From 2d929e46655e5c16f26afef477fdc83fcb646ece Mon Sep 17 00:00:00 2001
From: Evan Hemsley <evan@moonside.games>
Date: Fri, 12 Jul 2019 17:37:31 -0700
Subject: [PATCH] adds EntityExists method + fixes crash when destroying an
 entity that has no components

---
 encompass-cs/ComponentManager.cs | 10 ++++----
 encompass-cs/Engine.cs           |  5 ++++
 encompass-cs/EntityManager.cs    |  6 +++++
 encompass-cs/RenderManager.cs    |  2 +-
 encompass-cs/Renderer.cs         |  5 ++++
 test/EngineTest.cs               | 39 ++++++++++++++++++++++++++++++++
 6 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/encompass-cs/ComponentManager.cs b/encompass-cs/ComponentManager.cs
index a9ff095..ea5e2fc 100644
--- a/encompass-cs/ComponentManager.cs
+++ b/encompass-cs/ComponentManager.cs
@@ -37,6 +37,11 @@ namespace Encompass
             this.entitiesWithRemovedComponents = entitiesWithRemovedComponents;
         }
 
+        internal void RegisterEntity(Guid entityID)
+        {
+            entityIDToComponentIDs.Add(entityID, new List<Guid>());
+        }
+
         internal Guid AddComponent<TComponent>(Guid entityID, TComponent component) where TComponent : struct, IComponent
         {
             var componentID = Guid.NewGuid();
@@ -51,11 +56,6 @@ namespace Encompass
 
             typeToComponentIDs[typeof(TComponent)].Add(componentID);
 
-            if (!entityIDToComponentIDs.ContainsKey(entityID))
-            {
-                entityIDToComponentIDs.Add(entityID, new List<Guid>());
-            }
-
             entityIDToComponentIDs[entityID].Add(componentID);
             componentIDToEntityID[componentID] = entityID;
 
diff --git a/encompass-cs/Engine.cs b/encompass-cs/Engine.cs
index 89aa8db..027830e 100644
--- a/encompass-cs/Engine.cs
+++ b/encompass-cs/Engine.cs
@@ -59,6 +59,11 @@ namespace Encompass
             return entityManager.CreateEntity();
         }
 
+        protected bool EntityExists(Guid entityID)
+        {
+            return entityManager.EntityExists(entityID);
+        }
+
         protected Entity GetEntity(Guid entityID)
         {
             return entityManager.GetEntity(entityID);
diff --git a/encompass-cs/EntityManager.cs b/encompass-cs/EntityManager.cs
index 3f0d107..a8266da 100644
--- a/encompass-cs/EntityManager.cs
+++ b/encompass-cs/EntityManager.cs
@@ -33,9 +33,15 @@ namespace Encompass
             var id = NextID();
             var entity = new Entity(id, componentManager);
             IDToEntity[id] = entity;
+            componentManager.RegisterEntity(id);
             return entity;
         }
 
+        public bool EntityExists(Guid id)
+        {
+            return IDToEntity.ContainsKey(id);
+        }
+
         public Entity GetEntity(Guid id)
         {
             return IDToEntity[id];
diff --git a/encompass-cs/RenderManager.cs b/encompass-cs/RenderManager.cs
index 093c5e1..6d0e9a8 100644
--- a/encompass-cs/RenderManager.cs
+++ b/encompass-cs/RenderManager.cs
@@ -54,7 +54,7 @@ namespace Encompass
                         var renderer = drawComponentTypeToEntityRenderer[componentType];
                         var entityID = componentManager.GetEntityIDByComponentID(componentID);
 
-                        if (renderer.IsTracking(entityID))
+                        if (renderer.IsTracking(entityID) && entityManager.EntityExists(entityID))
                         {
                             var entity = entityManager.GetEntity(entityID);
                             renderer.Render(entity);
diff --git a/encompass-cs/Renderer.cs b/encompass-cs/Renderer.cs
index 9f4c860..d2d82d6 100644
--- a/encompass-cs/Renderer.cs
+++ b/encompass-cs/Renderer.cs
@@ -19,6 +19,11 @@ namespace Encompass
             this.componentManager = componentManager;
         }
 
+        protected bool EntityExists(Guid entityID)
+        {
+            return entityManager.EntityExists(entityID);
+        }
+
         protected Entity GetEntity(Guid entityID)
         {
             return entityManager.GetEntity(entityID);
diff --git a/test/EngineTest.cs b/test/EngineTest.cs
index d9397bc..4c844d3 100644
--- a/test/EngineTest.cs
+++ b/test/EngineTest.cs
@@ -556,5 +556,44 @@ namespace Tests
 
             Assert.Throws<ComponentTypeMismatchException>(() => world.Update(0.01f));
         }
+
+        struct EntityIDComponent : IComponent { public Guid entityID;  }
+        static bool hasEntity;
+        class HasEntityTestEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                foreach (var (mockComponentID, mockComponent) in ReadComponents<EntityIDComponent>())
+                {
+                    hasEntity = EntityExists(mockComponent.entityID);
+                    if (hasEntity) { Destroy(mockComponent.entityID); }
+                }
+            }
+        }
+
+        [Test]
+        public void EntityExists()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new HasEntityTestEngine());
+
+            var entity = worldBuilder.CreateEntity();
+            var entityTwo = worldBuilder.CreateEntity();
+
+            EntityIDComponent entityIDComponent;
+            entityIDComponent.entityID = entityTwo.id;
+
+            entity.AddComponent(entityIDComponent);
+
+            var world = worldBuilder.Build();
+
+            world.Update(0.01);
+
+            Assert.IsTrue(hasEntity);
+
+            world.Update(0.01);
+
+            Assert.IsFalse(hasEntity);
+        }
     }
 }