var crypto = require('crypto')

/**
 * @param  {Number} len
 */
var random = (len = 32) => {
  var buf = crypto.randomBytes(len)
  return buf.toString('hex')
}

/**
 *
 * @param {string} str
 */
var sha256 = (str, tostr = 'base64') => {
  return crypto.createHash('sha256').update(str).digest(tostr)
}

/**
 *
 * @param {string} str
 */
var genPassHash = (str) => {
  var hash = random(16)
  var pass = sha256(str + hash)
  return `$${hash}$${pass}`
}

/**
 *
 * @param {string} plain
 * @param {string} hash
 */
var comparePass = (plain, hash) => {
  var match = hash.match(/^\$(.+?)\$(.+)$/)
  if (match == null || match.length < 3 || !match[1] || !match[2]) return false
  var pass = sha256(plain + match[1])
  if (pass === match[2]) return true
  return false
}

const pbkdf2 = (pass, salt, count, len, tostr = false) => {
  let hlen = crypto.createHash('sha256').update('').digest().length
  let blockCount = Math.ceil(len / hlen)

  let s256 = (s) => { return crypto.createHash('sha256').update(s).digest() }

  let out = []
  for (let i = 0; i < blockCount; i++) {
    let loopBuf = Buffer.alloc(4)
    loopBuf.writeInt32BE(i)
    let saltBuf = Buffer.from(salt)
    let last = Buffer.concat([saltBuf, loopBuf], saltBuf.length + loopBuf.length)
    let passBuf = Buffer.from(pass)
    last = s256(Buffer.concat([passBuf, last], passBuf.length + last.length))
    let xor = Buffer.from(last)
    for (let j = 1; j < count; j++) {
      last = s256(Buffer.concat([passBuf, last], passBuf.length + last.length))
      xor = last.map((t, idx) => {
        return t ^ xor[idx]
      })
    }
    out.push(xor)
  }
  let olen = 0
  for (let i in out) {
    olen += out[i].length
  }
  let raw = Buffer.concat([...out], olen)
  if (!tostr) {
    return raw.slice(0, len)
  } else {
    return Buffer.from(raw.slice(0, len)).toString('hex')
  }
}

module.exports = {
  random,
  sha256,
  genPassHash,
  comparePass,
  pbkdf2
}