using System;

using Org.BouncyCastle.Asn1.Oiw;
using Org.BouncyCastle.Asn1.X509;

namespace Org.BouncyCastle.Asn1.Pkcs
{
    public class RsassaPssParameters
		: Asn1Encodable
	{
		public readonly static AlgorithmIdentifier DefaultHashAlgorithm = new AlgorithmIdentifier(OiwObjectIdentifiers.IdSha1, DerNull.Instance);
        public readonly static AlgorithmIdentifier DefaultMaskGenAlgorithm = new AlgorithmIdentifier(PkcsObjectIdentifiers.IdMgf1, DefaultHashAlgorithm);
        [Obsolete("Use 'DefaultMaskGenAlgorithm' instead")]
        public readonly static AlgorithmIdentifier DefaultMaskGenFunction = DefaultMaskGenAlgorithm;
		public readonly static DerInteger DefaultSaltLength = new DerInteger(20);
		public readonly static DerInteger DefaultTrailerField = DerInteger.One;

        public static RsassaPssParameters GetInstance(object obj)
        {
            if (obj == null)
                return null;
            if (obj is RsassaPssParameters rsassaPssParameters)
                return rsassaPssParameters;
#pragma warning disable CS0618 // Type or member is obsolete
            return new RsassaPssParameters(Asn1Sequence.GetInstance(obj));
#pragma warning restore CS0618 // Type or member is obsolete
        }

        public static RsassaPssParameters GetInstance(Asn1TaggedObject taggedObject, bool declaredExplicit)
        {
#pragma warning disable CS0618 // Type or member is obsolete
            return new RsassaPssParameters(Asn1Sequence.GetInstance(taggedObject, declaredExplicit));
#pragma warning restore CS0618 // Type or member is obsolete
        }

        private readonly AlgorithmIdentifier m_hashAlgorithm;
        private readonly AlgorithmIdentifier m_maskGenAlgorithm;
        private readonly DerInteger m_saltLength;
        private readonly DerInteger m_trailerField;

        [Obsolete("Use 'GetInstance' instead")]
        public RsassaPssParameters(Asn1Sequence seq)
		{
            int count = seq.Count, pos = 0;
            if (count < 0 || count > 4)
                throw new ArgumentException("Bad sequence size: " + count, nameof(seq));

            m_hashAlgorithm = Asn1Utilities.ReadOptionalContextTagged(seq, ref pos, 0, true, AlgorithmIdentifier.GetTagged)
                ?? DefaultHashAlgorithm;

            m_maskGenAlgorithm = Asn1Utilities.ReadOptionalContextTagged(seq, ref pos, 1, true, AlgorithmIdentifier.GetTagged)
                ?? DefaultMaskGenAlgorithm;

            m_saltLength = Asn1Utilities.ReadOptionalContextTagged(seq, ref pos, 2, true, DerInteger.GetTagged)
                ?? DefaultSaltLength;

            m_trailerField = Asn1Utilities.ReadOptionalContextTagged(seq, ref pos, 3, true, DerInteger.GetTagged)
                ?? DefaultTrailerField;

            if (pos != count)
                throw new ArgumentException("Unexpected elements in sequence", nameof(seq));
		}

        /**
		 * The default version
		 */
        public RsassaPssParameters()
        {
            m_hashAlgorithm = DefaultHashAlgorithm;
            m_maskGenAlgorithm = DefaultMaskGenAlgorithm;
            m_saltLength = DefaultSaltLength;
            m_trailerField = DefaultTrailerField;
        }

        public RsassaPssParameters(AlgorithmIdentifier hashAlgorithm, AlgorithmIdentifier maskGenAlgorithm,
            DerInteger saltLength, DerInteger trailerField)
        {
            m_hashAlgorithm = hashAlgorithm ?? DefaultHashAlgorithm;
            m_maskGenAlgorithm = maskGenAlgorithm ?? DefaultMaskGenAlgorithm;
            m_saltLength = saltLength ?? DefaultSaltLength;
            m_trailerField = trailerField ?? DefaultTrailerField;
        }

		public AlgorithmIdentifier HashAlgorithm => m_hashAlgorithm;

		public AlgorithmIdentifier MaskGenAlgorithm => m_maskGenAlgorithm;

		public DerInteger SaltLength => m_saltLength;

		public DerInteger TrailerField => m_trailerField;

		/**
		 * <pre>
		 * RSASSA-PSS-params ::= SEQUENCE {
		 *   hashAlgorithm      [0] OAEP-PSSDigestAlgorithms  DEFAULT sha1,
		 *    maskGenAlgorithm   [1] PKCS1MGFAlgorithms  DEFAULT mgf1SHA1,
		 *    saltLength         [2] INTEGER  DEFAULT 20,
		 *    trailerField       [3] TrailerField  DEFAULT trailerFieldBC
		 *  }
		 *
		 * OAEP-PSSDigestAlgorithms    ALGORITHM-IDENTIFIER ::= {
		 *    { OID id-sha1 PARAMETERS NULL   }|
		 *    { OID id-sha256 PARAMETERS NULL }|
		 *    { OID id-sha384 PARAMETERS NULL }|
		 *    { OID id-sha512 PARAMETERS NULL },
		 *    ...  -- Allows for future expansion --
		 * }
		 *
		 * PKCS1MGFAlgorithms    ALGORITHM-IDENTIFIER ::= {
		 *   { OID id-mgf1 PARAMETERS OAEP-PSSDigestAlgorithms },
		 *    ...  -- Allows for future expansion --
		 * }
		 *
		 * TrailerField ::= INTEGER { trailerFieldBC(1) }
		 * </pre>
		 * @return the asn1 primitive representing the parameters.
		 */
		public override Asn1Object ToAsn1Object()
		{
			Asn1EncodableVector v = new Asn1EncodableVector(4);

			if (!DefaultHashAlgorithm.Equals(m_hashAlgorithm))
			{
				v.Add(new DerTaggedObject(true, 0, m_hashAlgorithm));
			}

			if (!DefaultMaskGenAlgorithm.Equals(m_maskGenAlgorithm))
			{
				v.Add(new DerTaggedObject(true, 1, m_maskGenAlgorithm));
			}

			if (!DefaultSaltLength.Equals(m_saltLength))
			{
				v.Add(new DerTaggedObject(true, 2, m_saltLength));
			}

			if (!DefaultTrailerField.Equals(m_trailerField))
			{
				v.Add(new DerTaggedObject(true, 3, m_trailerField));
			}

			return new DerSequence(v);
		}
	}
}