From e964055ec191f411d02a639b7817bd93b0f7cd0c Mon Sep 17 00:00:00 2001
From: Evan Hemsley <evan@moonside.games>
Date: Fri, 21 Jun 2019 17:44:07 -0700
Subject: [PATCH] add some convenience methods to Engines

---
 encompass-cs/Engine.cs                        | 17 ++++
 .../ComponentTypeMismatchException.cs         | 12 +++
 test/EngineTest.cs                            | 86 +++++++++++++++++++
 3 files changed, 115 insertions(+)
 create mode 100644 encompass-cs/exceptions/ComponentTypeMismatchException.cs

diff --git a/encompass-cs/Engine.cs b/encompass-cs/Engine.cs
index 5853d61..30cd58d 100644
--- a/encompass-cs/Engine.cs
+++ b/encompass-cs/Engine.cs
@@ -68,6 +68,23 @@ namespace Encompass
             return componentManager.GetEntityIDFromComponentID(componentID);
         }
 
+        protected Entity GetEntityFromComponentID(Guid componentID)
+        {
+            return GetEntity(GetEntityIDFromComponentID(componentID));
+        }
+
+        protected TComponent GetComponentByID<TComponent>(Guid componentID) where TComponent : struct, IComponent
+        {
+            if (componentManager.GetComponentTypeByID(componentID) == typeof(TComponent))
+            {
+                return (TComponent)componentManager.GetComponentByID(componentID);
+            }
+            else
+            {
+                throw new ComponentTypeMismatchException("Expected Component to be of type {0} but was actually of type {1}", typeof(TComponent).Name, componentManager.GetComponentTypeByID(componentID).Name);
+            }
+        }
+
         protected IEnumerable<KeyValuePair<Guid, TComponent>> ReadComponents<TComponent>() where TComponent : struct, IComponent
         {
             return componentManager.GetActiveComponentsByType<TComponent>();
diff --git a/encompass-cs/exceptions/ComponentTypeMismatchException.cs b/encompass-cs/exceptions/ComponentTypeMismatchException.cs
new file mode 100644
index 0000000..d28e7c4
--- /dev/null
+++ b/encompass-cs/exceptions/ComponentTypeMismatchException.cs
@@ -0,0 +1,12 @@
+using System;
+
+namespace Encompass
+{
+    public class ComponentTypeMismatchException : Exception
+    {
+        public ComponentTypeMismatchException(
+            string format,
+            params object[] args
+        ) : base(string.Format(format, args)) { }
+    }
+}
diff --git a/test/EngineTest.cs b/test/EngineTest.cs
index c38a0ae..c8d85d8 100644
--- a/test/EngineTest.cs
+++ b/test/EngineTest.cs
@@ -435,5 +435,91 @@ namespace Tests
             Assert.That(results, Does.Not.Contain(new KeyValuePair<Guid, MockComponent>(componentID, mockComponent)));
             Assert.That(results, Does.Not.Contain(new KeyValuePair<Guid, MockComponent>(componentBID, mockComponent)));
         }
+
+        static Entity entityFromComponentIDResult;
+        class GetEntityFromComponentIDEngine : Engine
+        {
+            public override void Update(float dt)
+            {
+                var componentID = ReadComponent<MockComponent>().Key;
+                entityFromComponentIDResult = GetEntityFromComponentID(componentID);
+            }
+        }
+
+        [Test]
+        public void GetEntityFromComponentID()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine<GetEntityFromComponentIDEngine>();
+
+            MockComponent component;
+            component.myInt = 2;
+            component.myString = "howdy";
+
+            var entity = worldBuilder.CreateEntity();
+            entity.AddComponent(component);
+
+            var world = worldBuilder.Build();
+            world.Update(0.01f);
+
+            Assert.That(entity, Is.EqualTo(entityFromComponentIDResult));
+        }
+
+        static MockComponent mockComponentByIDResult;
+        class GetComponentByIDEngine : Engine
+        {
+            public override void Update(float dt)
+            {
+                var componentID = ReadComponent<MockComponent>().Key;
+                mockComponentByIDResult = GetComponentByID<MockComponent>(componentID);
+            }
+        }
+        [Test]
+        public void GetComponentByID()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine<GetComponentByIDEngine>();
+
+            MockComponent component;
+            component.myInt = 2;
+            component.myString = "howdy";
+
+            var entity = worldBuilder.CreateEntity();
+            entity.AddComponent(component);
+
+            var world = worldBuilder.Build();
+            world.Update(0.01f);
+
+            Assert.That(component, Is.EqualTo(mockComponentByIDResult));
+        }
+
+        struct OtherComponent : IComponent { }
+
+        class GetComponentByIDWithTypeMismatchEngine : Engine
+        {
+            public override void Update(float dt)
+            {
+                var componentID = ReadComponent<MockComponent>().Key;
+                GetComponentByID<OtherComponent>(componentID);
+            }
+        }
+
+        [Test]
+        public void GetComponentByIDWithTypeMismatch()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine<GetComponentByIDWithTypeMismatchEngine>();
+
+            MockComponent component;
+            component.myInt = 2;
+            component.myString = "howdy";
+
+            var entity = worldBuilder.CreateEntity();
+            entity.AddComponent(component);
+
+            var world = worldBuilder.Build();
+
+            Assert.Throws<ComponentTypeMismatchException>(() => world.Update(0.01f));
+        }
     }
 }