mcp-host-macros 0.1.1

//! Procedural macros for mcp-host
//!
//! Provides derive macros for MCP tools and resources.
//!
//! ## Attributes
//!
//! ### Struct-level attributes
//! - `#[mcp(name = "...")]` - Override the tool/resource name (default: struct name)
//! - `#[mcp(description = "...")]` - Set the description
//!
//! ### Field-level attributes
//! - `#[mcp(skip)]` - Exclude field from input schema (for internal state fields)
//!
//! ## Example
//!
//! ```rust,ignore
//! #[derive(McpTool)]
//! #[mcp(name = "my_tool", description = "Does something useful")]
//! pub struct MyTool {
//!     #[mcp(skip)]
//!     pub state: Arc<Mutex<State>>,  // Internal, not in schema
//!     pub input: String,              // Included in schema
//! }
//! ```

use proc_macro::TokenStream;
use quote::quote;
use syn::{Data, DeriveInput, Expr, Field, Fields, Lit, Meta, Type};

/// Derive macro for MCP tools
#[proc_macro_derive(McpTool, attributes(mcp))]
pub fn derive_mcp_tool(input: TokenStream) -> TokenStream {
    let input: DeriveInput = syn::parse2(input.into()).expect("Failed to parse input");

    let struct_name = &input.ident;
    let name_token = get_name(&input.attrs, struct_name);
    let description_token = get_description(&input.attrs);

    let schema = match &input.data {
        Data::Struct(data_struct) => match &data_struct.fields {
            Fields::Named(fields) => generate_schema_fields(fields.named.iter().collect()),
            Fields::Unnamed(_) => panic!("McpTool does not support unnamed fields"),
            Fields::Unit => quote! { {} },
        },
        Data::Enum(_) => panic!("McpTool does not support enums"),
        Data::Union(_) => panic!("McpTool does not support unions"),
    };

    let expanded = quote! {
        #[async_trait::async_trait]
        impl Tool for #struct_name {
            fn name(&self) -> &str {
                #name_token
            }

            fn description(&self) -> Option<&str> {
                #description_token
            }

            fn input_schema(&self) -> serde_json::Value {
                serde_json::json!({
                    "type": "object",
                    "properties": #schema,
                    "required": []
                })
            }

            fn execution(&self) -> Option<mcp_host::protocol::types::ToolExecution> {
                None
            }

            fn is_visible(&self, _ctx: &mcp_host::server::visibility::VisibilityContext) -> bool {
                true
            }

            async fn execute(&self, ctx: ExecutionContext<'_>) -> Result<Vec<Box<dyn Content>>, ToolError> {
                unimplemented!("User must implement execute for {}", #name_token)
            }
        }
    };

    TokenStream::from(expanded)
}

/// Derive macro for MCP resources
#[proc_macro_derive(McpResource, attributes(mcp))]
pub fn derive_mcp_resource(input: TokenStream) -> TokenStream {
    let input: DeriveInput = syn::parse2(input.into()).expect("Failed to parse input");

    let struct_name = &input.ident;
    let name_token = get_name(&input.attrs, struct_name);
    let description_token = get_description(&input.attrs);

    let (uri, mime_type) = match &input.data {
        Data::Struct(data_struct) => match &data_struct.fields {
            Fields::Named(fields) => extract_resource_fields(fields.named.iter().collect()),
            Fields::Unnamed(_) => panic!("McpResource does not support unnamed fields"),
            Fields::Unit => (quote! { "default:///" }, quote! { None }),
        },
        Data::Enum(_) => panic!("McpResource does not support enums"),
        Data::Union(_) => panic!("McpResource does not support unions"),
    };

    let expanded = quote! {
        #[async_trait::async_trait]
        impl Resource for #struct_name {
            fn uri(&self) -> &str {
                #uri
            }

            fn name(&self) -> &str {
                #name_token
            }

            fn description(&self) -> Option<&str> {
                #description_token
            }

            fn mime_type(&self) -> Option<&str> {
                #mime_type
            }

            fn is_visible(&self, _ctx: &mcp_host::server::visibility::VisibilityContext) -> bool {
                true
            }
        }
    };

    TokenStream::from(expanded)
}

/// Check if a field has `#[mcp(skip)]` attribute
fn has_skip_attr(field: &Field) -> bool {
    for attr in &field.attrs {
        if attr.path().is_ident("mcp") {
            // Try parsing as a simple ident (e.g., #[mcp(skip)])
            if let Ok(ident) = attr.parse_args::<syn::Ident>() {
                if ident == "skip" {
                    return true;
                }
            }
        }
    }
    false
}

/// Get name from `#[mcp(name = "...")]` or default to struct name
fn get_name(attrs: &[syn::Attribute], default: &syn::Ident) -> proc_macro2::TokenStream {
    for attr in attrs {
        if attr.path().is_ident("mcp") {
            if let Ok(Meta::NameValue(nv)) = attr.parse_args::<Meta>() {
                if nv.path.is_ident("name") {
                    if let Expr::Lit(expr_lit) = &nv.value {
                        if let Lit::Str(lit_str) = &expr_lit.lit {
                            let name = lit_str.value();
                            return quote! { #name };
                        }
                    }
                }
            }
            // Try parsing as a list of meta items: #[mcp(name = "...", description = "...")]
            if let Ok(list) = attr.parse_args_with(
                syn::punctuated::Punctuated::<Meta, syn::Token![,]>::parse_terminated,
            ) {
                for meta in list {
                    if let Meta::NameValue(nv) = meta {
                        if nv.path.is_ident("name") {
                            if let Expr::Lit(expr_lit) = &nv.value {
                                if let Lit::Str(lit_str) = &expr_lit.lit {
                                    let name = lit_str.value();
                                    return quote! { #name };
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    // Default to struct name (lowercase)
    let default_name = default.to_string();
    quote! { #default_name }
}

/// Get description from `#[mcp(description = "...")]`
fn get_description(attrs: &[syn::Attribute]) -> proc_macro2::TokenStream {
    for attr in attrs {
        if attr.path().is_ident("mcp") {
            // Try single meta: #[mcp(description = "...")]
            if let Ok(Meta::NameValue(nv)) = attr.parse_args::<Meta>() {
                if nv.path.is_ident("description") {
                    if let Expr::Lit(expr_lit) = &nv.value {
                        if let Lit::Str(lit_str) = &expr_lit.lit {
                            let desc = lit_str.value();
                            return quote! { Some(#desc) };
                        }
                    }
                }
            }
            // Try parsing as a list of meta items
            if let Ok(list) = attr.parse_args_with(
                syn::punctuated::Punctuated::<Meta, syn::Token![,]>::parse_terminated,
            ) {
                for meta in list {
                    if let Meta::NameValue(nv) = meta {
                        if nv.path.is_ident("description") {
                            if let Expr::Lit(expr_lit) = &nv.value {
                                if let Lit::Str(lit_str) = &expr_lit.lit {
                                    let desc = lit_str.value();
                                    return quote! { Some(#desc) };
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    quote! { None }
}

/// Generate schema fields from struct fields, skipping `#[mcp(skip)]` fields
fn generate_schema_fields(fields: Vec<&Field>) -> proc_macro2::TokenStream {
    let mut properties = Vec::new();

    for field in fields {
        // Skip fields marked with #[mcp(skip)]
        if has_skip_attr(field) {
            continue;
        }

        let field_name = &field.ident.as_ref().expect("Field should have identifier");
        let field_name_str = field_name.to_string();
        let field_type = &field.ty;

        let schema_prop = match parse_type_to_schema(field_type) {
            Ok(schema) => schema,
            Err(_) => {
                // Skip unsupported types (like Arc<Mutex<...>>)
                continue;
            }
        };

        properties.push(quote! {
            #field_name_str: #schema_prop
        });
    }

    quote! {
        { #(#properties,)* }
    }
}

/// Extract URI and MIME type fields for resources
fn extract_resource_fields(
    fields: Vec<&Field>,
) -> (proc_macro2::TokenStream, proc_macro2::TokenStream) {
    let mut uri = quote! { "default:///" };
    let mut mime_type = quote! { None };

    for field in fields {
        // Skip fields marked with #[mcp(skip)]
        if has_skip_attr(field) {
            continue;
        }

        let field_name = &field.ident.as_ref().expect("Field should have identifier");
        let field_name_str = field_name.to_string();

        if field_name_str == "uri" || field_name_str == "uri_template" {
            uri = quote! { self.#field_name.as_str() };
        }

        if field_name_str == "mime_type" {
            mime_type = quote! { self.#field_name.as_deref() };
        }
    }

    (uri, mime_type)
}

/// Parse Rust type to JSON schema
fn parse_type_to_schema(ty: &Type) -> Result<proc_macro2::TokenStream, String> {
    match ty {
        Type::Path(type_path) => {
            if type_path.path.segments.is_empty() {
                return Err("Empty type path".to_string());
            }
            let type_segment = &type_path.path.segments[0];
            match type_segment.ident.to_string().as_str() {
                "String" => Ok(quote! { { "type": "string" } }),
                "i8" | "i16" | "i32" | "i64" | "i128" | "isize" | "u8" | "u16" | "u32" | "u64"
                | "u128" | "usize" => Ok(quote! { { "type": "integer" } }),
                "f32" | "f64" => Ok(quote! { { "type": "number" } }),
                "bool" => Ok(quote! { { "type": "boolean" } }),
                "Vec" => Ok(quote! { { "type": "array", "items": { "type": "string" } } }),
                "Option" => Ok(quote! { { "type": ["string", "null"] } }),
                // Skip complex types like Arc, Mutex, etc.
                "Arc" | "Mutex" | "RwLock" | "Rc" | "RefCell" | "Box" => {
                    Err("Internal type, skip".to_string())
                }
                _ => Err(format!("Unsupported type: {}", type_segment.ident)),
            }
        }
        _ => Err("Complex types not yet supported".to_string()),
    }
}

#[cfg(test)]
mod tests {
    // Tests would go here but proc-macro crates have limited testing capabilities
    // Real testing happens in integration tests with the main crate
}