Engine-Pong/Shared/Network/NetworkManager.cs

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

using Syntriax.Engine.Core;

namespace Syntriax.Engine.Network;

public class NetworkManager : UniverseObject, INetworkManager
{
    private INetworkCommunicator networkCommunicator = null!;
    private readonly List<(Type packetType, Delegate callback)> delegates = [];

    public INetworkCommunicator NetworkCommunicator
    {
        get => networkCommunicator;
        set
        {
            if (networkCommunicator == value)
                return;

            var previousCommunicator = networkCommunicator;
            networkCommunicator = value;

            if (previousCommunicator is not null) UnsubscribeDelegates(networkCommunicator);
            if (networkCommunicator is not null) SubscribeDelegates(networkCommunicator);
        }
    }

    private readonly Dictionary<Type, Dictionary<string, PacketListenerData>> clientPacketListeners = [];
    private readonly Dictionary<Type, Dictionary<string, PacketListenerData>> serverPacketListeners = [];

    private readonly Dictionary<string, INetworkEntity> _networkEntities = [];
    public IReadOnlyDictionary<string, INetworkEntity> NetworkEntities => _networkEntities;

    private readonly BehaviourCollector<INetworkEntity> _networkEntityCollector = new();
    public IBehaviourCollector<INetworkEntity> NetworkEntityCollector => _networkEntityCollector;

    public NetworkManager()
    {
        CacheDelegates();

        _networkEntityCollector.OnCollected += OnCollected;
        _networkEntityCollector.OnRemoved += OnRemoved;
    }

    private void CacheDelegates()
    {
        // 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 onPacketArrivedMethod = GetType()
            .GetMethod(nameof(OnPacketReceived), BindingFlags.NonPublic | BindingFlags.Instance)!;

        foreach (Type packetType in packetTypes)
        {
            MethodInfo genericOnPacketArrivedMethod = onPacketArrivedMethod.MakeGenericMethod(packetType);

            Type genericDelegateType = typeof(Action<,>).MakeGenericType(packetType, typeof(string));
            Delegate genericPacketReceivedDelegate = Delegate.CreateDelegate(genericDelegateType, this, genericOnPacketArrivedMethod);

            delegates.Add((packetType, genericPacketReceivedDelegate));
        }
    }

    private void SubscribeDelegates(INetworkCommunicator networkCommunicator)
    {
        MethodInfo subscribeToPacketsMethod = typeof(INetworkCommunicator)
            .GetMethod(nameof(INetworkCommunicator.SubscribeToPackets), BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance)!;

        foreach ((Type packetType, Delegate callback) in delegates)
        {
            MethodInfo genericSubscribeMethod = subscribeToPacketsMethod.MakeGenericMethod(packetType);

            genericSubscribeMethod.Invoke(networkCommunicator, [callback]);
        }
    }

    private void UnsubscribeDelegates(INetworkCommunicator networkCommunicator)
    {
        MethodInfo unsubscribeFromPacketsMethod = typeof(INetworkCommunicator)
            .GetMethod(nameof(INetworkCommunicator.UnsubscribeFromPackets), BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance)!;

        foreach ((Type packetType, Delegate callback) in delegates)
        {
            MethodInfo genericUnsubscribeMethod = unsubscribeFromPacketsMethod.MakeGenericMethod(packetType);

            genericUnsubscribeMethod.Invoke(networkCommunicator, [callback]);
        }
    }

    private void OnPacketReceived<T>(T entityDataPacket, string fromClientId)
    {
        Type packetType = typeof(T);

        if (entityDataPacket is IEntityNetworkPacket entityPacket)
        {
            if (networkCommunicator is INetworkCommunicatorClient)
                if (clientPacketListeners.TryGetValue(packetType, out Dictionary<string, PacketListenerData>? clientListeners))
                    if (clientListeners.TryGetValue(entityPacket.EntityId, out PacketListenerData clientListenerData))
                        clientListenerData.ListenerMethod.Invoke(clientListenerData.Object, [entityDataPacket]);

            if (networkCommunicator is INetworkCommunicatorServer)
                if (serverPacketListeners.TryGetValue(packetType, out Dictionary<string, PacketListenerData>? serverListeners))
                    if (serverListeners.TryGetValue(entityPacket.EntityId, out PacketListenerData serverListenerData))
                        serverListenerData.ListenerMethod.Invoke(serverListenerData.Object, [entityDataPacket, fromClientId]);

            return;
        }

        if (networkCommunicator is INetworkCommunicatorClient)
            if (clientPacketListeners.TryGetValue(packetType, out Dictionary<string, PacketListenerData>? clientListeners))
                foreach ((string id, PacketListenerData clientListenerData) in clientListeners)
                    clientListenerData.ListenerMethod.Invoke(clientListenerData.Object, [entityDataPacket]);

        if (networkCommunicator is INetworkCommunicatorServer)
            if (serverPacketListeners.TryGetValue(packetType, out Dictionary<string, PacketListenerData>? serverListeners))
                foreach ((string id, PacketListenerData serverListenerData) in serverListeners)
                    serverListenerData.ListenerMethod.Invoke(serverListenerData.Object, [entityDataPacket, fromClientId]);
    }

    private void OnCollected(IBehaviourCollector<INetworkEntity> sender, INetworkEntity behaviourCollected)
    {
        if (!_networkEntities.TryAdd(behaviourCollected.Id, behaviourCollected))
            throw new($"Unable to add {behaviourCollected.Id} to {nameof(NetworkManager)}");

        foreach (Type clientListenerType in behaviourCollected.GetType().GetInterfaces().Where(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IPacketListenerClient<>)))
        {
            Type clientListenerParameterType = clientListenerType.GetGenericArguments().First();
            MethodInfo clientListenerReceiveMethod = clientListenerType.GetMethods().First(m => m.Name == nameof(IPacketListenerClient<INetworkEntity>.OnClientPacketArrived));

            if (!clientPacketListeners.TryGetValue(clientListenerParameterType, out Dictionary<string, PacketListenerData>? clientListeners))
            {
                clientListeners = [];
                clientPacketListeners.Add(clientListenerParameterType, clientListeners);
            }

            clientListeners.Add(behaviourCollected.Id, new(behaviourCollected, clientListenerReceiveMethod));
        }

        foreach (Type serverListenerType in behaviourCollected.GetType().GetInterfaces().Where(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IPacketListenerServer<>)))
        {
            Type serverListenerParameterType = serverListenerType.GetGenericArguments().First();
            MethodInfo serverListenerReceiveMethod = serverListenerType.GetMethods().First(m => m.Name == nameof(IPacketListenerServer<INetworkEntity>.OnServerPacketArrived));

            if (!serverPacketListeners.TryGetValue(serverListenerParameterType, out Dictionary<string, PacketListenerData>? serverListeners))
            {
                serverListeners = [];
                serverPacketListeners.Add(serverListenerParameterType, serverListeners);
            }

            serverListeners.Add(behaviourCollected.Id, new(behaviourCollected, serverListenerReceiveMethod));
        }
    }

    private void OnRemoved(IBehaviourCollector<INetworkEntity> sender, INetworkEntity behaviourRemoved)
    {
        _networkEntities.Remove(behaviourRemoved.Id);
    }

    protected override void OnExitingUniverse(IUniverse universe) => _networkEntityCollector.Unassign();
    protected override void OnEnteringUniverse(IUniverse universe)
    {
        _networkEntityCollector.Assign(universe);
        NetworkCommunicator = this.GetRequiredUniverseObjectInParent<INetworkCommunicator>();
    }

    private record struct PacketListenerData(object Object, MethodInfo ListenerMethod)
    {
        public static implicit operator (object @object, MethodInfo listenerMethod)(PacketListenerData value) => (value.Object, value.ListenerMethod);
        public static implicit operator PacketListenerData((object @object, MethodInfo listenerMethod) value) => new(value.@object, value.listenerMethod);
    }
}