message read checks + started AddComponent

TODO

@@ -5,7 +5,5 @@
 
 - auto destroy entities that no longer have components 
 
-- fast lookup for messages that contain entity references instead of `Where` loop?
-
 - look at test coverage
 - docs

encompass-cs/Engine.cs

@@ -53,6 +53,8 @@ namespace Encompass
             }
         }
 
+        private HashSet<int> _newlyCreatedEntities = new HashSet<int>();
+
         protected Engine()
         {
             ID = Guid.NewGuid();
@@ -158,6 +160,19 @@ namespace Encompass
             this.trackingManager = trackingManager;
         }
 
+        internal void CheckMessageRead<TMessage>() where TMessage : struct, IMessage
+        {
+            if (!receiveTypes.Contains(typeof(TMessage)))
+            {
+                throw new IllegalReadException("Engine {0} tried to read undeclared Message {1}", this.GetType().Name, typeof(TMessage).Name);
+            }
+        }
+
+        private bool EntityCreatedThisFrame(int entityID)
+        {
+            return _newlyCreatedEntities.Contains(entityID);
+        }
+
         /// <summary>
         /// Runs once per World update with the calculated delta-time.
         /// </summary>
@@ -169,7 +184,9 @@ namespace Encompass
         /// </summary>
         protected Entity CreateEntity()
         {
-            return entityManager.CreateEntity();
+            var entity = entityManager.CreateEntity();
+            _newlyCreatedEntities.Add(entity.ID);
+            return entity;
         }
 
         /// <summary>
@@ -448,6 +465,28 @@ namespace Encompass
             }
         }
 
+        /// <summary>
+        /// An alternative to SetComponent that can be used for new Entities and does not require setting write priority.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalWriteException">
+        /// Thrown when the Engine does not declare that it Writes the given Component Type.
+        /// </exception>
+        protected void AddComponent<TComponent>(Entity entity, TComponent component) where TComponent : struct, IComponent
+        {
+            if (!_newlyCreatedEntities.Contains(entity.ID))
+            {
+                throw new IllegalWriteException("AddComponent used on Entity that was not created in this context. Use SetComponent instead.");
+            }
+
+            componentManager.AddComponent(entity.ID, component);
+            trackingManager.RegisterAddition(entity.ID, typeof(TComponent));
+
+            if (component is IDrawableComponent drawableComponent)
+            {
+                componentManager.RegisterDrawableComponent(entity.ID, component, drawableComponent.Layer);
+            }
+        }
+
         /// <summary>
         /// Sends a Message.
         /// </summary>
@@ -490,11 +529,7 @@ namespace Encompass
         /// </exception>
         protected IEnumerable<TMessage> ReadMessages<TMessage>() where TMessage : struct, IMessage
         {
-            if (!receiveTypes.Contains(typeof(TMessage)))
-            {
-                throw new IllegalReadException("Engine {0} tried to read undeclared Message {1}", this.GetType().Name, typeof(TMessage).Name);
-            }
-
+            CheckMessageRead<TMessage>();
             return messageManager.GetMessagesByType<TMessage>();
         }
 
@@ -506,6 +541,7 @@ namespace Encompass
         /// </exception>
         protected TMessage ReadMessage<TMessage>() where TMessage : struct, IMessage
         {
+            CheckMessageRead<TMessage>();
             return messageManager.First<TMessage>();
         }
 
@@ -517,11 +553,7 @@ namespace Encompass
         /// </exception>
         protected bool SomeMessage<TMessage>() where TMessage : struct, IMessage
         {
-            if (!receiveTypes.Contains(typeof(TMessage)))
-            {
-                throw new IllegalReadException("Engine {0} tried to read undeclared Message {1}", GetType().Name, typeof(TMessage).Name);
-            }
-
+            CheckMessageRead<TMessage>();
             return messageManager.Any<TMessage>();
         }
 
@@ -648,18 +680,33 @@ namespace Encompass
         }
 
         /// <summary>
-        /// Efficiently reads Messages of a given type that all reference the same Entity.
+        /// Efficiently reads Messages of a given type that all reference the given Entity.
         /// </summary>
         /// <typeparam name="TMessage">The Message subtype.</typeparam>
         /// <param name="entity">The entity that all messages in the IEnumerable refer to.</param>
         /// <returns></returns>
         protected IEnumerable<TMessage> ReadMessagesWithEntity<TMessage>(Entity entity) where TMessage : struct, IMessage, IHasEntity
         {
+            CheckMessageRead<TMessage>();
             return messageManager.WithEntity<TMessage>(entity.ID);
         }
 
+        /// <summary>
+        /// Efficiently reads a single Message of a given type that references a given Entity.
+        /// It is recommended to use this method in conjunction with SomeMessageWithEntity to prevent errors.
+        /// </summary>
+        protected TMessage ReadMessageWithEntity<TMessage>(Entity entity) where TMessage : struct, IMessage, IHasEntity
+        {
+            CheckMessageRead<TMessage>();
+            return messageManager.WithEntitySingular<TMessage>(entity.ID);
+        }
+
+        /// <summary>
+        /// Efficiently checks if any Message of a given type referencing a given Entity exists.
+        /// </summary>
         protected bool SomeMessageWithEntity<TMessage>(Entity entity) where TMessage : struct, IMessage, IHasEntity
         {
+            CheckMessageRead<TMessage>();
             return messageManager.SomeWithEntity<TMessage>(entity.ID);
         }
 

encompass-cs/MessageManager.cs

@@ -57,6 +57,13 @@ namespace Encompass
             return messageStore.WithEntity<TMessage>(entityID);
         }
 
+        internal TMessage WithEntitySingular<TMessage>(int entityID) where TMessage : struct, IMessage, IHasEntity
+        {
+            var enumerator = messageStore.WithEntity<TMessage>(entityID).GetEnumerator();
+            enumerator.MoveNext();
+            return enumerator.Current;
+        }
+
         internal bool SomeWithEntity<TMessage>(int entityID) where TMessage : struct, IMessage, IHasEntity
         {
             return messageStore.SomeWithEntity<TMessage>(entityID);