using System;
using System.Security.Cryptography;
using SystemX509 = System.Security.Cryptography.X509Certificates;

using Org.BouncyCastle.Asn1.Pkcs;
using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Utilities;
using Org.BouncyCastle.X509;

namespace Org.BouncyCastle.Security
{
	/// <summary>
	/// A class containing methods to interface the BouncyCastle world to the .NET Crypto world.
	/// </summary>
	public sealed class DotNetUtilities
	{
		private DotNetUtilities()
		{
		}

		/// <summary>
		/// Create an System.Security.Cryptography.X509Certificate from an X509Certificate Structure.
		/// </summary>
		/// <param name="x509Struct"></param>
		/// <returns>A System.Security.Cryptography.X509Certificate.</returns>
		public static SystemX509.X509Certificate ToX509Certificate(
			X509CertificateStructure x509Struct)
		{
			return new SystemX509.X509Certificate(x509Struct.GetDerEncoded());
		}

		public static SystemX509.X509Certificate ToX509Certificate(
			X509Certificate x509Cert)
		{
			return new SystemX509.X509Certificate(x509Cert.GetEncoded());
		}

		public static X509Certificate FromX509Certificate(
			SystemX509.X509Certificate x509Cert)
		{
			return new X509CertificateParser().ReadCertificate(x509Cert.GetRawCertData());
		}

		public static AsymmetricCipherKeyPair GetDsaKeyPair(
			DSA dsa)
		{
			return GetDsaKeyPair(dsa.ExportParameters(true));
		}

		public static AsymmetricCipherKeyPair GetDsaKeyPair(
			DSAParameters dp)
		{
			DsaValidationParameters validationParameters = (dp.Seed != null)
				?	new DsaValidationParameters(dp.Seed, dp.Counter)
				:	null;

			DsaParameters parameters = new DsaParameters(
				new BigInteger(1, dp.P),
				new BigInteger(1, dp.Q),
				new BigInteger(1, dp.G),
				validationParameters);

			DsaPublicKeyParameters pubKey = new DsaPublicKeyParameters(
				new BigInteger(1, dp.Y),
				parameters);

			DsaPrivateKeyParameters privKey = new DsaPrivateKeyParameters(
				new BigInteger(1, dp.X),
				parameters);

			return new AsymmetricCipherKeyPair(pubKey, privKey);
		}

		public static DsaPublicKeyParameters GetDsaPublicKey(
			DSA dsa)
		{
			return GetDsaPublicKey(dsa.ExportParameters(false));
		}

		public static DsaPublicKeyParameters GetDsaPublicKey(
			DSAParameters dp)
		{
			DsaValidationParameters validationParameters = (dp.Seed != null)
				?	new DsaValidationParameters(dp.Seed, dp.Counter)
				:	null;

			DsaParameters parameters = new DsaParameters(
				new BigInteger(1, dp.P),
				new BigInteger(1, dp.Q),
				new BigInteger(1, dp.G),
				validationParameters);

			return new DsaPublicKeyParameters(
				new BigInteger(1, dp.Y),
				parameters);
		}

		public static AsymmetricCipherKeyPair GetRsaKeyPair(
			RSA rsa)
		{
			return GetRsaKeyPair(rsa.ExportParameters(true));
		}

		public static AsymmetricCipherKeyPair GetRsaKeyPair(
			RSAParameters rp)
		{
			BigInteger modulus = new BigInteger(1, rp.Modulus);
			BigInteger pubExp = new BigInteger(1, rp.Exponent);

			RsaKeyParameters pubKey = new RsaKeyParameters(
				false,
				modulus,
				pubExp);

			RsaPrivateCrtKeyParameters privKey = new RsaPrivateCrtKeyParameters(
				modulus,
				pubExp,
				new BigInteger(1, rp.D),
				new BigInteger(1, rp.P),
				new BigInteger(1, rp.Q),
				new BigInteger(1, rp.DP),
				new BigInteger(1, rp.DQ),
				new BigInteger(1, rp.InverseQ));

			return new AsymmetricCipherKeyPair(pubKey, privKey);
		}

		public static RsaKeyParameters GetRsaPublicKey(
			RSA rsa)
		{
			return GetRsaPublicKey(rsa.ExportParameters(false));
		}

		public static RsaKeyParameters GetRsaPublicKey(
			RSAParameters rp)
		{
			return new RsaKeyParameters(
				false,
				new BigInteger(1, rp.Modulus),
				new BigInteger(1, rp.Exponent));
		}

		public static AsymmetricCipherKeyPair GetKeyPair(AsymmetricAlgorithm privateKey)
		{
			if (privateKey is DSA)
			{
				return GetDsaKeyPair((DSA)privateKey);
			}

			if (privateKey is RSA)
			{
				return GetRsaKeyPair((RSA)privateKey);
			}

			throw new ArgumentException("Unsupported algorithm specified", "privateKey");
		}

		public static RSA ToRSA(RsaKeyParameters rsaKey)
		{
            // TODO This appears to not work for private keys (when no CRT info)
            return CreateRSAProvider(ToRSAParameters(rsaKey));
        }

		public static RSA ToRSA(RsaPrivateCrtKeyParameters privKey)
		{
            return CreateRSAProvider(ToRSAParameters(privKey));
        }

        public static RSA ToRSA(RsaPrivateKeyStructure privKey)
        {
            return CreateRSAProvider(ToRSAParameters(privKey));
        }

        public static RSAParameters ToRSAParameters(RsaKeyParameters rsaKey)
		{
			RSAParameters rp = new RSAParameters();
			rp.Modulus = rsaKey.Modulus.ToByteArrayUnsigned();
			if (rsaKey.IsPrivate)
				rp.D = ConvertRSAParametersField(rsaKey.Exponent, rp.Modulus.Length);
			else
				rp.Exponent = rsaKey.Exponent.ToByteArrayUnsigned();
			return rp;
		}

		public static RSAParameters ToRSAParameters(RsaPrivateCrtKeyParameters privKey)
		{
			RSAParameters rp = new RSAParameters();
			rp.Modulus = privKey.Modulus.ToByteArrayUnsigned();
			rp.Exponent = privKey.PublicExponent.ToByteArrayUnsigned();
			rp.P = privKey.P.ToByteArrayUnsigned();
			rp.Q = privKey.Q.ToByteArrayUnsigned();
			rp.D = ConvertRSAParametersField(privKey.Exponent, rp.Modulus.Length);
			rp.DP = ConvertRSAParametersField(privKey.DP, rp.P.Length);
			rp.DQ = ConvertRSAParametersField(privKey.DQ, rp.Q.Length);
			rp.InverseQ = ConvertRSAParametersField(privKey.QInv, rp.Q.Length);
			return rp;
		}

        public static RSAParameters ToRSAParameters(RsaPrivateKeyStructure privKey)
        {
            RSAParameters rp = new RSAParameters();
            rp.Modulus = privKey.Modulus.ToByteArrayUnsigned();
            rp.Exponent = privKey.PublicExponent.ToByteArrayUnsigned();
            rp.P = privKey.Prime1.ToByteArrayUnsigned();
            rp.Q = privKey.Prime2.ToByteArrayUnsigned();
            rp.D = ConvertRSAParametersField(privKey.PrivateExponent, rp.Modulus.Length);
            rp.DP = ConvertRSAParametersField(privKey.Exponent1, rp.P.Length);
            rp.DQ = ConvertRSAParametersField(privKey.Exponent2, rp.Q.Length);
            rp.InverseQ = ConvertRSAParametersField(privKey.Coefficient, rp.Q.Length);
            return rp;
        }

        // TODO Move functionality to more general class
		private static byte[] ConvertRSAParametersField(BigInteger n, int size)
		{
			byte[] bs = n.ToByteArrayUnsigned();

			if (bs.Length == size)
				return bs;

			if (bs.Length > size)
				throw new ArgumentException("Specified size too small", "size");

			byte[] padded = new byte[size];
			Array.Copy(bs, 0, padded, size - bs.Length, bs.Length);
			return padded;
		}

        private static RSA CreateRSAProvider(RSAParameters rp)
        {
            CspParameters csp = new CspParameters();
            csp.KeyContainerName = string.Format("BouncyCastle-{0}", Guid.NewGuid());
            RSACryptoServiceProvider rsaCsp = new RSACryptoServiceProvider(csp);
            rsaCsp.ImportParameters(rp);
            return rsaCsp;
        }
	}
}