using System;
using System.Collections;
using System.Text;

using Org.BouncyCastle.Asn1.IsisMtt;
using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Asn1.X500;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security.Certificates;
using Org.BouncyCastle.Utilities;
using Org.BouncyCastle.Utilities.Collections;
using Org.BouncyCastle.X509;
using Org.BouncyCastle.X509.Store;

namespace Org.BouncyCastle.Pkix
{
	/**
	* Implements the PKIX CertPathBuilding algorithm for BouncyCastle.
	*
	* @see CertPathBuilderSpi
	*/
	public class PkixCertPathBuilder
		//		: CertPathBuilderSpi
	{
		/**
		 * Build and validate a CertPath using the given parameter.
		 *
		 * @param params PKIXBuilderParameters object containing all information to
		 *            build the CertPath
		 */
		public virtual PkixCertPathBuilderResult Build(
			PkixBuilderParameters pkixParams)
		{
			// search target certificates

			IX509Selector certSelect = pkixParams.GetTargetCertConstraints();
			if (!(certSelect is X509CertStoreSelector))
			{
				throw new PkixCertPathBuilderException(
					"TargetConstraints must be an instance of "
					+ typeof(X509CertStoreSelector).FullName + " for "
					+ this.GetType() + " class.");
			}

			ISet targets = new HashSet();
			try
			{
				targets.AddAll(PkixCertPathValidatorUtilities.FindCertificates((X509CertStoreSelector)certSelect, pkixParams.GetStores()));
				// TODO Should this include an entry for pkixParams.GetAdditionalStores() too?
			}
			catch (Exception e)
			{
				throw new PkixCertPathBuilderException(
					"Error finding target certificate.", e);
			}

			if (targets.IsEmpty)
				throw new PkixCertPathBuilderException("No certificate found matching targetContraints.");

			PkixCertPathBuilderResult result = null;
			IList certPathList = Platform.CreateArrayList();

			// check all potential target certificates
			foreach (X509Certificate cert in targets)
			{
				result = Build(cert, pkixParams, certPathList);

				if (result != null)
					break;
			}

			if (result == null && certPathException != null)
			{
				throw new PkixCertPathBuilderException(certPathException.Message, certPathException.InnerException);
			}

			if (result == null && certPathException == null)
			{
				throw new PkixCertPathBuilderException("Unable to find certificate chain.");
			}

			return result;
		}

		private Exception certPathException;

		protected virtual PkixCertPathBuilderResult Build(
			X509Certificate			tbvCert,
			PkixBuilderParameters	pkixParams,
			IList					tbvPath)
		{
			// If tbvCert is readily present in tbvPath, it indicates having run
			// into a cycle in the PKI graph.
			if (tbvPath.Contains(tbvCert))
				return null;

			// step out, the certificate is not allowed to appear in a certification
			// chain.
			if (pkixParams.GetExcludedCerts().Contains(tbvCert))
				return null;

			// test if certificate path exceeds maximum length
			if (pkixParams.MaxPathLength != -1)
			{
				if (tbvPath.Count - 1 > pkixParams.MaxPathLength)
					return null;
			}

			tbvPath.Add(tbvCert);

//			X509CertificateParser certParser = new X509CertificateParser();
			PkixCertPathBuilderResult builderResult = null;
			PkixCertPathValidator validator = new PkixCertPathValidator();

			try
			{
				// check whether the issuer of <tbvCert> is a TrustAnchor
				if (PkixCertPathValidatorUtilities.FindTrustAnchor(tbvCert, pkixParams.GetTrustAnchors()) != null)
				{
					// exception message from possibly later tried certification
					// chains
					PkixCertPath certPath = null;
					try
					{
						certPath = new PkixCertPath(tbvPath);
					}
					catch (Exception e)
					{
						throw new Exception(
							"Certification path could not be constructed from certificate list.",
							e);
					}

					PkixCertPathValidatorResult result = null;
					try
					{
						result = (PkixCertPathValidatorResult)validator.Validate(
							certPath, pkixParams);
					}
					catch (Exception e)
					{
						throw new Exception(
							"Certification path could not be validated.", e);
					}

					return new PkixCertPathBuilderResult(certPath, result.TrustAnchor,
						result.PolicyTree, result.SubjectPublicKey);
				}
				else
				{
					// add additional X.509 stores from locations in certificate
					try
					{
						PkixCertPathValidatorUtilities.AddAdditionalStoresFromAltNames(
							tbvCert, pkixParams);
					}
					catch (CertificateParsingException e)
					{
						throw new Exception(
							"No additiontal X.509 stores can be added from certificate locations.",
							e);
					}

					// try to get the issuer certificate from one of the stores
					HashSet issuers = new HashSet();
					try
					{
						issuers.AddAll(PkixCertPathValidatorUtilities.FindIssuerCerts(tbvCert, pkixParams));
					}
					catch (Exception e)
					{
						throw new Exception(
							"Cannot find issuer certificate for certificate in certification path.",
							e);
					}

					if (issuers.IsEmpty)
						throw new Exception("No issuer certificate for certificate in certification path found.");

					foreach (X509Certificate issuer in issuers)
					{
						builderResult = Build(issuer, pkixParams, tbvPath);

						if (builderResult != null)
							break;
					}
				}
			}
			catch (Exception e)
			{
				certPathException = e;
			}

			if (builderResult == null)
			{
				tbvPath.Remove(tbvCert);
			}

			return builderResult;
		}
	}
}