/*
 * A JavaScript implementation of the Secure Hash Algorithm, SHA-1, as defined
 * in FIPS PUB 180-1
 * Version 2.1a Copyright Paul Johnston 2000 - 2002.
 * Other contributors: Greg Holt, Andrew Kepert, Ydnar, Lostinet
 * Distributed under the BSD License
 * See http://pajhome.org.uk/crypt/md5 for details.
 */

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

/*
 * Calculate the SHA-1 of an array of big-endian words, and a bit length
 */
function core_sha1(x, len) {
  /* append padding */
  x[len >> 5] |= 0x80 << (24 - (len % 32));
  x[(((len + 64) >> 9) << 4) + 15] = len;

  var w = Array(80);
  var a = 1732584193;
  var b = -271733879;
  var c = -1732584194;
  var d = 271733878;
  var e = -1009589776;

  for (var i = 0; i < x.length; i += 16) {
    var olda = a;
    var oldb = b;
    var oldc = c;
    var oldd = d;
    var olde = e;

    for (var j = 0; j < 80; j++) {
      if (j < 16) w[j] = x[i + j];
      else w[j] = rol(w[j - 3] ^ w[j - 8] ^ w[j - 14] ^ w[j - 16], 1);
      var t = safe_add(safe_add(rol(a, 5), sha1_ft(j, b, c, d)), safe_add(safe_add(e, w[j]), sha1_kt(j)));
      e = d;
      d = c;
      c = rol(b, 30);
      b = a;
      a = t;
    }

    a = safe_add(a, olda);
    b = safe_add(b, oldb);
    c = safe_add(c, oldc);
    d = safe_add(d, oldd);
    e = safe_add(e, olde);
  }
  return Array(a, b, c, d, e);
}

/*
 * Perform the appropriate triplet combination function for the current
 * iteration
 */
function sha1_ft(t, b, c, d) {
  if (t < 20) return (b & c) | (~b & d);
  if (t < 40) return b ^ c ^ d;
  if (t < 60) return (b & c) | (b & d) | (c & d);
  return b ^ c ^ d;
}

/*
 * Determine the appropriate additive constant for the current iteration
 */
function sha1_kt(t) {
  return t < 20 ? 1518500249 : t < 40 ? 1859775393 : t < 60 ? -1894007588 : -899497514;
}

/*
 * Add integers, wrapping at 2^32. This uses 16-bit operations internally
 * to work around bugs in some JS interpreters.
 */
function safe_add(x, y) {
  var lsw = (x & 0xffff) + (y & 0xffff);
  var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
  return (msw << 16) | (lsw & 0xffff);
}

/*
 * Bitwise rotate a 32-bit number to the left.
 */
function rol(num, cnt) {
  return (num << cnt) | (num >>> (32 - cnt));
}

module.exports = function sha1(buf) {
  return helpers.hash(buf, core_sha1, 20, true);
};
