using System;

using Org.BouncyCastle.Utilities;

namespace Org.BouncyCastle.Asn1.X509
{
	/**
	* This class helps to support crossCerfificatePairs in a LDAP directory
	* according RFC 2587
	*
	* <pre>
	*     crossCertificatePairATTRIBUTE::={
	*       WITH SYNTAX   CertificatePair
	*       EQUALITY MATCHING RULE certificatePairExactMatch
	*       ID joint-iso-ccitt(2) ds(5) attributeType(4) crossCertificatePair(40)}
	* </pre>
	*
	* <blockquote> The forward elements of the crossCertificatePair attribute of a
	* CA's directory entry shall be used to store all, except self-issued
	* certificates issued to this CA. Optionally, the reverse elements of the
	* crossCertificatePair attribute, of a CA's directory entry may contain a
	* subset of certificates issued by this CA to other CAs. When both the forward
	* and the reverse elements are present in a single attribute value, issuer name
	* in one certificate shall match the subject name in the other and vice versa,
	* and the subject public key in one certificate shall be capable of verifying
	* the digital signature on the other certificate and vice versa.
	*
	* When a reverse element is present, the forward element value and the reverse
	* element value need not be stored in the same attribute value; in other words,
	* they can be stored in either a single attribute value or two attribute
	* values. </blockquote>
	*
	* <pre>
	*       CertificatePair ::= SEQUENCE {
	*         forward		[0]	Certificate OPTIONAL,
	*         reverse		[1]	Certificate OPTIONAL,
	*         -- at least one of the pair shall be present -- }
	* </pre>
	*/
	public class CertificatePair
		: Asn1Encodable
	{
		private X509CertificateStructure forward, reverse;

		public static CertificatePair GetInstance(
			object obj)
		{
			if (obj == null || obj is CertificatePair)
			{
				return (CertificatePair) obj;
			}

			if (obj is Asn1Sequence)
			{
				return new CertificatePair((Asn1Sequence) obj);
			}

            throw new ArgumentException("unknown object in factory: " + Platform.GetTypeName(obj), "obj");
		}

		/**
		* Constructor from Asn1Sequence.
		* <p/>
		* The sequence is of type CertificatePair:
		* <p/>
		* <pre>
		*       CertificatePair ::= SEQUENCE {
		*         forward		[0]	Certificate OPTIONAL,
		*         reverse		[1]	Certificate OPTIONAL,
		*         -- at least one of the pair shall be present -- }
		* </pre>
		*
		* @param seq The ASN.1 sequence.
		*/
		private CertificatePair(
			Asn1Sequence seq)
		{
			if (seq.Count != 1 && seq.Count != 2)
			{
				throw new ArgumentException("Bad sequence size: " + seq.Count, "seq");
			}

			foreach (object obj in seq)
			{
				Asn1TaggedObject o = Asn1TaggedObject.GetInstance(obj);
				if (o.TagNo == 0)
				{
					forward = X509CertificateStructure.GetInstance(o, true);
				}
				else if (o.TagNo == 1)
				{
					reverse = X509CertificateStructure.GetInstance(o, true);
				}
				else
				{
					throw new ArgumentException("Bad tag number: " + o.TagNo);
				}
			}
		}

		/**
		* Constructor from a given details.
		*
		* @param forward Certificates issued to this CA.
		* @param reverse Certificates issued by this CA to other CAs.
		*/
		public CertificatePair(
			X509CertificateStructure	forward,
			X509CertificateStructure	reverse)
		{
			this.forward = forward;
			this.reverse = reverse;
		}

		/**
		* Produce an object suitable for an Asn1OutputStream.
		* <p/>
		* Returns:
		* <p/>
		* <pre>
		*       CertificatePair ::= SEQUENCE {
		*         forward		[0]	Certificate OPTIONAL,
		*         reverse		[1]	Certificate OPTIONAL,
		*         -- at least one of the pair shall be present -- }
		* </pre>
		*
		* @return a DERObject
		*/
		public override Asn1Object ToAsn1Object()
		{
			Asn1EncodableVector vec = new Asn1EncodableVector();

			if (forward != null)
			{
				vec.Add(new DerTaggedObject(0, forward));
			}

			if (reverse != null)
			{
				vec.Add(new DerTaggedObject(1, reverse));
			}

			return new DerSequence(vec);
		}

		/**
		* @return Returns the forward.
		*/
		public X509CertificateStructure Forward
		{
			get { return forward; }
		}

		/**
		* @return Returns the reverse.
		*/
		public X509CertificateStructure Reverse
		{
			get { return reverse; }
		}
	}
}