feat: add initial architecture

src/Shared/Events/InMemoryEventBus.cs

@@ -0,0 +1,87 @@
+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;
+        }
+    }
+}