Syntriax.Engine/Engine.Integration/Engine.Integration.LiteNetLib/LiteNetLibCommunicatorBase.cs

using System.Reflection;

using Engine.Core;
using Engine.Core.Debug;
using Engine.Systems.Network.Packers;

using LiteNetLib;
using LiteNetLib.Utils;

namespace Engine.Systems.Network;

public abstract class LiteNetLibCommunicatorBase : Behaviour, IEnterUniverse, IExitUniverse, INetworkCommunicator
{
    protected readonly NetPacketProcessor netPacketProcessor = new();
    protected readonly PacketCryptor cryptor = new("At4ywW9PGoWH3g==", "NmpMFTvd3pvUbA=="); // TODO implement public key exchange

    private readonly Dictionary<Type, Event<IConnection, object>> listeners = [];
    private readonly Dictionary<string, IConnection> _connections = [];

    private readonly Dictionary<int, IConnection> localPeerIdToConnectionDictionary = [];

    protected ILogger? logger = null;

    public IReadOnlyDictionary<string, IConnection> Connections => _connections;
    public EventBasedNetListener Listener { get; private set; } = null!;
    public NetManager Manager { get; private set; } = null!;

    public Event<INetworkCommunicator, IConnection> OnConnectionEstablished { get; } = new();
    public Event<INetworkCommunicator, IConnection> OnConnectionAbolished { get; } = new();

    public INetworkCommunicator Stop()
    {
        Manager.Stop();
        return this;
    }

    public virtual void EnterUniverse(IUniverse universe)
    {
        logger = universe.FindBehaviour<ILogger>();
    }

    public virtual void ExitUniverse(IUniverse universe)
    {
        logger = null;
        Stop();
    }

    protected virtual void OnPacketArrived<T>(T packet, NetPeer peer) where T : INetworkPacket
    {
        if (!listeners.TryGetValue(typeof(T), out Event<IConnection, object>? @event))
            return;

        @event.Invoke(localPeerIdToConnectionDictionary[peer.Id], packet);
    }

    private void NetworkReceiveEvent(NetPeer peer, NetPacketReader reader, byte channel, DeliveryMethod deliveryMethod)
    {
        try
        {
            bool isEncrypted = reader.GetBool();
            if (isEncrypted) // TODO performance improvements 
            {
                byte[] encryptedData = reader.GetBytesWithLength();
                byte[] decryptedData = cryptor.Decrypt(encryptedData);
                NetDataReader innerReader = new(decryptedData);
                netPacketProcessor.ReadAllPackets(innerReader, peer);
                return;
            }

            netPacketProcessor.ReadAllPackets(reader, peer);
        }
        catch (Exception exception) { logger?.LogException(this, exception, force: true); }
    }

    protected abstract IConnection GetConnection(NetPeer peer);
    private void ConnectionEstablished(NetPeer peer)
    {
        IConnection connection = GetConnection(peer);

        localPeerIdToConnectionDictionary.Add(peer.Id, connection);
        _connections.Add(connection.Id, connection);

        logger?.Log(this, $"Connection established with ip '{peer.Address}' and id '{connection.Id}'");
        OnConnectionEstablished.Invoke(this, connection);
    }

    private void ConnectionAbolished(NetPeer peer, DisconnectInfo disconnectInfo)
    {
        if (!localPeerIdToConnectionDictionary.TryGetValue(peer.Id, out IConnection? connection))
            return;

        localPeerIdToConnectionDictionary.Remove(peer.Id);
        _connections.Remove(connection.Id);

        logger?.Log(this, $"Connection abolished with ip '{peer.Address}' and id '{connection.Id}'");
        OnConnectionAbolished.Invoke(this, connection);
    }

    private void SetupPackets()
    {
        // Find network packets implementing INetworkPacket
        IEnumerable<Type> packetTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(a => a.GetTypes())
            .Where(t => typeof(INetworkPacket).IsAssignableFrom(t) && !t.IsInterface && !t.IsAbstract && !t.IsGenericType);

        MethodInfo subscribeReusableMethod = typeof(NetPacketProcessor)
            .GetMethods()
            .FirstOrDefault(m => m.Name == nameof(NetPacketProcessor.SubscribeReusable) &&
                m.GetParameters().Length == 1 &&
                m.GetParameters()[0].ParameterType.GetGenericTypeDefinition() == typeof(Action<,>)
            )!;

        MethodInfo registerNestedTypeMethod = typeof(NetPacketProcessor)
            .GetMethods()
            .FirstOrDefault(m => m.Name == nameof(NetPacketProcessor.RegisterNestedType) &&
                m.GetParameters().Length == 0
            )!;

        MethodInfo onPacketArrivedMethod = typeof(LiteNetLibCommunicatorBase)
            .GetMethod(nameof(OnPacketArrived), BindingFlags.NonPublic | BindingFlags.Instance)!;

        // Register all network packets by calling the methods bellow where T is our found network packet type
        // NetPacketProcessor.SubscribeReusable<T, NetPeer>(Action<T, NetPeer> onReceive)
        // NetPacketProcessor.RegisterNestedType<T>()
        foreach (Type packetType in packetTypes)
        {
            if (!packetType.IsClass)
            {
                MethodInfo genericRegisterNestedTypeMethod = registerNestedTypeMethod.MakeGenericMethod(packetType);
                genericRegisterNestedTypeMethod.Invoke(netPacketProcessor, []);
                continue;
            }

            MethodInfo genericOnPacketArrivedMethod = onPacketArrivedMethod.MakeGenericMethod(packetType);

            Type delegateType = typeof(Action<,>).MakeGenericType(packetType, typeof(NetPeer));
            Delegate delegateHandler = Delegate.CreateDelegate(delegateType, this, genericOnPacketArrivedMethod);

            MethodInfo genericSubscribeReusableMethod = subscribeReusableMethod.MakeGenericMethod(packetType, typeof(NetPeer));
            genericSubscribeReusableMethod.Invoke(netPacketProcessor, [delegateHandler]);
        }
    }

    public LiteNetLibCommunicatorBase()
    {
        Listener = new EventBasedNetListener();
        Manager = new NetManager(Listener);

        Listener.NetworkReceiveEvent += NetworkReceiveEvent;
        Listener.PeerConnectedEvent += ConnectionEstablished;
        Listener.PeerDisconnectedEvent += ConnectionAbolished;

        SetupEnginePackets();
        SetupPackets();
    }

    private void SetupEnginePackets()
    {
        // I know, ugly af. I need to find a better way
        netPacketProcessor.RegisterNestedType(AABB2DNetPacker.Write, AABB2DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(AABB3DNetPacker.Write, AABB3DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(CircleNetPacker.Write, CircleNetPacker.Read);
        netPacketProcessor.RegisterNestedType(ColorHSVNetPacker.Write, ColorHSVNetPacker.Read);
        netPacketProcessor.RegisterNestedType(ColorHSVANetPacker.Write, ColorHSVANetPacker.Read);
        netPacketProcessor.RegisterNestedType(ColorRGBNetPacker.Write, ColorRGBNetPacker.Read);
        netPacketProcessor.RegisterNestedType(ColorRGBANetPacker.Write, ColorRGBANetPacker.Read);
        netPacketProcessor.RegisterNestedType(Line2DNetPacker.Write, Line2DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Line2DEquationNetPacker.Write, Line2DEquationNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Line3DNetPacker.Write, Line3DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Projection1DNetPacker.Write, Projection1DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(QuaternionNetPacker.Write, QuaternionNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Ray2DNetPacker.Write, Ray2DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Ray3DNetPacker.Write, Ray3DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Shape2DNetPacker.Write, Shape2DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Sphere3DNetPacker.Write, Sphere3DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(TriangleNetPacker.Write, TriangleNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Vector2DNetPacker.Write, Vector2DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Vector2DIntNetPacker.Write, Vector2DIntNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Vector3DNetPacker.Write, Vector3DNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Vector3DIntNetPacker.Write, Vector3DIntNetPacker.Read);
        netPacketProcessor.RegisterNestedType(Vector4DNetPacker.Write, Vector4DNetPacker.Read);
    }

    public INetworkCommunicator SubscribeToPackets<T>(Event<IConnection, T>.EventHandler callback)
    {
        Type type = typeof(T);
        if (!listeners.TryGetValue(type, out Event<IConnection, object>? @event))
        {
            @event = new();
            listeners.Add(type, @event);
        }

        @event.AddListener(EventDelegateWrapper(callback));
        return this;
    }

    public INetworkCommunicator UnsubscribeFromPackets<T>(Event<IConnection, T>.EventHandler callback)
    {
        Type type = typeof(T);
        if (!listeners.TryGetValue(type, out Event<IConnection, object>? @event))
            return this;

        @event.RemoveListener(EventDelegateWrapper(callback));
        return this;
    }

    private static Event<IConnection, object>.EventHandler EventDelegateWrapper<T>(Event<IConnection, T>.EventHandler callback) => (sender, @object) => callback.Invoke(sender, (T)@object);
}