// GPG4Browsers - An OpenPGP implementation in javascript
// Copyright (C) 2011 Recurity Labs GmbH
// 
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// 
// This library 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
// Lesser General Public License for more details.
// 
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

/**
 * Implementation of the One-Pass Signature Packets (Tag 4)<br/>
 * <br/>
 * RFC4880 5.4:
 * The One-Pass Signature packet precedes the signed data and contains
 * enough information to allow the receiver to begin calculating any
 * hashes needed to verify the signature.  It allows the Signature
 * packet to be placed at the end of the message, so that the signer
 * can compute the entire signed message in one pass.
 * @requires enums
 * @requires type/keyid
 * @module packet/one_pass_signature
*/

var enums = require('../enums.js'),
  type_keyid = require('../type/keyid.js');

/**
 * @constructor
 */
module.exports = function one_pass_signature() {
  this.version = null; // A one-octet version number.  The current version is 3.
  this.type = null; // A one-octet signature type.  Signature types are described in RFC4880 Section 5.2.1.
  this.hashAlgorithm = null; // A one-octet number describing the hash algorithm used. (See RFC4880 9.4)
  this.publicKeyAlgorithm = null; // A one-octet number describing the public-key algorithm used. (See RFC4880 9.1)
  this.signingKeyId = null; // An eight-octet number holding the Key ID of the signing key.
  this.flags = null; //  A one-octet number holding a flag showing whether the signature is nested.  A zero value indicates that the next packet is another One-Pass Signature packet that describes another signature to be applied to the same message data.

  /**
   * parsing function for a one-pass signature packet (tag 4).
   * @param {String} bytes payload of a tag 4 packet
   * @return {module:packet/one_pass_signature} object representation
   */
  this.read = function (bytes) {
    var mypos = 0;
    // A one-octet version number.  The current version is 3.
    this.version = bytes.charCodeAt(mypos++);

    // A one-octet signature type.  Signature types are described in
    //   Section 5.2.1.
    this.type = enums.read(enums.signature, bytes.charCodeAt(mypos++));

    // A one-octet number describing the hash algorithm used.
    this.hashAlgorithm = enums.read(enums.hash, bytes.charCodeAt(mypos++));

    // A one-octet number describing the public-key algorithm used.
    this.publicKeyAlgorithm = enums.read(enums.publicKey, bytes.charCodeAt(mypos++));

    // An eight-octet number holding the Key ID of the signing key.
    this.signingKeyId = new type_keyid();
    this.signingKeyId.read(bytes.substr(mypos));
    mypos += 8;

    // A one-octet number holding a flag showing whether the signature
    //   is nested.  A zero value indicates that the next packet is
    //   another One-Pass Signature packet that describes another
    //   signature to be applied to the same message data.
    this.flags = bytes.charCodeAt(mypos++);
    return this;
  };

  /**
   * creates a string representation of a one-pass signature packet
   * @return {String} a string representation of a one-pass signature packet
   */
  this.write = function () {
    var result = "";

    result += String.fromCharCode(3);
    result += String.fromCharCode(enums.write(enums.signature, this.type));
    result += String.fromCharCode(enums.write(enums.hash, this.hashAlgorithm));
    result += String.fromCharCode(enums.write(enums.publicKey, this.publicKeyAlgorithm));
    result += this.signingKeyId.write();
    result += String.fromCharCode(this.flags);

    return result;
  };
};