feat(ecs): add component added event

1 files changed, 75 insertions, 0 deletions

diff --git a/ecs/src/event/component.rs b/ecs/src/event/component.rs
new file mode 100644
index 0000000..306d43f
--- /dev/null
+++ b/ecs/src/event/component.rs
@@ -0,0 +1,75 @@
+//! Component events.
+
+use std::fmt::{Debug, Formatter};
+use std::marker::PhantomData;
+
+use ecs_macros::Component;
+
+use crate::component::{Component, Id as ComponentId};
+use crate::event::{Event, Id};
+use crate::tuple::{ReduceElement as TupleReduceElement, With as TupleWith};
+
+/// Event emitted when:
+/// a) A entity with component `ComponentT` is spawned.
+/// b) A component `ComponentT` is added to a entity.
+pub struct Added<ComponentT>
+where
+    ComponentT: Component,
+{
+    _pd: PhantomData<ComponentT>,
+}
+
+impl<ComponentT> Debug for Added<ComponentT>
+where
+    ComponentT: Component,
+{
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> std::fmt::Result
+    {
+        formatter
+            .debug_struct("Added")
+            .field("_pd", &self._pd)
+            .finish()
+    }
+}
+
+impl<ComponentT> Default for Added<ComponentT>
+where
+    ComponentT: Component,
+{
+    fn default() -> Self
+    {
+        Self { _pd: PhantomData }
+    }
+}
+
+impl<ComponentT> Event for Added<ComponentT>
+where
+    ComponentT: Component,
+{
+    fn id() -> Id
+    where
+        Self: Sized,
+    {
+        Id::new::<Added<ComponentForId>, _>(Some(ComponentId::of::<ComponentT>()))
+    }
+}
+
+pub fn create_added_id(component_id: ComponentId) -> Id
+{
+    Id::new::<Added<ComponentForId>, _>(Some(component_id))
+}
+
+pub struct ComponentToAddedEvent;
+
+impl<ComponentT: Component, Accumulator>
+    TupleReduceElement<Accumulator, ComponentToAddedEvent> for ComponentT
+where
+    Accumulator: TupleWith<Added<Self>>,
+{
+    type Return = Accumulator::With;
+}
+
+use crate as ecs;
+
+#[derive(Debug, Component)]
+struct ComponentForId;