send_erc20.js

const fs = require('fs')
const path = require('path')
const httpStatus = require('http-status')
const EthereumTx = require('ethereumjs-tx')
const etherwallet = require('ethereumjs-wallet')
const { web3, engine } = require('../../config/web3provider')

const getERC20Balance = async (address_without_0x, contractAddress) => {
  return new Promise(async (resolve, reject) => {
    // '0x70a08231' is the contract 'balanceOf()' ERC20 token function in hex. A zero buffer is required and then we add the previously defined address with tokens
    let contractData = ('0x70a08231000000000000000000000000' + address_without_0x)
    // Now we call the token contract with the variables from above, response will be a big number string
    web3.eth.call({
      to: contractAddress, // Contract address, used call the token balance of the address in question
      data: contractData // Combination of contractData and tknAddress, required to call the balance of an address 
    }, (err, result) => {
      if (result) {
        // Convert the result to a usable number string
        var tokens = web3.toBigNumber(result).toString()
        resolve(web3.fromWei(tokens, 'ether'))
      } else {
        reject(err)
      }
    })
  })
}

module.exports = async (req, res) => {

  let contract_address = '0x0000000000085d4780B73119b644AE5ecd22b376' // TUSD
  let send_to_address_with_0x = '0xFaF30e58A5ba4454E4a323Fe897A2d66E4CBe176'
  let token_amount = 0.1
  let private_key_buffer = ''
  let network_id = 1 // 1 = mainnet, 3 = ropsten

  // sender wallet
  let wallet = etherwallet.fromPrivateKey(Buffer.from(private_key_buffer, 'hex'))

  // sender address
  let address = wallet.getAddress().toString('hex')
  console.log('Address', address)

  // console.log(web3)
  let contractAddress = contract_address

  // contract ABI
  let contractABI = JSON.parse(fs.readFileSync(path.join(__dirname, '../../../../shared/ethereum/abi/StandardERC20.json'), 'utf8'))
  
  // create contract instance
  let contract = new web3.eth.contract(contractABI).at(contractAddress)
  
  // sender balance
  let senderBalance = await getERC20Balance(address, contractAddress)

  // get balance of sender and send rest of balance
  // var weiAmount
  // if (send_all === 'all') {
  //   weiAmount = senderBalance
  // } else {
  // }
  let weiAmount = parseInt(web3.toWei(token_amount, 'ether'))

  // validate address 
  let isAddress = web3.isAddress(send_to_address_with_0x)
  if (!isAddress) {
    return res.status(httpStatus.BAD_REQUEST).json({
      msg: 'Invalid address'
    })
  }

  // validate amount
  if (weiAmount < 0 ) {
    return res.status(httpStatus.BAD_REQUEST).json({
      msg: 'Not enough balance'
    })
  }

  web3.eth.getTransactionCount(`0x${address}`, (err, nonce) => {

    const gasLimit = 861947
    let gasPrice

    if (network_id === 1) {
      gasPrice = 6000000000 // 6 GWei
    } else if (network_id === 3) {
      gasPrice = 410000000000 // 41 GWei
    } else {
      gasPrice = 21000000000 // 2 GWei by defualt
    }

    const txParams = {
      nonce: web3.toHex( nonce ),
      gasPrice: web3.toHex( gasPrice ), // fixed rate  0.00001 ETH
      gasLimit: web3.toHex( gasLimit ), // converts the gwei price to wei
      "to": contractAddress,
      "value": "0x00",
      "data": contract.transfer.getData(send_to_address_with_0x, weiAmount, {from: `0x${address}`}),
      // EIP 155 chainId - mainnet: 1, ropsten: 3
      chainId: network_id
    }
    
    const tx = new EthereumTx(txParams)
    tx.sign(Buffer.from(private_key_buffer, 'hex'))
    const serializedTx = tx.serialize()

    /**
     * We're ready! Submit the raw transaction details to the provider configured above.
     */
    web3.eth.sendRawTransaction('0x' + serializedTx.toString('hex'), (err, hash) => {
      if (err) console.log('sendRawTransaction error:', err)
      if (hash) {
        return res.status(httpStatus.OK).json({
          hash
        })
      }
    })
  })

}