1 files changed, 190 insertions, 0 deletions
diff --git a/ecs/src/relationship.rs b/ecs/src/relationship.rs
new file mode 100644
index 0000000..9004f0f
--- /dev/null
+++ b/ecs/src/relationship.rs
@@ -0,0 +1,190 @@
+use std::any::{type_name, Any};
+use std::marker::PhantomData;
+use std::sync::{Arc, Weak};
+
+use crate::component::storage::Storage as ComponentStorage;
+use crate::component::{
+    is_optional as component_is_optional,
+    Component,
+    FromOptional as ComponentFromOptional,
+    Id as ComponentId,
+    Metadata as ComponentMetadata,
+};
+use crate::entity::Uid as EntityUid;
+use crate::lock::{Lock, ReadGuard};
+use crate::system::{ComponentRefMut, Input as SystemInput};
+use crate::type_name::TypeName;
+use crate::{World, WorldData};
+
+#[derive(Debug)]
+pub struct Relationship<Kind, ComponentT: Component>
+{
+    entity_uid: EntityUid,
+    component_storage: Weak<Lock<ComponentStorage>>,
+    _pd: PhantomData<(Kind, ComponentT)>,
+}
+
+impl<Kind, ComponentT> Relationship<Kind, ComponentT>
+where
+    ComponentT: Component,
+{
+    pub fn new(world: &World, entity_uid: EntityUid) -> Self
+    {
+        Self {
+            entity_uid,
+            component_storage: Arc::downgrade(&world.data.component_storage),
+            _pd: PhantomData,
+        }
+    }
+}
+
+impl<Kind, ComponentT> Component for Relationship<Kind, ComponentT>
+where
+    Kind: 'static,
+    ComponentT: Component,
+{
+    type Component = Self;
+    type RefMut<'component> = Relation<'component, Kind, ComponentT>;
+
+    fn id(&self) -> ComponentId
+    {
+        ComponentId::of::<Self>()
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any
+    {
+        self
+    }
+
+    fn as_any(&self) -> &dyn Any
+    {
+        self
+    }
+
+    #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
+    fn prepare(world_data: &WorldData)
+    where
+        Self: Sized,
+    {
+        let mut component_storage_lock = world_data
+            .component_storage
+            .write_nonblock()
+            .expect("Failed to acquire read-write component storage lock");
+
+        #[cfg(feature = "debug")]
+        tracing::debug!(
+            "Adding archetypes lookup entry for component: {}",
+            std::any::type_name::<ComponentT>()
+        );
+
+        component_storage_lock.add_archetype_lookup_entry([ComponentMetadata {
+            id: ComponentId::of::<ComponentT>(),
+            is_optional: component_is_optional::<ComponentT>().into(),
+        }]);
+    }
+}
+
+impl<Kind, ComponentT> SystemInput for Relationship<Kind, ComponentT>
+where
+    Kind: 'static,
+    ComponentT: Component,
+{
+}
+
+impl<Kind, ComponentT: Component> TypeName for Relationship<Kind, ComponentT>
+where
+    ComponentT: Component,
+{
+    fn type_name(&self) -> &'static str
+    {
+        type_name::<Self>()
+    }
+}
+
+pub struct Relation<'rel_comp, Kind, ComponentT>
+where
+    Kind: 'static,
+    ComponentT: Component,
+{
+    component_storage_lock: ReadGuard<'static, ComponentStorage>,
+    relationship_comp: ComponentRefMut<'rel_comp, Relationship<Kind, ComponentT>>,
+    _component_storage: Arc<Lock<ComponentStorage>>,
+}
+
+impl<'rel_comp, Kind, ComponentT> ComponentFromOptional<'rel_comp>
+    for Relation<'rel_comp, Kind, ComponentT>
+where
+    ComponentT: Component,
+{
+    fn from_optional_component(
+        optional_component: Option<
+            crate::lock::WriteGuard<'rel_comp, Box<dyn Component>>,
+        >,
+    ) -> Self
+    {
+        let relationship_comp =
+            ComponentRefMut::<Relationship<Kind, ComponentT>>::from_optional_component(
+                optional_component,
+            );
+
+        let component_storage = relationship_comp
+            .component_storage
+            .upgrade()
+            .expect("World has been dropped");
+
+        let component_storage_lock = component_storage
+            .read_nonblock()
+            .expect("Failed to aquire read-only component storage lock");
+
+        Self {
+            relationship_comp,
+            // SAFETY: The component lock is not used for longer than the original
+            // lifetime
+            component_storage_lock: unsafe { component_storage_lock.upgrade_lifetime() },
+            _component_storage: component_storage,
+        }
+    }
+}
+
+impl<'rel_comp, Kind, ComponentT> Relation<'rel_comp, Kind, ComponentT>
+where
+    ComponentT: Component,
+{
+    /// Retrieves the related-to component.
+    pub fn get(&self) -> Option<ComponentRefMut<'_, ComponentT>>
+    {
+        let mut archetype_iter =
+            self.component_storage_lock
+                .find_entities([ComponentMetadata {
+                    id: ComponentId::of::<ComponentT>(),
+                    is_optional: component_is_optional::<ComponentT>().into(),
+                }]);
+
+        let (entity, archetype) = archetype_iter.find_map(|archetype| {
+            let Some(entity) = archetype.get_entity(self.relationship_comp.entity_uid)
+            else {
+                return None;
+            };
+
+            Some((entity, archetype))
+        })?;
+
+        let component_index =
+            archetype.get_index_for_component(&ComponentId::of::<ComponentT>())?;
+
+        let component = ComponentRefMut::new(
+            entity
+                .get(component_index)?
+                .component
+                .write_nonblock()
+                .unwrap_or_else(|_| {
+                    panic!(
+                        "Failed to aquire read-write lock of component {}",
+                        type_name::<ComponentT>()
+                    )
+                }),
+        );
+
+        Some(component)
+    }
+}