/** @fileOverview Javascript SHA-1 implementation.
 *
 * Based on the implementation in RFC 3174, method 1, and on the SJCL
 * SHA-256 implementation.
 *
 * @author Quinn Slack
 */

/**
 * Context for a SHA-1 operation in progress.
 * @constructor
 */
sjcl.hash.sha1 = function (hash) {
  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 5 big-endian words.
 */
sjcl.hash.sha1.hash = function (data) {
  return (new sjcl.hash.sha1()).update(data).finalize();
};

sjcl.hash.sha1.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);
    if (nl > 9007199254740991){
      throw new sjcl.exception.invalid("Cannot hash more than 2^53 - 1 bits");
    }

    if (typeof Uint32Array !== 'undefined') {
	var c = new Uint32Array(b);
    	var j = 0;
    	for (i = this.blockSize+ol - ((this.blockSize+ol) & (this.blockSize-1)); i <= nl;
		i+= this.blockSize) {
      	    this._block(c.subarray(16 * j, 16 * (j+1)));
      	    j += 1;
    	}
    	b.splice(0, 16 * j);
    } else {
    	for (i = this.blockSize+ol - ((this.blockSize+ol) & (this.blockSize-1)); i <= nl;
             i+= this.blockSize) {
      	     this._block(b.splice(0,16));
      	}
    }
    return this;
  },
  
  /**
   * Complete hashing and output the hash value.
   * @return {bitArray} The hash value, an array of 5 big-endian words. TODO
   */
  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-1 initialization vector.
   * @private
   */
  _init:[0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0],

  /**
   * The SHA-1 hash key.
   * @private
   */
  _key:[0x5A827999, 0x6ED9EBA1, 0x8F1BBCDC, 0xCA62C1D6],

  /**
   * The SHA-1 logical functions f(0), f(1), ..., f(79).
   * @private
   */
  _f:function(t, b, c, d) {
    if (t <= 19) {
      return (b & c) | (~b & d);
    } else if (t <= 39) {
      return b ^ c ^ d;
    } else if (t <= 59) {
      return (b & c) | (b & d) | (c & d);
    } else if (t <= 79) {
      return b ^ c ^ d;
    }
  },

  /**
   * Circular left-shift operator.
   * @private
   */
  _S:function(n, x) {
    return (x << n) | (x >>> 32-n);
  },
  
  /**
   * Perform one cycle of SHA-1.
   * @param {Uint32Array|bitArray} words one block of words.
   * @private
   */
  _block:function (words) {
    var t, tmp, a, b, c, d, e,
    h = this._h;
    var w;
    if (typeof Uint32Array !== 'undefined') {
        // When words is passed to _block, it has 16 elements. SHA1 _block
        // function extends words with new elements (at the end there are 80 elements). 
        // The problem is that if we use Uint32Array instead of Array, 
        // the length of Uint32Array cannot be changed. Thus, we replace words with a 
        // normal Array here.
        w = Array(80); // do not use Uint32Array here as the instantiation is slower
        for (var j=0; j<16; j++){
            w[j] = words[j];
        }
    } else {
        w = words;
    }

    a = h[0]; b = h[1]; c = h[2]; d = h[3]; e = h[4]; 

    for (t=0; t<=79; t++) {
      if (t >= 16) {
        w[t] = this._S(1, w[t-3] ^ w[t-8] ^ w[t-14] ^ w[t-16]);
      }
      tmp = (this._S(5, a) + this._f(t, b, c, d) + e + w[t] +
             this._key[Math.floor(t/20)]) | 0;
      e = d;
      d = c;
      c = this._S(30, b);
      b = a;
      a = tmp;
   }

   h[0] = (h[0]+a) |0;
   h[1] = (h[1]+b) |0;
   h[2] = (h[2]+c) |0;
   h[3] = (h[3]+d) |0;
   h[4] = (h[4]+e) |0;
  }
};