'use strict'
var Buffer = require('safe-buffer').Buffer
var createHash = require('create-hash')
var BN = require('bn.js')
var EC = require('elliptic').ec

var messages = require('../messages.json')

var ec = new EC('secp256k1')
var ecparams = ec.curve

function loadCompressedPublicKey (first, xBuffer) {
  var x = new BN(xBuffer)

  // overflow
  if (x.cmp(ecparams.p) >= 0) return null
  x = x.toRed(ecparams.red)

  // compute corresponding Y
  var y = x.redSqr().redIMul(x).redIAdd(ecparams.b).redSqrt()
  if ((first === 0x03) !== y.isOdd()) y = y.redNeg()

  return ec.keyPair({ pub: { x: x, y: y } })
}

function loadUncompressedPublicKey (first, xBuffer, yBuffer) {
  var x = new BN(xBuffer)
  var y = new BN(yBuffer)

  // overflow
  if (x.cmp(ecparams.p) >= 0 || y.cmp(ecparams.p) >= 0) return null

  x = x.toRed(ecparams.red)
  y = y.toRed(ecparams.red)

  // is odd flag
  if ((first === 0x06 || first === 0x07) && y.isOdd() !== (first === 0x07)) return null

  // x*x*x + b = y*y
  var x3 = x.redSqr().redIMul(x)
  if (!y.redSqr().redISub(x3.redIAdd(ecparams.b)).isZero()) return null

  return ec.keyPair({ pub: { x: x, y: y } })
}

function loadPublicKey (publicKey) {
  var first = publicKey[0]
  switch (first) {
    case 0x02:
    case 0x03:
      if (publicKey.length !== 33) return null
      return loadCompressedPublicKey(first, publicKey.slice(1, 33))
    case 0x04:
    case 0x06:
    case 0x07:
      if (publicKey.length !== 65) return null
      return loadUncompressedPublicKey(first, publicKey.slice(1, 33), publicKey.slice(33, 65))
    default:
      return null
  }
}

exports.privateKeyVerify = function (privateKey) {
  var bn = new BN(privateKey)
  return bn.cmp(ecparams.n) < 0 && !bn.isZero()
}

exports.privateKeyExport = function (privateKey, compressed) {
  var d = new BN(privateKey)
  if (d.cmp(ecparams.n) >= 0 || d.isZero()) throw new Error(messages.EC_PRIVATE_KEY_EXPORT_DER_FAIL)

  return Buffer.from(ec.keyFromPrivate(privateKey).getPublic(compressed, true))
}

exports.privateKeyNegate = function (privateKey) {
  var bn = new BN(privateKey)
  return bn.isZero() ? Buffer.alloc(32) : ecparams.n.sub(bn).umod(ecparams.n).toArrayLike(Buffer, 'be', 32)
}

exports.privateKeyModInverse = function (privateKey) {
  var bn = new BN(privateKey)
  if (bn.cmp(ecparams.n) >= 0 || bn.isZero()) throw new Error(messages.EC_PRIVATE_KEY_RANGE_INVALID)

  return bn.invm(ecparams.n).toArrayLike(Buffer, 'be', 32)
}

exports.privateKeyTweakAdd = function (privateKey, tweak) {
  var bn = new BN(tweak)
  if (bn.cmp(ecparams.n) >= 0) throw new Error(messages.EC_PRIVATE_KEY_TWEAK_ADD_FAIL)

  bn.iadd(new BN(privateKey))
  if (bn.cmp(ecparams.n) >= 0) bn.isub(ecparams.n)
  if (bn.isZero()) throw new Error(messages.EC_PRIVATE_KEY_TWEAK_ADD_FAIL)

  return bn.toArrayLike(Buffer, 'be', 32)
}

exports.privateKeyTweakMul = function (privateKey, tweak) {
  var bn = new BN(tweak)
  if (bn.cmp(ecparams.n) >= 0 || bn.isZero()) throw new Error(messages.EC_PRIVATE_KEY_TWEAK_MUL_FAIL)

  bn.imul(new BN(privateKey))
  if (bn.cmp(ecparams.n)) bn = bn.umod(ecparams.n)

  return bn.toArrayLike(Buffer, 'be', 32)
}

exports.publicKeyCreate = function (privateKey, compressed) {
  var d = new BN(privateKey)
  if (d.cmp(ecparams.n) >= 0 || d.isZero()) throw new Error(messages.EC_PUBLIC_KEY_CREATE_FAIL)

  return Buffer.from(ec.keyFromPrivate(privateKey).getPublic(compressed, true))
}

exports.publicKeyConvert = function (publicKey, compressed) {
  var pair = loadPublicKey(publicKey)
  if (pair === null) throw new Error(messages.EC_PUBLIC_KEY_PARSE_FAIL)

  return Buffer.from(pair.getPublic(compressed, true))
}

exports.publicKeyVerify = function (publicKey) {
  return loadPublicKey(publicKey) !== null
}

exports.publicKeyTweakAdd = function (publicKey, tweak, compressed) {
  var pair = loadPublicKey(publicKey)
  if (pair === null) throw new Error(messages.EC_PUBLIC_KEY_PARSE_FAIL)

  tweak = new BN(tweak)
  if (tweak.cmp(ecparams.n) >= 0) throw new Error(messages.EC_PUBLIC_KEY_TWEAK_ADD_FAIL)

  var point = ecparams.g.mul(tweak).add(pair.pub)
  if (point.isInfinity()) throw new Error(messages.EC_PUBLIC_KEY_TWEAK_ADD_FAIL)

  return Buffer.from(point.encode(true, compressed))
}

exports.publicKeyTweakMul = function (publicKey, tweak, compressed) {
  var pair = loadPublicKey(publicKey)
  if (pair === null) throw new Error(messages.EC_PUBLIC_KEY_PARSE_FAIL)

  tweak = new BN(tweak)
  if (tweak.cmp(ecparams.n) >= 0 || tweak.isZero()) throw new Error(messages.EC_PUBLIC_KEY_TWEAK_MUL_FAIL)

  return Buffer.from(pair.pub.mul(tweak).encode(true, compressed))
}

exports.publicKeyCombine = function (publicKeys, compressed) {
  var pairs = new Array(publicKeys.length)
  for (var i = 0; i < publicKeys.length; ++i) {
    pairs[i] = loadPublicKey(publicKeys[i])
    if (pairs[i] === null) throw new Error(messages.EC_PUBLIC_KEY_PARSE_FAIL)
  }

  var point = pairs[0].pub
  for (var j = 1; j < pairs.length; ++j) point = point.add(pairs[j].pub)
  if (point.isInfinity()) throw new Error(messages.EC_PUBLIC_KEY_COMBINE_FAIL)

  return Buffer.from(point.encode(true, compressed))
}

exports.signatureNormalize = function (signature) {
  var r = new BN(signature.slice(0, 32))
  var s = new BN(signature.slice(32, 64))
  if (r.cmp(ecparams.n) >= 0 || s.cmp(ecparams.n) >= 0) throw new Error(messages.ECDSA_SIGNATURE_PARSE_FAIL)

  var result = Buffer.from(signature)
  if (s.cmp(ec.nh) === 1) ecparams.n.sub(s).toArrayLike(Buffer, 'be', 32).copy(result, 32)

  return result
}

exports.signatureExport = function (signature) {
  var r = signature.slice(0, 32)
  var s = signature.slice(32, 64)
  if (new BN(r).cmp(ecparams.n) >= 0 || new BN(s).cmp(ecparams.n) >= 0) throw new Error(messages.ECDSA_SIGNATURE_PARSE_FAIL)

  return { r: r, s: s }
}

exports.signatureImport = function (sigObj) {
  var r = new BN(sigObj.r)
  if (r.cmp(ecparams.n) >= 0) r = new BN(0)

  var s = new BN(sigObj.s)
  if (s.cmp(ecparams.n) >= 0) s = new BN(0)

  return Buffer.concat([
    r.toArrayLike(Buffer, 'be', 32),
    s.toArrayLike(Buffer, 'be', 32)
  ])
}

exports.sign = function (message, privateKey, noncefn, data) {
  if (typeof noncefn === 'function') {
    var getNonce = noncefn
    noncefn = function (counter) {
      var nonce = getNonce(message, privateKey, null, data, counter)
      if (!Buffer.isBuffer(nonce) || nonce.length !== 32) throw new Error(messages.ECDSA_SIGN_FAIL)

      return new BN(nonce)
    }
  }

  var d = new BN(privateKey)
  if (d.cmp(ecparams.n) >= 0 || d.isZero()) throw new Error(messages.ECDSA_SIGN_FAIL)

  var result = ec.sign(message, privateKey, { canonical: true, k: noncefn, pers: data })
  return {
    signature: Buffer.concat([
      result.r.toArrayLike(Buffer, 'be', 32),
      result.s.toArrayLike(Buffer, 'be', 32)
    ]),
    recovery: result.recoveryParam
  }
}

exports.verify = function (message, signature, publicKey) {
  var sigObj = { r: signature.slice(0, 32), s: signature.slice(32, 64) }

  var sigr = new BN(sigObj.r)
  var sigs = new BN(sigObj.s)
  if (sigr.cmp(ecparams.n) >= 0 || sigs.cmp(ecparams.n) >= 0) throw new Error(messages.ECDSA_SIGNATURE_PARSE_FAIL)
  if (sigs.cmp(ec.nh) === 1 || sigr.isZero() || sigs.isZero()) return false

  var pair = loadPublicKey(publicKey)
  if (pair === null) throw new Error(messages.EC_PUBLIC_KEY_PARSE_FAIL)

  return ec.verify(message, sigObj, { x: pair.pub.x, y: pair.pub.y })
}

exports.recover = function (message, signature, recovery, compressed) {
  var sigObj = { r: signature.slice(0, 32), s: signature.slice(32, 64) }

  var sigr = new BN(sigObj.r)
  var sigs = new BN(sigObj.s)
  if (sigr.cmp(ecparams.n) >= 0 || sigs.cmp(ecparams.n) >= 0) throw new Error(messages.ECDSA_SIGNATURE_PARSE_FAIL)

  try {
    if (sigr.isZero() || sigs.isZero()) throw new Error()

    var point = ec.recoverPubKey(message, sigObj, recovery)
    return Buffer.from(point.encode(true, compressed))
  } catch (err) {
    throw new Error(messages.ECDSA_RECOVER_FAIL)
  }
}

exports.ecdh = function (publicKey, privateKey) {
  var shared = exports.ecdhUnsafe(publicKey, privateKey, true)
  return createHash('sha256').update(shared).digest()
}

exports.ecdhUnsafe = function (publicKey, privateKey, compressed) {
  var pair = loadPublicKey(publicKey)
  if (pair === null) throw new Error(messages.EC_PUBLIC_KEY_PARSE_FAIL)

  var scalar = new BN(privateKey)
  if (scalar.cmp(ecparams.n) >= 0 || scalar.isZero()) throw new Error(messages.ECDH_FAIL)

  return Buffer.from(pair.pub.mul(scalar).encode(true, compressed))
}