Toolkit2/Framework/Foundation/Lifecycles/Mediator.cs

using Microsoft.Extensions.DependencyInjection;
using System.Collections.Concurrent;

namespace Toolkit.Framework.Foundation;

public class Mediator : IMediator
{
    private readonly IServiceProvider factory;
    private readonly ConcurrentDictionary<Type, HashSet<dynamic>> subscriptions = new();

    public Mediator(IServiceProvider factory)
    {
        this.factory = factory;
    }

    public ValueTask Publish<TNotification>(TNotification notification, CancellationToken cancellationToken = default) where TNotification : INotification
    {
        List<INotificationHandler<TNotification>> handlers = factory.GetServices<INotificationHandler<TNotification>>().ToList();

        foreach (dynamic handler in subscriptions[typeof(TNotification)])
        {
            handlers.Add(handler);
        }

        if (handlers.Count == 0)
        {
            return default;
        }
        else if (handlers.Count == 1)
        {
            return handlers[0].Handle(notification, cancellationToken);
        }

        return default;
    }

    public ValueTask<TResponse> Send<TResponse>(IRequest<TResponse> request, CancellationToken cancellationToken = default)
    {
        dynamic? handler = factory.GetService(typeof(RequestClassHandlerWrapper<,>).MakeGenericType(request.GetType(), typeof(TResponse)));
        if (handler is not null)
        {
            return handler.Handle((dynamic)request, cancellationToken);
        }

        return default;
    }

    public ValueTask<TResponse> Send<TResponse>(ICommand<TResponse> command, CancellationToken cancellationToken = default)
    {
        dynamic? handler = factory.GetService(typeof(CommandClassHandlerWrapper<,>).MakeGenericType(command.GetType(), typeof(TResponse)));
        if (handler is not null)
        {
            return handler.Handle((dynamic)command, cancellationToken);
        }

        return default;
    }

    public ValueTask<TResponse> Send<TResponse>(IQuery<TResponse> query, CancellationToken cancellationToken = default)
    {
        dynamic? handler = factory.GetService(typeof(QueryClassHandlerWrapper<,>).MakeGenericType(query.GetType(), typeof(TResponse)));
        if (handler is not null)
        {
            return handler.Handle((dynamic)query, cancellationToken);
        }

        return default;
    }

    public ValueTask<object?> Send(object message, CancellationToken cancellationToken = default)
    {
        if (message.GetType().GetInterface(typeof(IRequest<>).Name) is { } requestType)
        {
            if (requestType.GetGenericArguments() is { Length: 1 } arguments)
            {
                Type responseType = arguments[0];

                dynamic? handler = factory.GetService(typeof(RequestClassHandlerWrapper<,>).MakeGenericType(message.GetType(), responseType));
                if (handler is not null)
                {
                    return handler.Handle((dynamic)message, cancellationToken);
                }
            }
        }

        if (message.GetType().GetInterface(typeof(ICommand<>).Name) is { } commandType)
        {
            if (commandType.GetGenericArguments() is { Length: 1 } arguments)
            {
                Type responseType = arguments[0];

                dynamic? handler = factory.GetService(typeof(CommandClassHandlerWrapper<,>).MakeGenericType(message.GetType(), responseType));
                if (handler is not null)
                {
                    return handler.Handle((dynamic)message, cancellationToken);
                }
            }
        }

        if (message.GetType().GetInterface(typeof(IQuery<>).Name) is { } queryType)
        {
            if (queryType.GetGenericArguments() is { Length: 1 } arguments)
            {
                Type responseType = arguments[0];

                dynamic? handler = factory.GetService(typeof(QueryClassHandlerWrapper<,>).MakeGenericType(message.GetType(), responseType));
                if (handler is not null)
                {
                    return handler.Handle((dynamic)message, cancellationToken);
                }
            }
        }

        return default;
    }

    public void Subscribe(object subscriber)
    {
        Type[] interfaceTypes = subscriber.GetType().GetInterfaces();
        foreach (Type interfaceType in interfaceTypes.Where(x => x.IsGenericType))
        {
            if (interfaceType.GetGenericTypeDefinition() == typeof(INotificationHandler<>))
            {
                if (interfaceType.GetGenericArguments() is { Length: 1 } arguments)
                {
                    Type notificationType = arguments[0];

                    subscriptions.AddOrUpdate(notificationType, new HashSet<dynamic> { subscriber }, (type, hashSet) =>
                    {
                        hashSet.Add(subscriber);
                        return hashSet;
                    });
                }
            }
        }
    }
}