feat: entity register for serialized entity references

Engine.Core/Serialization/EntityReference.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Collections.Generic;
+
+namespace Syntriax.Engine.Core.Serialization;
+
+public record class EntityReference(string? Id = null);
+
+public class EntityRegistry
+{
+    public event EntityRegisteredEventHandler? OnEntityRegistered = null!;
+
+    private readonly Dictionary<string, Action<IEntity>?> assignCallbacks = [];
+    private readonly Dictionary<string, IEntity> registeredEntities = [];
+    public IReadOnlyDictionary<string, IEntity> RegisteredEntities => registeredEntities;
+
+    public void Add(IEntity entity)
+    {
+        if (registeredEntities.TryAdd(entity.Id, entity))
+            OnEntityRegistered?.InvokeSafe(this, entity);
+    }
+
+    public void QueueAssign(string id, Action<IEntity> setMethod)
+    {
+        assignCallbacks.TryAdd(id, null);
+        assignCallbacks[id] = assignCallbacks[id] + setMethod;
+    }
+
+    public void AssignAll()
+    {
+        foreach ((string id, Action<IEntity>? action) in assignCallbacks)
+            action?.InvokeSafe(registeredEntities[id]);
+    }
+
+    public delegate void EntityRegisteredEventHandler(EntityRegistry sender, IEntity entity);
+}