/*
  Copyright (C) 2013 Grégory Soutadé
  
  This file is part of gPass.
  
  gPass is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.
  
  gPass is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with gPass.  If not, see <http://www.gnu.org/licenses/>.
*/

var hmac256 = require("hmac").hmac;

// http://stackoverflow.com/questions/3745666/how-to-convert-from-hex-to-ascii-in-javascript
function hex2a(hex) {
    var str = '';
    for (var i = 0; i < hex.length; i += 2)
        str += String.fromCharCode(parseInt(hex.substr(i, 2), 16));
    return str;
}

exports.pkdbf2 = {
    pkdbf2 : function(password, salt, iterations, outlen) {
	var result = "";
	var temp = "";
	var temp2 = "";
	var temp_res = "";
	var temp_res2 = "";

	for (i=1; result.length < outlen; i++)
	{
	    temp = hex2a(hmac256.hmac(salt + 
				String.fromCharCode((i & 0xff000000) >> 24) +
				String.fromCharCode((i & 0x00ff0000) >> 16) +
				String.fromCharCode((i & 0x0000ff00) >>  8) +
				String.fromCharCode((i & 0x000000ff) >>  0),
				      password));
	    temp_res = temp;

	    for(a=1; a<iterations; a++)
	    {
		temp2 = hex2a(hmac256.hmac(temp, password));
		temp_res2 = "";
		for(b = 0; b<temp_res.length; b++)
		    temp_res2 += String.fromCharCode(temp_res.charCodeAt(b) ^ temp2.charCodeAt(b));
		temp_res = temp_res2;
		temp = temp2;
	    }

	    result += temp_res;
	}

	return result.substr(0, outlen);
    }
};