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crates/utils/proc-macros/src/lib.rs

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+/*
+ * SPDX-FileCopyrightText: 2020 Stalwart Labs Ltd <hello@stalw.art>
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
+ */
+
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, Data, DeriveInput};
+
+#[proc_macro_derive(EnumMethods)]
+pub fn enum_id(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let name = &input.ident;
+
+    let variants = match input.data {
+        Data::Enum(ref data) => &data.variants,
+        _ => panic!("EnumMethods only works on enums"),
+    };
+
+    let variant_count = variants.len();
+    let variant_names: Vec<_> = variants.iter().map(|v| &v.ident).collect();
+    let variant_ids: Vec<usize> = (0..variant_count).collect();
+    let snake_case_names: Vec<String> = variant_names
+        .iter()
+        .map(|name| to_snake_case(&name.to_string()))
+        .collect();
+
+    let expanded = quote! {
+        impl #name {
+            pub const COUNT: usize = #variant_count;
+
+            pub const fn id(&self) -> usize {
+                match self {
+                    #(#name::#variant_names => #variant_ids,)*
+                }
+            }
+
+            pub fn from_id(id: usize) -> Option<Self> {
+                match id {
+                    #(#variant_ids => Some(#name::#variant_names),)*
+                    _ => None,
+                }
+            }
+
+            pub fn name(&self) -> &'static str {
+                match self {
+                    #(#name::#variant_names => #snake_case_names,)*
+                }
+            }
+
+            pub fn from_name(name: &str) -> Option<Self> {
+                match name {
+                    #(#snake_case_names => Some(#name::#variant_names),)*
+                    _ => None,
+                }
+            }
+        }
+    };
+
+    TokenStream::from(expanded)
+}
+
+fn to_snake_case(s: &str) -> String {
+    let mut result = String::new();
+    for (i, ch) in s.char_indices() {
+        if ch.is_uppercase() {
+            if i > 0 {
+                result.push('-');
+            }
+            result.push(ch.to_ascii_lowercase());
+        } else {
+            result.push(ch);
+        }
+    }
+    result
+}