feat(ecs): add support for singleton components

1 files changed, 54 insertions, 0 deletions

diff --git a/ecs/src/lib.rs b/ecs/src/lib.rs
index 33d981b..ce1a7d1 100644
--- a/ecs/src/lib.rs
+++ b/ecs/src/lib.rs
@@ -89,6 +89,20 @@ impl World
             });
     }
 
+    /// Adds a single component. This component will be globally shared.
+    ///
+    /// # Errors
+    /// Returns `Err` if this component has already been added as a single component.
+    pub fn add_single_component<SingleComponent>(
+        &mut self,
+        single_component: SingleComponent,
+    ) -> Result<(), SingleComponentAlreadyExistsError>
+    where
+        SingleComponent: Component,
+    {
+        self.data.single_component_storage.insert(single_component)
+    }
+
     pub fn register_system<'this, SystemImpl>(
         &'this mut self,
         event: &impl Event,
@@ -206,6 +220,7 @@ pub struct WorldData
 {
     events: HashMap<EventId, Vec<usize>>,
     component_storage: Arc<Lock<ComponentStorage>>,
+    single_component_storage: SingleComponentStorage,
     action_queue: Arc<Lock<ActionQueue>>,
 }
 
@@ -324,3 +339,42 @@ impl Drop for ComponentStorage
         }
     }
 }
+
+#[derive(Debug, thiserror::Error)]
+#[error("Single component {0} already exists")]
+pub struct SingleComponentAlreadyExistsError(pub &'static str);
+
+#[derive(Debug, Default)]
+struct SingleComponentStorage
+{
+    storage: HashMap<TypeId, Lock<Box<dyn Component>>>,
+}
+
+impl SingleComponentStorage
+{
+    fn get<SingleComponent: Component>(&self) -> Option<&Lock<Box<dyn Component>>>
+    {
+        self.storage.get(&TypeId::of::<SingleComponent>())
+    }
+
+    fn insert<SingleComponent: Component>(
+        &mut self,
+        single_component: SingleComponent,
+    ) -> Result<(), SingleComponentAlreadyExistsError>
+    {
+        let single_component_type_id = TypeId::of::<SingleComponent>();
+
+        if self.storage.contains_key(&single_component_type_id) {
+            return Err(SingleComponentAlreadyExistsError(type_name::<
+                SingleComponent,
+            >()));
+        }
+
+        self.storage.insert(
+            single_component_type_id,
+            Lock::new(Box::new(single_component)),
+        );
+
+        Ok(())
+    }
+}