feat(ecs): add queueing up spawning entities from systems

2 files changed, 81 insertions, 0 deletions

diff --git a/ecs/src/actions.rs b/ecs/src/actions.rs
new file mode 100644
index 0000000..d67f895
--- /dev/null
+++ b/ecs/src/actions.rs
@@ -0,0 +1,63 @@
+use std::any::Any;
+
+use crate::component::{Component, Sequence as ComponentSequence};
+use crate::system::{NoInitParamFlag, Param as SystemParam, System};
+use crate::tuple::FilterExclude as TupleFilterExclude;
+use crate::WorldData;
+
+/// Used to to queue up actions for a [`World`] to perform.
+#[derive(Debug)]
+pub struct Actions<'world>
+{
+    world_data: &'world mut WorldData,
+}
+
+impl<'world> Actions<'world>
+{
+    /// Adds a spawning a new entity to the action queue.
+    pub fn spawn<Comps: ComponentSequence>(&mut self, components: Comps)
+    {
+        self.world_data
+            .action_queue
+            .push(Action::Spawn(components.into_vec()));
+    }
+}
+
+unsafe impl<'world> SystemParam<'world> for Actions<'world>
+{
+    type Flags = NoInitParamFlag;
+    type Input = TupleFilterExclude;
+
+    fn initialize<SystemImpl>(_system: &mut impl System<SystemImpl>, _input: Self::Input)
+    {
+    }
+
+    fn new<SystemImpl>(
+        _system: &'world mut impl System<SystemImpl>,
+        world_data: &'world mut WorldData,
+    ) -> Self
+    {
+        Self { world_data }
+    }
+
+    fn is_compatible<Other: SystemParam<'world>>() -> bool
+    {
+        let other_comparable = Other::get_comparable();
+
+        other_comparable.downcast_ref::<Comparable>().is_none()
+    }
+
+    fn get_comparable() -> Box<dyn Any>
+    {
+        Box::new(())
+    }
+}
+
+/// A action for a [`System`] to perform.
+#[derive(Debug)]
+pub enum Action
+{
+    Spawn(Vec<Box<dyn Component>>),
+}
+
+struct Comparable;
diff --git a/ecs/src/lib.rs b/ecs/src/lib.rs
index 0c06472..6b9373c 100644
--- a/ecs/src/lib.rs
+++ b/ecs/src/lib.rs
@@ -6,6 +6,7 @@ use std::fmt::Debug;
 use std::marker::PhantomData;
 use std::slice::{Iter as SliceIter, IterMut as SliceIterMut};
 
+use crate::actions::Action;
 use crate::component::{Component, Sequence as ComponentSequence};
 use crate::event::{Event, Id as EventId};
 use crate::system::{
@@ -16,6 +17,7 @@ use crate::system::{
 };
 use crate::tuple::FilterExclude as TupleFilterExclude;
 
+pub mod actions;
 pub mod component;
 pub mod event;
 pub mod system;
@@ -94,6 +96,21 @@ impl World
     {
         Query::new(&mut self.data)
     }
+
+    /// Peforms the actions that have been queued up using [`Actions`].
+    pub fn perform_queued_actions(&mut self)
+    {
+        for action in self.data.action_queue.drain(..) {
+            match action {
+                Action::Spawn(components) => {
+                    self.data
+                        .component_storage
+                        .entities
+                        .push(Entity { components });
+                }
+            }
+        }
+    }
 }
 
 #[derive(Debug, Default)]
@@ -101,6 +118,7 @@ pub struct WorldData
 {
     events: HashMap<EventId, Vec<usize>>,
     component_storage: ComponentStorage,
+    action_queue: Vec<Action>,
 }
 
 #[derive(Debug)]