Engine-Pong/Game/Network/NetworkBase.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using LiteNetLib;
using LiteNetLib.Utils;

using Syntriax.Engine.Core;
using Syntriax.Engine.Network.Abstract;

namespace Syntriax.Engine.Network;

public abstract class NetworkBase : BehaviourOverride, INetworkCommunicator
{
    public event INetworkCommunicator.OnPacketReceivedDelegate? OnPacketReceived = null;

    protected readonly NetPacketProcessor netPacketProcessor = new();

    protected readonly Dictionary<uint, INetworkEntity> networkEntities = [];

    protected BehaviourCollector<INetworkEntity> networkEntityCollector = null!;

    public EventBasedNetListener Listener { get; private set; } = null!;
    public NetManager Manager { get; private set; } = null!;

    public NetworkBase()
    {
        Priority = 10;

        Listener = new EventBasedNetListener();
        Manager = new NetManager(Listener);

        Listener.NetworkReceiveEvent += NetworkReceiveEvent;

        netPacketProcessor.RegisterNestedType<Pong.Behaviours.PaddleBehaviour.PaddleInputs>();
        RegisterPackets();
    }

    public void RegisterPackets()
    {
        var packetTypes = Assembly.GetExecutingAssembly().GetTypes()
            .Where(t => typeof(INetworkPacket).IsAssignableFrom(t) && !t.IsInterface)
            .ToList();

        MethodInfo[] subscribeMethods = netPacketProcessor.GetType()
            .GetMethods()
            .Where(m => m.Name == nameof(NetPacketProcessor.SubscribeReusable))
            .ToArray();

        MethodInfo subscribeMethod = subscribeMethods
            .FirstOrDefault(m =>
                m.GetParameters().Length == 1 &&
                m.GetParameters()[0].ParameterType.GetGenericTypeDefinition() == typeof(Action<,>)
            ) ?? throw new Exception();

        MethodInfo[] methodInfos = typeof(NetworkBase)
            .GetMethods(BindingFlags.NonPublic | BindingFlags.Instance);

        MethodInfo method = methodInfos
            .FirstOrDefault(
                m => m.Name == nameof(OnPacketArrived) &&
                m.IsGenericMethodDefinition
            ) ?? throw new Exception();

        foreach (var packetType in packetTypes)
        {
            var networkPacketType = typeof(NetworkPacket<>).MakeGenericType(packetType);
            MethodInfo genericSubscribe = subscribeMethod.MakeGenericMethod(networkPacketType, typeof(NetPeer));

            Action<object, NetPeer> handler = (packet, peer) =>
            {
                MethodInfo handlerMethod = method.MakeGenericMethod(packetType);
                handlerMethod.Invoke(this, [packet, peer]);
            };
            genericSubscribe.Invoke(netPacketProcessor, [handler]);
        }
    }

    private void OnPacketArrived<T>(NetworkPacket<T> packet, NetPeer peer) where T : INetworkPacket
    {
        if (networkEntities.TryGetValue(packet.NetworkId, out INetworkEntity? entity))
            entity.ReceiveData(packet.Data);

        OnPacketReceived?.Invoke(this, packet);
    }

    protected override void OnInitialize()
    {
        base.OnInitialize();

        networkEntityCollector = new(GameObject.GameManager);
        networkEntityCollector.OnCollected += OnNetworkEntityCollected;
        networkEntityCollector.OnRemoved += OnNetworkEntityRemoved;
    }

    protected override void OnFinalize()
    {
        networkEntityCollector.OnCollected -= OnNetworkEntityCollected;
        networkEntityCollector.OnRemoved -= OnNetworkEntityRemoved;
        Stop();
    }

    private void OnNetworkEntityCollected(BehaviourCollector<INetworkEntity> sender, INetworkEntity behaviourCollected)
    {
        if (behaviourCollected.NetworkId != 0)
            networkEntities.Add(behaviourCollected.NetworkId, behaviourCollected);

        behaviourCollected.OnNetworkIdChanged += OnNetworkIdChanged;
    }

    private void OnNetworkIdChanged(INetworkEntity sender, uint previousId)
    {
        if (networkEntities.TryGetValue(previousId, out INetworkEntity? networkEntity) && sender == networkEntity)
            networkEntities.Remove(previousId);

        networkEntities.Add(sender.NetworkId, sender);
    }

    private void OnNetworkEntityRemoved(BehaviourCollector<INetworkEntity> sender, INetworkEntity behaviourRemoved)
    {
        networkEntities.Remove(behaviourRemoved.NetworkId);
        behaviourRemoved.OnNetworkIdChanged -= OnNetworkIdChanged;
    }

    private void NetworkReceiveEvent(NetPeer peer, NetPacketReader reader, byte channel, DeliveryMethod deliveryMethod)
    {
        try
        {
            netPacketProcessor.ReadAllPackets(reader, peer);
        }
        catch { }
    }

    public void PollEvents() => Manager.PollEvents();
    public void Stop() => Manager.Stop();

    protected override void OnUpdate() => PollEvents();

    public abstract void Send<T>(NetworkPacket<T> packet);
}