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

namespace DDD
{
    public static class EventBus
    {
        private static readonly Dictionary<Type, List<object>> HandlerDictionary = new();

        public static void Register<T>(IEventHandler<T> handler) where T : IEvent
        {
            var type = typeof(T);
            if (!HandlerDictionary.ContainsKey(type))
            {
                HandlerDictionary[type] = new List<object>();
            }
            
            HandlerDictionary[type].Add(handler);
        }

        public static void Unregister<T>(IEventHandler<T> handler) where T : IEvent
        {
            var type = typeof(T);
            if (HandlerDictionary.TryGetValue(type, out var list))
            {
                list.Remove(handler);
                if (list.Count == 0)
                {
                    HandlerDictionary.Remove(type);
                }
            }
        }

        public static void Publish<T>(T evt) where T : IEvent
        {
            var type = typeof(T);
            if (HandlerDictionary.TryGetValue(type, out var list))
            {
                foreach (var handler in list.Cast<IEventHandler<T>>())
                {
                    handler.Handle(evt);
                }
            }
        }

        public static void ClearAll()
        {
            HandlerDictionary.Clear();
        }
    }
}