegistryContract(this._web3Wrapper, abi, address);
         this._tokenRegistryContractIfExists = contractInstance;
         return this._tokenRegistryContractIfExists;
     }
diff --git a/packages/0x.js/src/contract_wrappers/token_transfer_proxy_wrapper.ts b/packages/0x.js/src/contract_wrappers/token_transfer_proxy_wrapper.ts
index f0cbf364d..211c7dfb4 100644
--- a/packages/0x.js/src/contract_wrappers/token_transfer_proxy_wrapper.ts
+++ b/packages/0x.js/src/contract_wrappers/token_transfer_proxy_wrapper.ts
@@ -59,14 +59,11 @@ export class TokenTransferProxyWrapper extends ContractWrapper {
         if (!_.isUndefined(this._tokenTransferProxyContractIfExists)) {
             return this._tokenTransferProxyContractIfExists;
         }
-        const web3ContractInstance = await this._instantiateContractIfExistsAsync(
+        const [abi, address] = await this._getContractAbiAndAddressFromArtifactsAsync(
             artifacts.TokenTransferProxyArtifact,
             this._contractAddressIfExists,
         );
-        const contractInstance = new TokenTransferProxyContract(
-            web3ContractInstance,
-            this._web3Wrapper.getContractDefaults(),
-        );
+        const contractInstance = new TokenTransferProxyContract(this._web3Wrapper, abi, address);
         this._tokenTransferProxyContractIfExists = contractInstance;
         return this._tokenTransferProxyContractIfExists;
     }
diff --git a/packages/0x.js/src/contract_wrappers/token_wrapper.ts b/packages/0x.js/src/contract_wrappers/token_wrapper.ts
index 11a7670c0..0ec9ad707 100644
--- a/packages/0x.js/src/contract_wrappers/token_wrapper.ts
+++ b/packages/0x.js/src/contract_wrappers/token_wrapper.ts
@@ -419,11 +419,11 @@ export class TokenWrapper extends ContractWrapper {
         if (!_.isUndefined(tokenContract)) {
             return tokenContract;
         }
-        const web3ContractInstance = await this._instantiateContractIfExistsAsync(
+        const [abi, address] = await this._getContractAbiAndAddressFromArtifactsAsync(
             artifacts.TokenArtifact,
             normalizedTokenAddress,
         );
-        const contractInstance = new TokenContract(web3ContractInstance, this._web3Wrapper.getContractDefaults());
+        const contractInstance = new TokenContract(this._web3Wrapper, abi, address);
         tokenContract = contractInstance;
         this._tokenContractsByAddress[normalizedTokenAddress] = tokenContract;
         return tokenContract;
diff --git a/packages/0x.js/src/globals.d.ts b/packages/0x.js/src/globals.d.ts
index 0e103d057..702f35149 100644
--- a/packages/0x.js/src/globals.d.ts
+++ b/packages/0x.js/src/globals.d.ts
@@ -41,3 +41,31 @@ declare module 'truffle-hdwallet-provider' {
     }
     export = HDWalletProvider;
 }
+
+declare module 'ethers-contracts' {
+    export interface TransactionDescription {
+        name: string;
+        signature: string;
+        sighash: string;
+        data: string;
+    }
+    export interface CallDescription extends TransactionDescription {
+        parse: (...args: any[]) => any;
+    }
+    export interface FunctionDescription {
+        (...params: any[]): TransactionDescription | CallDescription;
+        inputs: { names: string[]; types: string[] };
+        outputs: { names: string[]; types: string[] };
+    }
+    export interface EventDescription {
+        inputs: { names: string[]; types: string[] };
+        signature: string;
+        topic: string;
+    }
+    // tslint:disable-next-line:max-classes-per-file
+    export class Interface {
+        public functions: { [functionName: string]: FunctionDescription };
+        public events: { [eventName: string]: EventDescription };
+        constructor(abi: any);
+    }
+}
diff --git a/packages/0x.js/src/types.ts b/packages/0x.js/src/types.ts
index 0a3037258..2f17e30c2 100644
--- a/packages/0x.js/src/types.ts
+++ b/packages/0x.js/src/types.ts
@@ -127,7 +127,7 @@ export interface SignedOrder extends Order {
 }
 
 //                          [address, name, symbol, decimals, ipfsHash, swarmHash]
-export type TokenMetadata = [string, string, string, BigNumber, string, string];
+export type TokenMetadata = [string, string, string, number, string, string];
 
 export interface Token {
     name: string;
diff --git a/packages/0x.js/test/utils/fill_scenarios.ts b/packages/0x.js/test/utils/fill_scenarios.ts
index 1a61487f4..8b1308298 100644
--- a/packages/0x.js/test/utils/fill_scenarios.ts
+++ b/packages/0x.js/test/utils/fill_scenarios.ts
@@ -35,12 +35,8 @@ export class FillScenarios {
         const web3Wrapper = (this._zeroEx as any)._web3Wrapper as Web3Wrapper;
         for (const token of this._tokens) {
             if (token.symbol !== 'ZRX' && token.symbol !== 'WETH') {
-                const contractInstance = web3Wrapper.getContractInstance(
-                    artifacts.DummyTokenArtifact.abi,
-                    token.address,
-                );
                 const defaults = {};
-                const dummyToken = new DummyTokenContract(contractInstance, defaults);
+                const dummyToken = new DummyTokenContract(web3Wrapper, artifacts.DummyTokenArtifact.abi, token.address);
                 const tokenSupply = ZeroEx.toBaseUnitAmount(INITIAL_COINBASE_TOKEN_SUPPLY_IN_UNITS, token.decimals);
                 const txHash = await dummyToken.setBalance.sendTransactionAsync(this._coinbase, tokenSupply, {
                     from: this._coinbase,
diff --git a/packages/abi-gen/CHANGELOG.md b/packages/abi-gen/CHANGELOG.md
index c86d6fb55..7e589551e 100644
--- a/packages/abi-gen/CHANGELOG.md
+++ b/packages/abi-gen/CHANGELOG.md
@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## v0.2.3 - _TBD, 2018_
+
+    * Add a `backend` parameter that allows you to specify your backend (web3 or ethers). Ethers auto-converts small ints to numbers (#TBD)
+
 ## v0.2.1 - _February 9, 2018_
 
     * Fix publishing issue where .npmignore was not properly excluding undesired content (#389)
diff --git a/packages/abi-gen/src/index.ts b/packages/abi-gen/src/index.ts
index bc5a974a9..d34d74cdf 100644
--- a/packages/abi-gen/src/index.ts
+++ b/packages/abi-gen/src/index.ts
@@ -11,13 +11,14 @@ import * as yargs from 'yargs';
 import toSnakeCase = require('to-snake-case');
 import * as Web3 from 'web3';
 
-import { ContextData, ParamKind } from './types';
+import { ContextData, ContractsBackend, ParamKind } from './types';
 import { utils } from './utils';
 
 const ABI_TYPE_CONSTRUCTOR = 'constructor';
 const ABI_TYPE_METHOD = 'function';
 const ABI_TYPE_EVENT = 'event';
 const DEFAULT_NETWORK_ID = 50;
+const DEFAULT_BACKEND = 'web3';
 
 const args = yargs
     .option('abis', {
@@ -43,6 +44,12 @@ const args = yargs
         demandOption: true,
         normalize: true,
     })
+    .option('backend', {
+        describe: 'Which backend do you plan to use. Either web3 or ethers',
+        type: 'string',
+        choices: [ContractsBackend.Web3, ContractsBackend.Ethers],
+        default: DEFAULT_BACKEND,
+    })
     .option('network-id', {
         describe: 'ID of the network where contract ABIs are nested in artifacts',
         type: 'number',
@@ -73,8 +80,8 @@ function writeOutputFile(name: string, renderedTsCode: string): void {
     utils.log(`Created: ${chalk.bold(filePath)}`);
 }
 
-Handlebars.registerHelper('parameterType', utils.solTypeToTsType.bind(utils, ParamKind.Input));
-Handlebars.registerHelper('returnType', utils.solTypeToTsType.bind(utils, ParamKind.Output));
+Handlebars.registerHelper('parameterType', utils.solTypeToTsType.bind(utils, ParamKind.Input, args.backend));
+Handlebars.registerHelper('returnType', utils.solTypeToTsType.bind(utils, ParamKind.Output, args.backend));
 
 if (args.partials) {
     registerPartials(args.partials);
diff --git a/packages/abi-gen/src/types.ts b/packages/abi-gen/src/types.ts
index e82ab824b..402e0105e 100644
--- a/packages/abi-gen/src/types.ts
+++ b/packages/abi-gen/src/types.ts
@@ -12,6 +12,11 @@ export enum AbiType {
     Fallback = 'fallback',
 }
 
+export enum ContractsBackend {
+    Web3 = 'web3',
+    Ethers = 'ethers',
+}
+
 export interface Method extends Web3.MethodAbi {
     singleReturnValue: boolean;
 }
diff --git a/packages/abi-gen/src/utils.ts b/packages/abi-gen/src/utils.ts
index 14255643a..dc2c5390e 100644
--- a/packages/abi-gen/src/utils.ts
+++ b/packages/abi-gen/src/utils.ts
@@ -3,14 +3,14 @@ import * as _ from 'lodash';
 import * as path from 'path';
 import * as Web3 from 'web3';
 
-import { AbiType, ParamKind } from './types';
+import { AbiType, ContractsBackend, ParamKind } from './types';
 
 export const utils = {
-    solTypeToTsType(paramKind: ParamKind, solType: string): string {
+    solTypeToTsType(paramKind: ParamKind, backend: ContractsBackend, solType: string): string {
         const trailingArrayRegex = /\[\d*\]$/;
         if (solType.match(trailingArrayRegex)) {
             const arrayItemSolType = solType.replace(trailingArrayRegex, '');
-            const arrayItemTsType = utils.solTypeToTsType(paramKind, arrayItemSolType);
+            const arrayItemTsType = utils.solTypeToTsType(paramKind, backend, arrayItemSolType);
             const arrayTsType = utils.isUnionType(arrayItemTsType)
                 ? `Array<${arrayItemTsType}>`
                 : `${arrayItemTsType}[]`;
@@ -24,13 +24,21 @@ export const utils = {
                 { regex: '^bytes\\d*$', tsType: 'string' },
             ];
             if (paramKind === ParamKind.Input) {
-                // web3 allows to pass those an non-bignumbers and that's nice
-                // but it always returns stuff as BigNumbers
+                // web3 and ethers allow to pass those as numbers instead of bignumbers
                 solTypeRegexToTsType.unshift({
                     regex: '^u?int(8|16|32)?$',
                     tsType: 'number|BigNumber',
                 });
             }
+            if (backend === ContractsBackend.Ethers) {
+                if (paramKind === ParamKind.Output) {
+                    // ethers-contracts automatically converts small BigNumbers to numbers
+                    solTypeRegexToTsType.unshift({
+                        regex: '^u?int(8|16|32|48)?$',
+                        tsType: 'number',
+                    });
+                }
+            }
             for (const regexAndTxType of solTypeRegexToTsType) {
                 const { regex, tsType } = regexAndTxType;
                 if (solType.match(regex)) {