const Web3 = require('web3')
const Tx = require('ethereumjs-tx').Transaction

// connect to Infura node
const web3 = new Web3(new Web3.providers.HttpProvider('https://mainnet.infura.io/INFURA_KEY'))

// the address that will send the test transaction
const addressFrom = '0x1889EF49cDBaad420EB4D6f04066CA4093088Bbd'
const privateKey = new Buffer('PRIVATE_KEY', 'hex')

// the destination address
const addressTo = '0x1463500476a3ADDa33ef1dF530063fE126203186'

// construct the transaction data
// NOTE: property 'nonce' must be merged in from web3.eth.getTransactionCount 
// before the transaction data is passed to new Tx(); see sendRawTransaction below.
const txData = {
  gasLimit: web3.utils.toHex(25000),
  gasPrice: web3.utils.toHex(10e9), // 10 Gwei
  to: addressTo,
  from: addressFrom,
  value: web3.utils.toHex(web3.utils.toWei('123', 'wei')) // thanks @abel30567
  // if you want to send raw data (e.g. contract execution) rather than sending tokens,
  // use 'data' instead of 'value' (thanks @AlecZadikian9001)
  // e.g. myContract.methods.myMethod(123).encodeABI() (thanks @NguyenHoangSon96)
}

/** Signs the given transaction data and sends it. Abstracts some of the details of 
  * buffering and serializing the transaction for web3.
  * @returns A promise of an object that emits events: transactionHash, receipt, confirmaton, error
*/
const sendRawTransaction = txData =>
  // get the number of transactions sent so far so we can create a fresh nonce
  web3.eth.getTransactionCount(addressFrom).then(txCount => {
    const newNonce = web3.utils.toHex(txCount)
    const transaction = new Tx({ ...txData, nonce: newNonce }, { chain: 'mainnet' }) // or 'rinkeby'
    transaction.sign(privateKey)
    const serializedTx = transaction.serialize().toString('hex')
    return web3.eth.sendSignedTransaction('0x' + serializedTx)
  })


// fire away!
// (thanks @AndreiD)
sendRawTransaction(txData).then(result =>
  result
    .on('transactionHash', txHash => {
      console.log('transactionHash:', txHash)
    })
    .on('receipt', receipt => {
      console.log('receipt:', receipt)
    })
    .on('confirmation', (confirmationNumber, receipt) => {
      if (confirmationNumber >= 1) {
        console.log('confirmations:', confirmationNumber, receipt)
      }
    })
    .on('error:', error => {
      console.error(error)
    })
)