Web3 Swift ERC20 helper

Web3SwiftERC20.swift

import Web3

struct ERC20 {

    let address: EthereumAddress

    let reading: Reading
    let writing: Writing

    init(contractAddress: EthereumAddress) {
        self.address = contractAddress
        self.reading = Reading(contractAddress: contractAddress)
        self.writing = Writing(contractAddress: contractAddress)
    }

    struct Reading {

        let address: EthereumAddress

        init(contractAddress: EthereumAddress) {
            self.address = contractAddress
        }

        func name() -> EthereumCall {
            let data = EthereumData(bytes: [0x06, 0xfd, 0xde, 0x03])
            return EthereumCall(to: address, data: data)
        }

        func symbol() -> EthereumCall {
            let data = EthereumData(bytes: [0x95, 0xd8, 0x9b, 0x41])
            return EthereumCall(to: address, data: data)
        }

        func decimals() -> EthereumCall {
            let data = EthereumData(bytes: [0x31, 0x3c, 0xe5, 0x67])
            return EthereumCall(to: address, data: data)
        }

        func totalSupply() -> EthereumCall {
            let data = EthereumData(bytes: [0x18, 0x16, 0x0d, 0xdd])
            return EthereumCall(to: address, data: data)
        }

        func balanceOf(owner: EthereumAddress) -> EthereumCall {
            var bytes: [UInt8] = [0x70, 0xa0, 0x82, 0x31]
            bytes.append(contentsOf: owner.rawAddress.leftPad(with: 0, multipleOf: 32))
            let data = EthereumData(bytes: bytes)
            return EthereumCall(to: address, data: data)
        }

        func allowance(owner: EthereumAddress, spender: EthereumAddress) -> EthereumCall {
            var bytes: [UInt8] = [0xdd, 0x62, 0xed, 0x3e]
            bytes.append(contentsOf: owner.rawAddress.leftPad(with: 0, multipleOf: 32))
            bytes.append(contentsOf: spender.rawAddress.leftPad(with: 0, multipleOf: 32))
            let data = EthereumData(bytes: bytes)
            return EthereumCall(to: self.address, data: data)
        }
    }

    struct Writing {

        let address: EthereumAddress

        init(contractAddress: EthereumAddress) {
            self.address = contractAddress
        }

        func transfer(
            nonce: EthereumQuantity,
            gasPrice: EthereumQuantity,
            gasLimit: EthereumQuantity,
            to: EthereumAddress,
            value: EthereumQuantity,
            chainId: EthereumQuantity
        ) -> EthereumTransaction {
            var bytes: [UInt8] = [0xa9, 0x05, 0x9c, 0xbb]
            bytes.append(contentsOf: to.rawAddress.leftPad(with: 0, multipleOf: 32))
            bytes.append(contentsOf: value.quantity.makeBytes().leftPad(with: 0, to: 32))
            let data = EthereumData(bytes: bytes)

            let tx = EthereumTransaction(nonce: nonce, gasPrice: gasPrice, gasLimit: gasLimit, to: address, value: 0, data: data, chainId: chainId)

            return tx
        }

        func transferFrom(
            nonce: EthereumQuantity,
            gasPrice: EthereumQuantity,
            gasLimit: EthereumQuantity,
            from: EthereumAddress,
            to: EthereumAddress,
            value: EthereumQuantity,
            chainId: EthereumQuantity
        ) -> EthereumTransaction {
            var bytes: [UInt8] = [0x23, 0xb8, 0x72, 0xdd]
            bytes.append(contentsOf: from.rawAddress.leftPad(with: 0, multipleOf: 32))
            bytes.append(contentsOf: to.rawAddress.leftPad(with: 0, multipleOf: 32))
            bytes.append(contentsOf: value.quantity.makeBytes().leftPad(with: 0, to: 32))
            let data = EthereumData(bytes: bytes)

            let tx = EthereumTransaction(nonce: nonce, gasPrice: gasPrice, gasLimit: gasLimit, to: address, value: 0, data: data, chainId: chainId)

            return tx
        }

        func approve(
            nonce: EthereumQuantity,
            gasPrice: EthereumQuantity,
            gasLimit: EthereumQuantity,
            spender: EthereumAddress,
            value: EthereumQuantity,
            chainId: EthereumQuantity
        ) -> EthereumTransaction {
            var bytes: [UInt8] = [0x09, 0x5e, 0xa7, 0xb3]
            bytes.append(contentsOf: spender.rawAddress.leftPad(with: 0, multipleOf: 32))
            bytes.append(contentsOf: value.quantity.makeBytes().leftPad(with: 0, to: 32))
            let data = EthereumData(bytes: bytes)

            let tx = EthereumTransaction(nonce: nonce, gasPrice: gasPrice, gasLimit: gasLimit, to: address, value: 0, data: data, chainId: chainId)

            return tx
        }
    }
}

fileprivate extension Array where Element == UInt8 {

    func leftPad(with: UInt8, multipleOf: Int) -> [UInt8] {
        let paddingSize = multipleOf - (count % multipleOf)
        let padding = [UInt8].init(repeating: with, count: paddingSize)

        var newArray = self
        newArray.insert(contentsOf: padding, at: 0)

        return newArray
    }

    func leftPad(with: UInt8, to: Int) -> [UInt8] {
        if count >= to {
            return self
        }
        let paddingSize = to - count
        let padding = [UInt8].init(repeating: with, count: paddingSize)

        var newArray = self
        newArray.insert(contentsOf: padding, at: 0)

        return newArray
    }
}