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

using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.Pkcs;
using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Security.Certificates;
using Org.BouncyCastle.Utilities.IO;

namespace Org.BouncyCastle.X509
{
	/**
	 * class for dealing with X509 certificates.
	 * <p>
	 * At the moment this will deal with "-----BEGIN CERTIFICATE-----" to "-----END CERTIFICATE-----"
	 * base 64 encoded certs, as well as the BER binaries of certificates and some classes of PKCS#7
	 * objects.</p>
	 */
	public class X509CertificateParser
	{
		private static readonly PemParser PemCertParser = new PemParser("CERTIFICATE");

		private Asn1Set sData;
		private int sDataObjectCount;
		private Stream currentStream;

		private X509Certificate ReadDerCertificate(Asn1InputStream dIn)
		{
			Asn1Sequence seq = (Asn1Sequence)dIn.ReadObject();

			if (seq.Count > 1 && seq[0] is DerObjectIdentifier)
			{
				if (seq[0].Equals(PkcsObjectIdentifiers.SignedData))
				{
					sData = SignedData.GetInstance(
						Asn1Sequence.GetInstance((Asn1TaggedObject) seq[1], true)).Certificates;

					return GetCertificate();
				}
			}

			return new X509Certificate(X509CertificateStructure.GetInstance(seq));
		}

		private X509Certificate ReadPemCertificate(Stream inStream)
		{
			Asn1Sequence seq = PemCertParser.ReadPemObject(inStream);

			return seq == null ? null : new X509Certificate(X509CertificateStructure.GetInstance(seq));
		}

		private X509Certificate GetCertificate()
		{
			if (sData != null)
			{
				while (sDataObjectCount < sData.Count)
				{
					object obj = sData[sDataObjectCount++];

					if (obj is Asn1Sequence)
						return new X509Certificate(X509CertificateStructure.GetInstance(obj));
				}
			}

			return null;
		}

		/// <summary>
		/// Create loading data from byte array.
		/// </summary>
		/// <param name="input"></param>
		public X509Certificate ReadCertificate(byte[] input)
		{
			return ReadCertificate(new MemoryStream(input, false));
		}

		/// <summary>
		/// Create loading data from byte array.
		/// </summary>
		/// <param name="input"></param>
		public IList<X509Certificate> ReadCertificates(byte[] input)
		{
			return ReadCertificates(new MemoryStream(input, false));
		}

		/**
		 * Generates a certificate object and initializes it with the data
		 * read from the input stream inStream.
		 */
		public X509Certificate ReadCertificate(Stream inStream)
		{
			if (inStream == null)
				throw new ArgumentNullException("inStream");
			if (!inStream.CanRead)
				throw new ArgumentException("inStream must be read-able", "inStream");

			if (currentStream == null)
			{
				currentStream = inStream;
				sData = null;
				sDataObjectCount = 0;
			}
			else if (currentStream != inStream) // reset if input stream has changed
			{
				currentStream = inStream;
				sData = null;
				sDataObjectCount = 0;
			}

			try
			{
				if (sData != null)
				{
					if (sDataObjectCount != sData.Count)
						return GetCertificate();

					sData = null;
					sDataObjectCount = 0;
					return null;
				}

                int tag = inStream.ReadByte();
                if (tag < 0)
                    return null;

                if (inStream.CanSeek)
                {
                    inStream.Seek(-1L, SeekOrigin.Current);
                }
                else
                {
                    PushbackStream pis = new PushbackStream(inStream);
                    pis.Unread(tag);
                    inStream = pis;
                }

                if (tag != 0x30)  // assume ascii PEM encoded.
					return ReadPemCertificate(inStream);

				using (var asn1In = new Asn1InputStream(inStream, int.MaxValue, leaveOpen: true))
				{
					return ReadDerCertificate(asn1In);
				}
			}
			catch (CertificateException)
			{
				throw;
			}
			catch (Exception e)
			{
				throw new CertificateException("Failed to read certificate", e);
			}
		}

		/**
		 * Returns a (possibly empty) collection view of the certificates
		 * read from the given input stream inStream.
		 */
		public IList<X509Certificate> ReadCertificates(Stream inStream)
		{
			return new List<X509Certificate>(ParseCertificates(inStream));
		}

		public IEnumerable<X509Certificate> ParseCertificates(Stream inStream)
		{
			X509Certificate cert;
			while ((cert = ReadCertificate(inStream)) != null)
			{
				yield return cert;
			}
		}
	}
}