var xor = require('buffer-xor')

function incr32 (iv) {
  var len = iv.length
  var item
  while (len--) {
    item = iv.readUInt8(len)
    if (item === 255) {
      iv.writeUInt8(0, len)
    } else {
      item++
      iv.writeUInt8(item, len)
      break
    }
  }
}

function getBlock (self) {
  var out = self._cipher.encryptBlock(self._prev)
  incr32(self._prev)
  return out
}

exports.encrypt = function (self, chunk) {
  while (self._cache.length < chunk.length) {
    self._cache = Buffer.concat([self._cache, getBlock(self)])
  }
  var pad = self._cache.slice(0, chunk.length)
  self._cache = self._cache.slice(chunk.length)
  return xor(chunk, pad)
}