using GostCryptography.Asn1.Ber;
using GostCryptography.Properties;

namespace GostCryptography.Asn1.Gost
{
    public abstract class GostAsn1Choice : Asn1Choice
    {
        private const byte Null = 1;
        private const byte Params = 2;

        protected abstract short TagForm { get; }
        protected abstract int TagIdCode { get; }
        protected abstract Asn1Type CreateParams();

        public override string ElemName
        {
            get
            {
                switch (ChoiceId)
                {
                    case Null:
                        return "null_";
                    case Params:
                        return "params_";
                }

                return "UNDEFINED";
            }
        }

        public override void Decode(Asn1BerDecodeBuffer buffer, bool explicitTagging, int implicitLength)
        {
            var tag = new Asn1Tag();
            buffer.Mark();

            var num = buffer.DecodeTagAndLength(tag);

            if (tag.Equals(0, 0, NullTypeCode))
            {
                buffer.Reset();

                SetElement(Null, new NullParams());
                Element.Decode(buffer, true, num);
            }
            else
            {
                if (!tag.Equals(0, TagForm, TagIdCode))
                {
                    throw ExceptionUtility.CryptographicException(Resources.Asn1InvalidChoiceOptionTagException, tag, buffer.ByteCount);
                }

                buffer.Reset();

                SetElement(Params, CreateParams());
                Element.Decode(buffer, true, num);
            }
        }

        public override int Encode(Asn1BerEncodeBuffer buffer, bool explicitTagging)
        {
            switch (ChoiceId)
            {
                case Null:
                    return GetElement().Encode(buffer, true);
                case Params:
                    return GetElement().Encode(buffer, true);
            }

            throw ExceptionUtility.CryptographicException(Resources.Asn1InvalidChoiceOptionException);
        }
    }
}