1 files changed, 98 insertions, 0 deletions
diff --git a/ecs/build.rs b/ecs/build.rs
new file mode 100644
index 0000000..1fbde2a
--- /dev/null
+++ b/ecs/build.rs
@@ -0,0 +1,98 @@
+use std::collections::HashSet;
+use std::path::PathBuf;
+
+use itertools::Itertools;
+use proc_macro2::{Delimiter, Group, Ident};
+use quote::{format_ident, quote, ToTokens};
+
+const CNT: usize = 4;
+
+fn main()
+{
+    let out_dir = PathBuf::from(std::env::var("OUT_DIR").unwrap());
+
+    let impls = (0..CNT).flat_map(create_input_filter_impls).join("\n");
+
+    std::fs::write(out_dir.join("system_input_impls.rs"), impls).unwrap();
+}
+
+fn create_input_filter_impls(cnt: usize) -> Vec<proc_macro2::TokenStream>
+{
+    let mut present = HashSet::new();
+
+    let elements = (0..cnt)
+        .map(|_| ElementKind::Element)
+        .chain(vec![ElementKind::Excluded; cnt])
+        .permutations(cnt)
+        .filter(|combination| {
+            if present.contains(combination) {
+                return false;
+            }
+
+            present.insert(combination.clone());
+
+            true
+        })
+        .map(|elements| {
+            elements
+                .into_iter()
+                .enumerate()
+                .map(|(index, element)| match element {
+                    ElementKind::Element => {
+                        IdentOrTuple::Ident(format_ident!("Elem{index}"))
+                    }
+                    ElementKind::Excluded => IdentOrTuple::Tuple,
+                })
+                .collect::<Vec<_>>()
+        })
+        .collect::<Vec<_>>();
+
+    elements
+        .into_iter()
+        .map(create_single_input_filter_impl)
+        .collect()
+}
+
+fn create_single_input_filter_impl(
+    elements: Vec<IdentOrTuple>,
+) -> proc_macro2::TokenStream
+{
+    let ident_elements = elements
+        .iter()
+        .filter(|element| matches!(element, IdentOrTuple::Ident(_)))
+        .collect::<Vec<_>>();
+
+    quote! {
+        impl<#(#ident_elements: Input,)*> InputFilter for (#(#elements,)*) {
+            type Filtered = (#(#ident_elements,)*);
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+enum ElementKind
+{
+    Element,
+    Excluded,
+}
+
+#[derive(Debug)]
+enum IdentOrTuple
+{
+    Ident(Ident),
+    Tuple,
+}
+
+impl ToTokens for IdentOrTuple
+{
+    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream)
+    {
+        match self {
+            Self::Ident(ident) => ident.to_tokens(tokens),
+            Self::Tuple => {
+                Group::new(Delimiter::Parenthesis, proc_macro2::TokenStream::new())
+                    .to_tokens(tokens)
+            }
+        }
+    }
+}