From a06ac08560cee332254de4c8ad09538b08c1f8ee Mon Sep 17 00:00:00 2001
From: mars <mars@tebibyte.media>
Date: Tue, 24 May 2022 02:28:55 -0600
Subject: [PATCH] Implement Decode derive macro

---
 protocol-derive/src/lib.rs | 35 +++++++++++++++++++++++++++++++++++
 src/main.rs                |  8 ++++++--
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/protocol-derive/src/lib.rs b/protocol-derive/src/lib.rs
index cdf56c2..4f51b99 100644
--- a/protocol-derive/src/lib.rs
+++ b/protocol-derive/src/lib.rs
@@ -37,3 +37,38 @@ pub fn derive_encode(input: TokenStream) -> TokenStream {
 
     expanded.into()
 }
+
+#[proc_macro_derive(Decode)]
+pub fn derive_decode(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let name = input.ident;
+    let data = &input.data;
+
+    let decode_members = match data {
+        Data::Struct(ref data) => match data.fields {
+            Fields::Named(ref fields) => {
+                let recurse = fields.named.iter().map(|f| {
+                    let name = &f.ident;
+                    quote_spanned! { f.span() =>
+                        #name: ::protocol::Decode::decode(reader)?,
+                    }
+                });
+                quote! { #(#recurse)* }
+            }
+            _ => unimplemented!(),
+        },
+        _ => unimplemented!(),
+    };
+
+    let expanded = quote! {
+        impl ::protocol::Decode for #name {
+            fn decode(reader: &mut impl ::std::io::Read) -> ::std::io::Result<Self> {
+                Ok(Self {
+                    #decode_members
+                })
+            }
+        }
+    };
+
+    expanded.into()
+}
diff --git a/src/main.rs b/src/main.rs
index fc4cc3e..ef51216 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,7 +1,7 @@
 use protocol::*;
-use protocol_derive::Encode;
+use protocol_derive::{Decode, Encode};
 
-#[derive(Debug, Encode)]
+#[derive(Debug, Decode, Encode)]
 struct TestData {
     var_int: Var<u32>,
     string: String,
@@ -16,4 +16,8 @@ fn main() {
     let mut buf = Vec::new();
     data.encode(&mut buf).unwrap();
     println!("encoded: {:?}", buf);
+
+    let mut reader = buf.as_slice();
+    let decoded = TestData::decode(&mut reader).unwrap();
+    println!("decoded: {:#?}", decoded);
 }