using GostCryptography.Properties;

namespace GostCryptography.Asn1.Ber
{
    public class Asn1BerDecodeContext
    {
        private readonly int _decBufByteCount;
        private readonly Asn1BerDecodeBuffer _decodeBuffer;
        private readonly int _elemLength;
        private readonly Asn1Tag _tagHolder;

        public Asn1BerDecodeContext(Asn1BerDecodeBuffer decodeBuffer, int elemLength)
        {
            _decodeBuffer = decodeBuffer;
            _decBufByteCount = decodeBuffer.ByteCount;
            _elemLength = elemLength;
            _tagHolder = new Asn1Tag();
        }

        public virtual bool Expired()
        {
            if (_elemLength == Asn1Status.IndefiniteLength)
            {
                var parsedLen = new IntHolder();
                var flag = _decodeBuffer.MatchTag(0, 0, 0, null, parsedLen);

                if (flag)
                {
                    _decodeBuffer.Reset();
                }

                return flag;
            }

            var num = _decodeBuffer.ByteCount - _decBufByteCount;

            return (num >= _elemLength);
        }

        public virtual bool MatchElemTag(Asn1Tag tag, IntHolder parsedLen, bool advance)
        {
            return MatchElemTag(tag.Class, tag.Form, tag.IdCode, parsedLen, advance);
        }

        public virtual bool MatchElemTag(short tagClass, short tagForm, int tagIdCode, IntHolder parsedLen, bool advance)
        {
            if (Expired())
            {
                return false;
            }

            var flag = _decodeBuffer.MatchTag(tagClass, tagForm, tagIdCode, _tagHolder, parsedLen);

            if ((_elemLength != Asn1Status.IndefiniteLength) && (parsedLen.Value != Asn1Status.IndefiniteLength))
            {
                var num = _decodeBuffer.ByteCount - _decBufByteCount;

                if ((parsedLen.Value < 0) || (parsedLen.Value > (_elemLength - num)))
                {
                    throw ExceptionUtility.CryptographicException(Resources.Asn1InvalidLengthException);
                }
            }

            if (flag && !advance)
            {
                _decodeBuffer.Reset();
            }

            return flag;
        }
    }
}