My ludicrous and naive attempt to implement another Event hub for .NET : The Most Simple Possible Event Aggregator

MSPEventAggregator

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;

namespace MSPEventAggregator {

    void sample_usage() {
        var hub = new MessageHub();
        
        var token = hub.Subscribe<string>(s => Console.Write(s));
        hub.Publish("hello");
        hub.Unsubscribe(token);
    }

    public class MessageHub {
        ConcurrentDictionary<Type, ConcurrentBag<ISubscription>> subscriptions = new ConcurrentDictionary<Type, ConcurrentBag<ISubscription>>();

        public void Publish<T>(T message) {
            ConcurrentBag<ISubscription> messageSubscriptions;
            if (subscriptions.TryGetValue(typeof(T), out messageSubscriptions))
                foreach (Subscription<T> messageSubscription in messageSubscriptions)
                    messageSubscription.Action(message);
        }

        public ISubscription Subscribe<T>(Action<T> doThis) {
            var subscription = new Subscription<T>(doThis, typeof(T));
            var messageSubscriptions = subscriptions.GetOrAdd(typeof(T), new ConcurrentBag<ISubscription>());
            messageSubscriptions.Add(subscription);
            return subscription;
        }

        public void Unsubscribe(ISubscription subscription) {
            ConcurrentBag<ISubscription> messageSubscriptions;
            if (subscriptions.TryGetValue(subscription.MessageType, out messageSubscriptions)) {
                messageSubscriptions.TryTake(out subscription);
                if (!messageSubscriptions.Any())
                    subscriptions.TryRemove(subscription.MessageType, out messageSubscriptions);
            }
        }
    }

    public class Subscription<T> : ISubscription {

        public Subscription(Action<T> action, Type type) {
            Action = action;
            MessageType = type;
        }

        public Action<T> Action { get; }

        public Type MessageType { get; }
    }

    public interface ISubscription {
        Type MessageType { get; }
    }
}