1 files changed, 100 insertions, 0 deletions
diff --git a/util-macros/src/lib.rs b/util-macros/src/lib.rs
new file mode 100644
index 0000000..036ffc8
--- /dev/null
+++ b/util-macros/src/lib.rs
@@ -0,0 +1,100 @@
+use proc_macro::{TokenStream, TokenTree};
+use quote::quote;
+
+/// Subtracts two numbers and calls a given callback macro with the result.
+///
+/// # Input
+/// `number - number, callback`
+///
+/// # Examples
+/// ```
+/// # use std::any::TypeId;
+/// use util_macros::sub;
+///
+/// macro_rules! sub_cb {
+///     ($num: literal) => {
+///         $num
+///     };
+/// }
+///
+/// type Foo = [u8; sub!(5 - 2, sub_cb)];
+///
+/// assert_eq!(TypeId::of::<Foo>(), TypeId::of::<[u8; 3]>());
+/// ```
+/// <br>
+///
+/// The callback is called with the identifier `overflow` if a overflow occurs.
+/// ```
+/// # use std::any::TypeId;
+/// use util_macros::sub;
+///
+/// macro_rules! sub_cb {
+///     ($num: literal) => {
+///         $num
+///     };
+///
+///     (overflow) => {
+///         128
+///     };
+/// }
+///
+/// type Foo = [u8; sub!(3 - 10, sub_cb)];
+///
+/// assert_eq!(TypeId::of::<Foo>(), TypeId::of::<[u8; 128]>());
+/// ```
+#[proc_macro]
+pub fn sub(input: TokenStream) -> TokenStream
+{
+    let mut input_tt_iter = input.into_iter();
+
+    let num_a = match input_tt_iter.next().unwrap() {
+        TokenTree::Literal(lit) => lit.to_string().parse::<u32>().unwrap(),
+        _ => {
+            panic!("Expected a number literal");
+        }
+    };
+
+    match input_tt_iter.next().unwrap() {
+        TokenTree::Punct(punct) if punct.as_char() == '-' => {}
+        _ => {
+            panic!("Expected a '-' token");
+        }
+    };
+
+    let num_b = match input_tt_iter.next().unwrap() {
+        TokenTree::Literal(lit) => lit.to_string().parse::<u32>().unwrap(),
+        _ => {
+            panic!("Expected a number literal");
+        }
+    };
+
+    match input_tt_iter.next().unwrap() {
+        TokenTree::Punct(punct) if punct.as_char() == ',' => {}
+        _ => {
+            panic!("Expected a ',' token");
+        }
+    };
+
+    let cb_ident = match input_tt_iter.next().unwrap() {
+        TokenTree::Ident(cb_ident) => {
+            proc_macro2::Ident::new(&cb_ident.to_string(), cb_ident.span().into())
+        }
+        _ => {
+            panic!("Expected a identifier");
+        }
+    };
+
+    let Some(subtracted) = num_a.checked_sub(num_b) else {
+        return quote! {
+            #cb_ident!(overflow)
+        }
+        .into();
+    };
+
+    let subtracted_lit = proc_macro2::Literal::u32_unsuffixed(subtracted);
+
+    quote! {
+        #cb_ident!(#subtracted_lit)
+    }
+    .into()
+}