mxaccess/src/MxNativeCodec/NmxItemControlMessage.cs

using System.Buffers.Binary;

namespace MxNativeCodec;

public enum NmxItemControlCommand : byte
{
    Advise = 0x1f,
    AdviseSupervisory = 0x1f,
    UnAdvise = 0x21,
}

public sealed record NmxItemControlMessage(
    NmxItemControlCommand Command,
    Guid ItemCorrelationId,
    ushort ObjectId,
    ushort ObjectSignature,
    short PrimitiveId,
    short AttributeId,
    short PropertyId,
    ushort AttributeSignature,
    short AttributeIndex,
    uint Tail)
{
    private const ushort Version = 1;
    private const int HeaderLength = 3;
    private const int GuidLength = 16;
    private const int AdviseExtraLength = 2;
    private const int PayloadLength = 18;

    public static int GetEncodedLength(NmxItemControlCommand command)
    {
        return HeaderLength
            + GuidLength
            + (command == NmxItemControlCommand.AdviseSupervisory ? AdviseExtraLength : 0)
            + PayloadLength;
    }

    public static NmxItemControlMessage Parse(ReadOnlySpan<byte> body)
    {
        if (body.Length < HeaderLength + GuidLength + PayloadLength)
        {
            throw new ArgumentException("NMX item-control body is too short.", nameof(body));
        }

        var command = (NmxItemControlCommand)body[0];
        if (command is not (NmxItemControlCommand.AdviseSupervisory or NmxItemControlCommand.UnAdvise))
        {
            throw new ArgumentException($"Unsupported item-control command 0x{body[0]:X2}.", nameof(body));
        }

        ushort version = BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(1, sizeof(ushort)));
        if (version != Version)
        {
            throw new ArgumentException($"Unsupported item-control version {version}.", nameof(body));
        }

        int expectedLength = GetEncodedLength(command);
        if (body.Length != expectedLength)
        {
            throw new ArgumentException($"Unexpected item-control body length {body.Length}; expected {expectedLength}.", nameof(body));
        }

        int offset = HeaderLength;
        var itemCorrelationId = new Guid(body.Slice(offset, GuidLength));
        offset += GuidLength;
        if (command == NmxItemControlCommand.AdviseSupervisory)
        {
            offset += AdviseExtraLength;
        }

        return new NmxItemControlMessage(
            command,
            itemCorrelationId,
            BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(offset, sizeof(ushort))),
            BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(offset + 2, sizeof(ushort))),
            BinaryPrimitives.ReadInt16LittleEndian(body.Slice(offset + 4, sizeof(short))),
            BinaryPrimitives.ReadInt16LittleEndian(body.Slice(offset + 6, sizeof(short))),
            BinaryPrimitives.ReadInt16LittleEndian(body.Slice(offset + 8, sizeof(short))),
            BinaryPrimitives.ReadUInt16LittleEndian(body.Slice(offset + 10, sizeof(ushort))),
            BinaryPrimitives.ReadInt16LittleEndian(body.Slice(offset + 12, sizeof(short))),
            BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(offset + 14, sizeof(uint))));
    }

    public static NmxItemControlMessage FromReferenceHandle(
        NmxItemControlCommand command,
        Guid itemCorrelationId,
        MxReferenceHandle referenceHandle,
        uint tail = 3)
    {
        return new NmxItemControlMessage(
            command,
            itemCorrelationId,
            referenceHandle.ObjectId,
            referenceHandle.ObjectSignature,
            referenceHandle.PrimitiveId,
            referenceHandle.AttributeId,
            referenceHandle.PropertyId,
            referenceHandle.AttributeSignature,
            referenceHandle.AttributeIndex,
            tail);
    }

    public MxReferenceHandle ToReferenceHandle(
        byte galaxyId = 1,
        ushort platformId = 1,
        ushort engineId = 1)
    {
        return new MxReferenceHandle(
            galaxyId,
            platformId,
            engineId,
            ObjectId,
            ObjectSignature,
            PrimitiveId,
            AttributeId,
            PropertyId,
            AttributeSignature,
            AttributeIndex);
    }

    public byte[] Encode()
    {
        byte[] body = new byte[GetEncodedLength(Command)];
        body[0] = (byte)Command;
        BinaryPrimitives.WriteUInt16LittleEndian(body.AsSpan(1, sizeof(ushort)), Version);
        int offset = HeaderLength;
        ItemCorrelationId.TryWriteBytes(body.AsSpan(offset, GuidLength));
        offset += GuidLength;
        if (Command == NmxItemControlCommand.AdviseSupervisory)
        {
            offset += AdviseExtraLength;
        }

        BinaryPrimitives.WriteUInt16LittleEndian(body.AsSpan(offset, sizeof(ushort)), ObjectId);
        BinaryPrimitives.WriteUInt16LittleEndian(body.AsSpan(offset + 2, sizeof(ushort)), ObjectSignature);
        BinaryPrimitives.WriteInt16LittleEndian(body.AsSpan(offset + 4, sizeof(short)), PrimitiveId);
        BinaryPrimitives.WriteInt16LittleEndian(body.AsSpan(offset + 6, sizeof(short)), AttributeId);
        BinaryPrimitives.WriteInt16LittleEndian(body.AsSpan(offset + 8, sizeof(short)), PropertyId);
        BinaryPrimitives.WriteUInt16LittleEndian(body.AsSpan(offset + 10, sizeof(ushort)), AttributeSignature);
        BinaryPrimitives.WriteInt16LittleEndian(body.AsSpan(offset + 12, sizeof(short)), AttributeIndex);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(offset + 14, sizeof(uint)), Tail);
        return body;
    }

    public NmxItemControlMessage ToUnAdvise()
    {
        return this with { Command = NmxItemControlCommand.UnAdvise };
    }

    public NmxItemControlMessage ToAdviseSupervisory()
    {
        return this with { Command = NmxItemControlCommand.AdviseSupervisory };
    }
}