feat(ecs): add weak reference actions

2 files changed, 71 insertions, 21 deletions

diff --git a/ecs/src/actions.rs b/ecs/src/actions.rs
index a5aaf0c..cc27f09 100644
--- a/ecs/src/actions.rs
+++ b/ecs/src/actions.rs
@@ -1,44 +1,55 @@
 use std::any::Any;
+use std::marker::PhantomData;
+use std::sync::{Arc, Weak};
 
 use crate::component::{Component, Sequence as ComponentSequence};
+use crate::lock::{Lock, WriteGuard};
 use crate::system::{NoInitParamFlag, Param as SystemParam, System};
 use crate::tuple::FilterExclude as TupleFilterExclude;
-use crate::WorldData;
+use crate::{ActionQueue, WorldData};
 
 /// Used to to queue up actions for a [`World`] to perform.
 #[derive(Debug)]
 pub struct Actions<'world>
 {
-    world_data: &'world WorldData,
+    action_queue: WriteGuard<'world, ActionQueue>,
+    action_queue_weak: Weak<Lock<ActionQueue>>,
 }
 
 impl<'world> Actions<'world>
 {
     /// Adds a spawning a new entity to the action queue.
-    ///
-    /// # Panics
-    /// Will panic if a mutable internal lock cannot be acquired.
     pub fn spawn<Comps: ComponentSequence>(&mut self, components: Comps)
     {
-        self.world_data
-            .action_queue
-            .write_nonblock()
-            .expect("Failed to aquire read-write action queue lock")
-            .push(Action::Spawn(components.into_vec()));
+        self.action_queue.push(Action::Spawn(components.into_vec()));
     }
 
-    /// Adds stopping the loop in [`Engine::event_loop`] at the next oppertune time to the
+    /// Adds stopping the loop in [`Engine::event_loop`] at the next opportune time to the
     /// action queue.
-    ///
-    /// # Panics
-    /// Will panic if a mutable internal lock cannot be acquired.
     pub fn stop(&mut self)
     {
-        self.world_data
-            .action_queue
-            .write_nonblock()
-            .expect("Failed to aquire read-write action queue lock")
-            .push(Action::Stop);
+        self.action_queue.push(Action::Stop);
+    }
+
+    /// Returns a struct which holds a weak reference to the [`World`] that `Actions`
+    /// references and that can be used to aquire a new `Actions` instance if the
+    /// referenced [`World`] is still alive.
+    #[must_use]
+    pub fn to_weak_ref(&self) -> WeakRef
+    {
+        WeakRef {
+            action_queue: self.action_queue_weak.clone(),
+        }
+    }
+
+    fn new(action_queue: &'world Arc<Lock<ActionQueue>>) -> Self
+    {
+        Self {
+            action_queue: action_queue
+                .write_nonblock()
+                .expect("Failed to aquire read-write action queue lock"),
+            action_queue_weak: Arc::downgrade(action_queue),
+        }
     }
 }
 
@@ -59,7 +70,7 @@ unsafe impl<'world> SystemParam<'world> for Actions<'world>
         world_data: &'world WorldData,
     ) -> Self
     {
-        Self { world_data }
+        Self::new(&world_data.action_queue)
     }
 
     fn is_compatible<Other: SystemParam<'world>>() -> bool
@@ -75,6 +86,45 @@ unsafe impl<'world> SystemParam<'world> for Actions<'world>
     }
 }
 
+#[derive(Debug, Clone)]
+pub struct WeakRef
+{
+    action_queue: Weak<Lock<ActionQueue>>,
+}
+
+impl WeakRef
+{
+    /// Returns a struct which can be used to retrieve a [`Actions`].
+    ///
+    /// Returns [`None`] if the referenced [`World`] has been dropped.
+    #[must_use]
+    pub fn access(&self) -> Option<Ref<'_>>
+    {
+        Some(Ref {
+            action_queue: self.action_queue.upgrade()?,
+            _pd: PhantomData,
+        })
+    }
+}
+
+/// Intermediate between [`Actions`] and [`WeakRef`]. Contains a strong reference to
+/// a world which is not allowed direct access to.
+#[derive(Debug, Clone)]
+pub struct Ref<'weak_ref>
+{
+    action_queue: Arc<Lock<ActionQueue>>,
+    _pd: PhantomData<&'weak_ref ()>,
+}
+
+impl<'weak_ref> Ref<'weak_ref>
+{
+    #[must_use]
+    pub fn to_actions(&self) -> Actions<'_>
+    {
+        Actions::new(&self.action_queue)
+    }
+}
+
 /// A action for a [`System`] to perform.
 #[derive(Debug)]
 pub(crate) enum Action
diff --git a/ecs/src/lib.rs b/ecs/src/lib.rs
index 1c4e44f..a2fc36e 100644
--- a/ecs/src/lib.rs
+++ b/ecs/src/lib.rs
@@ -211,7 +211,7 @@ pub struct WorldData
 {
     events: HashMap<EventId, Vec<usize>>,
     component_storage: Arc<Lock<ComponentStorage>>,
-    action_queue: Lock<ActionQueue>,
+    action_queue: Arc<Lock<ActionQueue>>,
 }
 
 #[derive(Debug, Default)]