openapi_to_rust/

client_generator.rs

//! HTTP client generation for OpenAPI specifications.
//!
//! This module is part of the code generator that creates production-ready HTTP clients
//! from OpenAPI specifications. It generates clients with middleware support including
//! retry logic and request tracing.
//!
//! # Overview
//!
//! The client generator creates:
//! - `HttpClient` struct with middleware stack (reqwest-middleware)
//! - Retry logic with exponential backoff (reqwest-retry)
//! - Request/response tracing (reqwest-tracing)
//! - Direct methods for all API operations (GET, POST, PUT, DELETE, PATCH)
//! - Comprehensive error handling with [`HttpError`](crate::http_error::HttpError)
//! - Builder pattern for configuration
//!
//! # Generated Code Structure
//!
//! For each OpenAPI specification, the generator creates:
//!
//! ```rust,ignore
//! // Generated client.rs file
//!
//! use crate::types::*;
//! use reqwest_middleware::{ClientBuilder, ClientWithMiddleware};
//! use std::collections::BTreeMap;
//!
//! pub struct HttpClient {
//!     base_url: String,
//!     api_key: Option<String>,
//!     http_client: ClientWithMiddleware,
//!     custom_headers: BTreeMap<String, String>,
//! }
//!
//! impl HttpClient {
//!     pub fn new() -> Self { /* ... */ }
//!     pub fn with_config(retry_config: Option<RetryConfig>, enable_tracing: bool) -> Self { /* ... */ }
//!     pub fn with_base_url(self, base_url: String) -> Self { /* ... */ }
//!     pub fn with_api_key(self, api_key: String) -> Self { /* ... */ }
//!     pub fn with_header(self, key: String, value: String) -> Self { /* ... */ }
//!
//!     // Generated operation methods
//!     pub async fn list_items(&self) -> Result<ItemList, HttpError> { /* ... */ }
//!     pub async fn create_item(&self, request: CreateItemRequest) -> Result<Item, HttpError> { /* ... */ }
//!     pub async fn get_item(&self, id: impl AsRef<str>) -> Result<Item, HttpError> { /* ... */ }
//! }
//! ```
//!
//! # Middleware Stack
//!
//! The generated client uses `reqwest-middleware` to build a composable middleware stack:
//!
//! 1. **Tracing Middleware** (optional, enabled by default)
//!    - Logs HTTP requests/responses
//!    - Creates spans for distributed tracing
//!    - Integrates with `tracing` ecosystem
//!
//! 2. **Retry Middleware** (optional, configured via TOML)
//!    - Exponential backoff retry policy
//!    - Automatically retries transient errors (429, 500, 502, 503, 504)
//!    - Configurable max retries and delay bounds
//!
//! # Configuration
//!
//! ## Via TOML
//!
//! ```toml
//! [http_client]
//! base_url = "https://api.example.com"
//! timeout_seconds = 30
//!
//! [http_client.retry]
//! max_retries = 3
//! initial_delay_ms = 500
//! max_delay_ms = 16000
//!
//! [http_client.tracing]
//! enabled = true
//! ```
//!
//! ## Via Rust API
//!
//! ```no_run
//! use openapi_to_rust::{GeneratorConfig, http_config::*};
//! use std::path::PathBuf;
//!
//! let config = GeneratorConfig {
//!     spec_path: PathBuf::from("openapi.json"),
//!     enable_async_client: true,
//!     retry_config: Some(RetryConfig {
//!         max_retries: 3,
//!         initial_delay_ms: 500,
//!         max_delay_ms: 16000,
//!     }),
//!     tracing_enabled: true,
//!     // ... other fields
//!     ..Default::default()
//! };
//! ```
//!
//! # Generated Client Usage
//!
//! ```rust,ignore
//! use crate::generated::client::HttpClient;
//!
//! #[tokio::main]
//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
//!     // Create client with retry and tracing
//!     let client = HttpClient::new()
//!         .with_base_url("https://api.example.com".to_string())
//!         .with_api_key("your-api-key".to_string())
//!         .with_header("X-Custom-Header".to_string(), "value".to_string());
//!
//!     // Make API calls - retries happen automatically
//!     let items = client.list_items().await?;
//!     println!("Found {} items", items.items.len());
//!
//!     Ok(())
//! }
//! ```
//!
//! # HTTP Method Support
//!
//! The generator supports all standard HTTP methods:
//! - `GET` - List and retrieve operations
//! - `POST` - Create operations
//! - `PUT` - Full update operations
//! - `PATCH` - Partial update operations
//! - `DELETE` - Delete operations
//!
//! # Error Handling
//!
//! All generated methods return `Result<T, HttpError>` where `HttpError` provides:
//! - Detailed error information
//! - Retry detection via `is_retryable()`
//! - Error categorization (client errors, server errors)
//!
//! See [`http_error`](crate::http_error) module for details.
//!
//! # Implementation Details
//!
//! The generator uses the following approach:
//! 1. Analyzes OpenAPI operations to extract HTTP methods, paths, parameters
//! 2. Generates typed request/response handling
//! 3. Creates method signatures with proper parameter types
//! 4. Generates path parameter substitution
//! 5. Handles query parameters and request bodies
//! 6. Configures middleware stack based on generator config

use crate::analysis::{OperationInfo, ParameterInfo, SchemaAnalysis};
use crate::generator::CodeGenerator;
use heck::{ToPascalCase, ToSnakeCase};
use proc_macro2::TokenStream;
use quote::{format_ident, quote};
use std::collections::BTreeMap;

struct AllocatedOperationParam<'a> {
    param: &'a ParameterInfo,
    ident: syn::Ident,
}

#[derive(Clone)]
struct BodyFieldPlan {
    wire_name: String,
    preferred_method_name: String,
    value_ident: syn::Ident,
    value_type: TokenStream,
    access_path: Vec<syn::Ident>,
}

enum RequiredBodyConstruction {
    Default,
    New(Vec<BodyConstructorParam>),
    Whole,
}

struct BodyConstructorParam {
    preferred_ident: syn::Ident,
    value_type: TokenStream,
}

struct BodyModelPlan {
    body_ident: syn::Ident,
    body_type: TokenStream,
    required_construction: RequiredBodyConstruction,
    optional_fields: Vec<BodyFieldPlan>,
}

impl CodeGenerator {
    /// Generate the HTTP client struct with middleware support
    pub fn generate_http_client_struct(&self) -> TokenStream {
        let has_retry = self.config().retry_config.is_some();
        let has_tracing = self.config().tracing_enabled;

        // Generate RetryConfig struct if needed
        let retry_config_struct = if has_retry {
            quote! {
                /// Retry configuration for HTTP requests
                #[derive(Debug, Clone)]
                pub struct RetryConfig {
                    pub max_retries: u32,
                    pub initial_delay_ms: u64,
                    pub max_delay_ms: u64,
                }

                impl Default for RetryConfig {
                    fn default() -> Self {
                        Self {
                            max_retries: 3,
                            initial_delay_ms: 500,
                            max_delay_ms: 16000,
                        }
                    }
                }
            }
        } else {
            quote! {}
        };

        // Generate the main HttpClient struct
        let client_struct = quote! {
            use reqwest_middleware::{ClientBuilder, ClientWithMiddleware};
            use std::collections::BTreeMap;

            /// HTTP client for making API requests
            #[derive(Clone)]
            pub struct HttpClient {
                base_url: String,
                api_key: Option<String>,
                http_client: ClientWithMiddleware,
                custom_headers: BTreeMap<String, String>,
            }
        };

        // Generate constructor
        let constructor = self.generate_constructor(has_retry, has_tracing);

        // Generate builder methods
        let builder_methods = self.generate_builder_methods();

        // Generate Default implementation
        let default_impl = quote! {
            impl Default for HttpClient {
                fn default() -> Self {
                    Self::new()
                }
            }
        };

        // Path-segment percent encoder, used by url construction (T5).
        // Encodes per RFC3986 §3.3: only ALPHA, DIGIT, and `-._~` pass through;
        // everything else becomes `%XX`.
        let path_encoder = quote! {
            fn __pct_encode_path_segment(s: &str) -> String {
                let mut out = String::with_capacity(s.len());
                for &b in s.as_bytes() {
                    match b {
                        b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'-' | b'.' | b'_' | b'~' => {
                            out.push(b as char);
                        }
                        _ => {
                            out.push('%');
                            out.push_str(&format!("{:02X}", b));
                        }
                    }
                }
                out
            }
        };

        // Combine all parts
        quote! {
            #retry_config_struct
            #client_struct

            impl HttpClient {
                #constructor
                #builder_methods
            }

            #default_impl
            #path_encoder
        }
    }

    /// Generate the constructor method
    fn generate_constructor(&self, has_retry: bool, has_tracing: bool) -> TokenStream {
        let retry_param = if has_retry {
            quote! { retry_config: Option<RetryConfig>, }
        } else {
            quote! {}
        };

        let tracing_param = if has_tracing {
            quote! { enable_tracing: bool, }
        } else {
            quote! {}
        };

        let retry_middleware = if has_retry {
            quote! {
                if let Some(config) = retry_config {
                    use reqwest_retry::{RetryTransientMiddleware, policies::ExponentialBackoff};

                    let retry_policy = ExponentialBackoff::builder()
                        .retry_bounds(
                            std::time::Duration::from_millis(config.initial_delay_ms),
                            std::time::Duration::from_millis(config.max_delay_ms),
                        )
                        .build_with_max_retries(config.max_retries);

                    let retry_middleware = RetryTransientMiddleware::new_with_policy(retry_policy);
                    client_builder = client_builder.with(retry_middleware);
                }
            }
        } else {
            quote! {}
        };

        let tracing_middleware = if has_tracing {
            quote! {
                if enable_tracing {
                    use reqwest_tracing::TracingMiddleware;
                    client_builder = client_builder.with(TracingMiddleware::default());
                }
            }
        } else {
            quote! {}
        };

        let default_constructor = if has_retry && has_tracing {
            quote! {
                /// Create a new HTTP client with default configuration
                pub fn new() -> Self {
                    Self::with_config(None, true)
                }
            }
        } else if has_retry {
            quote! {
                /// Create a new HTTP client with default configuration
                pub fn new() -> Self {
                    Self::with_config(None)
                }
            }
        } else if has_tracing {
            quote! {
                /// Create a new HTTP client with default configuration
                pub fn new() -> Self {
                    Self::with_config(true)
                }
            }
        } else {
            quote! {
                /// Create a new HTTP client with default configuration
                pub fn new() -> Self {
                    let reqwest_client = reqwest::Client::new();
                    let client_builder = ClientBuilder::new(reqwest_client);
                    let http_client = client_builder.build();

                    Self {
                        base_url: String::new(),
                        api_key: None,
                        http_client,
                        custom_headers: BTreeMap::new(),
                    }
                }
            }
        };

        if has_retry || has_tracing {
            quote! {
                #default_constructor

                /// Create a new HTTP client with custom configuration
                pub fn with_config(#retry_param #tracing_param) -> Self {
                    let reqwest_client = reqwest::Client::new();
                    let mut client_builder = ClientBuilder::new(reqwest_client);

                    #tracing_middleware
                    #retry_middleware

                    let http_client = client_builder.build();

                    Self {
                        base_url: String::new(),
                        api_key: None,
                        http_client,
                        custom_headers: BTreeMap::new(),
                    }
                }
            }
        } else {
            default_constructor
        }
    }

    /// Generate builder methods for configuration
    fn generate_builder_methods(&self) -> TokenStream {
        quote! {
            /// Set the base URL for all requests
            pub fn with_base_url(mut self, base_url: impl Into<String>) -> Self {
                self.base_url = base_url.into();
                self
            }

            /// Set the API key for authentication
            pub fn with_api_key(mut self, api_key: impl Into<String>) -> Self {
                self.api_key = Some(api_key.into());
                self
            }

            /// Add a custom header to all requests
            pub fn with_header(mut self, name: impl Into<String>, value: impl Into<String>) -> Self {
                self.custom_headers.insert(name.into(), value.into());
                self
            }

            /// Add multiple custom headers
            pub fn with_headers(mut self, headers: BTreeMap<String, String>) -> Self {
                self.custom_headers.extend(headers);
                self
            }
        }
    }

    /// Generate HTTP operation methods for the client.
    ///
    /// Emits per-operation typed error enums (one variant per declared non-2xx
    /// response with a body schema) BEFORE the `impl HttpClient` block so the
    /// generated method signatures can reference them. This low-level helper
    /// intentionally emits every analyzed operation; use
    /// [`Self::generate_http_client`] or [`Self::generate_all`] to honor the
    /// configured `[client].operations` scope.
    pub fn generate_operation_methods(&self, analysis: &SchemaAnalysis) -> TokenStream {
        let operations: Vec<&OperationInfo> = analysis.operations.values().collect();
        self.generate_operation_methods_for(analysis, &operations)
    }

    /// Generate every operation-owned client artifact from one resolved
    /// operation slice. This keeps methods, parameter enums, and typed error
    /// enums in lockstep for selective clients.
    pub(crate) fn generate_operation_methods_for(
        &self,
        analysis: &SchemaAnalysis,
        operations: &[&OperationInfo],
    ) -> TokenStream {
        let param_enums = self.generate_param_enum_types(operations);

        let op_error_enums: Vec<TokenStream> = operations
            .iter()
            .copied()
            .filter_map(|op| self.generate_op_error_enum(op))
            .collect();

        let methods: Vec<TokenStream> = operations
            .iter()
            .copied()
            .map(|op| self.generate_single_operation_method(op))
            .collect();

        let (operation_builders, builder_entries) =
            self.generate_operation_builders(analysis, operations);

        quote! {
            #param_enums

            #(#op_error_enums)*

            #(#operation_builders)*

            impl HttpClient {
                #(#methods)*
                #(#builder_entries)*
            }
        }
    }

    fn generate_operation_builders(
        &self,
        analysis: &SchemaAnalysis,
        operations: &[&OperationInfo],
    ) -> (Vec<TokenStream>, Vec<TokenStream>) {
        if !self.config().builders.enabled {
            return (Vec::new(), Vec::new());
        }

        let mut used_entry_methods: std::collections::HashSet<String> = operations
            .iter()
            .map(|operation| self.get_method_name(operation).to_string())
            .collect();
        let mut used_type_names = std::collections::HashSet::new();
        for schema_name in analysis.schemas.keys() {
            let rust_name = self.to_rust_type_name(schema_name);
            used_type_names.insert(rust_name.clone());
            // Request-model builders live in `types.rs` and are imported by
            // glob into the client module. Reserve their conventional names
            // so operation builders cannot create ambiguous re-exports.
            used_type_names.insert(format!("{rust_name}Builder"));
        }
        used_type_names.insert("HttpClient".to_string());
        used_type_names.insert("ApiOpError".to_string());
        used_type_names.extend(
            [
                "ClientBuilder",
                "ClientWithMiddleware",
                "RetryConfig",
                "HttpError",
                "BTreeMap",
            ]
            .into_iter()
            .map(str::to_string),
        );
        for operation in operations {
            used_type_names.insert(self.op_error_enum_ident(operation).to_string());
            used_type_names.extend(
                operation
                    .parameters
                    .iter()
                    .filter(|parameter| parameter.enum_values.is_some())
                    .map(|parameter| parameter.rust_type.clone()),
            );
        }

        let mut definitions = Vec::new();
        let mut entries = Vec::new();
        for operation in operations {
            let allocated_params = self.allocated_operation_params(operation);
            let body_plan = self.body_model_plan(operation, analysis);
            let optional_param_count = allocated_params
                .iter()
                .filter(|allocated| !Self::builder_param_is_required(allocated.param))
                .count();
            let optional_body_count =
                usize::from(operation.request_body.is_some() && !operation.request_body_required);
            let body_field_count = body_plan
                .as_ref()
                .filter(|plan| {
                    operation.request_body_required
                        || matches!(
                            &plan.required_construction,
                            RequiredBodyConstruction::Default
                        )
                })
                .map_or(0, |plan| plan.optional_fields.len());
            let optional_count = optional_param_count + optional_body_count + body_field_count;
            if optional_count <= self.config().builders.threshold {
                continue;
            }

            let flat_method = self.get_method_name(operation);
            let entry_base = format!("{flat_method}_builder");
            let entry_name = Self::allocate_name(&entry_base, &mut used_entry_methods);
            let entry_ident = Self::to_field_ident(&entry_name);

            let builder_base = format!("{}Builder", flat_method.to_string().to_pascal_case());
            let builder_name = Self::allocate_type_name(&builder_base, &mut used_type_names);
            let builder_ident = format_ident!("{builder_name}");

            let (definition, entry) = self.generate_single_operation_builder(
                operation,
                &allocated_params,
                body_plan,
                &flat_method,
                &entry_ident,
                &builder_ident,
            );
            definitions.push(definition);
            entries.push(entry);
        }

        (definitions, entries)
    }

    fn generate_single_operation_builder(
        &self,
        operation: &OperationInfo,
        allocated_params: &[AllocatedOperationParam<'_>],
        body_plan: Option<BodyModelPlan>,
        flat_method: &syn::Ident,
        entry_ident: &syn::Ident,
        builder_ident: &syn::Ident,
    ) -> (TokenStream, TokenStream) {
        let mut fields = vec![quote! { client: &'a HttpClient }];
        let mut entry_parameters = Vec::new();
        let mut initializers = vec![quote! { client: self }];
        let mut call_arguments = Vec::new();
        let mut setters = Vec::new();
        let mut used_entry_params = std::collections::HashSet::new();
        let mut used_methods = std::collections::HashSet::from(["send".to_string()]);

        for allocated in allocated_params {
            let field_ident = &allocated.ident;
            let storage_type = self.builder_param_storage_type(allocated.param);
            if Self::builder_param_is_required(allocated.param) {
                fields.push(quote! { #field_ident: #storage_type });
                let entry_name =
                    Self::allocate_name(&field_ident.to_string(), &mut used_entry_params);
                let entry_param = Self::to_field_ident(&entry_name);
                if Self::param_has_impl_as_ref_type(allocated.param) {
                    entry_parameters.push(quote! { #entry_param: impl Into<String> });
                    initializers.push(quote! { #field_ident: #entry_param.into() });
                } else {
                    entry_parameters.push(quote! { #entry_param: #storage_type });
                    initializers.push(quote! { #field_ident: #entry_param });
                }
            } else {
                fields.push(quote! { #field_ident: Option<#storage_type> });
                initializers.push(quote! { #field_ident: None });
                let setter_ident =
                    Self::allocate_builder_method(&field_ident.to_string(), &mut used_methods);
                let wire_name = &allocated.param.name;
                let assignment = if Self::param_has_impl_as_ref_type(allocated.param) {
                    quote! { self.#field_ident = Some(#field_ident.into()); }
                } else {
                    quote! { self.#field_ident = Some(#field_ident); }
                };
                let setter_type = if Self::param_has_impl_as_ref_type(allocated.param) {
                    quote! { impl Into<String> }
                } else {
                    storage_type.clone()
                };
                setters.push(quote! {
                    #[doc = concat!("Set the optional `", #wire_name, "` operation parameter.")]
                    #[must_use]
                    pub fn #setter_ident(mut self, #field_ident: #setter_type) -> Self {
                        #assignment
                        self
                    }
                });
            }
            call_arguments.push(quote! { self.#field_ident });
        }

        if let Some(body_plan) = body_plan {
            let BodyModelPlan {
                body_ident,
                body_type,
                required_construction,
                optional_fields,
            } = body_plan;
            let can_initialize_optional_body =
                matches!(&required_construction, RequiredBodyConstruction::Default);
            if operation.request_body_required {
                fields.push(quote! { #body_ident: #body_type });
                match required_construction {
                    RequiredBodyConstruction::Default => {
                        initializers.push(quote! { #body_ident: Default::default() });
                    }
                    RequiredBodyConstruction::New(constructor_params) => {
                        let mut constructor_args = Vec::new();
                        for constructor in constructor_params {
                            let preferred = constructor.preferred_ident.to_string();
                            let entry_name =
                                Self::allocate_name(&preferred, &mut used_entry_params);
                            let entry_param = Self::to_field_ident(&entry_name);
                            let value_type = constructor.value_type;
                            entry_parameters.push(quote! { #entry_param: #value_type });
                            constructor_args.push(entry_param);
                        }
                        initializers.push(quote! {
                            #body_ident: #body_type::new(#(#constructor_args),*)
                        });
                    }
                    RequiredBodyConstruction::Whole => {
                        let entry_name =
                            Self::allocate_name(&body_ident.to_string(), &mut used_entry_params);
                        let entry_param = Self::to_field_ident(&entry_name);
                        entry_parameters.push(quote! { #entry_param: #body_type });
                        initializers.push(quote! { #body_ident: #entry_param });
                    }
                }
            } else {
                fields.push(quote! { #body_ident: Option<#body_type> });
                initializers.push(quote! { #body_ident: None });
            }

            let body_setter =
                Self::allocate_builder_method(&body_ident.to_string(), &mut used_methods);
            let body_assignment = if operation.request_body_required {
                quote! { self.#body_ident = #body_ident; }
            } else {
                quote! { self.#body_ident = Some(#body_ident); }
            };
            setters.push(quote! {
                /// Replace the complete request body.
                #[must_use]
                pub fn #body_setter(mut self, #body_ident: #body_type) -> Self {
                    #body_assignment
                    self
                }
            });

            if operation.request_body_required || can_initialize_optional_body {
                for field in optional_fields {
                    let setter_ident = Self::allocate_builder_method(
                        &field.preferred_method_name,
                        &mut used_methods,
                    );
                    let value_ident = field.value_ident;
                    let value_type = field.value_type;
                    let wire_name = field.wire_name;
                    let access_path = field.access_path;
                    let assignment = if operation.request_body_required {
                        let mut target = quote! { self.#body_ident };
                        for access in &access_path {
                            target = quote! { #target.#access };
                        }
                        quote! { #target = Some(#value_ident); }
                    } else {
                        let mut target = quote! { request };
                        for access in &access_path {
                            target = quote! { #target.#access };
                        }
                        quote! {
                            let request = self.#body_ident.get_or_insert_with(Default::default);
                            #target = Some(#value_ident);
                        }
                    };
                    setters.push(quote! {
                        #[doc = concat!("Set the optional request-body field `", #wire_name, "`.")]
                        #[must_use]
                        pub fn #setter_ident(mut self, #value_ident: #value_type) -> Self {
                            #assignment
                            self
                        }
                    });
                }
            }
            call_arguments.push(quote! { self.#body_ident });
        }

        let response_type = self.get_response_type(operation);
        let error_type = self.op_error_type_token(operation);
        let operation_id = &operation.operation_id;
        let definition = quote! {
            #[doc = concat!("Additive request builder for `", #operation_id, "`.")]
            #[must_use]
            pub struct #builder_ident<'a> {
                #(#fields,)*
            }

            impl<'a> #builder_ident<'a> {
                #(#setters)*

                /// Send the request through the existing flat operation method.
                pub async fn send(self) -> Result<#response_type, ApiOpError<#error_type>> {
                    self.client.#flat_method(#(#call_arguments),*).await
                }
            }
        };
        let entry = quote! {
            #[doc = concat!("Start an additive builder for `", #operation_id, "`.")]
            pub fn #entry_ident(
                &self,
                #(#entry_parameters),*
            ) -> #builder_ident<'_> {
                #builder_ident {
                    #(#initializers,)*
                }
            }
        };
        (definition, entry)
    }

    fn allocate_name(base: &str, used: &mut std::collections::HashSet<String>) -> String {
        let mut candidate = base.to_string();
        let mut suffix = 2;
        while !used.insert(candidate.clone()) {
            candidate = format!("{base}_{suffix}");
            suffix += 1;
        }
        candidate
    }

    fn allocate_type_name(base: &str, used: &mut std::collections::HashSet<String>) -> String {
        if used.insert(base.to_string()) {
            return base.to_string();
        }

        let mut suffix = 2;
        loop {
            let candidate = format!("{base}{suffix}");
            if used.insert(candidate.clone()) {
                return candidate;
            }
            suffix += 1;
        }
    }

    fn allocate_builder_method(
        preferred: &str,
        used: &mut std::collections::HashSet<String>,
    ) -> syn::Ident {
        let plain = preferred.strip_prefix("r#").unwrap_or(preferred);
        let base = if used.contains(preferred) {
            format!("with_{plain}")
        } else {
            preferred.to_string()
        };
        let allocated = Self::allocate_name(&base, used);
        Self::to_field_ident(&allocated)
    }

    fn allocated_operation_params<'a>(
        &self,
        operation: &'a OperationInfo,
    ) -> Vec<AllocatedOperationParam<'a>> {
        // Builder-internal storage uses these names. Operation parameters are
        // positional when delegated to the flat method, so suffixing only the
        // builder field is safe and prevents duplicate struct fields.
        let mut used = std::collections::HashSet::from([
            "client".to_string(),
            "request".to_string(),
            "form".to_string(),
            "body".to_string(),
        ]);
        let mut allocated = Vec::new();
        for location in ["path", "query", "header", "cookie"] {
            for parameter in &operation.parameters {
                if parameter.location != location {
                    continue;
                }
                let raw = self.param_ident_str(parameter);
                let chosen = Self::allocate_name(&raw, &mut used);
                allocated.push(AllocatedOperationParam {
                    param: parameter,
                    ident: Self::to_field_ident(&chosen),
                });
            }
        }
        allocated
    }

    fn builder_param_is_required(parameter: &ParameterInfo) -> bool {
        // The existing flat signature always emits path parameters as bare
        // values. Invalid real-world specs sometimes omit `required: true`;
        // mirror the flat contract so builder delegation remains type-correct.
        parameter.location == "path" || parameter.required
    }

    fn builder_param_storage_type(&self, parameter: &ParameterInfo) -> TokenStream {
        self.get_param_owned_rust_type(parameter)
    }

    fn param_has_impl_as_ref_type(parameter: &ParameterInfo) -> bool {
        !matches!(
            &parameter.query_serialization,
            Some(
                crate::analysis::QuerySerialization::FormExplodedArray { .. }
                    | crate::analysis::QuerySerialization::FormArray { .. }
            )
        ) && Self::param_uses_as_ref_str(parameter)
    }

    fn body_model_plan(
        &self,
        operation: &OperationInfo,
        analysis: &SchemaAnalysis,
    ) -> Option<BodyModelPlan> {
        use crate::analysis::{ObjectAdditionalProperties, RequestBodyContent, SchemaType};

        let request_body = operation.request_body.as_ref()?;
        let (body_name, body_ident) = match request_body {
            RequestBodyContent::Json { schema_name, .. }
            | RequestBodyContent::FormUrlEncoded { schema_name, .. } => {
                (schema_name.as_str(), format_ident!("request"))
            }
            RequestBodyContent::Multipart => {
                return Some(BodyModelPlan {
                    body_ident: format_ident!("form"),
                    body_type: quote! { reqwest::multipart::Form },
                    required_construction: RequiredBodyConstruction::Whole,
                    optional_fields: Vec::new(),
                });
            }
            RequestBodyContent::OctetStream | RequestBodyContent::Unsupported { .. } => {
                return Some(BodyModelPlan {
                    body_ident: format_ident!("body"),
                    body_type: quote! { Vec<u8> },
                    required_construction: RequiredBodyConstruction::Whole,
                    optional_fields: Vec::new(),
                });
            }
            RequestBodyContent::TextPlain => {
                return Some(BodyModelPlan {
                    body_ident: format_ident!("body"),
                    body_type: quote! { String },
                    required_construction: RequiredBodyConstruction::Whole,
                    optional_fields: Vec::new(),
                });
            }
            RequestBodyContent::SchemaLess { .. } => return None,
        };
        let body_type_name = self.to_rust_type_name(body_name);
        let body_type = syn::Ident::new(&body_type_name, proc_macro2::Span::call_site());
        let Some((resolved_name, resolved_schema)) =
            self.resolve_reference_schema(body_name, analysis)
        else {
            return Some(BodyModelPlan {
                body_ident,
                body_type: quote! { #body_type },
                required_construction: RequiredBodyConstruction::Whole,
                optional_fields: Vec::new(),
            });
        };

        let mut optional_fields = Vec::new();
        let mut stack = std::collections::HashSet::new();
        self.collect_optional_body_fields(
            resolved_name,
            Vec::new(),
            analysis,
            &mut stack,
            &mut optional_fields,
        );

        let required_construction = match &resolved_schema.schema_type {
            SchemaType::Object {
                properties,
                required,
                additional_properties,
            } if !self.is_discriminated_variant(resolved_name, analysis) => {
                let emitted = self.emitted_object_properties(
                    resolved_name,
                    properties,
                    required,
                    additional_properties,
                    analysis,
                    None,
                );
                let required_fields: Vec<_> = emitted
                    .iter()
                    .filter(|field| field.is_required)
                    .map(|field| BodyConstructorParam {
                        preferred_ident: field.ident.clone(),
                        value_type: field.field_type.clone(),
                    })
                    .collect();
                if required_fields.is_empty() {
                    RequiredBodyConstruction::Default
                } else if emitted.iter().any(|field| !field.is_required)
                    || !matches!(additional_properties, ObjectAdditionalProperties::Forbidden)
                {
                    RequiredBodyConstruction::New(required_fields)
                } else {
                    RequiredBodyConstruction::Whole
                }
            }
            _ => RequiredBodyConstruction::Whole,
        };

        Some(BodyModelPlan {
            body_ident,
            body_type: quote! { #body_type },
            required_construction,
            optional_fields,
        })
    }

    fn resolve_reference_schema<'a>(
        &self,
        schema_name: &'a str,
        analysis: &'a SchemaAnalysis,
    ) -> Option<(&'a str, &'a crate::analysis::AnalyzedSchema)> {
        let mut current = schema_name;
        let mut visited = std::collections::HashSet::new();
        loop {
            if !visited.insert(current) {
                return None;
            }
            let schema = analysis.schemas.get(current)?;
            if let crate::analysis::SchemaType::Reference { target } = &schema.schema_type {
                current = target;
            } else {
                return Some((current, schema));
            }
        }
    }

    fn collect_optional_body_fields(
        &self,
        schema_name: &str,
        access_path: Vec<syn::Ident>,
        analysis: &SchemaAnalysis,
        stack: &mut std::collections::HashSet<String>,
        output: &mut Vec<BodyFieldPlan>,
    ) {
        use crate::analysis::SchemaType;
        if !stack.insert(schema_name.to_string()) {
            return;
        }
        let Some(schema) = analysis.schemas.get(schema_name) else {
            stack.remove(schema_name);
            return;
        };
        match &schema.schema_type {
            SchemaType::Reference { target } => {
                self.collect_optional_body_fields(target, access_path, analysis, stack, output);
            }
            SchemaType::Object {
                properties,
                required,
                additional_properties,
            } if !self.is_discriminated_variant(schema_name, analysis) => {
                for field in self.emitted_object_properties(
                    schema_name,
                    properties,
                    required,
                    additional_properties,
                    analysis,
                    None,
                ) {
                    if field.is_required {
                        continue;
                    }
                    let mut field_path = access_path.clone();
                    field_path.push(field.ident.clone());
                    output.push(BodyFieldPlan {
                        wire_name: field.wire_name.to_string(),
                        preferred_method_name: field.ident.to_string(),
                        value_ident: field.ident.clone(),
                        value_type: self.generate_property_base_type(
                            schema_name,
                            field.wire_name,
                            field.property,
                            analysis,
                        ),
                        access_path: field_path,
                    });
                }
            }
            SchemaType::Composition { schemas } => {
                for (index, schema_ref) in schemas.iter().enumerate() {
                    let mut nested_path = access_path.clone();
                    nested_path.push(format_ident!("part_{index}"));
                    self.collect_optional_body_fields(
                        &schema_ref.target,
                        nested_path,
                        analysis,
                        stack,
                        output,
                    );
                }
            }
            _ => {}
        }
        stack.remove(schema_name);
    }

    fn is_discriminated_variant(&self, schema_name: &str, analysis: &SchemaAnalysis) -> bool {
        analysis.schemas.values().any(|schema| {
            matches!(
                &schema.schema_type,
                crate::analysis::SchemaType::DiscriminatedUnion { variants, .. }
                    if variants.iter().any(|variant| variant.type_name == schema_name)
            )
        })
    }

    /// Emit inline enum types for parameters whose schema is `type: string`
    /// with `enum` or `const`. The generated enum implements `Display` so it
    /// drops into the existing `format!`-based path/query templating without
    /// any special-casing at the call site. See issue #10 follow-up.
    fn generate_param_enum_types(&self, operations: &[&OperationInfo]) -> TokenStream {
        let mut by_name: BTreeMap<String, &ParameterInfo> = BTreeMap::new();
        for op in operations {
            for param in &op.parameters {
                if param.enum_values.is_some() {
                    by_name.entry(param.rust_type.clone()).or_insert(param);
                }
            }
        }

        if by_name.is_empty() {
            return quote! {};
        }

        let defs: Vec<TokenStream> = by_name
            .values()
            .map(|param| self.generate_single_param_enum(param))
            .collect();

        quote! { #(#defs)* }
    }

    fn generate_single_param_enum(&self, param: &ParameterInfo) -> TokenStream {
        let Some(values) = param.enum_values.as_deref() else {
            return quote! {};
        };

        let enum_ident = format_ident!("{}", param.rust_type);

        // Dedupe variant names. Real-world specs use sort enums like
        // `["created_at", "-created_at"]` (descending prefix), and both
        // PascalCase to `CreatedAt`. Suffix collisions with `_2`/`_3`/…
        // while keeping each `serde(rename)` pointing at the original
        // wire string.
        let mut used: std::collections::HashSet<String> = std::collections::HashSet::new();
        let variant_names: Vec<String> = values
            .iter()
            .map(|value| {
                let base = self.to_rust_enum_variant(value);
                let mut chosen = base.clone();
                let mut suffix = 2;
                while !used.insert(chosen.clone()) {
                    chosen = format!("{base}_{suffix}");
                    suffix += 1;
                }
                chosen
            })
            .collect();

        let variants: Vec<TokenStream> = values
            .iter()
            .zip(&variant_names)
            .map(|(value, name)| {
                let variant_ident = format_ident!("{}", name);
                quote! {
                    #[serde(rename = #value)]
                    #variant_ident,
                }
            })
            .collect();

        let display_arms: Vec<TokenStream> = values
            .iter()
            .zip(&variant_names)
            .map(|(value, name)| {
                let variant_ident = format_ident!("{}", name);
                quote! { Self::#variant_ident => #value, }
            })
            .collect();

        let doc = format!(
            "Allowed values for the `{}` {} parameter.",
            param.name, param.location
        );

        quote! {
            #[doc = #doc]
            #[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Deserialize, serde::Serialize)]
            pub enum #enum_ident {
                #(#variants)*
            }

            impl #enum_ident {
                pub fn as_str(&self) -> &'static str {
                    match self {
                        #(#display_arms)*
                    }
                }
            }

            impl std::fmt::Display for #enum_ident {
                fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                    f.write_str(self.as_str())
                }
            }

            impl AsRef<str> for #enum_ident {
                fn as_ref(&self) -> &str {
                    self.as_str()
                }
            }
        }
    }

    /// Generate the per-operation typed error enum, if the op has any non-2xx
    /// responses with a body schema. Returns None when the op has no declared
    /// error bodies — those operations use `ApiOpError<serde_json::Value>` so
    /// the raw response body is still inspectable.
    fn generate_op_error_enum(&self, op: &OperationInfo) -> Option<TokenStream> {
        let variants: Vec<(String, String)> = op
            .response_schemas
            .iter()
            .filter(|(code, _)| !code.starts_with('2'))
            .map(|(code, schema)| (code.clone(), schema.clone()))
            .collect();

        if variants.is_empty() {
            return None;
        }

        let enum_ident = self.op_error_enum_ident(op);
        let variant_decls: Vec<TokenStream> = variants
            .iter()
            .map(|(code, schema)| {
                let variant_ident = Self::op_error_variant_ident(code);
                let payload_ty_name = self.to_rust_type_name(schema);
                let payload_ty = syn::Ident::new(&payload_ty_name, proc_macro2::Span::call_site());
                quote! { #variant_ident(#payload_ty) }
            })
            .collect();

        let doc = format!(
            "Typed error responses for `{}`. One variant per declared non-2xx response.",
            op.operation_id
        );

        Some(quote! {
            #[doc = #doc]
            #[derive(Debug, Clone)]
            pub enum #enum_ident {
                #(#variant_decls,)*
            }
        })
    }

    /// Type name (Ident) for the per-op error enum, e.g. `ListTodosApiError`.
    fn op_error_enum_ident(&self, op: &OperationInfo) -> syn::Ident {
        use heck::ToPascalCase;
        let name = format!(
            "{}ApiError",
            op.operation_id.replace('.', "_").to_pascal_case()
        );
        syn::Ident::new(&name, proc_macro2::Span::call_site())
    }

    /// Variant name for a status code: "400" → Status400, "default" → Default,
    /// "4XX" → Status4xx.
    fn op_error_variant_ident(status_code: &str) -> syn::Ident {
        let raw = match status_code {
            "default" | "Default" => "Default".to_string(),
            other if other.chars().all(|c| c.is_ascii_digit()) => format!("Status{other}"),
            other => format!("Status{}", other.to_ascii_lowercase()),
        };
        syn::Ident::new(&raw, proc_macro2::Span::call_site())
    }

    /// Token stream for the type plugged into `ApiOpError<T>` for an op:
    /// either the per-op enum, or `serde_json::Value` for ops with no
    /// declared error body schemas.
    fn op_error_type_token(&self, op: &OperationInfo) -> TokenStream {
        if op
            .response_schemas
            .iter()
            .any(|(code, _)| !code.starts_with('2'))
        {
            let ident = self.op_error_enum_ident(op);
            quote! { #ident }
        } else {
            quote! { serde_json::Value }
        }
    }

    /// Generate a single operation method
    fn generate_single_operation_method(&self, op: &OperationInfo) -> TokenStream {
        let method_name = self.get_method_name(op);
        let http_method_call = self.http_method_call(op);
        let path = &op.path;
        let request_param = self.generate_request_param(op);
        let request_body = self.generate_request_body(op);
        let query_params = self.generate_query_params(op);
        let header_params = self.generate_header_params(op);
        let cookie_params = self.generate_cookie_params(op);
        let auth_application = self.generate_auth_application();
        let response_type = self.get_response_type(op);
        let has_response_body = self.get_success_response_schema(op).is_some();
        let op_error_type = self.op_error_type_token(op);
        let error_handling = self.generate_error_handling(op, has_response_body);
        let url_construction = self.generate_url_construction(path, op);
        let doc_comment = self.generate_operation_doc_comment(op);

        quote! {
            #doc_comment
            pub async fn #method_name(
                &self,
                #request_param
            ) -> Result<#response_type, ApiOpError<#op_error_type>> {
                #url_construction

                let mut req = #http_method_call;
                #request_body

                #query_params
                #header_params
                #cookie_params

                // Apply configured authentication (T3). Was previously
                // hardcoded to bearer_auth regardless of GeneratorConfig.
                #auth_application

                // Add custom headers
                for (name, value) in &self.custom_headers {
                    req = req.header(name, value);
                }

                let response = req.send().await?;
                #error_handling
            }
        }
    }

    /// T3: emit the auth-token application based on the configured AuthConfig.
    /// Default (no config) is Bearer on Authorization. ApiKey emits a custom
    /// header. Custom honors header_value_prefix.
    fn generate_auth_application(&self) -> TokenStream {
        use crate::http_config::AuthConfig;
        match &self.config().auth_config {
            Some(AuthConfig::Bearer { header_name }) if header_name == "Authorization" => quote! {
                if let Some(api_key) = &self.api_key {
                    req = req.bearer_auth(api_key);
                }
            },
            Some(AuthConfig::Bearer { header_name }) => {
                let h = header_name.clone();
                quote! {
                    if let Some(api_key) = &self.api_key {
                        req = req.header(#h, format!("Bearer {}", api_key));
                    }
                }
            }
            Some(AuthConfig::ApiKey { header_name }) => {
                let h = header_name.clone();
                quote! {
                    if let Some(api_key) = &self.api_key {
                        req = req.header(#h, api_key.as_str());
                    }
                }
            }
            Some(AuthConfig::Custom {
                header_name,
                header_value_prefix,
            }) => {
                let h = header_name.clone();
                let prefix = header_value_prefix.clone().unwrap_or_default();
                if prefix.is_empty() {
                    quote! {
                        if let Some(api_key) = &self.api_key {
                            req = req.header(#h, api_key.as_str());
                        }
                    }
                } else {
                    let format_str = format!("{}{{}}", prefix);
                    quote! {
                        if let Some(api_key) = &self.api_key {
                            req = req.header(#h, format!(#format_str, api_key));
                        }
                    }
                }
            }
            None => quote! {
                if let Some(api_key) = &self.api_key {
                    req = req.bearer_auth(api_key);
                }
            },
        }
    }

    /// Generate header-parameter handling. Emits `req = req.header(name, ...)`
    /// for each `in: header` parameter — required headers unconditionally,
    /// optional ones gated on `Some(_)`.
    fn generate_header_params(&self, op: &OperationInfo) -> TokenStream {
        let header_params: Vec<_> = op
            .parameters
            .iter()
            .filter(|p| p.location == "header")
            .collect();
        if header_params.is_empty() {
            return quote! {};
        }
        let mut emit = Vec::new();
        for param in header_params {
            let param_name_snake = self.param_ident_str(param);
            let param_ident = Self::to_field_ident(&param_name_snake);
            let header_name = &param.name;
            if param.required {
                if Self::param_uses_as_ref_str(param) {
                    emit.push(quote! {
                        req = req.header(#header_name, #param_ident.as_ref());
                    });
                } else {
                    emit.push(quote! {
                        req = req.header(#header_name, #param_ident.to_string());
                    });
                }
            } else if Self::param_uses_as_ref_str(param) {
                emit.push(quote! {
                    if let Some(v) = #param_ident {
                        req = req.header(#header_name, v.as_ref());
                    }
                });
            } else {
                emit.push(quote! {
                    if let Some(v) = #param_ident {
                        req = req.header(#header_name, v.to_string());
                    }
                });
            }
        }
        quote! {
            #(#emit)*
        }
    }

    fn generate_cookie_params(&self, op: &OperationInfo) -> TokenStream {
        let cookie_params: Vec<_> = op
            .parameters
            .iter()
            .filter(|parameter| parameter.location == "cookie")
            .collect();
        if cookie_params.is_empty() {
            return quote! {};
        }
        let mut emit = Vec::new();
        for parameter in cookie_params {
            let ident = Self::to_field_ident(&self.param_ident_str(parameter));
            let wire_name = parameter.name.as_str();
            if parameter.required {
                emit.push(quote! {
                    __cookie_fields.push(format!("{}={}", #wire_name, #ident));
                });
            } else {
                emit.push(quote! {
                    if let Some(value) = #ident {
                        __cookie_fields.push(format!("{}={}", #wire_name, value));
                    }
                });
            }
        }
        quote! {
            let mut __cookie_fields = Vec::new();
            #(#emit)*
            if !__cookie_fields.is_empty() {
                req = req.header(::reqwest::header::COOKIE, __cookie_fields.join("; "));
            }
        }
    }

    /// Generate query parameter handling
    fn generate_query_params(&self, op: &OperationInfo) -> TokenStream {
        let query_params: Vec<_> = op
            .parameters
            .iter()
            .filter(|p| p.location == "query")
            .collect();

        if query_params.is_empty() {
            return quote! {};
        }

        let mut param_building = Vec::new();
        // Serialization applied on `req` directly, after the pair-vector
        // block: form-exploded objects and deepObject objects, whose keys
        // aren't the static parameter name.
        let mut req_appends = Vec::new();

        for param in query_params {
            use crate::analysis::QuerySerialization;

            // Use snake_case for Rust variable name with keyword escaping
            let param_name_snake = self.param_ident_str(param);
            let param_name = Self::to_field_ident(&param_name_snake);

            // Use the original parameter name from OpenAPI spec as the query string key
            let param_key = &param.name;

            match &param.query_serialization {
                Some(QuerySerialization::FormExplodedObject) => {
                    // Issue #27: reqwest serializes the struct through
                    // serde_urlencoded, so each property becomes its own
                    // `key=value` pair; the parameter's own name never
                    // appears in the query string (RFC 6570 form-explosion).
                    // `name[]=` is the shared zero-cardinality marker used to
                    // preserve Some(empty) and required-empty values.
                    let apply = quote! {
                        let __empty = match serde_json::to_value(&v)
                            .map_err(HttpError::serialization_error)?
                        {
                            serde_json::Value::Object(map) => map.is_empty(),
                            _ => false,
                        };
                        if __empty {
                            req = req.query(&[(format!("{}[]", #param_key), String::new())]);
                        } else {
                            req = req.query(&v);
                        }
                    };
                    if param.required {
                        req_appends.push(quote! {
                            {
                                let v = #param_name;
                                #apply
                            }
                        });
                    } else {
                        req_appends.push(quote! {
                            if let Some(v) = #param_name {
                                #apply
                            }
                        });
                    }
                    continue;
                }
                Some(QuerySerialization::DeepObject) => {
                    // `?filter[color]=red&filter[size]=5`. Property values
                    // stringify through their JSON form; Null (unset
                    // Option) properties are skipped.
                    let apply = quote! {
                        let map = match serde_json::to_value(&v)
                            .map_err(HttpError::serialization_error)?
                        {
                            serde_json::Value::Object(map) => map,
                            _ => return Err(HttpError::serialization_error(
                                format!("query parameter `{}` did not serialize as an object", #param_key)
                            ).into()),
                        };
                        let mut deep_params: Vec<(String, String)> = Vec::new();
                        for (k, val) in map {
                            let s = match val {
                                serde_json::Value::Null => continue,
                                serde_json::Value::String(s) => s,
                                other => other.to_string(),
                            };
                            deep_params.push((format!("{}[{}]", #param_key, k), s));
                        }
                        if deep_params.is_empty() {
                            deep_params.push((format!("{}[]", #param_key), String::new()));
                        }
                        req = req.query(&deep_params);
                    };
                    if param.required {
                        req_appends.push(quote! {
                            {
                                let v = #param_name;
                                #apply
                            }
                        });
                    } else {
                        req_appends.push(quote! {
                            if let Some(v) = #param_name {
                                #apply
                            }
                        });
                    }
                    continue;
                }
                Some(QuerySerialization::FormObject) => {
                    // `?filter=color,red,size,big` — one pair whose value is
                    // the comma-joined key,value list (RFC 6570 form,
                    // explode=false).
                    let apply = quote! {
                        let map = match serde_json::to_value(&v)
                            .map_err(HttpError::serialization_error)?
                        {
                            serde_json::Value::Object(map) => map,
                            _ => return Err(HttpError::serialization_error(
                                format!("query parameter `{}` did not serialize as an object", #param_key)
                            ).into()),
                        };
                        let mut parts: Vec<String> = Vec::new();
                        for (k, val) in map {
                            let s = match val {
                                serde_json::Value::Null => continue,
                                serde_json::Value::String(s) => s,
                                other => other.to_string(),
                            };
                            if k.contains(',') || s.contains(',') {
                                return Err(HttpError::serialization_error(
                                    format!(
                                        "query object `{}` contains a comma in key `{}`; use explode=true for lossless string values",
                                        #param_key,
                                        k,
                                    )
                                ).into());
                            }
                            parts.push(k);
                            parts.push(s);
                        }
                        if parts.is_empty() {
                            query_params.push((
                                format!("{}[]", #param_key),
                                String::new(),
                            ));
                        } else {
                            query_params.push((#param_key.to_string(), parts.join(",")));
                        }
                    };
                    if param.required {
                        param_building.push(quote! {
                            {
                                let v = #param_name;
                                #apply
                            }
                        });
                    } else {
                        param_building.push(quote! {
                            if let Some(v) = #param_name {
                                #apply
                            }
                        });
                    }
                    continue;
                }
                Some(QuerySerialization::FormExplodedArray { .. }) => {
                    // `?tags=a&tags=b` — one pair per element.
                    if param.required {
                        param_building.push(quote! {
                            if #param_name.is_empty() {
                                query_params.push((
                                    format!("{}[]", #param_key),
                                    String::new(),
                                ));
                            } else {
                                for item in #param_name {
                                    query_params.push((#param_key.to_string(), item.to_string()));
                                }
                            }
                        });
                    } else {
                        param_building.push(quote! {
                            if let Some(v) = #param_name {
                                if v.is_empty() {
                                    query_params.push((
                                        format!("{}[]", #param_key),
                                        String::new(),
                                    ));
                                } else {
                                    for item in v {
                                        query_params.push((#param_key.to_string(), item.to_string()));
                                    }
                                }
                            }
                        });
                    }
                    continue;
                }
                Some(QuerySerialization::FormArray { .. }) => {
                    // `?tags=a,b,c` — one comma-joined pair. Empty vectors
                    // use the shared `tags[]=` zero-cardinality marker.
                    let apply = quote! {
                        if v.is_empty() {
                            query_params.push((
                                format!("{}[]", #param_key),
                                String::new(),
                            ));
                        } else {
                            let mut parts = Vec::with_capacity(v.len());
                            for item in &v {
                                let item = item.to_string();
                                if item.contains(',') {
                                    return Err(HttpError::serialization_error(
                                        format!(
                                            "query array `{}` contains a comma; use explode=true for lossless string values",
                                            #param_key,
                                        )
                                    ).into());
                                }
                                parts.push(item);
                            }
                            query_params.push((
                                #param_key.to_string(),
                                parts.join(","),
                            ));
                        }
                    };
                    if param.required {
                        param_building.push(quote! {
                            {
                                let v = #param_name;
                                #apply
                            }
                        });
                    } else {
                        param_building.push(quote! {
                            if let Some(v) = #param_name {
                                #apply
                            }
                        });
                    }
                    continue;
                }
                Some(QuerySerialization::Unsupported { .. }) => {}
                None => {}
            }

            if param.required {
                // Required parameters: always add
                if Self::param_uses_as_ref_str(param) {
                    param_building.push(quote! {
                        query_params.push((#param_key.to_string(), #param_name.as_ref().to_string()));
                    });
                } else {
                    param_building.push(quote! {
                        query_params.push((#param_key.to_string(), #param_name.to_string()));
                    });
                }
            } else {
                // Optional parameters: add only if Some
                if Self::param_uses_as_ref_str(param) {
                    param_building.push(quote! {
                        if let Some(v) = #param_name {
                            query_params.push((#param_key.to_string(), v.as_ref().to_string()));
                        }
                    });
                } else {
                    param_building.push(quote! {
                        if let Some(v) = #param_name {
                            query_params.push((#param_key.to_string(), v.to_string()));
                        }
                    });
                }
            }
        }

        // Ops whose query params all serialize on `req` directly skip the
        // pair-vector block entirely.
        let pairs_block = if param_building.is_empty() {
            quote! {}
        } else {
            quote! {
                {
                    let mut query_params: Vec<(String, String)> = Vec::new();
                    #(#param_building)*
                    if !query_params.is_empty() {
                        req = req.query(&query_params);
                    }
                }
            }
        };

        quote! {
            // Add query parameters
            #pairs_block
            #(#req_appends)*
        }
    }

    /// Generate the rustdoc block for an operation, surfacing summary,
    /// description, the HTTP method+path, and any tags from the OAS spec
    /// (T13). Also marks the method `#[deprecated]` if the operation is.
    fn generate_operation_doc_comment(&self, op: &OperationInfo) -> TokenStream {
        let method = op.method.to_uppercase();
        let path = &op.path;
        let mut docs: Vec<String> = Vec::new();
        if let Some(s) = &op.summary {
            if !s.is_empty() {
                docs.push(s.clone());
                docs.push(String::new());
            }
        }
        if let Some(d) = &op.description {
            if !d.is_empty() {
                for line in d.lines() {
                    docs.push(line.to_string());
                }
                docs.push(String::new());
            }
        }
        docs.push(format!("`{} {}`", method, path));
        let doc_attrs: Vec<TokenStream> = docs
            .iter()
            .map(|line| {
                let prefixed = if line.is_empty() {
                    String::new()
                } else {
                    format!(" {line}")
                };
                quote! { #[doc = #prefixed] }
            })
            .collect();
        quote! { #(#doc_attrs)* }
    }

    /// Get the method name from the operation
    fn get_method_name(&self, op: &OperationInfo) -> syn::Ident {
        let name = if !op.operation_id.is_empty() {
            op.operation_id.to_snake_case()
        } else {
            // Fallback: generate from HTTP method and path
            format!(
                "{}_{}",
                op.method,
                op.path.replace('/', "_").replace(['{', '}'], "")
            )
            .to_snake_case()
        };

        syn::Ident::new(&name, proc_macro2::Span::call_site())
    }

    /// Build the request-builder expression for the operation's HTTP method.
    /// Named reqwest methods (`.get`/`.post`/…) are used where available;
    /// OPTIONS and TRACE go through `Client::request(Method::OPTIONS, _)` since
    /// reqwest doesn't expose those as named methods.
    fn http_method_call(&self, op: &OperationInfo) -> TokenStream {
        match op.method.to_uppercase().as_str() {
            "GET" => quote! { self.http_client.get(request_url) },
            "POST" => quote! { self.http_client.post(request_url) },
            "PUT" => quote! { self.http_client.put(request_url) },
            "DELETE" => quote! { self.http_client.delete(request_url) },
            "PATCH" => quote! { self.http_client.patch(request_url) },
            "HEAD" => quote! { self.http_client.head(request_url) },
            "OPTIONS" => quote! {
                self.http_client.request(reqwest::Method::OPTIONS, request_url)
            },
            "TRACE" => quote! {
                self.http_client.request(reqwest::Method::TRACE, request_url)
            },
            // D1: 3.2 `QUERY` verb + any custom verb from
            // PathItem.additionalOperations. reqwest's Method::from_bytes
            // accepts arbitrary uppercase tokens that match the RFC7230
            // method grammar.
            other => {
                let upper = other.to_string();
                quote! {
                    self.http_client.request(
                        reqwest::Method::from_bytes(#upper.as_bytes())
                            .expect("invalid HTTP method"),
                        request_url,
                    )
                }
            }
        }
    }

    /// Generate request parameters including path, query, header, and request body.
    fn generate_request_param(&self, op: &OperationInfo) -> TokenStream {
        let mut params = Vec::new();
        // Dedup parameter Rust idents within this method signature. Real-world
        // specs sometimes declare two parameters that sanitize to the same
        // snake_case name (modern-treasury declared `name` twice across
        // different param objects). Suffixing with `_2`, `_3`, … keeps each
        // parameter accessible while preserving the original wire-level name
        // (which is used elsewhere as the query/path/header key).
        let mut used: std::collections::HashSet<String> = std::collections::HashSet::new();
        let mut unique_param_ident = |raw: String| -> syn::Ident {
            let mut chosen = raw.clone();
            let mut suffix = 2;
            while !used.insert(chosen.clone()) {
                chosen = format!("{raw}_{suffix}");
                suffix += 1;
            }
            Self::to_field_ident(&chosen)
        };

        // Add path parameters
        for param in &op.parameters {
            if param.location == "path" {
                let param_name_snake = self.param_ident_str(param);
                let param_name = unique_param_ident(param_name_snake);
                let param_type = self.get_param_rust_type(param);
                params.push(quote! { #param_name: #param_type });
            }
        }

        // Add query parameters (all as Option<T>)
        for param in &op.parameters {
            if param.location == "query" {
                let param_name_snake = self.param_ident_str(param);
                let param_name = unique_param_ident(param_name_snake);
                let param_type = self.get_param_rust_type(param);

                // Query parameters should be Option unless explicitly required
                if param.required {
                    params.push(quote! { #param_name: #param_type });
                } else {
                    params.push(quote! { #param_name: Option<#param_type> });
                }
            }
        }

        // Add header parameters. Required headers are bare; optional ones are
        // Option<T>. Per OAS 3.x §"Parameter Object", header names matching
        // `Accept`, `Content-Type`, and `Authorization` are forbidden — those
        // are described by other mechanisms — but we leave that validation to
        // analysis.
        for param in &op.parameters {
            if param.location == "header" {
                let param_name_snake = self.param_ident_str(param);
                let param_name = unique_param_ident(param_name_snake);
                let param_type = self.get_param_rust_type(param);
                if param.required {
                    params.push(quote! { #param_name: #param_type });
                } else {
                    params.push(quote! { #param_name: Option<#param_type> });
                }
            }
        }

        for param in &op.parameters {
            if param.location == "cookie" {
                let param_name_snake = self.param_ident_str(param);
                let param_name = unique_param_ident(param_name_snake);
                let param_type = self.get_param_rust_type(param);
                if param.required {
                    params.push(quote! { #param_name: #param_type });
                } else {
                    params.push(quote! { #param_name: Option<#param_type> });
                }
            }
        }

        // Add request body parameter based on content type. Optional bodies
        // (`requestBody.required` is false or absent) become `Option<T>` per T11.
        if let Some(ref rb) = op.request_body {
            use crate::analysis::RequestBodyContent;
            if matches!(rb, RequestBodyContent::SchemaLess { .. }) {
                return if params.is_empty() {
                    quote! {}
                } else {
                    quote! { #(#params),* }
                };
            }
            let required = op.request_body_required;
            let body_type = match rb {
                RequestBodyContent::Json { schema_name, .. }
                | RequestBodyContent::FormUrlEncoded { schema_name, .. } => {
                    let rust_type_name = self.to_rust_type_name(schema_name);
                    let request_ident =
                        syn::Ident::new(&rust_type_name, proc_macro2::Span::call_site());
                    quote! { #request_ident }
                }
                RequestBodyContent::Multipart => quote! { reqwest::multipart::Form },
                RequestBodyContent::OctetStream => quote! { Vec<u8> },
                RequestBodyContent::TextPlain => quote! { String },
                RequestBodyContent::Unsupported { .. } => quote! { Vec<u8> },
                RequestBodyContent::SchemaLess { .. } => unreachable!(
                    "schema-less request bodies preserve the historical client signature"
                ),
            };
            let body_ident = match rb {
                RequestBodyContent::Multipart => quote! { form },
                RequestBodyContent::OctetStream
                | RequestBodyContent::TextPlain
                | RequestBodyContent::Unsupported { .. } => quote! { body },
                RequestBodyContent::SchemaLess { .. } => unreachable!(
                    "schema-less request bodies preserve the historical client signature"
                ),
                _ => quote! { request },
            };
            if required {
                params.push(quote! { #body_ident: #body_type });
            } else {
                params.push(quote! { #body_ident: Option<#body_type> });
            }
        }

        if params.is_empty() {
            quote! {}
        } else {
            quote! { #(#params),* }
        }
    }

    /// Get the Rust type for a parameter
    fn get_param_rust_type(&self, param: &crate::analysis::ParameterInfo) -> TokenStream {
        if Self::param_has_impl_as_ref_type(param) {
            quote! { impl AsRef<str> }
        } else {
            self.get_param_owned_rust_type(param)
        }
    }

    /// Owned parameter type shared by client-builder storage and generated
    /// server extraction. [`ParameterInfo::query_serialization`] is the
    /// authoritative projection for typed query objects and arrays.
    pub(crate) fn get_param_owned_rust_type(
        &self,
        param: &crate::analysis::ParameterInfo,
    ) -> TokenStream {
        use crate::analysis::QuerySerialization;
        // Typed form-style arrays take Vec<item> (openapi-generator-anu).
        // Scalars parse as-is (they may be type paths from [type_mappings]);
        // enum refs are raw schema names and go through the same
        // to_rust_type_name sanitization as every other schema reference
        // (cloudflare has enum schemas like `resource-sharing_resource_type`).
        if let Some(
            QuerySerialization::FormExplodedArray { item_type }
            | QuerySerialization::FormArray { item_type },
        ) = &param.query_serialization
        {
            use crate::analysis::ArrayItemType;
            let item_ty: syn::Type = match item_type {
                ArrayItemType::Scalar(rust_type) => syn::parse_str(rust_type)
                    .unwrap_or_else(|_| panic!("invalid scalar item type `{rust_type}`")),
                ArrayItemType::EnumRef(schema_name) => {
                    let rust_name = self.to_rust_type_name(schema_name);
                    syn::parse_str(&rust_name)
                        .unwrap_or_else(|_| panic!("invalid enum item type `{rust_name}`"))
                }
            };
            return quote! { Vec<#item_ty> };
        }
        // T10: $ref-typed parameters used to lose their type because we only
        // consulted `rust_type` (which stays "String"). Now: prefer the
        // resolved schema reference if present.
        if let Some(ref schema_name) = param.schema_ref {
            let rust_name = self.to_rust_type_name(schema_name);
            let ident = syn::Ident::new(&rust_name, proc_macro2::Span::call_site());
            return quote! { #ident };
        }
        syn::parse_str::<syn::Type>(&param.rust_type)
            .map(|ty| quote! { #ty })
            .unwrap_or_else(|_| {
                let type_ident = syn::Ident::new(&param.rust_type, proc_macro2::Span::call_site());
                quote! { #type_ident }
            })
    }

    /// True when the parameter's compile-time type is `impl AsRef<str>` and
    /// we should call `.as_ref()` on it before stringifying. False for any
    /// $ref-resolved type (T10) or non-String primitive — those just call
    /// `.to_string()`.
    fn param_uses_as_ref_str(param: &crate::analysis::ParameterInfo) -> bool {
        param.schema_ref.is_none() && param.rust_type == "String"
    }

    /// Generate request body serialization based on content type
    /// Emit statements that mutate `req` to apply the request body. Returns
    /// `quote!{}` if the operation has no body. Optional bodies (T11) gate the
    /// application on `Some(_)`; required bodies apply unconditionally.
    fn generate_request_body(&self, op: &OperationInfo) -> TokenStream {
        let Some(rb) = op.request_body.as_ref() else {
            return quote! {};
        };
        use crate::analysis::RequestBodyContent;
        let required = op.request_body_required;
        let (ident, apply): (TokenStream, TokenStream) = match rb {
            RequestBodyContent::Json { media_type, .. } => (
                quote! { request },
                quote! {
                    req = req
                        .body(serde_json::to_vec(&request).map_err(HttpError::serialization_error)?)
                        .header("content-type", #media_type);
                },
            ),
            RequestBodyContent::FormUrlEncoded { media_type, .. } => (
                quote! { request },
                quote! {
                    req = req
                        .body(serde_urlencoded::to_string(&request).map_err(HttpError::serialization_error)?)
                        .header("content-type", #media_type);
                },
            ),
            RequestBodyContent::Multipart => (
                quote! { form },
                quote! {
                    req = req.multipart(form);
                },
            ),
            RequestBodyContent::OctetStream => (
                quote! { body },
                quote! {
                    req = req
                        .body(body)
                        .header("content-type", "application/octet-stream");
                },
            ),
            RequestBodyContent::TextPlain => (
                quote! { body },
                quote! {
                    req = req
                        .body(body)
                        .header("content-type", "text/plain");
                },
            ),
            RequestBodyContent::Unsupported { media_types } => {
                let media_type = media_types
                    .first()
                    .map(String::as_str)
                    .unwrap_or("application/octet-stream");
                (
                    quote! { body },
                    quote! {
                        req = req
                            .body(body)
                            .header("content-type", #media_type);
                    },
                )
            }
            RequestBodyContent::SchemaLess { .. } => return quote! {},
        };
        if required {
            apply
        } else {
            quote! {
                if let Some(#ident) = #ident {
                    #apply
                }
            }
        }
    }

    /// Find the success (2xx) response schema name, if any.
    ///
    /// Only considers 2xx status codes. Error schemas (4xx, 5xx) are ignored
    /// so that endpoints like 204 No Content correctly return `()` instead of
    /// accidentally picking up the error schema (e.g. `BadRequestError`).
    fn get_success_response_schema<'a>(&self, op: &'a OperationInfo) -> Option<&'a String> {
        op.response_schemas
            .get("200")
            .or_else(|| op.response_schemas.get("201"))
            .or_else(|| {
                op.response_schemas
                    .iter()
                    .find(|(code, _)| code.starts_with('2'))
                    .map(|(_, v)| v)
            })
    }

    /// Get response type
    fn get_response_type(&self, op: &OperationInfo) -> TokenStream {
        if let Some(response_type) = self.get_success_response_schema(op) {
            // Convert schema name to Rust type name (handles underscores, etc.)
            let rust_type_name = self.to_rust_type_name(response_type);
            let response_ident = syn::Ident::new(&rust_type_name, proc_macro2::Span::call_site());
            quote! { #response_ident }
        } else {
            quote! { () }
        }
    }

    /// Generate error handling.
    ///
    /// Always reads the response body to a string before attempting any typed
    /// deserialization, so the raw body and headers are preserved on the error
    /// path even when JSON parsing fails. On 2xx the body is parsed into the
    /// success type; on non-2xx the body is parsed into the matching variant
    /// of the per-operation error enum (when one is declared) and wrapped in
    /// `ApiError<E>`.
    fn generate_error_handling(&self, op: &OperationInfo, has_response_body: bool) -> TokenStream {
        let op_error_type = self.op_error_type_token(op);

        let success_branch = if has_response_body {
            quote! {
                match serde_json::from_str(&body_text) {
                    Ok(body) => Ok(body),
                    Err(e) => Err(ApiOpError::Api(ApiError {
                        status: status_code,
                        headers: headers,
                        body: body_text,
                        typed: None,
                        parse_error: Some(format!(
                            "failed to deserialize 2xx response body: {}",
                            e
                        )),
                    })),
                }
            }
        } else {
            quote! {
                let _ = body_text;
                let _ = headers;
                Ok(())
            }
        };

        let error_match_arms = self.generate_error_match_arms(op);

        quote! {
            let status = response.status();
            let status_code = status.as_u16();
            let headers = response.headers().clone();
            let body_text = response.text().await
                .map_err(|e| ApiOpError::Transport(HttpError::Network(e)))?;

            if status.is_success() {
                #success_branch
            } else {
                let typed: Option<#op_error_type>;
                let parse_error: Option<String>;
                #error_match_arms
                Err(ApiOpError::Api(ApiError {
                    status: status_code,
                    headers,
                    body: body_text,
                    typed,
                    parse_error,
                }))
            }
        }
    }

    /// Generate the match arms that select which per-op error variant to
    /// deserialize the response body into based on the runtime status code.
    fn generate_error_match_arms(&self, op: &OperationInfo) -> TokenStream {
        let arms: Vec<TokenStream> = op
            .response_schemas
            .iter()
            .filter(|(code, _)| !code.starts_with('2'))
            .filter_map(|(code, schema)| {
                let variant_ident = Self::op_error_variant_ident(code);
                let payload_ty_name = self.to_rust_type_name(schema);
                let payload_ty = syn::Ident::new(&payload_ty_name, proc_macro2::Span::call_site());
                let enum_ident = self.op_error_enum_ident(op);

                // T8: range-keyed responses (1XX/2XX/3XX/4XX/5XX) per OAS
                // 3.x §"Responses Object". Specific codes still take priority
                // (handled by ordering — concrete codes deserialize first
                // because the generic dispatch is a generic `_ if (range)`).
                let pattern = match code.as_str() {
                    "default" | "Default" => return None, // handled in fallback
                    other if other.chars().all(|c| c.is_ascii_digit()) => {
                        let n: u16 = other.parse().ok()?;
                        quote! { #n }
                    }
                    "1XX" | "1xx" => quote! { code if (100..=199).contains(&code) },
                    "2XX" | "2xx" => quote! { code if (200..=299).contains(&code) },
                    "3XX" | "3xx" => quote! { code if (300..=399).contains(&code) },
                    "4XX" | "4xx" => quote! { code if (400..=499).contains(&code) },
                    "5XX" | "5xx" => quote! { code if (500..=599).contains(&code) },
                    _ => return None,
                };

                Some(quote! {
                    #pattern => {
                        match serde_json::from_str::<#payload_ty>(&body_text) {
                            Ok(v) => {
                                typed = Some(#enum_ident::#variant_ident(v));
                                parse_error = None;
                            }
                            Err(e) => {
                                typed = None;
                                parse_error = Some(e.to_string());
                            }
                        }
                    }
                })
            })
            .collect();

        // Fallback for "default" or undeclared status codes: try to parse
        // as `serde_json::Value` for inspectability when the op's error
        // type is generic, otherwise leave typed = None.
        // Must mirror op_error_type_token: if op_error_type is the typed
        // enum (any non-2xx response, including `default`), the fallback arm
        // can't deserialize into `serde_json::Value` because `typed` is the
        // enum. Default to `typed = None` in that case.
        let has_typed_enum = op
            .response_schemas
            .iter()
            .any(|(code, _)| !code.starts_with('2'));

        let default_arm = if has_typed_enum {
            quote! {
                _ => {
                    typed = None;
                    parse_error = None;
                }
            }
        } else {
            // No typed enum — op_error_type is serde_json::Value.
            quote! {
                _ => {
                    match serde_json::from_str::<serde_json::Value>(&body_text) {
                        Ok(v) => {
                            typed = Some(v);
                            parse_error = None;
                        }
                        Err(e) => {
                            typed = None;
                            parse_error = Some(e.to_string());
                        }
                    }
                }
            }
        };

        if arms.is_empty() {
            // No declared status arms — just the fallback.
            quote! {
                match status_code {
                    #default_arm
                }
            }
        } else {
            quote! {
                match status_code {
                    #(#arms)*
                    #default_arm
                }
            }
        }
    }

    /// Generate URL construction with path parameter substitution
    fn generate_url_construction(&self, path: &str, op: &OperationInfo) -> TokenStream {
        // Check if path has parameters (contains {...})
        if path.contains('{') {
            self.generate_url_with_params(path, op)
        } else {
            quote! {
                let request_url = format!("{}{}", self.base_url, #path);
            }
        }
    }

    /// Generate URL with path parameters
    fn generate_url_with_params(&self, path: &str, op: &OperationInfo) -> TokenStream {
        // Find all path parameters in the operation.
        let path_params: Vec<_> = op
            .parameters
            .iter()
            .filter(|p| p.location == "path")
            .collect();

        // T5: percent-encode each path-template variable per RFC3986 §3.3.
        // We build a positional-arg format string by walking the template
        // left-to-right and emitting one `{}` + one format arg per
        // placeholder occurrence. Cloudflare has paths like
        // `/accounts/{account_id}/.../accounts/{account_id}` — the same
        // variable appears twice. A naive `replace_all` produced two `{}`
        // placeholders but only one format arg (E0277). Per-occurrence
        // emission keeps them in sync.
        let mut format_string = String::with_capacity(path.len());
        let mut format_args: Vec<TokenStream> = Vec::new();
        let mut chars = path.chars().peekable();
        while let Some(c) = chars.next() {
            if c != '{' {
                format_string.push(c);
                continue;
            }
            // Read until the matching '}'.
            let mut name = String::new();
            while let Some(&n) = chars.peek() {
                chars.next();
                if n == '}' {
                    break;
                }
                name.push(n);
            }
            // Resolve to a path param. If no match, leave the placeholder
            // verbatim (real-world spec bug — this op shouldn't have made
            // it past analysis).
            let param = path_params.iter().find(|p| p.name == name);
            let Some(param) = param else {
                format_string.push('{');
                format_string.push_str(&name);
                format_string.push('}');
                continue;
            };
            format_string.push_str("{}");
            let param_name_snake = self.param_ident_str(param);
            let param_ident = Self::to_field_ident(&param_name_snake);
            if Self::param_uses_as_ref_str(param) {
                format_args.push(quote! {
                    __pct_encode_path_segment(#param_ident.as_ref())
                });
            } else {
                format_args.push(quote! {
                    __pct_encode_path_segment(&#param_ident.to_string())
                });
            }
        }

        if format_args.is_empty() {
            quote! {
                let request_url = format!("{}{}", self.base_url, #path);
            }
        } else {
            quote! {
                let request_url = format!("{}{}", self.base_url, format!(#format_string, #(#format_args),*));
            }
        }
    }

    /// Resolve the Rust ident for a parameter. Prefers the disambiguated
    /// `rust_ident` set by the analyzer (which dedupes across the whole
    /// operation), falling back to a fresh sanitize of the wire name when
    /// no analyzer-side ident is present.
    pub(crate) fn param_ident_str(&self, param: &crate::analysis::ParameterInfo) -> String {
        if let Some(ident) = &param.rust_ident {
            // Apply the keyword-escape and self/super/crate dance the
            // sanitize fn does. The analyzer's base ident is already the
            // snake/kebab-aware shape; we only need post-processing.
            return self.escape_keyword_ident(ident);
        }
        self.sanitize_param_name(&param.name)
    }

    fn escape_keyword_ident(&self, snake_case: &str) -> String {
        if matches!(snake_case, "self" | "super" | "crate" | "Self") {
            return format!("{snake_case}_param");
        }
        if Self::is_rust_keyword(snake_case) {
            format!("r#{snake_case}")
        } else {
            snake_case.to_string()
        }
    }

    /// Sanitize a parameter name by escaping Rust reserved keywords with raw
    /// identifiers and disambiguating Twilio-style suffix operators
    /// (`StartTime`, `StartTime<`, `StartTime>` would otherwise all snake-
    /// case to `start_time`).
    fn sanitize_param_name(&self, name: &str) -> String {
        // Disambiguate before stripping. `<`, `>`, `<=`, `>=` are common in
        // filter-style query params; map them to `_lt` / `_gt` etc. so the
        // Rust ident is unique while the wire-level param name stays the
        // original string elsewhere in the codegen.
        let suffix = if name.ends_with("<=") {
            "_lte"
        } else if name.ends_with(">=") {
            "_gte"
        } else if name.ends_with('<') {
            "_lt"
        } else if name.ends_with('>') {
            "_gt"
        } else {
            ""
        };
        let stripped = name.trim_end_matches(['<', '>', '=']);
        let mut snake_case = stripped.to_snake_case();
        if snake_case.is_empty() {
            snake_case.push_str("parameter");
        } else if snake_case.starts_with(|character: char| character.is_ascii_digit()) {
            snake_case.insert(0, '_');
        }
        snake_case.push_str(suffix);

        if matches!(snake_case.as_str(), "self" | "super" | "crate" | "Self") {
            return format!("{snake_case}_param");
        }
        if Self::is_rust_keyword(&snake_case) {
            format!("r#{snake_case}")
        } else {
            snake_case
        }
    }
}