feat(ecs): add basic component storage for ECS

src/ecs/mod.rs

@@ -0,0 +1,137 @@
+use core::{any::TypeId, num::NonZeroU64, sync::atomic::AtomicU64};
+use std::{collections::BTreeMap, sync::RwLock};
+
+use allocator_api2::alloc::Allocator;
+use bytemuck::Contiguous;
+
+use crate::collections::SparseSet;
+
+pub type ECS = EntityComponentSystem;
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Entity(u64);
+
+static COMPONENT_ID_CREATOR: AtomicU64 = AtomicU64::new(1);
+static COMPONENT_IDS: RwLock<BTreeMap<TypeId, ComponentId>> = RwLock::new(BTreeMap::new());
+
+fn create_component_id<T>() -> ComponentId
+where
+    T: 'static + Sized,
+{
+    let type_id = core::any::TypeId::of::<T>();
+    {
+        // unwrap-justification: this only errors if RwLock is poisoned
+        let component_read = COMPONENT_IDS.read().unwrap();
+        if let Some(id) = component_read.get(&type_id) {
+            return *id;
+        }
+    }
+    let new_id = ComponentId(
+        NonZeroU64::new(COMPONENT_ID_CREATOR.fetch_add(1, core::sync::atomic::Ordering::Relaxed))
+            .unwrap(),
+    );
+    {
+        // unwrap-justification: see above
+        let mut component_write = COMPONENT_IDS.write().unwrap();
+        component_write.insert(type_id, new_id);
+    }
+    new_id
+}
+
+pub trait ComponentAllocator: Allocator {
+    fn new() -> Self;
+}
+
+pub trait Component: core::fmt::Debug + Send + Sized + 'static {
+    type Allocator: ComponentAllocator;
+
+    fn id() -> ComponentId {
+        static COMPONENT_ID: AtomicU64 = AtomicU64::new(0);
+        // TODO: reevaluate ordering later
+        let mut current_id = COMPONENT_ID.load(core::sync::atomic::Ordering::SeqCst);
+        if current_id == 0 {
+            current_id = create_component_id::<Self>().0.into_integer();
+            COMPONENT_ID.store(current_id, core::sync::atomic::Ordering::SeqCst);
+        }
+        ComponentId(NonZeroU64::new(current_id).unwrap())
+    }
+}
+
+pub trait ComponentStorage: core::fmt::Debug + 'static {}
+
+impl<T, SparseAlloc> ComponentStorage for SparseSet<T, T::Allocator, SparseAlloc>
+where
+    T: Component,
+    SparseAlloc: Allocator + Clone + 'static,
+{
+}
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ComponentId(NonZeroU64);
+
+#[derive(Debug)]
+pub struct ComponentSet<A = allocator_api2::alloc::Global> {
+    sets: SparseSet<Box<dyn ComponentStorage>>,
+    cold_alloc: A,
+}
+
+pub struct EntityComponentSystem {
+    components: ComponentSet,
+}
+
+impl ComponentSet {
+    fn new() -> Self {
+        Self {
+            sets: SparseSet::new(),
+            cold_alloc: allocator_api2::alloc::Global,
+        }
+    }
+}
+
+impl<A> ComponentSet<A>
+where
+    A: Allocator + Clone + 'static,
+{
+    fn new_in(alloc: A) -> Self {
+        Self {
+            sets: SparseSet::new(),
+            cold_alloc: alloc,
+        }
+    }
+
+    fn get_component_set<T: Component>(&self) -> Option<&SparseSet<T, T::Allocator, A>> {
+        let set = self.sets.get(T::id().0.into_integer() as usize)?;
+        (set as &dyn core::any::Any).downcast_ref()
+    }
+
+    fn get_component_set_mut<T: Component>(
+        &mut self,
+    ) -> Option<&mut SparseSet<T, T::Allocator, A>> {
+        let set = self.sets.get_mut(T::id().0.into_integer() as usize)?;
+        (set as &mut dyn core::any::Any).downcast_mut()
+    }
+
+    fn insert_component_set<T: Component>(&mut self) -> &mut SparseSet<T, T::Allocator, A> {
+        if self.sets.contains(T::id().0.into_integer() as usize) {
+            self.get_component_set_mut::<T>().unwrap()
+        } else {
+            let set = SparseSet::<T, _, _>::new_in(T::Allocator::new(), self.cold_alloc.clone());
+            self.sets
+                .insert(T::id().0.into_integer() as usize, Box::new(set) as Box<_>);
+            self.get_component_set_mut::<T>().unwrap()
+        }
+    }
+
+    fn add_to_entity<T: Component>(&mut self, entity: Entity, data: T) -> Option<T> {
+        let set = self.insert_component_set::<T>();
+        set.insert(entity.0 as usize, data)
+    }
+}
+
+impl Default for ComponentSet {
+    fn default() -> Self {
+        Self::new()
+    }
+}