using System;
using System.Collections.Generic;

namespace Game.Shared.Events;

public sealed class InMemoryEventBus : IEventBus
{
    private readonly Dictionary<Type, List<Delegate>> _handlers = [];
    private readonly object _lock = new();

    public IDisposable Subscribe<TEvent>(Action<TEvent> handler) where TEvent : IEvent
    {
        ArgumentNullException.ThrowIfNull(handler);

        var eventType = typeof(TEvent);

        lock (_lock)
        {
            if (!_handlers.TryGetValue(eventType, out var list))
            {
                list = [];
                _handlers[eventType] = list;
            }

            list.Add(handler);
        }

        return new EventSubscription(() => Unsubscribe(eventType, handler));
    }

    public void Publish<TEvent>(TEvent gameEvent) where TEvent : IEvent
    {
        ArgumentNullException.ThrowIfNull(gameEvent);

        List<Delegate> snapshot = null;
        var eventType = typeof(TEvent);

        lock (_lock)
        {
            if (_handlers.TryGetValue(eventType, out var list))
            {
                snapshot = new List<Delegate>(list);
            }
        }

        if (snapshot == null) return;

        foreach (var subscriber in snapshot)
        {
            ((Action<TEvent>)subscriber)(gameEvent);
        }
    }

    private void Unsubscribe(Type eventType, Delegate handler)
    {
        lock (_lock)
        {
            if (!_handlers.TryGetValue(eventType, out var list)) return;

            list.Remove(handler);

            if (list.Count == 0)
            {
                _handlers.Remove(eventType);
            }
        }
    }

    public void Clear()
    {
        lock (_lock)
        {
            _handlers.Clear();
        }
    }

    private sealed class EventSubscription(Action unsubscribeAction) : IDisposable
    {
        private Action _unsubscribeAction = unsubscribeAction;

        public void Dispose()
        {
            _unsubscribeAction?.Invoke();
            _unsubscribeAction = null;
        }
    }
}