using System;
using System.Collections;
using System.IO;

using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Math;

namespace Org.BouncyCastle.Asn1.Pkcs
{
    public class PrivateKeyInfo
        : Asn1Encodable
    {
        private readonly Asn1Object				privKey;
        private readonly AlgorithmIdentifier	algID;
		private readonly Asn1Set				attributes;

		public static PrivateKeyInfo GetInstance(
			object obj)
		{
			if (obj is PrivateKeyInfo)
				return (PrivateKeyInfo) obj;

			if (obj != null)
				return new PrivateKeyInfo(Asn1Sequence.GetInstance(obj));

			return null;
		}

		public PrivateKeyInfo(
            AlgorithmIdentifier	algID,
            Asn1Object			privateKey)
			: this(algID, privateKey, null)
		{
		}

		public PrivateKeyInfo(
			AlgorithmIdentifier	algID,
			Asn1Object			privateKey,
			Asn1Set				attributes)
		{
			this.privKey = privateKey;
			this.algID = algID;
			this.attributes = attributes;
		}

		private PrivateKeyInfo(
            Asn1Sequence seq)
        {
            IEnumerator e = seq.GetEnumerator();

			e.MoveNext();
            BigInteger version = ((DerInteger) e.Current).Value;
            if (version.IntValue != 0)
            {
                throw new ArgumentException("wrong version for private key info: " + version.IntValue);
            }

            e.MoveNext();
            algID = AlgorithmIdentifier.GetInstance(e.Current);

			try
            {
				e.MoveNext();
				Asn1OctetString data = (Asn1OctetString) e.Current;

				privKey = Asn1Object.FromByteArray(data.GetOctets());
            }
            catch (IOException)
            {
				throw new ArgumentException("Error recoverying private key from sequence");
            }

			if (e.MoveNext())
			{
				attributes = Asn1Set.GetInstance((Asn1TaggedObject) e.Current, false);
			}
		}

		public AlgorithmIdentifier AlgorithmID
		{
			get { return algID; }
		}

		public Asn1Object PrivateKey
		{
			get { return privKey; }
		}

    	public Asn1Set Attributes
    	{
    		get { return attributes; }
    	}

		/**
         * write out an RSA private key with its associated information
         * as described in Pkcs8.
         * <pre>
         *      PrivateKeyInfo ::= Sequence {
         *                              version Version,
         *                              privateKeyAlgorithm AlgorithmIdentifier {{PrivateKeyAlgorithms}},
         *                              privateKey PrivateKey,
         *                              attributes [0] IMPLICIT Attributes OPTIONAL
         *                          }
         *      Version ::= Integer {v1(0)} (v1,...)
         *
         *      PrivateKey ::= OCTET STRING
         *
         *      Attributes ::= Set OF Attr
         * </pre>
         */
        public override Asn1Object ToAsn1Object()
        {
			Asn1EncodableVector v = new Asn1EncodableVector(
				new DerInteger(0),
				algID,
				new DerOctetString(privKey));

			if (attributes != null)
			{
				v.Add(new DerTaggedObject(false, 0, attributes));
			}

			return new DerSequence(v);
        }
    }
}