/**
 * A JavaScript implementation of the Secure Hash Algorithm, SHA-256, as defined
 * in FIPS 180-2
 * Version 2.2-beta Copyright Angel Marin, Paul Johnston 2000 - 2009.
 * Other contributors: Greg Holt, Andrew Kepert, Ydnar, Lostinet
 *
 */

var inherits = require('inherits')
var Hash = require('./hash')

var K = [
  0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5,
  0x3956C25B, 0x59F111F1, 0x923F82A4, 0xAB1C5ED5,
  0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3,
  0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174,
  0xE49B69C1, 0xEFBE4786, 0x0FC19DC6, 0x240CA1CC,
  0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA,
  0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7,
  0xC6E00BF3, 0xD5A79147, 0x06CA6351, 0x14292967,
  0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13,
  0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85,
  0xA2BFE8A1, 0xA81A664B, 0xC24B8B70, 0xC76C51A3,
  0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070,
  0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5,
  0x391C0CB3, 0x4ED8AA4A, 0x5B9CCA4F, 0x682E6FF3,
  0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208,
  0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2
]

var W = new Array(64)

function Sha256 () {
  this.init()

  this._w = W // new Array(64)

  Hash.call(this, 64, 56)
}

inherits(Sha256, Hash)

Sha256.prototype.init = function () {
  this._a = 0x6a09e667 | 0
  this._b = 0xbb67ae85 | 0
  this._c = 0x3c6ef372 | 0
  this._d = 0xa54ff53a | 0
  this._e = 0x510e527f | 0
  this._f = 0x9b05688c | 0
  this._g = 0x1f83d9ab | 0
  this._h = 0x5be0cd19 | 0

  return this
}

function S (X, n) {
  return (X >>> n) | (X << (32 - n))
}

function R (X, n) {
  return (X >>> n)
}

function Ch (x, y, z) {
  return ((x & y) ^ ((~x) & z))
}

function Maj (x, y, z) {
  return ((x & y) ^ (x & z) ^ (y & z))
}

function Sigma0256 (x) {
  return (S(x, 2) ^ S(x, 13) ^ S(x, 22))
}

function Sigma1256 (x) {
  return (S(x, 6) ^ S(x, 11) ^ S(x, 25))
}

function Gamma0256 (x) {
  return (S(x, 7) ^ S(x, 18) ^ R(x, 3))
}

function Gamma1256 (x) {
  return (S(x, 17) ^ S(x, 19) ^ R(x, 10))
}

Sha256.prototype._update = function (M) {
  var W = this._w

  var a = this._a | 0
  var b = this._b | 0
  var c = this._c | 0
  var d = this._d | 0
  var e = this._e | 0
  var f = this._f | 0
  var g = this._g | 0
  var h = this._h | 0

  var j = 0

  function calcW () { return Gamma1256(W[j - 2]) + W[j - 7] + Gamma0256(W[j - 15]) + W[j - 16] }
  function loop (w) {
    W[j] = w

    var T1 = h + Sigma1256(e) + Ch(e, f, g) + K[j] + w
    var T2 = Sigma0256(a) + Maj(a, b, c)

    h = g
    g = f
    f = e
    e = d + T1
    d = c
    c = b
    b = a
    a = T1 + T2

    j++
  }

  while (j < 16) loop(M.readInt32BE(j * 4))
  while (j < 64) loop(calcW())

  this._a = (a + this._a) | 0
  this._b = (b + this._b) | 0
  this._c = (c + this._c) | 0
  this._d = (d + this._d) | 0
  this._e = (e + this._e) | 0
  this._f = (f + this._f) | 0
  this._g = (g + this._g) | 0
  this._h = (h + this._h) | 0
}

Sha256.prototype._hash = function () {
  var H = new Buffer(32)

  H.writeInt32BE(this._a, 0)
  H.writeInt32BE(this._b, 4)
  H.writeInt32BE(this._c, 8)
  H.writeInt32BE(this._d, 12)
  H.writeInt32BE(this._e, 16)
  H.writeInt32BE(this._f, 20)
  H.writeInt32BE(this._g, 24)
  H.writeInt32BE(this._h, 28)

  return H
}

module.exports = Sha256
