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using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MyApp.ViewModel
{
    public class MessengerService : ObservableObject
    {
        private static readonly object creationLock = new object();
        private static readonly ConcurrentDictionary<MessengerServiceKey, object> subscribers = new ConcurrentDictionary<MessengerServiceKey, object>();
        private static readonly List<object> messageQueue = new List<object>();

        private static MessengerService instance;

        public static MessengerService Default
        {
            get
            {
                if (instance == null)
                {
                    lock (creationLock)
                    {
                        instance = new MessengerService();
                    }
                }
                return instance;
            }
        }

        public MessengerService()
        {
        }

        public void Subscribe<T>(object subscriber, Action<T> action)
        {
            subscribers.TryAdd(new MessengerServiceKey(subscriber), action);
        }

        public void Send<T>(T message)
        {
            foreach (var action in subscribers.Select(x => x.Value).OfType<Action<T>>())
            {
                action(message);
            }
        }

        public void AddToMessageQueue<T>(T message)
        {
            messageQueue.Add(message);
        }

        public void ProcessMessageQueue<T>()
        {
            while (messageQueue.Count > 0)
            {
                object message = messageQueue.OfType<T>().First();
                foreach (var action in subscribers.Select(x => x.Value).OfType<Action<T>>())
                {
                    action((T)message);
                }
                messageQueue.Remove(message);
            }
        }
    }

    public class MessengerServiceKey
    {
        public object Subscriber { get; set; }
        public Guid SubscriptionID { get; set; }

        public MessengerServiceKey(object subscriber)
        {
            Subscriber = subscriber;
            SubscriptionID = Guid.NewGuid();
        }
    }
}