using System;
using System.Diagnostics;
using System.IO;

using Org.BouncyCastle.Utilities;
using Org.BouncyCastle.Utilities.IO;

namespace Org.BouncyCastle.Asn1
{
    /**
     * a general purpose ASN.1 decoder - note: this class differs from the
     * others in that it returns null after it has read the last object in
     * the stream. If an ASN.1 Null is encountered a Der/BER Null object is
     * returned.
     */
    public class Asn1InputStream
        : FilterStream
    {
        private readonly int limit;

        internal readonly byte[][] tmpBuffers;

        internal static int FindLimit(Stream input)
        {
            if (input is LimitedInputStream)
                return ((LimitedInputStream)input).Limit;

            if (input is Asn1InputStream)
                return ((Asn1InputStream)input).Limit;

            if (input is MemoryStream)
            {
                MemoryStream mem = (MemoryStream)input;
                return (int)(mem.Length - mem.Position);
            }

            return int.MaxValue;
        }

        public Asn1InputStream(Stream input)
            : this(input, FindLimit(input))
        {
        }

        /**
         * Create an ASN1InputStream based on the input byte array. The length of DER objects in
         * the stream is automatically limited to the length of the input array.
         *
         * @param input array containing ASN.1 encoded data.
         */
        public Asn1InputStream(byte[] input)
            : this(new MemoryStream(input, false), input.Length)
        {
        }

        /**
         * Create an ASN1InputStream where no DER object will be longer than limit.
         *
         * @param input stream containing ASN.1 encoded data.
         * @param limit maximum size of a DER encoded object.
         */
        public Asn1InputStream(Stream input, int limit)
            : this(input, limit, new byte[16][])
        {
        }

        internal Asn1InputStream(Stream input, int limit, byte[][] tmpBuffers)
            : base(input)
        {
            this.limit = limit;
            this.tmpBuffers = tmpBuffers;
        }

        /**
        * build an object given its tag and the number of bytes to construct it from.
        */
        private Asn1Object BuildObject(
            int	tag,
            int	tagNo,
            int	length)
        {
            bool isConstructed = (tag & Asn1Tags.Constructed) != 0;

            DefiniteLengthInputStream defIn = new DefiniteLengthInputStream(this, length, limit);

            int tagClass = tag & Asn1Tags.Private;
            if (0 != tagClass)
            {
                if ((tag & Asn1Tags.Application) != 0)
                    return new DerApplicationSpecific(isConstructed, tagNo, defIn.ToArray());

                return new Asn1StreamParser(defIn, defIn.Remaining, tmpBuffers).ReadTaggedObject(isConstructed, tagNo);
            }

            if (!isConstructed)
                return CreatePrimitiveDerObject(tagNo, defIn, tmpBuffers);

            switch (tagNo)
            {
            case Asn1Tags.BitString:
            {
                return BuildConstructedBitString(ReadVector(defIn));
            }
            case Asn1Tags.OctetString:
            {
                //
                // yes, people actually do this...
                //
                return BuildConstructedOctetString(ReadVector(defIn));
            }
            case Asn1Tags.Sequence:
                return CreateDLSequence(defIn);
            case Asn1Tags.Set:
                return CreateDLSet(defIn);
            case Asn1Tags.External:
                return DLSequence.FromVector(ReadVector(defIn)).ToAsn1External();
            default:
                throw new IOException("unknown tag " + tagNo + " encountered");
            }
        }

        internal virtual Asn1EncodableVector ReadVector()
        {
            Asn1Object o = ReadObject();
            if (null == o)
                return new Asn1EncodableVector(0);

            Asn1EncodableVector v = new Asn1EncodableVector();
            do
            {
                v.Add(o);
            }
            while ((o = ReadObject()) != null);
            return v;
        }

        internal virtual Asn1EncodableVector ReadVector(DefiniteLengthInputStream defIn)
        {
            int remaining = defIn.Remaining;
            if (remaining < 1)
                return new Asn1EncodableVector(0);

            return new Asn1InputStream(defIn, remaining, tmpBuffers).ReadVector();
        }

        internal virtual Asn1Sequence CreateDLSequence(DefiniteLengthInputStream defIn)
        {
            return DLSequence.FromVector(ReadVector(defIn));
        }

        internal virtual Asn1Set CreateDLSet(DefiniteLengthInputStream defIn)
        {
            return DLSet.FromVector(ReadVector(defIn));
        }

        public Asn1Object ReadObject()
        {
            int tag = ReadByte();
            if (tag <= 0)
            {
                if (tag == 0)
                    throw new IOException("unexpected end-of-contents marker");

                return null;
            }

            int tagNo = ReadTagNumber(this, tag);
            int length = ReadLength(this, limit, false);

            if (length >= 0)
            {
                // definite-length
                try
                {
                    return BuildObject(tag, tagNo, length);
                }
                catch (ArgumentException e)
                {
                    throw new Asn1Exception("corrupted stream detected", e);
                }
            }

            // indefinite-length

            if (0 == (tag & Asn1Tags.Constructed))
                throw new IOException("indefinite-length primitive encoding encountered");

            IndefiniteLengthInputStream indIn = new IndefiniteLengthInputStream(this, limit);
            Asn1StreamParser sp = new Asn1StreamParser(indIn, limit, tmpBuffers);

            int tagClass = tag & Asn1Tags.Private;
            if (0 != tagClass)
            {
                if ((tag & Asn1Tags.Application) != 0)
                    return new BerApplicationSpecificParser(tagNo, sp).ToAsn1Object();

                return new BerTaggedObjectParser(true, tagNo, sp).ToAsn1Object();
            }

            // TODO There are other tags that may be constructed (e.g. BitString)
            switch (tagNo)
            {
            case Asn1Tags.OctetString:
                return BerOctetStringParser.Parse(sp);
            case Asn1Tags.Sequence:
                return BerSequenceParser.Parse(sp);
            case Asn1Tags.Set:
                return BerSetParser.Parse(sp);
            case Asn1Tags.External:
                return DerExternalParser.Parse(sp);
            default:
                throw new IOException("unknown BER object encountered");
            }
        }

        internal virtual DerBitString BuildConstructedBitString(Asn1EncodableVector contentsElements)
        {
            DerBitString[] bitStrings = new DerBitString[contentsElements.Count];

            for (int i = 0; i != bitStrings.Length; i++)
            {
                DerBitString bitString = contentsElements[i] as DerBitString;
                if (null == bitString)
                    throw new Asn1Exception("unknown object encountered in constructed BIT STRING: "
                        + Platform.GetTypeName(contentsElements[i]));

                bitStrings[i] = bitString;
            }

            // TODO Probably ought to be DLBitString
            return new BerBitString(bitStrings);
        }

        internal virtual Asn1OctetString BuildConstructedOctetString(Asn1EncodableVector contentsElements)
        {
            Asn1OctetString[] octetStrings = new Asn1OctetString[contentsElements.Count];

            for (int i = 0; i != octetStrings.Length; i++)
            {
                Asn1OctetString octetString = contentsElements[i] as Asn1OctetString;
                if (null == octetString)
                    throw new Asn1Exception("unknown object encountered in constructed OCTET STRING: "
                        + Platform.GetTypeName(contentsElements[i]));

                octetStrings[i] = octetString;
            }

            // TODO Probably ought to be DerOctetString (no DLOctetString available)
            return new BerOctetString(octetStrings);
        }

        internal virtual int Limit
        {
            get { return limit; }
        }

        internal static int ReadTagNumber(Stream s, int tag)
        {
            int tagNo = tag & 0x1f;

            //
            // with tagged object tag number is bottom 5 bits, or stored at the start of the content
            //
            if (tagNo == 0x1f)
            {
                tagNo = 0;

                int b = s.ReadByte();
                if (b < 31)
                {
                    if (b < 0)
                        throw new EndOfStreamException("EOF found inside tag value.");

                    throw new IOException("corrupted stream - high tag number < 31 found");
                }

                // X.690-0207 8.1.2.4.2
                // "c) bits 7 to 1 of the first subsequent octet shall not all be zero."
                if ((b & 0x7f) == 0)
                    throw new IOException("corrupted stream - invalid high tag number found");

                while ((b & 0x80) != 0)
                {
                    if (((uint)tagNo >> 24) != 0U)
                        throw new IOException("Tag number more than 31 bits");

                    tagNo |= b & 0x7f;
                    tagNo <<= 7;
                    b = s.ReadByte();
                    if (b < 0)
                        throw new EndOfStreamException("EOF found inside tag value.");
                }

                tagNo |= b & 0x7f;
            }

            return tagNo;
        }

        internal static int ReadLength(Stream s, int limit, bool isParsing)
        {
            int length = s.ReadByte();
            if (0U == ((uint)length >> 7))
            {
                // definite-length short form 
                return length;
            }
            if (0x80 == length)
            {
                // indefinite-length
                return -1;
            }
            if (length < 0)
            {
                throw new EndOfStreamException("EOF found when length expected");
            }
            if (0xFF == length)
            {
                throw new IOException("invalid long form definite-length 0xFF");
            }

            int octetsCount = length & 0x7F, octetsPos = 0;

            length = 0;
            do
            {
                int octet = s.ReadByte();
                if (octet < 0)
                    throw new EndOfStreamException("EOF found reading length");

                if (((uint)length >> 23) != 0U)
                    throw new IOException("long form definite-length more than 31 bits");

                length = (length << 8) + octet;
            }
            while (++octetsPos < octetsCount);

            if (length >= limit && !isParsing)   // after all we must have read at least 1 byte
                throw new IOException("corrupted stream - out of bounds length found: " + length + " >= " + limit);

            return length;
        }

        private static byte[] GetBuffer(DefiniteLengthInputStream defIn, byte[][] tmpBuffers)
        {
            int len = defIn.Remaining;
            if (len >= tmpBuffers.Length)
            {
                return defIn.ToArray();
            }

            byte[] buf = tmpBuffers[len];
            if (buf == null)
            {
                buf = tmpBuffers[len] = new byte[len];
            }

            defIn.ReadAllIntoByteArray(buf);

            return buf;
        }

        private static char[] GetBmpCharBuffer(DefiniteLengthInputStream defIn)
        {
            int remainingBytes = defIn.Remaining;
            if (0 != (remainingBytes & 1))
                throw new IOException("malformed BMPString encoding encountered");

            char[] str = new char[remainingBytes / 2];
            int stringPos = 0;

            byte[] buf = new byte[8];
            while (remainingBytes >= 8)
            {
                if (Streams.ReadFully(defIn, buf, 0, 8) != 8)
                    throw new EndOfStreamException("EOF encountered in middle of BMPString");

                str[stringPos    ] = (char)((buf[0] << 8) | (buf[1] & 0xFF));
                str[stringPos + 1] = (char)((buf[2] << 8) | (buf[3] & 0xFF));
                str[stringPos + 2] = (char)((buf[4] << 8) | (buf[5] & 0xFF));
                str[stringPos + 3] = (char)((buf[6] << 8) | (buf[7] & 0xFF));
                stringPos += 4;
                remainingBytes -= 8;
            }
            if (remainingBytes > 0)
            {
                if (Streams.ReadFully(defIn, buf, 0, remainingBytes) != remainingBytes)
                    throw new EndOfStreamException("EOF encountered in middle of BMPString");

                int bufPos = 0;
                do
                {
                    int b1 = buf[bufPos++] << 8;
                    int b2 = buf[bufPos++] & 0xFF;
                    str[stringPos++] = (char)(b1 | b2);
                }
                while (bufPos < remainingBytes);
            }

            if (0 != defIn.Remaining || str.Length != stringPos)
                throw new InvalidOperationException();

            return str;
        }

        internal static Asn1Object CreatePrimitiveDerObject(
            int                         tagNo,
            DefiniteLengthInputStream   defIn,
            byte[][]                    tmpBuffers)
        {
            switch (tagNo)
            {
                case Asn1Tags.BmpString:
                    return new DerBmpString(GetBmpCharBuffer(defIn));
                case Asn1Tags.Boolean:
                    return DerBoolean.FromOctetString(GetBuffer(defIn, tmpBuffers));
                case Asn1Tags.Enumerated:
                    return DerEnumerated.FromOctetString(GetBuffer(defIn, tmpBuffers));
                case Asn1Tags.ObjectIdentifier:
                    // TODO Ideally only clone if we used a buffer
                    return DerObjectIdentifier.CreatePrimitive(GetBuffer(defIn, tmpBuffers), true);
            }

            byte[] bytes = defIn.ToArray();

            switch (tagNo)
            {
                case Asn1Tags.BitString:
                    return DerBitString.CreatePrimitive(bytes);
                case Asn1Tags.GeneralizedTime:
                    return new DerGeneralizedTime(bytes);
                case Asn1Tags.GeneralString:
                    return new DerGeneralString(bytes);
                case Asn1Tags.GraphicString:
                    return DerGraphicString.CreatePrimitive(bytes);
                case Asn1Tags.IA5String:
                    return new DerIA5String(bytes);
                case Asn1Tags.Integer:
                    return new DerInteger(bytes, false);
                case Asn1Tags.Null:
                {
                    if (0 != bytes.Length)
                        throw new InvalidOperationException("malformed NULL encoding encountered");

                    return DerNull.Instance;
                }
                case Asn1Tags.NumericString:
                    return new DerNumericString(bytes);
                case Asn1Tags.ObjectDescriptor:
                    return Asn1ObjectDescriptor.CreatePrimitive(bytes);
                case Asn1Tags.OctetString:
                    return new DerOctetString(bytes);
                case Asn1Tags.PrintableString:
                    return new DerPrintableString(bytes);
                case Asn1Tags.RelativeOid:
                    return Asn1RelativeOid.CreatePrimitive(bytes, false);
                case Asn1Tags.T61String:
                    return new DerT61String(bytes);
                case Asn1Tags.UniversalString:
                    return new DerUniversalString(bytes);
                case Asn1Tags.UtcTime:
                    return new DerUtcTime(bytes);
                case Asn1Tags.Utf8String:
                    return new DerUtf8String(bytes);
                case Asn1Tags.VideotexString:
                    return new DerVideotexString(bytes);
                case Asn1Tags.VisibleString:
                    return new DerVisibleString(bytes);
                default:
                    throw new IOException("unknown tag " + tagNo + " encountered");
            }
        }
    }
}