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;

/// <summary>
/// Intermediary manager that looks up in it's hierarchy for a <see cref="INetworkCommunicator"/> to route/broadcast it's received packets to their destinations.
/// </summary>
public class NetworkManager : UniverseObject, INetworkManager
{
    private readonly Dictionary<Type, Dictionary<Type, List<MethodInfo>>> clientPacketArrivalMethods = [];
    private readonly Dictionary<Type, Dictionary<Type, List<MethodInfo>>> serverPacketArrivalMethods = [];

    private readonly Dictionary<Type, Dictionary<string, Event<string, object>>> clientPacketRouters = [];
    private readonly Dictionary<Type, Dictionary<string, Event<string, object>>> serverPacketRouters = [];

    private readonly List<(Type packetType, Delegate callback)> packetRetrievalDelegates = [];

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

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

    private INetworkCommunicator _networkCommunicator = null!;
    public INetworkCommunicator NetworkCommunicator
    {
        get => _networkCommunicator;
        set
        {
            if (_networkCommunicator == value)
                return;

            var previousCommunicator = _networkCommunicator;
            _networkCommunicator = value;

            if (previousCommunicator is not null) UnsubscribeCommunicatorMethods(previousCommunicator);
            if (_networkCommunicator is not null) SubscribeCommunicatorMethods(_networkCommunicator);
        }
    }

    #region Communicator Subscriptions
    private void SubscribeCommunicatorMethods(INetworkCommunicator networkCommunicator)
    {
        MethodInfo subscribeToPacketsMethod = typeof(INetworkCommunicator)
            .GetMethod(nameof(INetworkCommunicator.SubscribeToPackets), BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance)!;

        foreach ((Type packetType, Delegate callback) in packetRetrievalDelegates)
        {
            MethodInfo genericSubscribeMethod = subscribeToPacketsMethod.MakeGenericMethod(packetType);
            genericSubscribeMethod.Invoke(networkCommunicator, [callback]);
        }
    }

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

        foreach ((Type packetType, Delegate callback) in packetRetrievalDelegates)
        {
            MethodInfo genericUnsubscribeMethod = unsubscribeFromPacketsMethod.MakeGenericMethod(packetType);
            genericUnsubscribeMethod.Invoke(networkCommunicator, [callback]);
        }
    }
    #endregion

    #region Packet Routing
    private void OnPacketReceived<T>(string senderClientId, T entityDataPacket)
    {
        if (entityDataPacket is IEntityNetworkPacket entityPacket)
            RoutePacket(senderClientId, entityDataPacket, entityPacket);
        else
            BroadcastPacket(senderClientId, entityDataPacket);
    }

    private void RoutePacket<T>(string senderClientId, T entityDataPacket, IEntityNetworkPacket entityPacket)
    {
        if (NetworkCommunicator is INetworkCommunicatorClient)
            RoutePacket(clientPacketRouters, entityPacket.EntityId, senderClientId, entityDataPacket);
        if (NetworkCommunicator is INetworkCommunicatorServer)
            RoutePacket(serverPacketRouters, entityPacket.EntityId, senderClientId, entityDataPacket);
    }

    private void BroadcastPacket<T>(string senderClientId, T entityDataPacket)
    {
        if (NetworkCommunicator is INetworkCommunicatorClient)
            BroadcastPacket(clientPacketRouters, senderClientId, entityDataPacket);
        if (NetworkCommunicator is INetworkCommunicatorServer)
            BroadcastPacket(serverPacketRouters, senderClientId, entityDataPacket);
    }


    private static void BroadcastPacket<T>(
        Dictionary<Type, Dictionary<string, Event<string, object>>> packetRouters,
        string senderClientId,
        T entityDataPacket)
    {
        if (!packetRouters.TryGetValue(entityDataPacket!.GetType(), out Dictionary<string, Event<string, object>>? routers))
            return;

        foreach ((string id, Event<string, object> routerEvent) in routers)
            routerEvent.Invoke(senderClientId, entityDataPacket!);
    }

    private static void RoutePacket<T>(
        Dictionary<Type, Dictionary<string, Event<string, object>>> packetRouters,
        string entityId,
        string senderClientId,
        T entityDataPacket)
    {
        if (!packetRouters.TryGetValue(entityDataPacket!.GetType(), out Dictionary<string, Event<string, object>>? routers))
            return;

        if (!routers.TryGetValue(entityId, out Event<string, object>? routerEvent))
            return;

        routerEvent.Invoke(senderClientId, entityDataPacket!);
    }
    #endregion

    #region Packet Routers
    private static void RegisterPacketRoutersFor(
        INetworkEntity behaviour,
        Dictionary<Type, Dictionary<string, Event<string, object>>> packetRouters,
        Dictionary<Type, Dictionary<Type, List<MethodInfo>>> packetArrivalMethods,
        NetworkType networkType)
    {
        if (!packetArrivalMethods.TryGetValue(behaviour.GetType(), out Dictionary<Type, List<MethodInfo>>? arrivalMethods))
            return;

        foreach ((Type packetType, List<MethodInfo> methods) in arrivalMethods)
            foreach (MethodInfo receiveMethod in methods)
            {
                if (!packetRouters.TryGetValue(packetType, out Dictionary<string, Event<string, object>>? routers))
                {
                    routers = [];
                    packetRouters.Add(packetType, routers);
                }

                Event<string, object> packetListenerEvent = new();
                RegisterPacketListenerEvent(behaviour, packetListenerEvent, receiveMethod, networkType);
                routers.Add(behaviour.Id, packetListenerEvent);
            }
    }

    private static void RegisterPacketListenerEvent(
        INetworkEntity behaviour,
        Event<string, object> packetListenerEvent,
        MethodInfo receiveMethod,
        NetworkType networkType)
    {
        switch (networkType)
        {
            case NetworkType.Client: packetListenerEvent.AddListener((sender, @object) => receiveMethod.Invoke(behaviour, [@object])); break;
            case NetworkType.Server: packetListenerEvent.AddListener((sender, @object) => receiveMethod.Invoke(behaviour, [sender, @object])); break;
        }
    }

    private static void UnregisterPacketRoutersFor(
        INetworkEntity behaviour,
        Dictionary<Type, Dictionary<string, Event<string, object>>> packetRouters,
        Dictionary<Type, Dictionary<Type, List<MethodInfo>>> packetArrivalMethods)
    {
        if (!packetArrivalMethods.TryGetValue(behaviour.GetType(), out Dictionary<Type, List<MethodInfo>>? arrivalMethods))
            return;

        foreach ((Type packetType, List<MethodInfo> methods) in arrivalMethods)
        {
            if (!packetRouters.TryGetValue(packetType, out Dictionary<string, Event<string, object>>? routers))
                continue;

            if (!routers.TryGetValue(behaviour.Id, out Event<string, object>? routerEvent))
                continue;

            routers.Remove(behaviour.Id);
            routerEvent.Clear();
        }
    }
    #endregion

    #region Engine Callbacks
    private void OnCollected(IBehaviourCollector<INetworkEntity> sender, IBehaviourCollector<INetworkEntity>.BehaviourCollectedArguments args)
    {
        INetworkEntity collectedBehaviour = args.BehaviourCollected;

        if (!_networkEntities.TryAdd(collectedBehaviour.Id, collectedBehaviour))
            throw new($"Unable to add {collectedBehaviour.Id} to {nameof(NetworkManager)}");

        RegisterPacketRoutersFor(collectedBehaviour, clientPacketRouters, clientPacketArrivalMethods, NetworkType.Client);
        RegisterPacketRoutersFor(collectedBehaviour, serverPacketRouters, serverPacketArrivalMethods, NetworkType.Server);
    }

    private void OnRemoved(IBehaviourCollector<INetworkEntity> sender, IBehaviourCollector<INetworkEntity>.BehaviourRemovedArguments args)
    {
        INetworkEntity removedBehaviour = args.BehaviourRemoved;
        if (!_networkEntities.Remove(args.BehaviourRemoved.Id))
            return;

        UnregisterPacketRoutersFor(removedBehaviour, clientPacketRouters, clientPacketArrivalMethods);
        UnregisterPacketRoutersFor(removedBehaviour, serverPacketRouters, serverPacketArrivalMethods);
    }

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

    #region Initialization
    public NetworkManager()
    {
        CachePacketRetrievalDelegates();
        CachePacketArrivalMethods();

        _networkEntityCollector.OnCollected.AddListener(OnCollected);
        _networkEntityCollector.OnRemoved.AddListener(OnRemoved);
    }

    private void CachePacketRetrievalDelegates()
    {
        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(Event<,>.EventHandler).MakeGenericType(typeof(string), packetType);
            Delegate genericPacketReceivedDelegate = Delegate.CreateDelegate(genericDelegateType, this, genericOnPacketArrivedMethod);

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

    private void CachePacketArrivalMethods()
    {
        CachePacketArrivalMethods(clientPacketArrivalMethods, typeof(IPacketListenerClient<>), nameof(IPacketListenerClient<INetworkEntity>.OnClientPacketArrived));
        CachePacketArrivalMethods(serverPacketArrivalMethods, typeof(IPacketListenerServer<>), nameof(IPacketListenerServer<INetworkEntity>.OnServerPacketArrived));
    }

    private static void CachePacketArrivalMethods(Dictionary<Type, Dictionary<Type, List<MethodInfo>>> packetArrivalMethods, Type listenerType, string packetArrivalMethodName)
    {
        foreach (Type listenerClass in GetGenericsWith(listenerType))
        {
            Dictionary<Type, List<MethodInfo>> packetRouters = [];
            packetArrivalMethods.Add(listenerClass, packetRouters);

            foreach (Type packetListener in GetGenericInterfacesWith(listenerType, listenerClass))
            {
                Type packetType = packetListener.GetGenericArguments().First();

                List<MethodInfo> arrivalMethods = packetListener
                    .GetMethods()
                    .Where(m => m.Name == packetArrivalMethodName)
                    .ToList();

                packetRouters.Add(packetType, arrivalMethods);
            }
        }
    }

    private static IEnumerable<Type> GetGenericsWith(Type type)
        => AppDomain.CurrentDomain
            .GetAssemblies()
            .SelectMany(a =>
                a.GetTypes().Where(
                    t => t.GetInterfaces().Any(
                        i => i.IsGenericType && i.GetGenericTypeDefinition() == type
                    )
                )
            );

    private static IEnumerable<Type> GetGenericInterfacesWith(Type interfaceType, Type type)
        => type.GetInterfaces().Where(
            i => i.IsGenericType && i.GetGenericTypeDefinition() == interfaceType
        );
    #endregion

    private enum NetworkType { Client, Server }
}