From b0ef7f2cf8787c5732e0eb5554161ad75179a4b3 Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Tue, 20 Feb 2024 23:02:57 +0100
Subject: refactor(ecs): add system trait

---
 ecs/src/lib.rs    | 37 ++++++--------------------------
 ecs/src/system.rs | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+), 30 deletions(-)
 create mode 100644 ecs/src/system.rs

diff --git a/ecs/src/lib.rs b/ecs/src/lib.rs
index f824ebc..6106862 100644
--- a/ecs/src/lib.rs
+++ b/ecs/src/lib.rs
@@ -8,8 +8,10 @@ use std::marker::PhantomData;
 use std::slice::IterMut as SliceIterMut;
 
 use crate::component::{Component, Sequence as ComponentSequence};
+use crate::system::{System, TypeErased as TypeErasedSystem};
 
 pub mod component;
+pub mod system;
 
 #[derive(Debug)]
 struct Entity
@@ -20,7 +22,7 @@ struct Entity
 #[derive(Debug)]
 pub struct World<Event>
 {
-    systems: Vec<Box<dyn AnySystem>>,
+    systems: Vec<TypeErasedSystem>,
     events: HashMap<Event, Vec<usize>>,
     component_storage: ComponentStorage,
 }
@@ -46,12 +48,12 @@ impl<Event> World<Event>
             .push(Entity { components: components.into_vec() });
     }
 
-    pub fn register_system<Comps>(&mut self, event: Event, system: System<Comps>)
+    pub fn register_system<TSystem, SystemImpl>(&mut self, event: Event, system: TSystem)
     where
         Event: Hash + PartialEq + Eq,
-        Comps: ComponentSequence + 'static,
+        TSystem: System<SystemImpl>,
     {
-        self.systems.push(Box::new(system));
+        self.systems.push(system.into_type_erased());
 
         self.events
             .entry(event)
@@ -75,7 +77,7 @@ impl<Event> World<Event>
         for system_index in system_indices {
             let system = self.systems.get_mut(system_index).unwrap();
 
-            system.call(&mut self.component_storage);
+            system.run(&mut self.component_storage);
         }
     }
 
@@ -95,31 +97,6 @@ impl<Event> Default for World<Event>
     }
 }
 
-pub type System<Comps> = fn(Query<Comps>);
-
-trait AnySystem
-{
-    fn call(&self, component_storage: &mut ComponentStorage);
-}
-
-impl<Comps> AnySystem for System<Comps>
-where
-    Comps: ComponentSequence,
-{
-    fn call(&self, component_storage: &mut ComponentStorage)
-    {
-        self(Query::new(component_storage));
-    }
-}
-
-impl Debug for dyn AnySystem
-{
-    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
-    {
-        formatter.debug_struct("AnySystem").finish_non_exhaustive()
-    }
-}
-
 #[derive(Debug)]
 pub struct Query<'world, Comps>
 {
diff --git a/ecs/src/system.rs b/ecs/src/system.rs
new file mode 100644
index 0000000..ecf1885
--- /dev/null
+++ b/ecs/src/system.rs
@@ -0,0 +1,64 @@
+use std::any::Any;
+use std::fmt::Debug;
+
+use crate::component::Sequence as ComponentSequence;
+use crate::{ComponentStorage, Query};
+
+pub trait System<Impl>: 'static
+{
+    type Query<'a>;
+
+    fn run(&self, component_storage: &mut ComponentStorage);
+
+    fn into_type_erased(self) -> TypeErased;
+}
+
+impl<Func, Comps> System<fn(Query<Comps>)> for Func
+where
+    Func: Fn(Query<Comps>) + 'static,
+    Comps: ComponentSequence,
+{
+    type Query<'a> = Query<'a, Comps>;
+
+    fn run(&self, component_storage: &mut ComponentStorage)
+    {
+        self(Query::new(component_storage));
+    }
+
+    fn into_type_erased(self) -> TypeErased
+    {
+        TypeErased {
+            data: Box::new(self),
+            func: Box::new(|data, component_storage| {
+                let me = data.downcast_mut::<Func>().unwrap();
+
+                me.run(component_storage);
+            }),
+        }
+    }
+}
+
+pub struct TypeErased
+{
+    data: Box<dyn Any>,
+    func: Box<TypeErasedFunc>,
+}
+
+impl TypeErased
+{
+    pub fn run(&mut self, component_storage: &mut ComponentStorage)
+    {
+        (self.func)(self.data.as_mut(), component_storage);
+    }
+}
+
+impl Debug for TypeErased
+{
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
+    {
+        formatter.debug_struct("TypeErased").finish_non_exhaustive()
+    }
+}
+
+/// Function in [`TypeErased`] used to run the system.
+type TypeErasedFunc = dyn Fn(&mut dyn Any, &mut ComponentStorage);
-- 
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