using System.Buffers.Binary;

namespace MxNativeCodec;

public enum NmxTransferMessageKind : int
{
    Metadata = 1,
    ItemControl = 2,
    Write = 3,
}

public sealed record NmxTransferEnvelope(
    NmxTransferMessageKind MessageKind,
    int SourceGalaxyId,
    int SourcePlatformId,
    int LocalEngineId,
    int TargetGalaxyId,
    int TargetPlatformId,
    int TargetEngineId,
    int TimeoutMilliseconds,
    ReadOnlyMemory<byte> InnerBody)
{
    public const int HeaderLength = 46;
    private const ushort Version = 1;
    private const int InnerLengthOffset = 2;
    private const int ReservedOffset = 6;
    private const int MessageKindOffset = 10;
    private const int SourceGalaxyOffset = 14;
    private const int SourcePlatformOffset = 18;
    private const int LocalEngineOffset = 22;
    private const int TargetGalaxyOffset = 26;
    private const int TargetPlatformOffset = 30;
    private const int TargetEngineOffset = 34;
    private const int ProtocolMarkerOffset = 38;
    private const int TimeoutOffset = 42;
    private const int ProtocolMarker = 0x0201;
    private const int DefaultTimeoutMilliseconds = 30000;

    public static NmxTransferEnvelope Parse(ReadOnlyMemory<byte> transferBody)
    {
        if (transferBody.Length < HeaderLength)
        {
            throw new ArgumentException("NMX TransferData body is too short.", nameof(transferBody));
        }

        ReadOnlySpan<byte> span = transferBody.Span;
        ushort version = BinaryPrimitives.ReadUInt16LittleEndian(span[..sizeof(ushort)]);
        if (version != Version)
        {
            throw new ArgumentException($"Unsupported NMX TransferData version {version}.", nameof(transferBody));
        }

        int innerLength = BinaryPrimitives.ReadInt32LittleEndian(span.Slice(InnerLengthOffset, sizeof(int)));
        if (innerLength != transferBody.Length - HeaderLength)
        {
            throw new ArgumentException("NMX TransferData inner length does not match the body size.", nameof(transferBody));
        }

        int protocolMarker = BinaryPrimitives.ReadInt32LittleEndian(span.Slice(ProtocolMarkerOffset, sizeof(int)));
        if (protocolMarker != ProtocolMarker)
        {
            throw new ArgumentException($"Unsupported NMX TransferData protocol marker 0x{protocolMarker:X8}.", nameof(transferBody));
        }

        return new NmxTransferEnvelope(
            (NmxTransferMessageKind)BinaryPrimitives.ReadInt32LittleEndian(span.Slice(MessageKindOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(SourceGalaxyOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(SourcePlatformOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(LocalEngineOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(TargetGalaxyOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(TargetPlatformOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(TargetEngineOffset, sizeof(int))),
            BinaryPrimitives.ReadInt32LittleEndian(span.Slice(TimeoutOffset, sizeof(int))),
            transferBody[HeaderLength..]);
    }

    public static byte[] Encode(
        NmxTransferMessageKind messageKind,
        int localEngineId,
        int targetGalaxyId,
        int targetPlatformId,
        int targetEngineId,
        ReadOnlySpan<byte> innerBody,
        int sourceGalaxyId = 1,
        int sourcePlatformId = 1,
        int timeoutMilliseconds = DefaultTimeoutMilliseconds)
    {
        byte[] transferBody = new byte[HeaderLength + innerBody.Length];
        BinaryPrimitives.WriteUInt16LittleEndian(transferBody.AsSpan(0, sizeof(ushort)), Version);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(InnerLengthOffset, sizeof(int)), innerBody.Length);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(ReservedOffset, sizeof(int)), 0);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(MessageKindOffset, sizeof(int)), (int)messageKind);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(SourceGalaxyOffset, sizeof(int)), sourceGalaxyId);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(SourcePlatformOffset, sizeof(int)), sourcePlatformId);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(LocalEngineOffset, sizeof(int)), localEngineId);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(TargetGalaxyOffset, sizeof(int)), targetGalaxyId);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(TargetPlatformOffset, sizeof(int)), targetPlatformId);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(TargetEngineOffset, sizeof(int)), targetEngineId);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(ProtocolMarkerOffset, sizeof(int)), ProtocolMarker);
        BinaryPrimitives.WriteInt32LittleEndian(transferBody.AsSpan(TimeoutOffset, sizeof(int)), timeoutMilliseconds);
        innerBody.CopyTo(transferBody.AsSpan(HeaderLength));
        return transferBody;
    }
}