/**
 * 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 helpers = require('./helpers');

var safe_add = function (x, y) {
  var lsw = (x & 0xffff) + (y & 0xffff);
  var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
  return (msw << 16) | (lsw & 0xffff);
};

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

var R = function (X, n) {
  return X >>> n;
};

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

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

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

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

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

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

var core_sha256 = function (m, l) {
  var K = new Array(
    0x428a2f98,
    0x71374491,
    0xb5c0fbcf,
    0xe9b5dba5,
    0x3956c25b,
    0x59f111f1,
    0x923f82a4,
    0xab1c5ed5,
    0xd807aa98,
    0x12835b01,
    0x243185be,
    0x550c7dc3,
    0x72be5d74,
    0x80deb1fe,
    0x9bdc06a7,
    0xc19bf174,
    0xe49b69c1,
    0xefbe4786,
    0xfc19dc6,
    0x240ca1cc,
    0x2de92c6f,
    0x4a7484aa,
    0x5cb0a9dc,
    0x76f988da,
    0x983e5152,
    0xa831c66d,
    0xb00327c8,
    0xbf597fc7,
    0xc6e00bf3,
    0xd5a79147,
    0x6ca6351,
    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 HASH = new Array(0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19);
  var W = new Array(64);
  var a, b, c, d, e, f, g, h, i, j;
  var T1, T2;
  /* append padding */
  m[l >> 5] |= 0x80 << (24 - (l % 32));
  m[(((l + 64) >> 9) << 4) + 15] = l;
  for (var i = 0; i < m.length; i += 16) {
    a = HASH[0];
    b = HASH[1];
    c = HASH[2];
    d = HASH[3];
    e = HASH[4];
    f = HASH[5];
    g = HASH[6];
    h = HASH[7];
    for (var j = 0; j < 64; j++) {
      if (j < 16) {
        W[j] = m[j + i];
      } else {
        W[j] = safe_add(safe_add(safe_add(Gamma1256(W[j - 2]), W[j - 7]), Gamma0256(W[j - 15])), W[j - 16]);
      }
      T1 = safe_add(safe_add(safe_add(safe_add(h, Sigma1256(e)), Ch(e, f, g)), K[j]), W[j]);
      T2 = safe_add(Sigma0256(a), Maj(a, b, c));
      h = g;
      g = f;
      f = e;
      e = safe_add(d, T1);
      d = c;
      c = b;
      b = a;
      a = safe_add(T1, T2);
    }
    HASH[0] = safe_add(a, HASH[0]);
    HASH[1] = safe_add(b, HASH[1]);
    HASH[2] = safe_add(c, HASH[2]);
    HASH[3] = safe_add(d, HASH[3]);
    HASH[4] = safe_add(e, HASH[4]);
    HASH[5] = safe_add(f, HASH[5]);
    HASH[6] = safe_add(g, HASH[6]);
    HASH[7] = safe_add(h, HASH[7]);
  }
  return HASH;
};

module.exports = function sha256(buf) {
  return helpers.hash(buf, core_sha256, 32, true);
};