1 files changed, 126 insertions, 1 deletions

diff --git a/ecs/src/system/stateful.rs b/ecs/src/system/stateful.rs
index 7b2b608..e74ef31 100644
--- a/ecs/src/system/stateful.rs
+++ b/ecs/src/system/stateful.rs
@@ -1,10 +1,18 @@
+use std::mem::transmute;
 use std::panic::{RefUnwindSafe, UnwindSafe};
 
 use seq_macro::seq;
 
 use crate::component::local::SystemWithLocalComponents;
 use crate::component::Parts as ComponentParts;
+use crate::event::Emitted as EmittedEvent;
 use crate::system::initializable::{Initializable, MaybeInitializableParamTuple};
+use crate::system::observer::{
+    Observe,
+    Observed,
+    Observer,
+    WrapperComponent as ObserverWrapperComponent,
+};
 use crate::system::{Into as IntoSystem, Metadata, Param, System, TypeErased};
 use crate::World;
 
@@ -68,9 +76,10 @@ macro_rules! impl_system {
                 }
             }
 
-            impl<Func, #(TParam~I,)*> IntoSystem<fn(#(TParam~I,)*)>
+            impl<'world, Func, #(TParam~I,)*> IntoSystem<'world, fn(#(TParam~I,)*)>
                 for Func
             where
+                #(TParam~I: Param<'world>,)*
                 Func: Fn(#(TParam~I,)*) + Copy + 'static,
             {
                 type System = Stateful<Func>;
@@ -123,3 +132,119 @@ fn init_initializable_params<'world, SystemT, Params>(
 {
     Params::init_initializable(system, inputs);
 }
+
+macro_rules! impl_observer {
+    ($c: tt) => {
+        seq!(I in 0..$c {
+            impl<'world, ObservedT, Func, #(TParam~I,)*> System<
+                'world,
+                fn(Observe<'world, ObservedT>, #(TParam~I,)*)
+            > for Stateful<Func>
+            where
+                ObservedT: Observed,
+                Func: Fn(Observe<'world, ObservedT>, #(TParam~I,)*) + Copy + 'static,
+                #(TParam~I: Param<'world>,)*
+            {
+                type Callbacks = Callbacks;
+
+                fn finish(self) -> (TypeErased, Callbacks)
+                {
+                    unimplemented!();
+                }
+            }
+
+            impl<'world, ObservedT, Func, #(TParam~I,)*> Initializable<
+                'world,
+                fn(Observe<'world, ObservedT>, #(TParam~I,)*)
+            > for Stateful<Func>
+            where
+                ObservedT: Observed,
+                Func: Fn(Observe<'world, ObservedT>, #(TParam~I,)*) + Copy + 'static,
+                #(TParam~I: Param<'world>,)*
+                (#(TParam~I,)*): MaybeInitializableParamTuple<'world, Self>
+            {
+                type Inputs = <
+                    (#(TParam~I,)*) as MaybeInitializableParamTuple<'world, Self>
+                >::Inputs;
+
+                fn initialize(mut self, inputs: Self::Inputs) -> Self
+                {
+                    init_initializable_params::<_, (#(TParam~I,)*)>(&mut self, inputs);
+
+                    self
+                }
+            }
+
+            impl<'world, ObservedT, Func, #(TParam~I,)*> Observer<
+                'world,
+                fn(Observe<'world, ObservedT>, #(TParam~I,)*)
+            > for Stateful<Func>
+            where
+                ObservedT: Observed,
+                Func: Fn(Observe<'world, ObservedT>, #(TParam~I,)*) + Copy + 'static,
+                #(TParam~I: Param<'world>,)*
+            {
+                type ObservedEvents = ObservedT::Events;
+
+                fn observed_events() -> Self::ObservedEvents
+                {
+                    ObservedT::events()
+                }
+
+                fn finish_observer(self) -> (ObserverWrapperComponent, Callbacks)
+                {
+                    let Self { func, local_components } = self;
+
+                    let callbacks = Callbacks { local_components };
+
+                    let wrapper_comp = ObserverWrapperComponent::new(
+                        move |world, metadata, emitted_event| {
+                            // SAFETY: The caller of TypeErased::run ensures the lifetime
+                            // is correct
+                            let world = unsafe { &*std::ptr::from_ref(world) };
+
+                            // SAFETY: The caller of TypeErased::run ensures the lifetime
+                            // is correct
+                            let emitted_event = unsafe {
+                                transmute::<EmittedEvent<'_>, EmittedEvent<'_>>(
+                                    emitted_event
+                                )
+                            };
+
+                            func(Observe::new(world, emitted_event), #({
+                                TParam~I::new(world, &metadata)
+                            },)*);
+                        },
+                    );
+
+                    (wrapper_comp, callbacks)
+                }
+            }
+
+            impl<'world, Func, ObservedT, #(TParam~I,)*> IntoSystem<
+                'world,
+                fn(Observe<'world, ObservedT>,
+                #(TParam~I,)*)
+            > for Func
+            where
+                ObservedT: Observed,
+                #(TParam~I: Param<'world>,)*
+                Func: Fn(Observe<'world, ObservedT>, #(TParam~I,)*) + Copy + 'static,
+            {
+                type System = Stateful<Func>;
+
+                fn into_system(self) -> Stateful<Func>
+                {
+                    Stateful {
+                        func: self,
+                        local_components: Vec::new(), // TODO: Use Vec::with_capacity
+                    }
+                }
+            }
+        });
+    };
+}
+
+seq!(C in 1..16 {
+    impl_observer!(C);
+});