var randomBytes
if (typeof window !== 'undefined' && window.crypto) {
  randomBytes = function (len) {
    var array = new Uint32Array(len)
    return Buffer.from(window.crypto.getRandomValues(array))
  }
} else {
  randomBytes = require('crypto').randomBytes
}
var createHash = require('create-hash')
var pbkdf2 = require('pbkdf2').pbkdf2Sync

var ENGLISH_WORDLIST = require('./wordlists/english.json')
var DEFAULT_WORDLIST = ENGLISH_WORDLIST

var INVALID_MNEMONIC = 'Invalid mnemonic'
var INVALID_ENTROPY = 'Invalid entropy'
var INVALID_CHECKSUM = 'Invalid mnemonic checksum'

function lpad (str, padString, length) {
  while (str.length < length) str = padString + str
  return str
}

function binaryToByte (bin) {
  return parseInt(bin, 2)
}

function bytesToBinary (bytes) {
  return bytes.map(function (x) {
    return lpad(x.toString(2), '0', 8)
  }).join('')
}

function deriveChecksumBits (entropyBuffer) {
  var ENT = entropyBuffer.length * 8
  var CS = ENT / 32
  var hash = createHash('sha256').update(entropyBuffer).digest()

  return bytesToBinary([].slice.call(hash)).slice(0, CS)
}

function salt (password) {
  return 'mnemonic' + (password || '')
}

function mnemonicToSeed (mnemonic, password) {
  var mnemonicBuffer = Buffer.from(mnemonic, 'utf8')
  var saltBuffer = Buffer.from(salt(password), 'utf8')

  return pbkdf2(mnemonicBuffer, saltBuffer, 2048, 64, 'sha512')
}

function mnemonicToSeedHex (mnemonic, password) {
  return mnemonicToSeed(mnemonic, password).toString('hex')
}

function mnemonicToEntropy (mnemonic, wordlist) {
  wordlist = wordlist || DEFAULT_WORDLIST

  var words = mnemonic.split(' ')
  if (words.length % 3 !== 0) throw new Error(INVALID_MNEMONIC)

  // convert word indices to 11 bit binary strings
  var bits = words.map(function (word) {
    var index = wordlist.indexOf(word)
    if (index === -1) throw new Error(INVALID_MNEMONIC)

    return lpad(index.toString(2), '0', 11)
  }).join('')

  // split the binary string into ENT/CS
  var dividerIndex = Math.floor(bits.length / 33) * 32
  var entropyBits = bits.slice(0, dividerIndex)
  var checksumBits = bits.slice(dividerIndex)

  // calculate the checksum and compare
  var entropyBytes = entropyBits.match(/(.{1,8})/g).map(binaryToByte)
  if (entropyBytes.length < 16) throw new Error(INVALID_ENTROPY)
  if (entropyBytes.length > 32) throw new Error(INVALID_ENTROPY)
  if (entropyBytes.length % 4 !== 0) throw new Error(INVALID_ENTROPY)

  var entropy = Buffer.from(entropyBytes)
  var newChecksum = deriveChecksumBits(entropy)
  if (newChecksum !== checksumBits) throw new Error(INVALID_CHECKSUM)

  return entropy.toString('hex')
}

function entropyToMnemonic (entropy, wordlist) {
  if (!Buffer.isBuffer(entropy)) entropy = Buffer.from(entropy, 'hex')
  wordlist = wordlist || DEFAULT_WORDLIST

  // 128 <= ENT <= 256
  if (entropy.length < 16) throw new TypeError(INVALID_ENTROPY)
  if (entropy.length > 32) throw new TypeError(INVALID_ENTROPY)
  if (entropy.length % 4 !== 0) throw new TypeError(INVALID_ENTROPY)

  var entropyBits = bytesToBinary([].slice.call(entropy))
  var checksumBits = deriveChecksumBits(entropy)

  var bits = entropyBits + checksumBits
  var chunks = bits.match(/(.{1,11})/g)
  var words = chunks.map(function (binary) {
    var index = binaryToByte(binary)
    return wordlist[index]
  })

  return words.join(' ')
}

function generateMnemonic (strength, rng, wordlist) {
  strength = strength || 128
  if (strength % 32 !== 0) throw new TypeError(INVALID_ENTROPY)
  rng = rng || randomBytes

  return entropyToMnemonic(rng(strength / 8), wordlist)
}

function validateMnemonic (mnemonic, wordlist) {
  try {
    mnemonicToEntropy(mnemonic, wordlist)
  } catch (e) {
    return false
  }

  return true
}

module.exports = {
  mnemonicToSeed: mnemonicToSeed,
  mnemonicToSeedHex: mnemonicToSeedHex,
  mnemonicToEntropy: mnemonicToEntropy,
  entropyToMnemonic: entropyToMnemonic,
  generateMnemonic: generateMnemonic,
  validateMnemonic: validateMnemonic,
  wordlists: {
    EN: ENGLISH_WORDLIST
  }
}