/** @fileOverview Javascript SHA-256 implementation.
 *
 * An older version of this implementation is available in the public
 * domain, but this one is (c) Emily Stark, Mike Hamburg, Dan Boneh,
 * Stanford University 2008-2010 and BSD-licensed for liability
 * reasons.
 *
 * Special thanks to Aldo Cortesi for pointing out several bugs in
 * this code.
 *
 * @author Emily Stark
 * @author Mike Hamburg
 * @author Dan Boneh
 */

/**
 * Context for a SHA-256 operation in progress.
 * @constructor
 * @class Secure Hash Algorithm, 256 bits.
 */
sjcl.hash.sha256 = function (hash) {
  if (!this._key[0]) { this._precompute(); }
  if (hash) {
    this._h = hash._h.slice(0);
    this._buffer = hash._buffer.slice(0);
    this._length = hash._length;
  } else {
    this.reset();
  }
};

/**
 * Hash a string or an array of words.
 * @static
 * @param {bitArray|String} data the data to hash.
 * @return {bitArray} The hash value, an array of 16 big-endian words.
 */
sjcl.hash.sha256.hash = function (data) {
  return (new sjcl.hash.sha256()).update(data).finalize();
};

sjcl.hash.sha256.prototype = {
  /**
   * The hash's block size, in bits.
   * @constant
   */
  blockSize: 512,
   
  /**
   * Reset the hash state.
   * @return this
   */
  reset:function () {
    this._h = this._init.slice(0);
    this._buffer = [];
    this._length = 0;
    return this;
  },
  
  /**
   * Input several words to the hash.
   * @param {bitArray|String} data the data to hash.
   * @return this
   */
  update: function (data) {
    if (typeof data === "string") {
      data = sjcl.codec.utf8String.toBits(data);
    }
    var i, b = this._buffer = sjcl.bitArray.concat(this._buffer, data),
        ol = this._length,
        nl = this._length = ol + sjcl.bitArray.bitLength(data);
    for (i = 512+ol & -512; i <= nl; i+= 512) {
      this._block(b.splice(0,16));
    }
    return this;
  },
  
  /**
   * Complete hashing and output the hash value.
   * @return {bitArray} The hash value, an array of 16 big-endian words.
   */
  finalize:function () {
    var i, b = this._buffer, h = this._h;

    // Round out and push the buffer
    b = sjcl.bitArray.concat(b, [sjcl.bitArray.partial(1,1)]);
    
    // Round out the buffer to a multiple of 16 words, less the 2 length words.
    for (i = b.length + 2; i & 15; i++) {
      b.push(0);
    }
    
    // append the length
    b.push(Math.floor(this._length / 0x100000000));
    b.push(this._length | 0);

    while (b.length) {
      this._block(b.splice(0,16));
    }

    this.reset();
    return h;
  },

  /**
   * The SHA-256 initialization vector, to be precomputed.
   * @private
   */
  _init:[],
  /*
  _init:[0x6a09e667,0xbb67ae85,0x3c6ef372,0xa54ff53a,0x510e527f,0x9b05688c,0x1f83d9ab,0x5be0cd19],
  */
  
  /**
   * The SHA-256 hash key, to be precomputed.
   * @private
   */
  _key:[],
  /*
  _key:
    [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],
  */


  /**
   * Function to precompute _init and _key.
   * @private
   */
  _precompute: function () {
    var i = 0, prime = 2, factor;

    function frac(x) { return (x-Math.floor(x)) * 0x100000000 | 0; }

    outer: for (; i<64; prime++) {
      for (factor=2; factor*factor <= prime; factor++) {
        if (prime % factor === 0) {
          // not a prime
          continue outer;
        }
      }
      
      if (i<8) {
        this._init[i] = frac(Math.pow(prime, 1/2));
      }
      this._key[i] = frac(Math.pow(prime, 1/3));
      i++;
    }
  },
  
  /**
   * Perform one cycle of SHA-256.
   * @param {bitArray} words one block of words.
   * @private
   */
  _block:function (words) {  
    var i, tmp, a, b,
      w = words.slice(0),
      h = this._h,
      k = this._key,
      h0 = h[0], h1 = h[1], h2 = h[2], h3 = h[3],
      h4 = h[4], h5 = h[5], h6 = h[6], h7 = h[7];

    /* Rationale for placement of |0 :
     * If a value can overflow is original 32 bits by a factor of more than a few
     * million (2^23 ish), there is a possibility that it might overflow the
     * 53-bit mantissa and lose precision.
     *
     * To avoid this, we clamp back to 32 bits by |'ing with 0 on any value that
     * propagates around the loop, and on the hash state h[].  I don't believe
     * that the clamps on h4 and on h0 are strictly necessary, but it's close
     * (for h4 anyway), and better safe than sorry.
     *
     * The clamps on h[] are necessary for the output to be correct even in the
     * common case and for short inputs.
     */
    for (i=0; i<64; i++) {
      // load up the input word for this round
      if (i<16) {
        tmp = w[i];
      } else {
        a   = w[(i+1 ) & 15];
        b   = w[(i+14) & 15];
        tmp = w[i&15] = ((a>>>7  ^ a>>>18 ^ a>>>3  ^ a<<25 ^ a<<14) + 
                         (b>>>17 ^ b>>>19 ^ b>>>10 ^ b<<15 ^ b<<13) +
                         w[i&15] + w[(i+9) & 15]) | 0;
      }
      
      tmp = (tmp + h7 + (h4>>>6 ^ h4>>>11 ^ h4>>>25 ^ h4<<26 ^ h4<<21 ^ h4<<7) +  (h6 ^ h4&(h5^h6)) + k[i]); // | 0;
      
      // shift register
      h7 = h6; h6 = h5; h5 = h4;
      h4 = h3 + tmp | 0;
      h3 = h2; h2 = h1; h1 = h0;

      h0 = (tmp +  ((h1&h2) ^ (h3&(h1^h2))) + (h1>>>2 ^ h1>>>13 ^ h1>>>22 ^ h1<<30 ^ h1<<19 ^ h1<<10)) | 0;
    }

    h[0] = h[0]+h0 | 0;
    h[1] = h[1]+h1 | 0;
    h[2] = h[2]+h2 | 0;
    h[3] = h[3]+h3 | 0;
    h[4] = h[4]+h4 | 0;
    h[5] = h[5]+h5 | 0;
    h[6] = h[6]+h6 | 0;
    h[7] = h[7]+h7 | 0;
  }
};
