add filter callback system

src/Filter.cs

@@ -23,5 +23,15 @@ namespace MoonTools.ECS
 
 		// WARNING: this WILL crash if the index is out of range!
 		public Entity NthEntity(int index) => FilterStorage.FilterNthEntity(Signature, index);
+
+		public void RegisterAddCallback(Action<Entity> callback)
+		{
+			FilterStorage.RegisterAddCallback(Signature, callback);
+		}
+
+		public void RegisterRemoveCallback(Action<Entity> callback)
+		{
+			FilterStorage.RegisterRemoveCallback(Signature, callback);
+		}
 	}
 }

src/FilterStorage.cs

@@ -10,6 +10,9 @@ namespace MoonTools.ECS
 		private Dictionary<FilterSignature, IndexableSet<Entity>> filterSignatureToEntityIDs = new Dictionary<FilterSignature, IndexableSet<Entity>>();
 		private Dictionary<int, HashSet<FilterSignature>> typeToFilterSignatures = new Dictionary<int, HashSet<FilterSignature>>();
 
+		private Dictionary<FilterSignature, Action<Entity>> addCallbacks = new Dictionary<FilterSignature, Action<Entity>>();
+		private Dictionary<FilterSignature, Action<Entity>> removeCallbacks = new Dictionary<FilterSignature, Action<Entity>>();
+
 		public FilterStorage(EntityStorage entityStorage, TypeIndices componentTypeIndices)
 		{
 			EntityStorage = entityStorage;
@@ -116,6 +119,10 @@ namespace MoonTools.ECS
 				if (!EntityStorage.HasComponent(entityID, type))
 				{
 					filterSignatureToEntityIDs[filterSignature].Remove(entityID);
+					if (removeCallbacks.TryGetValue(filterSignature, out var removeCallback))
+					{
+						removeCallback(entityID);
+					}
 					return;
 				}
 			}
@@ -125,11 +132,19 @@ namespace MoonTools.ECS
 				if (EntityStorage.HasComponent(entityID, type))
 				{
 					filterSignatureToEntityIDs[filterSignature].Remove(entityID);
+					if (removeCallbacks.TryGetValue(filterSignature, out var removeCallback))
+					{
+						removeCallback(entityID);
+					}
 					return;
 				}
 			}
 
 			filterSignatureToEntityIDs[filterSignature].Add(entityID);
+			if (addCallbacks.TryGetValue(filterSignature, out var addCallback))
+			{
+				addCallback(entityID);
+			}
 		}
 
 		public void RemoveEntity(int entityID, int componentTypeIndex)
@@ -139,8 +154,22 @@ namespace MoonTools.ECS
 				foreach (var filterSignature in filterSignatures)
 				{
 					filterSignatureToEntityIDs[filterSignature].Remove(entityID);
+					if (removeCallbacks.TryGetValue(filterSignature, out var removeCallback))
+					{
+						removeCallback(entityID);
+					}
 				}
 			}
 		}
+
+		public void RegisterAddCallback(FilterSignature filterSignature, Action<Entity> callback)
+		{
+			addCallbacks.Add(filterSignature, callback);
+		}
+
+		public void RegisterRemoveCallback(FilterSignature filterSignature, Action<Entity> callback)
+		{
+			removeCallbacks.Add(filterSignature, callback);
+		}
 	}
 }

src/World.cs

@@ -38,12 +38,12 @@ namespace MoonTools.ECS
 				throw new InvalidOperationException("This entity is not valid!");
 			}
 #endif
+			ComponentDepot.Set<TComponent>(entity.ID, component);
+
 			if (EntityStorage.SetComponent(entity.ID, ComponentTypeIndices.GetIndex<TComponent>()))
 			{
 				FilterStorage.Check<TComponent>(entity.ID);
 			}
-
-			ComponentDepot.Set<TComponent>(entity.ID, component);
 		}
 
 		public Template CreateTemplate()