From 82daabb12005c6771f88baada3c09b918fbadacb Mon Sep 17 00:00:00 2001
From: Mike Bowers <mbowersjr@gmail.com>
Date: Tue, 11 Jun 2024 11:14:36 -0400
Subject: [PATCH] Updated ComponentManager to implement
 IEnumerable<ComponentMapper> (#823) (#888)

---
 .../ComponentManager.cs                       | 73 ++++++++++++++++++-
 .../ComponentManagerTests.cs                  | 42 ++++++++++-
 2 files changed, 109 insertions(+), 6 deletions(-)

diff --git a/source/MonoGame.Extended.Entities/ComponentManager.cs b/source/MonoGame.Extended.Entities/ComponentManager.cs
index a59c87ced..f89faa91d 100644
--- a/source/MonoGame.Extended.Entities/ComponentManager.cs
+++ b/source/MonoGame.Extended.Entities/ComponentManager.cs
@@ -1,18 +1,21 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Reflection;
 using Microsoft.Xna.Framework;
 using MonoGame.Extended.Collections;
 using MonoGame.Extended.Entities.Systems;
 
 namespace MonoGame.Extended.Entities
 {
-    public interface IComponentMapperService
+    public interface IComponentMapperService : IEnumerable<ComponentMapper>
     {
         ComponentMapper<T> GetMapper<T>() where T : class;
+        ComponentMapper this[Type type] { get; }
     }
 
-    public class ComponentManager : UpdateSystem, IComponentMapperService
+    public class ComponentManager : UpdateSystem, IComponentMapperService, IEnumerable<ComponentMapper>
     {
         public ComponentManager()
         {
@@ -20,11 +23,26 @@ public ComponentManager()
             _componentTypes = new Dictionary<Type, int>();
         }
 
-        private readonly Bag<ComponentMapper> _componentMappers;
-        private readonly Dictionary<Type, int> _componentTypes;
+        internal readonly Bag<ComponentMapper> _componentMappers;
+        internal readonly Dictionary<Type, int> _componentTypes;
 
         public Action<int> ComponentsChanged;
 
+        private ComponentMapper CreateMapperForType(Type type, int componentTypeId)
+        {
+            if (!type.IsClass)
+                throw new ArgumentException("Type must be a class type.", nameof(type));
+
+            // TODO: We can probably do better than this without a huge performance penalty by creating our own bit vector that grows after the first 32 bits.
+            if (componentTypeId >= 32)
+                throw new InvalidOperationException("Component type limit exceeded. We currently only allow 32 component types for performance reasons.");
+
+            var mapperType = typeof(ComponentMapper<>).MakeGenericType(type);
+            var mapper = Activator.CreateInstance(mapperType, args: new object[] { componentTypeId, ComponentsChanged });
+            _componentMappers[componentTypeId] = (ComponentMapper)mapper;
+            return (ComponentMapper)mapper;
+        }
+
         private ComponentMapper<T> CreateMapperForType<T>(int componentTypeId)
             where T : class
         {
@@ -86,5 +104,52 @@ public void Destroy(int entityId)
         public override void Update(GameTime gameTime)
         {
         }
+
+        public ComponentMapper this[Type type]
+        {
+            get
+            {
+                var componentTypeId = GetComponentTypeId(type);
+
+                if (_componentMappers[componentTypeId] != null)
+                    return _componentMappers[componentTypeId];
+
+                return CreateMapperForType(type, componentTypeId);
+            }
+        }
+
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+        public IEnumerator<ComponentMapper> GetEnumerator() => new ComponentMapperEnumerator(this);
+        
+        public struct ComponentMapperEnumerator : IEnumerator<ComponentMapper>
+        {
+            private readonly ComponentManager _componentManager;
+            private IEnumerator<ComponentMapper> _enumerator;
+
+            internal ComponentMapperEnumerator(ComponentManager componentManager)
+            {
+                _componentManager = componentManager;
+                _enumerator = _componentManager._componentMappers.GetEnumerator();
+            }
+
+            public bool MoveNext()
+            {
+                return _enumerator.MoveNext();
+            }
+
+            public void Reset()
+            {
+                _enumerator.Reset();
+            }
+
+            object IEnumerator.Current => _enumerator.Current;
+            public ComponentMapper Current => _enumerator.Current;
+
+            public void Dispose()
+            {
+                _enumerator?.Dispose();
+            }
+        }
     }
 }
diff --git a/tests/MonoGame.Extended.Entities.Tests/ComponentManagerTests.cs b/tests/MonoGame.Extended.Entities.Tests/ComponentManagerTests.cs
index 8d988e408..abf1a16d9 100644
--- a/tests/MonoGame.Extended.Entities.Tests/ComponentManagerTests.cs
+++ b/tests/MonoGame.Extended.Entities.Tests/ComponentManagerTests.cs
@@ -1,4 +1,5 @@
-using MonoGame.Extended.Sprites;
+using System.Collections.Generic;
+using MonoGame.Extended.Sprites;
 using Xunit;
 
 namespace MonoGame.Extended.Entities.Tests
@@ -43,5 +44,42 @@ public void GetComponentTypeId()
 
         //    Assert.Equal(0b101, identity);
         //}
+
+        
+        [Fact]
+        public void GetMapperForTypeByIndexer()
+        {
+            var componentManager = new ComponentManager();
+            var transformMapper = componentManager[typeof(Transform2)];
+            var spriteMapper = componentManager[typeof(Sprite)];
+
+            Assert.IsType<ComponentMapper<Transform2>>(transformMapper);
+            Assert.IsType<ComponentMapper<Sprite>>(spriteMapper);
+            Assert.Equal(0, transformMapper.Id);
+            Assert.Equal(1, spriteMapper.Id);
+            Assert.Same(spriteMapper, componentManager[typeof(Sprite)]);
+        }
+
+        [Fact]
+        public void EnumerateMappers()
+        {
+            var componentManager = new ComponentManager();
+
+            var transformMapper = componentManager.GetMapper<Transform2>();
+            var spriteMapper = componentManager.GetMapper<Sprite>();
+            var cameraMapper = componentManager.GetMapper<OrthographicCamera>();
+
+            List<ComponentMapper> enumeratedMappers = new List<ComponentMapper>();
+
+            foreach (ComponentMapper mapper in componentManager)
+            {
+                enumeratedMappers.Add(mapper);
+            }
+
+            Assert.Equal(3, enumeratedMappers.Count);
+            Assert.Contains(transformMapper, enumeratedMappers);
+            Assert.Contains(spriteMapper, enumeratedMappers);
+            Assert.Contains(cameraMapper, enumeratedMappers);
+        }
     }
-}
\ No newline at end of file
+}