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

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;

        private readonly byte[][] tmpBuffers;

        internal static int FindLimit(Stream input)
        {
            if (input is LimitedInputStream)
            {
                return ((LimitedInputStream)input).GetRemaining();
            }
            else if (input is MemoryStream)
            {
                MemoryStream mem = (MemoryStream)input;
                return (int)(mem.Length - mem.Position);
            }

            return int.MaxValue;
        }

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

        /**
         * 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	inputStream,
            int		limit)
            : base(inputStream)
        {
            this.limit = limit;
            this.tmpBuffers = new byte[16][];
        }

        /**
         * 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)
        {
        }

        /**
        * 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.s, length);

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

            if ((tag & Asn1Tags.Tagged) != 0)
            {
                return new Asn1StreamParser(defIn).ReadTaggedObject(isConstructed, tagNo);
            }

            if (isConstructed)
            {
                // TODO There are other tags that may be constructed (e.g. BitString)
                switch (tagNo)
                {
                    case Asn1Tags.OctetString:
                        //
                        // yes, people actually do this...
                        //
                        return new BerOctetString(ReadVector(defIn));
                    case Asn1Tags.Sequence:
                        return CreateDerSequence(defIn);
                    case Asn1Tags.Set:
                        return CreateDerSet(defIn);
                    case Asn1Tags.External:
                        return new DerExternal(ReadVector(defIn));                
                    default:
                        throw new IOException("unknown tag " + tagNo + " encountered");
                }
            }

            return CreatePrimitiveDerObject(tagNo, defIn, tmpBuffers);
        }

        internal virtual Asn1EncodableVector ReadVector(DefiniteLengthInputStream dIn)
        {
            if (dIn.Remaining < 1)
                return new Asn1EncodableVector(0);

            Asn1InputStream subStream = new Asn1InputStream(dIn);
            Asn1EncodableVector v = new Asn1EncodableVector();
            Asn1Object o;
            while ((o = subStream.ReadObject()) != null)
            {
                v.Add(o);
            }

            return v;
        }

        internal virtual DerSequence CreateDerSequence(
            DefiniteLengthInputStream dIn)
        {
            return DerSequence.FromVector(ReadVector(dIn));
        }

        internal virtual DerSet CreateDerSet(
            DefiniteLengthInputStream dIn)
        {
            return DerSet.FromVector(ReadVector(dIn), false);
        }

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

                return null;
            }

            //
            // calculate tag number
            //
            int tagNo = ReadTagNumber(this.s, tag);

            bool isConstructed = (tag & Asn1Tags.Constructed) != 0;

            //
            // calculate length
            //
            int length = ReadLength(this.s, limit);

            if (length < 0) // indefinite length method
            {
                if (!isConstructed)
                    throw new IOException("indefinite length primitive encoding encountered");

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

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

                if ((tag & Asn1Tags.Tagged) != 0)
                {
                    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 new BerOctetStringParser(sp).ToAsn1Object();
                    case Asn1Tags.Sequence:
                        return new BerSequenceParser(sp).ToAsn1Object();
                    case Asn1Tags.Set:
                        return new BerSetParser(sp).ToAsn1Object();
                    case Asn1Tags.External:
                        return new DerExternalParser(sp).ToAsn1Object();
                    default:
                        throw new IOException("unknown BER object encountered");
                }
            }
            else
            {
                try
                {
                    return BuildObject(tag, tagNo, length);
                }
                catch (ArgumentException e)
                {
                    throw new Asn1Exception("corrupted stream detected", e);
                }
            }
        }

        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();

                // 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) // Note: -1 will pass
                {
                    throw new IOException("Corrupted stream - invalid high tag number found");
                }

                while ((b >= 0) && ((b & 0x80) != 0))
                {
                    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)
        {
            int length = s.ReadByte();
            if (length < 0)
                throw new EndOfStreamException("EOF found when length expected");

            if (length == 0x80)
                return -1;      // indefinite-length encoding

            if (length > 127)
            {
                int size = length & 0x7f;

                // Note: The invalid long form "0xff" (see X.690 8.1.3.5c) will be caught here
                if (size > 4)
                    throw new IOException("DER length more than 4 bytes: " + size);

                length = 0;
                for (int i = 0; i < size; i++)
                {
                    int next = s.ReadByte();

                    if (next < 0)
                        throw new EndOfStreamException("EOF found reading length");

                    length = (length << 8) + next;
                }

                if (length < 0)
                    throw new IOException("Corrupted stream - negative length found");

                if (length >= limit)   // after all we must have read at least 1 byte
                    throw new IOException("Corrupted stream - out of bounds length found");
            }

            return length;
        }

        internal static byte[] GetBuffer(DefiniteLengthInputStream defIn, byte[][] tmpBuffers)
        {
            int len = defIn.GetRemaining();
            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;
        }

        internal static Asn1Object CreatePrimitiveDerObject(
            int                         tagNo,
            DefiniteLengthInputStream   defIn,
            byte[][]                    tmpBuffers)
        {
            switch (tagNo)
            {
                case Asn1Tags.Boolean:
                    return DerBoolean.FromOctetString(GetBuffer(defIn, tmpBuffers));
                case Asn1Tags.Enumerated:
                    return DerEnumerated.FromOctetString(GetBuffer(defIn, tmpBuffers));
                case Asn1Tags.ObjectIdentifier:
                    return DerObjectIdentifier.FromOctetString(GetBuffer(defIn, tmpBuffers));
            }

            byte[] bytes = defIn.ToArray();

            switch (tagNo)
            {
                case Asn1Tags.BitString:
                    return DerBitString.FromAsn1Octets(bytes);
                case Asn1Tags.BmpString:
                    return new DerBmpString(bytes);
                case Asn1Tags.GeneralizedTime:
                    return new DerGeneralizedTime(bytes);
                case Asn1Tags.GeneralString:
                    return new DerGeneralString(bytes);
                case Asn1Tags.GraphicString:
                    return new DerGraphicString(bytes);
                case Asn1Tags.IA5String:
                    return new DerIA5String(bytes);
                case Asn1Tags.Integer:
                    return new DerInteger(bytes);
                case Asn1Tags.Null:
                    return DerNull.Instance;   // actual content is ignored (enforce 0 length?)
                case Asn1Tags.NumericString:
                    return new DerNumericString(bytes);
                case Asn1Tags.OctetString:
                    return new DerOctetString(bytes);
                case Asn1Tags.PrintableString:
                    return new DerPrintableString(bytes);
                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");
            }
        }
    }
}