1 files changed, 150 insertions, 0 deletions
diff --git a/macros/src/caster.rs b/macros/src/caster.rs
new file mode 100644
index 0000000..b84bd4d
--- /dev/null
+++ b/macros/src/caster.rs
@@ -0,0 +1,150 @@
+/**
+ * Originally from Intertrait by CodeChain
+ *
+ * <https://github.com/CodeChain-io/intertrait>
+ * <https://crates.io/crates/intertrait/0.2.2>
+ *
+ * Licensed under either of
+ *
+ * Apache License, Version 2.0 (LICENSE-APACHE or <http://www.apache.org/licenses/LICENSE-2.0>)
+ * MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
+
+ * at your option.
+*/
+use std::str::from_utf8;
+
+use proc_macro2::{Ident, TokenStream};
+use quote::{format_ident, quote, ToTokens};
+use uuid::adapter::Simple;
+use uuid::Uuid;
+
+const CASTER_FN_NAME_PREFIX: &[u8] = b"__";
+
+const FN_BUF_LEN: usize = CASTER_FN_NAME_PREFIX.len() + Simple::LENGTH;
+
+pub fn generate_caster(
+    ty: &impl ToTokens,
+    dst_trait: &impl ToTokens,
+    sync: bool,
+) -> TokenStream
+{
+    let fn_ident = create_caster_fn_ident(Uuid::new_v4());
+
+    let new_caster = if sync {
+        quote! {
+            syrette::private::cast::Caster::<#dst_trait>::new_sync(
+                |from| {
+                    let concrete = from
+                        .downcast::<#ty>()
+                        .map_err(|_| syrette::private::cast::CasterError::CastBoxFailed)?;
+
+                    Ok(concrete as Box<#dst_trait>)
+                },
+                |from| {
+                    let concrete = from
+                        .downcast::<#ty>()
+                        .map_err(|_| syrette::private::cast::CasterError::CastRcFailed)?;
+
+                    Ok(concrete as std::rc::Rc<#dst_trait>)
+                },
+                |from| {
+                    let concrete = from
+                        .downcast::<#ty>()
+                        .map_err(|_| syrette::private::cast::CasterError::CastArcFailed)?;
+
+                    Ok(concrete as std::sync::Arc<#dst_trait>)
+                },
+            )
+        }
+    } else {
+        quote! {
+            syrette::private::cast::Caster::<#dst_trait>::new(
+                |from| {
+                    let concrete = from
+                        .downcast::<#ty>()
+                        .map_err(|_| syrette::private::cast::CasterError::CastBoxFailed)?;
+
+                    Ok(concrete as Box<#dst_trait>)
+                },
+                |from| {
+                    let concrete = from
+                        .downcast::<#ty>()
+                        .map_err(|_| syrette::private::cast::CasterError::CastRcFailed)?;
+
+                    Ok(concrete as std::rc::Rc<#dst_trait>)
+                },
+            )
+        }
+    };
+
+    quote! {
+        #[syrette::private::linkme::distributed_slice(syrette::private::cast::CASTERS)]
+        #[linkme(crate = syrette::private::linkme)]
+        fn #fn_ident() -> (::std::any::TypeId, syrette::private::cast::BoxedCaster) {
+            (::std::any::TypeId::of::<#ty>(), Box::new(#new_caster))
+        }
+    }
+}
+
+fn create_caster_fn_ident(uuid: impl IUuid) -> Ident
+{
+    let buf = &mut [0u8; FN_BUF_LEN];
+
+    buf[..CASTER_FN_NAME_PREFIX.len()].copy_from_slice(CASTER_FN_NAME_PREFIX);
+
+    uuid.encode_simple_lower_into(&mut buf[CASTER_FN_NAME_PREFIX.len()..]);
+
+    let fn_name =
+        from_utf8(&buf[..FN_BUF_LEN]).expect("Created caster function name is not UTF-8");
+
+    format_ident!("{}", fn_name)
+}
+
+/// Simple interface for `Uuid`.
+///
+/// Created for ease of testing the [`create_caster_fn_ident`] function.
+///
+/// [`Uuid`]: uuid::Uuid
+#[cfg_attr(test, mockall::automock)]
+trait IUuid
+{
+    /// Writes the Uuid as a simple lower-case string to `buf`.
+    fn encode_simple_lower_into(self, buf: &mut [u8]);
+}
+
+impl IUuid for Uuid
+{
+    fn encode_simple_lower_into(self, buf: &mut [u8])
+    {
+        self.to_simple().encode_lower(buf);
+    }
+}
+
+#[cfg(test)]
+mod tests
+{
+    use pretty_assertions::assert_eq;
+    use utility_macros::repeat_char;
+
+    use super::*;
+
+    #[test]
+    fn can_create_caster_fn_ident()
+    {
+        let mut uuid_mock = MockIUuid::new();
+
+        uuid_mock
+            .expect_encode_simple_lower_into()
+            .return_once(|buf| {
+                for index in 0..(FN_BUF_LEN - 2) {
+                    buf[index] = b'f';
+                }
+            })
+            .once();
+
+        assert_eq!(
+            create_caster_fn_ident(uuid_mock),
+            format_ident!(concat!("__", repeat_char!('f', 32)))
+        );
+    }
+}