1 files changed, 67 insertions, 0 deletions
diff --git a/ecs/src/system/stateful.rs b/ecs/src/system/stateful.rs
new file mode 100644
index 0000000..b641cf2
--- /dev/null
+++ b/ecs/src/system/stateful.rs
@@ -0,0 +1,67 @@
+use std::marker::PhantomData;
+
+use crate::component::Local;
+use crate::system::{System, TypeErased};
+use crate::{ComponentStorage, Query};
+
+/// A stateful system.
+pub struct Stateful<Func, LocalComponent, Comps>
+{
+    func: Func,
+    local_component: Option<LocalComponent>,
+    _comps_pd: PhantomData<Comps>,
+}
+
+impl<Func: 'static, Comps: 'static, LocalComponent: 'static>
+    System<fn(Query<Comps>, Local<LocalComponent>)>
+    for Stateful<Func, LocalComponent, Comps>
+where
+    Func: Fn(Query<Comps>, Local<LocalComponent>),
+{
+    type Input = LocalComponent;
+    type Query<'a> = Query<'a, Comps>;
+
+    fn initialize(mut self, input: Self::Input) -> Self
+    {
+        self.local_component = Some(input);
+
+        self
+    }
+
+    fn run(&mut self, component_storage: &mut ComponentStorage)
+    {
+        (self.func)(
+            Query::new(component_storage),
+            Local::new(self.local_component.as_mut().unwrap()),
+        );
+    }
+
+    fn into_type_erased(self) -> TypeErased
+    {
+        TypeErased {
+            data: Box::new(self),
+            func: Box::new(move |data, component_storage| {
+                let this = data.downcast_mut::<Self>().unwrap();
+
+                this.run(component_storage);
+            }),
+        }
+    }
+}
+
+impl<Func: 'static, Comps, LocalComponent: 'static>
+    crate::system::Into<fn(Query<Comps>, Local<LocalComponent>)> for Func
+where
+    Func: Fn(Query<Comps>, Local<LocalComponent>),
+{
+    type System = Stateful<Func, LocalComponent, Comps>;
+
+    fn into_system(self) -> Self::System
+    {
+        Self::System {
+            func: self,
+            local_component: None,
+            _comps_pd: PhantomData,
+        }
+    }
+}