1 files changed, 79 insertions, 0 deletions
diff --git a/ecs/src/component/local.rs b/ecs/src/component/local.rs
new file mode 100644
index 0000000..e1a0c1f
--- /dev/null
+++ b/ecs/src/component/local.rs
@@ -0,0 +1,79 @@
+use std::any::{Any, TypeId};
+use std::ops::{Deref, DerefMut};
+
+use crate::component::Component;
+use crate::system::{ComponentRefMut, Param as SystemParam, System};
+use crate::WorldData;
+
+/// Holds a component which is local to a single system.
+#[derive(Debug)]
+pub struct Local<'world, LocalComponent: Component>
+{
+    local_component: ComponentRefMut<'world, LocalComponent>,
+}
+
+unsafe impl<'world, LocalComponent> SystemParam<'world> for Local<'world, LocalComponent>
+where
+    LocalComponent: Component,
+{
+    type Flags = ();
+    type Input = LocalComponent;
+
+    fn initialize<SystemImpl>(
+        system: &mut impl System<'world, SystemImpl>,
+        input: Self::Input,
+    )
+    {
+        system.set_local_component(input);
+    }
+
+    fn new<SystemImpl>(
+        system: &'world impl System<'world, SystemImpl>,
+        _world_data: &'world WorldData,
+    ) -> Self
+    {
+        let local_component = system
+            .get_local_component_mut::<LocalComponent>()
+            .expect("Local component is uninitialized");
+
+        Self { local_component }
+    }
+
+    fn is_compatible<Other: SystemParam<'world>>() -> bool
+    {
+        let other_comparable = Other::get_comparable();
+
+        let Some(other_type_id) = other_comparable.downcast_ref::<TypeId>() else {
+            return true;
+        };
+
+        TypeId::of::<LocalComponent>() != *other_type_id
+    }
+
+    fn get_comparable() -> Box<dyn Any>
+    {
+        Box::new(TypeId::of::<LocalComponent>())
+    }
+}
+
+impl<'world, LocalComponent> Deref for Local<'world, LocalComponent>
+where
+    LocalComponent: Component,
+{
+    type Target = LocalComponent;
+
+    fn deref(&self) -> &Self::Target
+    {
+        &self.local_component
+    }
+}
+
+impl<'world, LocalComponent> DerefMut for Local<'world, LocalComponent>
+where
+    LocalComponent: Component,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target
+    {
+        &mut self.local_component
+    }
+}