/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  SHA-1 implementation in JavaScript                  (c) Chris Veness 2002-2014 / MIT Licence  */
/*                                                                                                */
/*  - see http://csrc.nist.gov/groups/ST/toolkit/secure_hashing.html                              */
/*        http://csrc.nist.gov/groups/ST/toolkit/examples.html                                    */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

/* jshint node:true */
/* global define, escape, unescape */
'use strict';


/**
 * SHA-1 hash function reference implementation.
 *
 * @namespace
 */
var Sha1 = {};


/**
 * Generates SHA-1 hash of string.
 *
 * @param   {string} msg - (Unicode) string to be hashed.
 * @returns {string} Hash of msg as hex character string.
 */
Sha1.hash = function (msg) {
  // convert string to UTF-8, as SHA only deals with byte-streams
  msg = msg.utf8Encode();

  // constants [§4.2.1]
  var K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];

  // PREPROCESSING

  msg += String.fromCharCode(0x80); // add trailing '1' bit (+ 0's padding) to string [§5.1.1]

  // convert string msg into 512-bit/16-integer blocks arrays of ints [§5.2.1]
  var l = msg.length / 4 + 2; // length (in 32-bit integers) of msg + ‘1’ + appended length
  var N = Math.ceil(l / 16); // number of 16-integer-blocks required to hold 'l' ints
  var M = new Array(N);

  for (var i = 0; i < N; i++) {
    M[i] = new Array(16);
    for (var j = 0; j < 16; j++) { // encode 4 chars per integer, big-endian encoding
      M[i][j] = (msg.charCodeAt(i * 64 + j * 4) << 24) | (msg.charCodeAt(i * 64 + j * 4 + 1) << 16) |
        (msg.charCodeAt(i * 64 + j * 4 + 2) << 8) | (msg.charCodeAt(i * 64 + j * 4 + 3));
    } // note running off the end of msg is ok 'cos bitwise ops on NaN return 0
  }
  // add length (in bits) into final pair of 32-bit integers (big-endian) [§5.1.1]
  // note: most significant word would be (len-1)*8 >>> 32, but since JS converts
  // bitwise-op args to 32 bits, we need to simulate this by arithmetic operators
  M[N - 1][14] = ((msg.length - 1) * 8) / Math.pow(2, 32);
  M[N - 1][14] = Math.floor(M[N - 1][14]);
  M[N - 1][15] = ((msg.length - 1) * 8) & 0xffffffff;

  // set initial hash value [§5.3.1]
  var H0 = 0x67452301;
  var H1 = 0xefcdab89;
  var H2 = 0x98badcfe;
  var H3 = 0x10325476;
  var H4 = 0xc3d2e1f0;

  // HASH COMPUTATION [§6.1.2]

  var W = new Array(80);
  var a, b, c, d, e;
  for (var i = 0; i < N; i++) {

    // 1 - prepare message schedule 'W'
    for (var t = 0; t < 16; t++) W[t] = M[i][t];
    for (var t = 16; t < 80; t++) W[t] = Sha1.ROTL(W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16], 1);

    // 2 - initialise five working variables a, b, c, d, e with previous hash value
    a = H0;
    b = H1;
    c = H2;
    d = H3;
    e = H4;

    // 3 - main loop
    for (var t = 0; t < 80; t++) {
      var s = Math.floor(t / 20); // seq for blocks of 'f' functions and 'K' constants
      var T = (Sha1.ROTL(a, 5) + Sha1.f(s, b, c, d) + e + K[s] + W[t]) & 0xffffffff;
      e = d;
      d = c;
      c = Sha1.ROTL(b, 30);
      b = a;
      a = T;
    }

    // 4 - compute the new intermediate hash value (note 'addition modulo 2^32')
    H0 = (H0 + a) & 0xffffffff;
    H1 = (H1 + b) & 0xffffffff;
    H2 = (H2 + c) & 0xffffffff;
    H3 = (H3 + d) & 0xffffffff;
    H4 = (H4 + e) & 0xffffffff;
  }

  return Sha1.toHexStr(H0) + Sha1.toHexStr(H1) + Sha1.toHexStr(H2) +
    Sha1.toHexStr(H3) + Sha1.toHexStr(H4);
};


/**
 * Function 'f' [§4.1.1].
 * @private
 */
Sha1.f = function (s, x, y, z) {
  switch (s) {
    case 0:
      return (x & y) ^ (~x & z); // Ch()
    case 1:
      return x ^ y ^ z; // Parity()
    case 2:
      return (x & y) ^ (x & z) ^ (y & z); // Maj()
    case 3:
      return x ^ y ^ z; // Parity()
  }
};

/**
 * Rotates left (circular left shift) value x by n positions [§3.2.5].
 * @private
 */
Sha1.ROTL = function (x, n) {
  return (x << n) | (x >>> (32 - n));
};


/**
 * Hexadecimal representation of a number.
 * @private
 */
Sha1.toHexStr = function (n) {
  // note can't use toString(16) as it is implementation-dependant,
  // and in IE returns signed numbers when used on full words
  var s = "",
    v;
  for (var i = 7; i >= 0; i--) {
    v = (n >>> (i * 4)) & 0xf;
    s += v.toString(16);
  }
  return s;
};


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */


/** Extend String object with method to encode multi-byte string to utf8
 *  - monsur.hossa.in/2012/07/20/utf-8-in-javascript.html */
if (typeof String.prototype.utf8Encode == 'undefined') {
  String.prototype.utf8Encode = function () {
    return unescape(encodeURIComponent(this));
  };
}

/** Extend String object with method to decode utf8 string to multi-byte */
if (typeof String.prototype.utf8Decode == 'undefined') {
  String.prototype.utf8Decode = function () {
    try {
      return decodeURIComponent(escape(this));
    } catch (e) {
      return this; // invalid UTF-8? return as-is
    }
  };
}