From b30923ade3f9e45c822345713e94055a80ba6e84 Mon Sep 17 00:00:00 2001
From: cosmonaut <evan@moonside.games>
Date: Sun, 6 Mar 2022 23:17:05 -0800
Subject: [PATCH] initial message system

---
 src/IHasEntity.cs     |  6 ++++++
 src/MessageDepot.cs   | 39 +++++++++++++++++++++++++++++++++++++
 src/MessageStorage.cs | 45 +++++++++++++++++++++++++++++++++++++++++++
 src/System.cs         | 20 +++++++++++++++++--
 src/World.cs          |  3 ++-
 5 files changed, 110 insertions(+), 3 deletions(-)
 create mode 100644 src/IHasEntity.cs
 create mode 100644 src/MessageDepot.cs
 create mode 100644 src/MessageStorage.cs

diff --git a/src/IHasEntity.cs b/src/IHasEntity.cs
new file mode 100644
index 0000000..ac186a8
--- /dev/null
+++ b/src/IHasEntity.cs
@@ -0,0 +1,6 @@
+namespace MoonTools.ECS;
+
+public interface IHasEntity
+{
+	Entity Entity { get; }
+}
diff --git a/src/MessageDepot.cs b/src/MessageDepot.cs
new file mode 100644
index 0000000..a5a66e9
--- /dev/null
+++ b/src/MessageDepot.cs
@@ -0,0 +1,39 @@
+namespace MoonTools.ECS;
+
+internal class MessageDepot
+{
+	private Dictionary<Type, MessageStorage> storages = new Dictionary<Type, MessageStorage>();
+
+	private MessageStorage<TMessage> Lookup<TMessage>() where TMessage : struct
+	{
+		if (!storages.ContainsKey(typeof(TMessage)))
+		{
+			storages.Add(typeof(TMessage), new MessageStorage<TMessage>());
+		}
+
+		return storages[typeof(TMessage)] as MessageStorage<TMessage>;
+	}
+
+	public void Add<TMessage>(in TMessage message) where TMessage : struct
+	{
+		Lookup<TMessage>().Add(message);
+	}
+
+	public bool Some<TMessage>() where TMessage : struct
+	{
+		return Lookup<TMessage>().Some();
+	}
+
+	public ReadOnlySpan<TMessage> Read<TMessage>() where TMessage : struct
+	{
+		return Lookup<TMessage>().All();
+	}
+
+	public void Clear()
+	{
+		foreach (var storage in storages.Values)
+		{
+			storage.Clear();
+		}
+	}
+}
diff --git a/src/MessageStorage.cs b/src/MessageStorage.cs
new file mode 100644
index 0000000..bf180cc
--- /dev/null
+++ b/src/MessageStorage.cs
@@ -0,0 +1,45 @@
+namespace MoonTools.ECS;
+
+internal abstract class MessageStorage
+{
+	public abstract void Clear();
+}
+
+internal class MessageStorage<TMessage> : MessageStorage where TMessage : struct
+{
+	private int count = 0;
+	private int capacity = 128;
+	private TMessage[] messages;
+
+	public MessageStorage()
+	{
+		messages = new TMessage[capacity];
+	}
+
+	public void Add(in TMessage message)
+	{
+		if (count == capacity)
+		{
+			capacity *= 2;
+			Array.Resize(ref messages, capacity);
+		}
+
+		messages[count] = message;
+		count += 1;
+	}
+
+	public bool Some()
+	{
+		return count > 0;
+	}
+
+	public ReadOnlySpan<TMessage> All()
+	{
+		return new ReadOnlySpan<TMessage>(messages, 0, count);
+	}
+
+	public override void Clear()
+	{
+		count = 0;
+	}
+}
diff --git a/src/System.cs b/src/System.cs
index 2610411..d9d71ec 100644
--- a/src/System.cs
+++ b/src/System.cs
@@ -2,8 +2,7 @@
 
 public abstract class System : EntityComponentReader
 {
-	public abstract void Update(TimeSpan delta);
-
+	internal MessageDepot MessageDepot;
 	public FilterBuilder FilterBuilder => new FilterBuilder(ComponentDepot);
 
 	public System(World world)
@@ -11,6 +10,13 @@ public abstract class System : EntityComponentReader
 		world.AddSystem(this);
 	}
 
+	internal void RegisterMessageDepot(MessageDepot messageDepot)
+	{
+		MessageDepot = messageDepot;
+	}
+
+	public abstract void Update(TimeSpan delta);
+
 	protected Entity CreateEntity()
 	{
 		return EntityStorage.Create();
@@ -26,6 +32,16 @@ public abstract class System : EntityComponentReader
 		ComponentDepot.Remove<TComponent>(entity.ID);
 	}
 
+	protected ReadOnlySpan<TMessage> ReadMessages<TMessage>() where TMessage : struct
+	{
+		return MessageDepot.Read<TMessage>();
+	}
+
+	protected bool SomeMessage<TMessage>() where TMessage : struct
+	{
+		return MessageDepot.Some<TMessage>();
+	}
+
 	protected void Destroy(in Entity entity)
 	{
 		ComponentDepot.OnEntityDestroy(entity.ID);
diff --git a/src/World.cs b/src/World.cs
index acf0886..dc62926 100644
--- a/src/World.cs
+++ b/src/World.cs
@@ -4,14 +4,15 @@ public class World
 {
 	private readonly List<System> Systems = new List<System>();
 	private readonly List<Renderer> Renderers = new List<Renderer>();
-	private readonly List<Filter> Filters = new List<Filter>();
 	private EntityStorage EntityStorage { get; } = new EntityStorage();
 	private ComponentDepot ComponentDepot { get; } = new ComponentDepot();
+	private MessageDepot MessageDepot { get; } = new MessageDepot();
 
 	internal void AddSystem(System system)
 	{
 		system.RegisterEntityStorage(EntityStorage);
 		system.RegisterComponentDepot(ComponentDepot);
+		system.RegisterMessageDepot(MessageDepot);
 		Systems.Add(system);
 	}