using System;

namespace Org.BouncyCastle.Asn1.X509
{
    public class AlgorithmIdentifier
        : Asn1Encodable
    {
        private readonly DerObjectIdentifier	objectID;
        private readonly Asn1Encodable			parameters;
        private readonly bool					parametersDefined;

        public static AlgorithmIdentifier GetInstance(
            Asn1TaggedObject	obj,
            bool				explicitly)
        {
            return GetInstance(Asn1Sequence.GetInstance(obj, explicitly));
        }

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

            // TODO: delete
            if (obj is DerObjectIdentifier)
                return new AlgorithmIdentifier((DerObjectIdentifier) obj);

            // TODO: delete
            if (obj is string)
                return new AlgorithmIdentifier((string) obj);

            return new AlgorithmIdentifier(Asn1Sequence.GetInstance(obj));
        }

        public AlgorithmIdentifier(
            DerObjectIdentifier objectID)
        {
            this.objectID = objectID;
        }

        public AlgorithmIdentifier(
            string objectID)
        {
            this.objectID = new DerObjectIdentifier(objectID);
        }

        public AlgorithmIdentifier(
            DerObjectIdentifier	objectID,
            Asn1Encodable		parameters)
        {
            this.objectID = objectID;
            this.parameters = parameters;
            this.parametersDefined = true;
        }

        internal AlgorithmIdentifier(
            Asn1Sequence seq)
        {
            if (seq.Count < 1 || seq.Count > 2)
                throw new ArgumentException("Bad sequence size: " + seq.Count);

            this.objectID = DerObjectIdentifier.GetInstance(seq[0]);
            this.parametersDefined = (seq.Count == 2);

            if (parametersDefined)
            {
                this.parameters = seq[1];
            }
        }

        /// <summary>
        /// Return the OID in the Algorithm entry of this identifier.
        /// </summary>
		public virtual DerObjectIdentifier Algorithm
		{
			get { return objectID; }
		}

        public virtual DerObjectIdentifier ObjectID
        {
            get { return objectID; }
        }

        /// <summary>
        /// Return the parameters structure in the Parameters entry of this identifier.
        /// </summary>
        public Asn1Encodable Parameters
        {
            get { return parameters; }
        }

        /**
         * Produce an object suitable for an Asn1OutputStream.
         * <pre>
         *      AlgorithmIdentifier ::= Sequence {
         *                            algorithm OBJECT IDENTIFIER,
         *                            parameters ANY DEFINED BY algorithm OPTIONAL }
         * </pre>
         */
        public override Asn1Object ToAsn1Object()
        {
            Asn1EncodableVector v = new Asn1EncodableVector(objectID);

            if (parametersDefined)
            {
                if (parameters != null)
                {
                    v.Add(parameters);
                }
                else
                {
                    v.Add(DerNull.Instance);
                }
            }

            return new DerSequence(v);
        }
    }
}