const ethUtil = require('ethereumjs-util')
const createHash = require('create-hash')


/**
 * Create a commitment hash with the amount of ENA coins to give to the user at the given dest address.
 */
const generateHash = (amount, dest, nonce, userId, privateKey) => {
  const privkeyBuffer = new Buffer(privateKey, 'hex')

  // generate a hash of all the input parameters
  const data = createHash('sha256')
    .update(numberToUint256(amount))
    .update(ethUtil.toBuffer(dest))
    .update(numberToUint256(nonce))
    .update(numberToUint256(userId))
    .digest()

  // sign the hash with the server's private key
  const hash = ethUtil.ecsign(data, privkeyBuffer)
  const publicKey = ethUtil.ecrecover(data, hash.v, hash.r, hash.s)

  return {
    publicKey: bufferToHex(ethUtil.pubToAddress(publicKey)),
    data: bufferToHex(data),
    hash: {
      r: bufferToHex(hash.r),
      s: bufferToHex(hash.s),
      v: hash.v
    }
  }
}


const numberToUint256 = num => {
  const n = new Buffer(32)
  n.writeInt32LE(num)
  return n.reverse()
}


const bufferToHex = buffer => `0x${buffer.toString('hex')}`