CodeLiturgy.Dashboard/BlueWest/Core/Events/EventManager.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace BlueWest.Tools
{	

	public sealed class EventManager 
	{
	    private readonly Dictionary<Type, List<EventListenerBase>> _subscribersList;

	    private static EventManager _instance;

		public EventManager(Dictionary<Type, List<EventListenerBase>> subscribersList)
	    {
	        _subscribersList = subscribersList;
	        _instance = this;
	    }

		public EventManager()
		{
			_subscribersList = new Dictionary<Type, List<EventListenerBase>>();
			_instance = this;
		}

	    /// <suary>
	    /// Adds a new subscriber to a certain event.
	    /// </suary>
		/// <param name="listener">listener.</param>
	    /// <typeparam name="TEvent">The event type.</typeparam>
	    public  void AddListener<TEvent>( EventListener<TEvent> listener ) where TEvent : struct
	    {
	        var eventType = typeof( TEvent );

	        if( !_subscribersList.ContainsKey( eventType ) )
	            _subscribersList[eventType] = new List<EventListenerBase>(10000);

	        //if( !SubscriptionExists( eventType, listener ) )
	            _subscribersList[eventType].Add( listener );
	    }

	    /// <suary>
	    /// Removes a subscriber from a certain event.
	    /// </suary>
		/// <param name="listener">listener.</param>
	    /// <typeparam name="TEvent">The event type.</typeparam>
	    public void RemoveListener<TEvent>( EventListener<TEvent> listener ) where TEvent : struct
	    {
	        var eventType = typeof( TEvent );

			List<EventListenerBase> subscriberList = _subscribersList[eventType];

			for (int i = 0; i<subscriberList.Count; i++)
			{
				if( subscriberList[i] == listener )
				{
					subscriberList.Remove( subscriberList[i] );

					if( subscriberList.Count == 0 )
						_subscribersList.Remove( eventType );

					return;
				}
			}
	    }

	    /// <suary>
	    /// Triggers an event. All instances that are subscribed to it will receive it (and will potentially act on it).
	    /// </suary>
		/// <param name="newEvent">The event to trigger.</param>
	    /// <typeparam name="TEvent">The 1st type parameter.</typeparam>
	    public void TriggerEvent<TEvent>( TEvent newEvent ) where TEvent : struct
	    {
	        var type = typeof(TEvent);
	        
	        #if DEBUG

		    if (!_subscribersList.ContainsKey(type))
		    {
			    Console.WriteLine($"{type.FullName} has no actual trigger, fix it...");
			    return;
		    }
		    
		    #endif
	        
	        List<EventListenerBase> list = _subscribersList[type];
	        
	        for (int i=0; i<list.Count; i++)
			{
				var eventListener = list[i];
				var casted = eventListener as EventListener<TEvent>;
#pragma warning disable CS8602
				casted.OnEvent( newEvent );
#pragma warning restore CS8602
			}
	    }

	    /// <suary>
	    /// Checks if there are subscribers for a certain type of events
	    /// </suary>
	    /// <returns><c>true</c>, if exists was subscriptioned, <c>false</c> otherwise.</returns>
	    /// <param name="type">Type.</param>
	    /// <param name="receiver">Receiver.</param>
	    private bool SubscriptionExists( Type type, EventListenerBase receiver )
	    {
		    if( !_subscribersList.TryGetValue( type, out var receivers ) ) return false;

	        bool exists = false;

			for (int i=0; i<receivers.Count; i++)
			{
				if( receivers[i] == receiver )
				{
					exists = true;
					break;
				}
			}

	        return exists;
	    }
	    
	    public  void EventStartListening<EventType>(  EventListener<EventType> caller ) where EventType : struct
	    {
		    AddListener<EventType>( caller );
	    }

	    public  void EventStopListening<EventType>( EventListener<EventType> caller ) where EventType : struct
	    {
		    RemoveListener<EventType>( caller );
	    }
	}

	/// <suary>
	/// Static class that allows any class to start or stop listening to events
	/// </suary>
	public static class EventRegister
	{
	    public delegate void Delegate<T>( T eventType );


	}

	/// <suary>
	/// TEvent listener basic interface
	/// </suary>
	public interface EventListenerBase { };

	/// <suary>
	/// A public interface you'll need to implement for each type of event you want to listen to.
	/// </suary>
	public interface EventListener<T> : EventListenerBase
	{
	    void OnEvent( T eventType );
	}
}