1 files changed, 131 insertions, 0 deletions
diff --git a/ecs/src/system/initializable.rs b/ecs/src/system/initializable.rs
new file mode 100644
index 0000000..40fbb0f
--- /dev/null
+++ b/ecs/src/system/initializable.rs
@@ -0,0 +1,131 @@
+use std::marker::PhantomData;
+
+use seq_macro::seq;
+
+use crate::system::{Input, Param as SystemParam, System};
+use crate::tuple::{Reduce as TupleReduce, ReduceElement as TupleReduceElement, Tuple};
+
+/// A initializable system.
+pub trait Initializable<'world, Impl>: System<'world, Impl>
+{
+    type Inputs;
+
+    #[must_use]
+    fn initialize(self, inputs: Self::Inputs) -> Self;
+}
+
+pub trait Param<'world, SystemT>: SystemParam<'world>
+{
+    fn initialize(system: &mut SystemT, input: Self::Input);
+}
+
+pub struct ParamTupleFilter<'world, SystemT>
+{
+    _pd: PhantomData<(&'world (), SystemT)>,
+}
+
+impl<'world, SystemT, ParamT, Accumulator>
+    TupleReduceElement<Accumulator, ParamTupleFilter<'world, SystemT>> for ParamT
+where
+    ParamT: SystemParam<
+        'world,
+        Input: AppendInitializableParam<'world, Accumulator, ParamT, SystemT>,
+    >,
+    Accumulator: Tuple,
+{
+    type Return = <ParamT::Input as AppendInitializableParam<
+        'world,
+        Accumulator,
+        ParamT,
+        SystemT,
+    >>::Return;
+}
+
+pub trait AppendInitializableParam<'world, Accumulator, ParamT, SystemT>
+{
+    type Return;
+}
+
+impl<'world, InputT, ParamT, Accumulator, SystemT>
+    AppendInitializableParam<'world, Accumulator, ParamT, SystemT> for InputT
+where
+    InputT: Input,
+    Accumulator: Tuple,
+    ParamT: Param<'world, SystemT>,
+{
+    type Return = Accumulator::WithElementAtEnd<ParamT>;
+}
+
+impl<'world, ParamT, Accumulator, SystemT>
+    AppendInitializableParam<'world, Accumulator, ParamT, SystemT> for ()
+where
+    Accumulator: Tuple,
+{
+    type Return = Accumulator;
+}
+
+pub trait ParamTuple<'world, SystemT>
+{
+    type Inputs;
+
+    fn initialize_all(system: &mut SystemT, inputs: Self::Inputs);
+}
+
+macro_rules! impl_initializable_param_tuple {
+    ($c: tt) => {
+        seq!(I in 0..$c {
+            impl<'world, SystemT, #(Param~I,)*> ParamTuple<'world, SystemT>
+                for (#(Param~I,)*)
+            where
+                #(Param~I: Param<'world, SystemT>,)*
+            {
+                type Inputs = (#(Param~I::Input,)*);
+
+                fn initialize_all(
+                    system: &mut SystemT,
+                    inputs: Self::Inputs,
+                ) {
+                    #(
+                        <Param~I as Param<'world, SystemT>>::initialize(
+                            system,
+                            inputs.I
+                        );
+                    )*
+                }
+            }
+        });
+    };
+}
+
+seq!(C in 1..16 {
+    impl_initializable_param_tuple!(C);
+});
+
+impl<'world, SystemT> ParamTuple<'world, SystemT> for ()
+{
+    type Inputs = ();
+
+    fn initialize_all(_system: &mut SystemT, _inputs: Self::Inputs) {}
+}
+
+/// A tuple of system parameters that may or may not be initializable.
+pub trait MaybeInitializableParamTuple<'world, SystemT>
+{
+    /// A tuple of the inputs of the initializable system parameters in this tuple.
+    type Inputs;
+
+    fn init_initializable(system: &mut SystemT, inputs: Self::Inputs);
+}
+
+impl<'world, SystemT, Params> MaybeInitializableParamTuple<'world, SystemT> for Params
+where
+    Params:
+        TupleReduce<ParamTupleFilter<'world, SystemT>, Out: ParamTuple<'world, SystemT>>,
+{
+    type Inputs = <Params::Out as ParamTuple<'world, SystemT>>::Inputs;
+
+    fn init_initializable(system: &mut SystemT, inputs: Self::Inputs)
+    {
+        Params::Out::initialize_all(system, inputs);
+    }
+}