/** @module crypto/signature */

var publicKey = require('./public_key'),
  pkcs1 = require('./pkcs1.js'),
  hashModule = require('./hash');

module.exports = {
  /**
   * 
   * @param {Integer} algo public Key algorithm
   * @param {Integer} hash_algo Hash algorithm
   * @param {Array<module:type/mpi>} msg_MPIs Signature multiprecision integers
   * @param {Array<module:type/mpi>} publickey_MPIs Public key multiprecision integers 
   * @param {String} data Data on where the signature was computed on.
   * @return {Boolean} true if signature (sig_data was equal to data over hash)
   */
  verify: function(algo, hash_algo, msg_MPIs, publickey_MPIs, data) {
    var calc_hash = hashModule.digest(hash_algo, data);

    switch (algo) {
      case 1:
        // RSA (Encrypt or Sign) [HAC]  
      case 2:
        // RSA Encrypt-Only [HAC]
      case 3:
        // RSA Sign-Only [HAC]
        var rsa = new publicKey.rsa();
        var n = publickey_MPIs[0].toBigInteger();
        var e = publickey_MPIs[1].toBigInteger();
        var x = msg_MPIs[0].toBigInteger();
        var dopublic = rsa.verify(x, e, n);
        var hash = pkcs1.emsa.decode(hash_algo, dopublic.toMPI().substring(2));
        if (hash == -1) {
          throw new Error('PKCS1 padding in message or key incorrect. Aborting...');
        }
        return hash == calc_hash;

      case 16:
        // Elgamal (Encrypt-Only) [ELGAMAL] [HAC]
        throw new Error("signing with Elgamal is not defined in the OpenPGP standard.");
      case 17:
        // DSA (Digital Signature Algorithm) [FIPS186] [HAC]
        var dsa = new publicKey.dsa();
        var s1 = msg_MPIs[0].toBigInteger();
        var s2 = msg_MPIs[1].toBigInteger();
        var p = publickey_MPIs[0].toBigInteger();
        var q = publickey_MPIs[1].toBigInteger();
        var g = publickey_MPIs[2].toBigInteger();
        var y = publickey_MPIs[3].toBigInteger();
        var m = data;
        var dopublic = dsa.verify(hash_algo, s1, s2, m, p, q, g, y);
        return dopublic.compareTo(s1) == 0;
      default:
        throw new Error('Invalid signature algorithm.');
    }

  },

  /**
   * Create a signature on data using the specified algorithm
   * @param {Integer} hash_algo hash Algorithm to use (See RFC4880 9.4)
   * @param {Integer} algo Asymmetric cipher algorithm to use (See RFC4880 9.1)
   * @param {Array<module:type/mpi>} publicMPIs Public key multiprecision integers 
   * of the private key 
   * @param {Array<module:type/mpi>} secretMPIs Private key multiprecision 
   * integers which is used to sign the data
   * @param {String} data Data to be signed
   * @return {Array<module:type/mpi>}
   */
  sign: function(hash_algo, algo, keyIntegers, data) {

    switch (algo) {
      case 1:
        // RSA (Encrypt or Sign) [HAC]  
      case 2:
        // RSA Encrypt-Only [HAC]
      case 3:
        // RSA Sign-Only [HAC]
        var rsa = new publicKey.rsa();
        var d = keyIntegers[2].toBigInteger();
        var n = keyIntegers[0].toBigInteger();
        var m = pkcs1.emsa.encode(hash_algo,
          data, keyIntegers[0].byteLength());

        return rsa.sign(m, d, n).toMPI();

      case 17:
        // DSA (Digital Signature Algorithm) [FIPS186] [HAC]
        var dsa = new publicKey.dsa();

        var p = keyIntegers[0].toBigInteger();
        var q = keyIntegers[1].toBigInteger();
        var g = keyIntegers[2].toBigInteger();
        var y = keyIntegers[3].toBigInteger();
        var x = keyIntegers[4].toBigInteger();
        var m = data;
        var result = dsa.sign(hash_algo, m, g, p, q, x);

        return result[0].toString() + result[1].toString();
      case 16:
        // Elgamal (Encrypt-Only) [ELGAMAL] [HAC]
        throw new Error('Signing with Elgamal is not defined in the OpenPGP standard.');
      default:
        throw new Error('Invalid signature algorithm.');
    }
  }
}