'use strict'

const forge = require('node-forge')

exports.exchanges = [
  'P-256',
  'P-384',
  'P-521'
]

exports.ciphers = [
  'AES-256',
  'AES-128',
  'Blowfish'
]

exports.hashes = [
  'SHA256',
  'SHA512'
]

// Determines which algorithm to use.  Note:  f(a, b) = f(b, a)
exports.theBest = (order, p1, p2) => {
  let first
  let second

  if (order < 0) {
    first = p2
    second = p1
  } else if (order > 0) {
    first = p1
    second = p2
  } else {
    return p1[0]
  }

  for (let firstCandidate of first) {
    for (let secondCandidate of second) {
      if (firstCandidate === secondCandidate) {
        return firstCandidate
      }
    }
  }

  throw new Error('No algorithms in common!')
}

exports.makeMacAndCipher = (target) => {
  target.mac = makeMac(target.hashT, target.keys.macKey)
  target.cipher = makeCipher(target.cipherT, target.keys.iv, target.keys.cipherKey)
}

const hashMap = {
  SHA1: 'sha1',
  SHA256: 'sha256',
  // workaround for https://github.com/digitalbazaar/forge/issues/401
  SHA512: forge.md.sha512.create()
}

function makeMac (hashType, key) {
  const hash = hashMap[hashType]

  if (!hash) {
    throw new Error(`unsupported hash type: ${hashType}`)
  }

  const mac = forge.hmac.create()
  mac.start(hash, key)
  return mac
}

function makeCipher (cipherType, iv, key) {
  if (cipherType === 'AES-128' || cipherType === 'AES-256') {
    // aes in counter (CTR) mode because that is what
    // is used in go (cipher.NewCTR)
    const cipher = forge.cipher.createCipher('AES-CTR', key)
    cipher.start({iv})
    return cipher
  }

  // TODO: Blowfish is not supported in node-forge, figure out if
  // it's needed and if so find a library for it.

  throw new Error(`unrecognized cipher type: ${cipherType}`)
}