alef 0.19.20

mod functions;
mod methods;
pub(super) mod types;

use functions::{gen_adapter_wrapper, gen_convert_with_visitor_wrapper, gen_function_wrapper};
use methods::{gen_method_wrapper, gen_streaming_method_wrapper};
use types::{
    gen_config_options, gen_enum_type, gen_last_error_helper, gen_opaque_type, gen_opaque_type_free_only,
    gen_ptr_helper, gen_struct_type, gen_unmarshal_bytes_helper, is_passthrough_raw_message_enum, is_tuple_field,
};

use crate::core::backend::{Backend, BuildConfig, BuildDependency, Capabilities, GeneratedFile};
use crate::core::config::workspace::ClientConstructorConfig;
use crate::core::config::{AdapterPattern, Language, ResolvedCrateConfig, resolve_output_dir};
use crate::core::hash::{self, CommentStyle};
use crate::core::ir::{ApiSurface, TypeDef, TypeRef};
use heck::ToPascalCase;
use std::collections::HashSet;
use std::path::PathBuf;

pub struct GoBackend;

impl GoBackend {
    /// Extract the package name from module path (last segment).
    /// Sanitize by removing hyphens and converting to lowercase.
    fn package_name(module_path: &str) -> String {
        module_path
            .split('/')
            .next_back()
            .unwrap_or("binding")
            .replace('-', "")
            .to_lowercase()
    }
}

impl Backend for GoBackend {
    fn name(&self) -> &str {
        "go"
    }

    fn language(&self) -> Language {
        Language::Go
    }

    fn capabilities(&self) -> Capabilities {
        Capabilities {
            supports_async: true,
            supports_classes: true,
            supports_enums: true,
            supports_option: true,
            supports_result: true,
            ..Capabilities::default()
        }
    }

    fn generate_bindings(&self, api: &ApiSurface, config: &ResolvedCrateConfig) -> anyhow::Result<Vec<GeneratedFile>> {
        let module_path = config.go_module();
        let pkg_name = config
            .go
            .as_ref()
            .and_then(|g| g.package_name.clone())
            .unwrap_or_else(|| Self::package_name(&module_path));
        let ffi_prefix = config.ffi_prefix();

        let output_dir = {
            let mut d = resolve_output_dir(config.output_paths.get("go"), &config.name, "packages/go/");
            if !d.ends_with('/') {
                d.push('/');
            }
            d
        };

        let ffi_lib_name = config.ffi_lib_name();
        let ffi_header = config.ffi_header_name();
        // Derive the FFI crate directory from the output path (e.g., "crates/sample-markdown-ffi/src/" → "crates/sample-markdown-ffi")
        let ffi_crate_dir = config
            .output_paths
            .get("ffi")
            .and_then(|p| {
                let path = p.as_path();
                path.ancestors()
                    .find(|a| {
                        a.file_name()
                            .is_some_and(|n| n != "src" && n != "lib" && n != "include")
                    })
                    .map(|a| a.to_string_lossy().to_string())
            })
            .unwrap_or_else(|| format!("crates/{ffi_lib_name}"));
        // Collect bridge param names from trait_bridges config so we can strip them
        // from generated function signatures and emit ConvertWithVisitor instead.
        let bridge_param_names: HashSet<String> = config
            .trait_bridges
            .iter()
            .filter_map(|b| b.param_name.clone())
            .collect();
        // Also collect type aliases used as bridge params (e.g. "VisitorHandle").
        let bridge_type_aliases: HashSet<String> = config
            .trait_bridges
            .iter()
            .filter_map(|b| b.type_alias.clone())
            .collect();
        // Determine if any bridge is configured for the visitor pattern.
        // Options-field bridges generate visitor.go regardless of visitor_callbacks.
        let visitor_callbacks_enabled = config.ffi.as_ref().is_some_and(|f| f.visitor_callbacks);
        let has_options_field_bridge = config
            .trait_bridges
            .iter()
            .any(|b| b.bind_via == crate::core::config::BridgeBinding::OptionsField);
        let has_visitor_bridge =
            has_options_field_bridge || (!config.trait_bridges.is_empty() && visitor_callbacks_enabled);

        // Determine if any plugin-style bridges (with register_fn) are configured.
        // These are independent of visitor_callbacks and generate trait_bridges.go.
        let has_plugin_bridges = config.trait_bridges.iter().any(|b| b.register_fn.is_some());

        // Map streaming adapter (owner_type, method_name) → item_type. The callback-based
        // FFI export (`<prefix>_<type>_<method>`) cannot be driven from CGO, but the
        // companion iterator-handle exports (`_start`, `_next`, `_free`) can — we emit a
        // dedicated Go method that drives them and returns a typed channel.
        // Adapters missing `owner_type` or `item_type` are skipped (treated as "no Go
        // streaming method emitted") rather than producing broken code.
        let streaming_methods: std::collections::HashMap<(String, String), String> = config
            .adapters
            .iter()
            .filter(|a| matches!(a.pattern, AdapterPattern::Streaming))
            .filter_map(|a| {
                let owner = a.owner_type.clone()?;
                let item = a.item_type.clone()?;
                Some(((owner, a.name.clone()), item))
            })
            .collect();

        // Collect functions excluded from FFI generation. Go bindings call C symbols directly
        // via cgo, so any function excluded from the FFI header must also be excluded here.
        let ffi_exclude_functions: HashSet<String> = config
            .ffi
            .as_ref()
            .map(|f| f.exclude_functions.iter().cloned().collect())
            .unwrap_or_default();
        let mut exclude_types: HashSet<String> = config
            .ffi
            .as_ref()
            .map(|f| f.exclude_types.iter().cloned().collect())
            .unwrap_or_default();
        if let Some(go_config) = &config.go {
            exclude_types.extend(go_config.exclude_types.iter().cloned());
        }

        // Collect value-only types (all fields are primitives). These don't have _to_json
        // functions emitted by the FFI backend, so Go codegen must construct them from
        // field accessors instead of JSON deserialization.
        let value_only_types: HashSet<String> = api
            .types
            .iter()
            .filter(|t| !t.is_opaque && t.fields.iter().all(|f| {
                matches!(f.ty, crate::core::ir::TypeRef::Primitive(_) | crate::core::ir::TypeRef::String | crate::core::ir::TypeRef::Char | crate::core::ir::TypeRef::Path)
                    || matches!(&f.ty, crate::core::ir::TypeRef::Optional(inner) if matches!(inner.as_ref(), crate::core::ir::TypeRef::Primitive(_) | crate::core::ir::TypeRef::String | crate::core::ir::TypeRef::Char | crate::core::ir::TypeRef::Path))
            }))
            .map(|t| t.name.clone())
            .collect();

        let content = format_go_code(&strip_trailing_whitespace(&gen_go_file(
            api,
            config,
            &ffi_prefix,
            &pkg_name,
            &ffi_lib_name,
            &ffi_header,
            &ffi_crate_dir,
            &output_dir,
            &bridge_param_names,
            &bridge_type_aliases,
            &streaming_methods,
            &ffi_exclude_functions,
            &exclude_types,
            &value_only_types,
            has_options_field_bridge,
        )));

        // Build adapter body map (consumed by generators via body substitution)
        let _adapter_bodies = crate::adapters::build_adapter_bodies(config, Language::Go)?;

        // Compute relative path from Go output dir to project root.
        let depth = output_dir.trim_end_matches('/').matches('/').count() + 1;
        let to_root = "../".repeat(depth);

        let mut files = vec![GeneratedFile {
            path: PathBuf::from(format!("{output_dir}binding.go")),
            content,
            generated_header: true,
        }];

        // Generate visitor.go when a visitor bridge is configured.
        if has_visitor_bridge {
            // Derive vtable_trait_name and options_field from the first options-field bridge,
            // falling back to sensible defaults for legacy function-param bridges.
            let visitor_bridge_cfg = config
                .trait_bridges
                .iter()
                .find(|b| b.bind_via == crate::core::config::BridgeBinding::OptionsField);
            let (vtable_trait_name, options_field) = visitor_bridge_cfg
                .and_then(|b| {
                    let field = b.resolved_options_field()?;
                    Some((b.trait_name.clone(), field.to_string()))
                })
                .unwrap_or_else(|| ("HtmlVisitor".to_string(), "visitor".to_string()));

            // Look up the visitor trait def in the IR.
            let trait_map: std::collections::HashMap<&str, &crate::core::ir::TypeDef> = api
                .types
                .iter()
                .filter(|t| t.is_trait)
                .map(|t| (t.name.as_str(), t))
                .collect();
            let visitor_trait = visitor_bridge_cfg.and_then(|b| trait_map.get(b.trait_name.as_str()).copied());

            let visitor_content = if let Some(vt) = visitor_trait {
                strip_trailing_whitespace(&crate::backends::go::gen_visitor::gen_visitor_file(
                    &pkg_name,
                    &ffi_prefix,
                    &ffi_header,
                    &ffi_crate_dir,
                    &to_root,
                    &vtable_trait_name,
                    &options_field,
                    vt,
                ))
            } else {
                eprintln!(
                    "[alef] gen_visitor_file(go): visitor trait `{vtable_trait_name}` not found in IR, skipping visitor.go"
                );
                String::new()
            };
            files.push(GeneratedFile {
                path: PathBuf::from(format!("{output_dir}visitor.go")),
                content: visitor_content,
                generated_header: true,
            });
        }

        // Generate trait_bridges.go for plugin-style bridges (with register_fn).
        // Per-call bridges (no register_fn) use visitor.go callbacks via convert() instead.
        // This is independent of visitor_callbacks, which only affects per-call bridges.
        if has_plugin_bridges {
            let trait_bridges_content = strip_trailing_whitespace(&super::trait_bridge::gen_trait_bridges_file(
                api,
                config,
                &pkg_name,
                &ffi_prefix,
                &ffi_header,
                &ffi_crate_dir,
                &to_root,
                &config.name,
            ));
            if !trait_bridges_content.trim().is_empty() && trait_bridges_content.len() > 100 {
                files.push(GeneratedFile {
                    path: PathBuf::from(format!("{output_dir}trait_bridges.go")),
                    content: trait_bridges_content,
                    generated_header: true,
                });
            }
        }

        // Generate generate.go with //go:generate directive for FFI library download
        let generate_go_content =
            crate::backends::go::template_env::render("generate_cgo_flags.go.jinja", minijinja::context! {});
        files.push(GeneratedFile {
            path: PathBuf::from(format!("{output_dir}generate.go")),
            content: generate_go_content,
            generated_header: false,
        });

        // Generate the download tool under cmd/download_ffi/main.go
        let crate_version = api.version.to_string();
        let repo_url = config.github_repo();
        let asset_prefix = config.name.clone();
        let download_tool_content = crate::backends::go::template_env::render(
            "cmd_download_ffi_main.go.jinja",
            minijinja::context! {
                ffi_lib_name => &ffi_lib_name,
                crate_version => &crate_version,
                repo_url => &repo_url,
                asset_prefix => &asset_prefix,
            },
        );
        files.push(GeneratedFile {
            path: PathBuf::from(format!("{output_dir}cmd/download_ffi/main.go")),
            content: download_tool_content,
            generated_header: false,
        });

        Ok(files)
    }

    /// Go bindings are already the public API (single .go file wrapping C FFI).
    /// This returns empty since the binding.go file serves as both the FFI layer
    /// and the high-level public API for consumers.
    fn generate_public_api(
        &self,
        _api: &ApiSurface,
        _config: &ResolvedCrateConfig,
    ) -> anyhow::Result<Vec<GeneratedFile>> {
        // Go's binding.go IS the public API — no additional wrapper needed.
        Ok(vec![])
    }

    fn build_config(&self) -> Option<BuildConfig> {
        Some(BuildConfig {
            tool: "go",
            crate_suffix: "",
            build_dep: BuildDependency::Ffi,
            post_build: vec![],
        })
    }
}

/// Strip trailing whitespace from every line and ensure the file ends with a single newline.
fn strip_trailing_whitespace(content: &str) -> String {
    let mut result: String = content
        .lines()
        .map(|line| line.trim_end())
        .collect::<Vec<_>>()
        .join("\n");
    if !result.ends_with('\n') {
        result.push('\n');
    }
    result
}

/// Run `gofmt -s` on generated Go code. Falls back to the original if gofmt is unavailable.
fn format_go_code(code: &str) -> String {
    use std::io::Write;
    use std::process::{Command, Stdio};
    let child = Command::new("gofmt")
        .arg("-s")
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::null())
        .spawn();
    match child {
        Ok(mut c) => {
            if let Some(ref mut stdin) = c.stdin.take() {
                let _ = stdin.write_all(code.as_bytes());
            }
            match c.wait_with_output() {
                Ok(output) if output.status.success() => {
                    String::from_utf8(output.stdout).unwrap_or_else(|_| code.to_string())
                }
                _ => code.to_string(),
            }
        }
        Err(_) => code.to_string(),
    }
}

/// Returns true if a `TypeRef::Named` type comes from `api.enums` (either unit or data enum)
/// and therefore does not have `_from_json`/`_to_json`/`_free` FFI helpers.
///
/// Only types in `api.types` (non-opaque struct types) have these helpers in the C header.
fn is_ffi_enum_type(name: &str, ffi_enum_names: &HashSet<String>) -> bool {
    ffi_enum_names.contains(name)
}

/// Returns true if a function references an enum type (from `api.enums`) as a parameter type
/// or return type, for which the FFI header lacks `_from_json`/`_to_json`/`_free` helpers.
///
/// Such functions cannot be generated correctly and must be skipped.
fn uses_ffi_enum_type(
    func_params: &[crate::core::ir::ParamDef],
    return_type: &TypeRef,
    ffi_enum_names: &HashSet<String>,
    opaque_names: &std::collections::HashSet<&str>,
) -> bool {
    let named_is_problem = |n: &str| is_ffi_enum_type(n, ffi_enum_names) && !opaque_names.contains(n);
    let return_uses = match return_type {
        TypeRef::Named(n) => named_is_problem(n),
        TypeRef::Optional(inner) => matches!(inner.as_ref(), TypeRef::Named(n) if named_is_problem(n)),
        _ => false,
    };
    if return_uses {
        return true;
    }
    func_params.iter().any(|p| match &p.ty {
        TypeRef::Named(n) => named_is_problem(n),
        TypeRef::Optional(inner) => matches!(inner.as_ref(), TypeRef::Named(n) if named_is_problem(n)),
        _ => false,
    })
}

/// Returns true if a type reference mentions any excluded type.
fn references_excluded_type(ty: &TypeRef, exclude_types: &HashSet<String>) -> bool {
    exclude_types.iter().any(|name| ty.references_named(name))
}

/// Returns true if any parameter or return type mentions an excluded type.
fn signature_references_excluded_type(
    params: &[crate::core::ir::ParamDef],
    return_type: &TypeRef,
    exclude_types: &HashSet<String>,
) -> bool {
    references_excluded_type(return_type, exclude_types)
        || params
            .iter()
            .any(|param| references_excluded_type(&param.ty, exclude_types))
}

/// Generate the complete Go binding file wrapping the C FFI layer.
#[allow(clippy::too_many_arguments)]
fn gen_go_file(
    api: &ApiSurface,
    config: &ResolvedCrateConfig,
    ffi_prefix: &str,
    pkg_name: &str,
    ffi_lib_name: &str,
    ffi_header: &str,
    ffi_crate_dir: &str,
    go_output_dir: &str,
    bridge_param_names: &HashSet<String>,
    bridge_type_aliases: &HashSet<String>,
    streaming_methods: &std::collections::HashMap<(String, String), String>,
    ffi_exclude_functions: &HashSet<String>,
    exclude_types: &HashSet<String>,
    value_only_types: &HashSet<String>,
    has_options_field_bridge: bool,
) -> String {
    let mut out = String::with_capacity(4096);

    // Go convention: generated file marker must appear before package declaration.
    // Blank line after header prevents revive from treating it as package doc.
    out.push_str(&hash::header(CommentStyle::DoubleSlash));
    out.push('\n');

    // Compute relative path from Go output dir to project root.
    // go_output_dir is like "packages/go/", so we need "../../" to reach root.
    let depth = go_output_dir.trim_end_matches('/').matches('/').count() + 1;
    let to_root = "../".repeat(depth);

    // Package header and cgo directives.
    // The package comment must immediately precede the package declaration with no blank line.
    out.push_str(&crate::backends::go::template_env::render(
        "package_doc_and_declaration.jinja",
        minijinja::context! {
            pkg_name => pkg_name,
            crate_name => &config.name,
        },
    ));
    out.push_str(&crate::backends::go::template_env::render(
        "cgo_preamble_binding.jinja",
        minijinja::context! {
            to_root => &to_root,
            ffi_crate_dir => ffi_crate_dir,
            ffi_lib_name => ffi_lib_name,
            ffi_header => ffi_header,
        },
    ));
    out.push('\n');
    // Determine which imports are needed based on generated code.
    let has_opaque_types = api.types.iter().any(|t| t.is_opaque);
    // Functions that are not skipped (non-async or with non-Named returns) need json + unsafe.
    // Opaque-returning functions are no longer skipped, so check all non-async functions.
    let has_sync_functions = api.functions.iter().any(|f| !f.is_async);
    let has_non_static_methods = api.types.iter().any(|t| t.methods.iter().any(|m| !m.is_static));
    let needs_json_and_unsafe = has_sync_functions || has_non_static_methods;

    // NOTE: imports_basic.jinja renders each value as-is (no extra quoting).
    // Pass bare package paths without surrounding quotes — the template does not add them.
    let mut imports = vec!["fmt"];
    if needs_json_and_unsafe {
        imports.insert(0, "encoding/json");
        imports.push("unsafe");
    } else if has_opaque_types {
        // Opaque types need unsafe for pointer wrapping even without JSON serialization.
        imports.push("unsafe");
    }
    if !api.errors.is_empty() {
        imports.insert(1.min(imports.len()), "errors");
    }
    out.push_str(&crate::backends::go::template_env::render(
        "imports_basic.jinja",
        minijinja::context! {
            imports => imports,
        },
    ));

    // Error helper functions
    out.push_str(&gen_last_error_helper(ffi_prefix));
    out.push_str("\n\n");

    // Bytes helper: emitted once per package, used by every method/function
    // returning `TypeRef::Bytes`. Defining it here (rather than inline at each
    // call site) avoids repeated declarations and keeps a single place to
    // adjust ownership semantics.
    out.push_str(&gen_unmarshal_bytes_helper());
    out.push_str("\n\n");

    // Pointer helper: emitted once per package, used by data DTOs to construct
    // pointers for optional fields without functional-options boilerplate.
    // Usage: &MyStruct{Field: Ptr("value")}
    out.push_str(&gen_ptr_helper());
    out.push_str("\n\n");

    // Generate trait bridge exports (//export trampolines called by C)
    let has_plugin_bridges = config.trait_bridges.iter().any(|b| b.register_fn.is_some());
    if has_plugin_bridges {
        let bridges: Vec<_> = config
            .trait_bridges
            .iter()
            .filter_map(|bridge_cfg| {
                api.types
                    .iter()
                    .find(|t| t.name == bridge_cfg.trait_name)
                    .map(|trait_def| {
                        minijinja::Value::from_serialize(serde_json::json!({
                            "pascal_name": trait_def.name,
                            "methods": trait_def.methods.iter().map(|m| serde_json::json!({
                                "name": m.name.to_pascal_case(),
                            })).collect::<Vec<_>>(),
                        }))
                    })
            })
            .collect();
        out.push_str(&crate::backends::go::template_env::render(
            "plugin_bridge_exports.jinja",
            minijinja::context! {
                bridges => bridges,
            },
        ));
        out.push('\n');
    }

    // Generate error types: a single consolidated sentinel `var (...)` block
    // across all ErrorDefs (variant-name collisions are disambiguated by
    // qualifying with the parent error's base name, e.g.
    // `ErrGraphQLValidationError` vs `ErrSchemaValidationError`), followed by
    // the per-error structured error struct + Error() method.
    if !api.errors.is_empty() {
        out.push_str(&crate::codegen::error_gen::gen_go_sentinel_errors(&api.errors));
        out.push_str("\n\n");
        for error in &api.errors {
            out.push_str(&crate::codegen::error_gen::gen_go_error_struct(error, pkg_name));
            out.push_str("\n\n");
        }
    }

    // When a visitor bridge is active, visitor.go defines the bridge's associated types
    // (e.g. NodeContext, VisitResult) with FFI-compatible fields. Skip them in binding.go
    // to avoid redeclarations.
    let bridge_associated_types = config.bridge_associated_types();
    let visitor_types: std::collections::HashSet<&str> = if !bridge_param_names.is_empty() {
        bridge_associated_types.iter().map(|s| s.as_str()).collect()
    } else {
        std::collections::HashSet::new()
    };

    // Generate enum types and constants
    // Both unit enums and newtype-tuple enums map to `type X string` in Go.
    // Unit enums: all variants have no fields.
    // Newtype-tuple enums: all data variants contain only positional tuple fields (which Go
    // cannot represent as struct fields and are therefore treated as raw string values).
    // Data enums with named fields become Go structs and must NOT be included here.
    let unit_enum_names: std::collections::HashSet<&str> = api
        .enums
        .iter()
        .filter(|e| {
            !exclude_types.contains(&e.name)
                && e.variants
                    .iter()
                    .all(|v| v.fields.is_empty() || v.fields.iter().all(is_tuple_field))
        })
        .filter(|e| !is_passthrough_raw_message_enum(e))
        .map(|e| e.name.as_str())
        .collect();
    let passthrough_enum_names: std::collections::HashSet<&str> = api
        .enums
        .iter()
        .filter(|e| is_passthrough_raw_message_enum(e))
        .filter(|e| !exclude_types.contains(&e.name))
        .map(|e| e.name.as_str())
        .collect();
    for enum_def in api
        .enums
        .iter()
        .filter(|e| !visitor_types.contains(e.name.as_str()) && !exclude_types.contains(&e.name))
    {
        out.push_str(&gen_enum_type(enum_def));
        out.push_str("\n\n");
    }

    // Error type names that are also opaque types — in this case the error struct emitted by
    // gen_go_error_types is the Go-side type and the opaque handle definition below would be a
    // duplicate. Skip re-generating the struct for such opaque types; the Free() method is still
    // generated separately.
    let error_names: std::collections::HashSet<&str> = api.errors.iter().map(|e| e.name.as_str()).collect();

    // Collect opaque type names — these are pointer-wrapped handles, not JSON-serializable structs.
    let opaque_names: std::collections::HashSet<&str> = api
        .types
        .iter()
        .filter(|t| t.is_opaque)
        .filter(|t| !exclude_types.contains(&t.name))
        .map(|t| t.name.as_str())
        .collect();

    // Collect all enum type names (both unit and data enums from api.enums).
    // These types do NOT have _from_json/_to_json/_free helpers in the FFI header —
    // only non-opaque api.types have those helpers. Functions that use an enum type
    // as a parameter or return value (via TypeRef::Named) cannot be correctly generated
    // (unless the type also appears as an opaque type in api.types) and are excluded.
    let ffi_enum_names: HashSet<String> = api.enums.iter().map(|e| e.name.clone()).collect();

    // Data enums (sealed interfaces): enums with named fields in at least one variant
    let data_enum_names: std::collections::HashSet<&str> = api
        .enums
        .iter()
        .filter(|e| {
            !exclude_types.contains(&e.name)
                && e.variants
                    .iter()
                    .any(|v| !v.fields.is_empty() && v.fields.iter().any(|f| !is_tuple_field(f)))
        })
        .map(|e| e.name.as_str())
        .collect();

    // Collect non-opaque struct type names — these are real struct types that should NOT fall back to *json.RawMessage
    let struct_names: std::collections::HashSet<&str> = api
        .types
        .iter()
        .filter(|t| !t.is_opaque && !exclude_types.contains(&t.name))
        .map(|t| t.name.as_str())
        .collect();

    // Generate struct types
    for typ in api
        .types
        .iter()
        .filter(|typ| !typ.is_trait && !visitor_types.contains(typ.name.as_str()) && !exclude_types.contains(&typ.name))
    {
        if typ.is_opaque {
            // If an error type has the same name as this opaque type, the structured error
            // struct was already emitted by gen_go_error_types. Skip the duplicate struct
            // definition but still emit the Free() method.
            if error_names.contains(typ.name.as_str()) {
                out.push_str(&gen_opaque_type_free_only(typ, ffi_prefix));
                out.push_str("\n\n");
            } else {
                out.push_str(&gen_opaque_type(typ, ffi_prefix));
                out.push_str("\n\n");
            }
            // Client constructor — emit New<TypeName> when configured.
            if let Some(ctor) = config.client_constructors.get(&typ.name) {
                out.push_str(&gen_go_opaque_constructor(typ, ffi_prefix, ctor));
                out.push_str("\n\n");
            }
        } else {
            out.push_str(&gen_struct_type(
                typ,
                &unit_enum_names,
                &passthrough_enum_names,
                &data_enum_names,
                &struct_names,
            ));
            out.push_str("\n\n");
            // Generate functional options pattern only if type is in the functional_options allowlist.
            // By default, pure data DTOs use idiomatic struct literals instead of functional options.
            // Skip "Update" types (e.g., ConversionOptionsUpdate) — they are partial update
            // structs that share field names with the primary config type, producing duplicate
            // With* function declarations.
            let empty_functional_options = vec![];
            let functional_options = config
                .go
                .as_ref()
                .map(|g| &g.functional_options)
                .unwrap_or(&empty_functional_options);
            if !typ.name.ends_with("Update") && functional_options.contains(&typ.name) {
                out.push_str(&gen_config_options(
                    typ,
                    &unit_enum_names,
                    &passthrough_enum_names,
                    &data_enum_names,
                ));
                out.push_str("\n\n");
            }
        }
    }

    // Generate free function wrappers.
    // Async functions are included — the underlying FFI uses block_on() for synchronous C calls.
    // Skip functions excluded from FFI generation (their C symbols don't exist in the header)
    // and functions whose parameter or return types are enum types without FFI JSON helpers.
    for func in api.functions.iter().filter(|f| {
        !ffi_exclude_functions.contains(&f.name)
            && !signature_references_excluded_type(&f.params, &f.return_type, exclude_types)
            && !uses_ffi_enum_type(&f.params, &f.return_type, &ffi_enum_names, &opaque_names)
            && !crate::codegen::generators::trait_bridge::is_trait_bridge_managed_fn(&f.name, &config.trait_bridges)
    }) {
        // For the convert function with visitor support, wrap it with visitor-awareness logic
        // instead of generating the basic wrapper.
        if func.name == "convert" && has_options_field_bridge {
            out.push_str(&gen_convert_with_visitor_wrapper(
                func,
                ffi_prefix,
                &opaque_names,
                value_only_types,
            ));
            out.push_str("\n\n");
        } else {
            out.push_str(&gen_function_wrapper(
                func,
                ffi_prefix,
                &opaque_names,
                bridge_param_names,
                bridge_type_aliases,
                value_only_types,
            ));
            out.push_str("\n\n");
        }
    }

    // Emit module-level wrapper functions for streaming adapters so tests/consumers
    // can call them as pkg.CrawlStream(engine, url) instead of engine.CrawlStream(url).
    // These wrap the instance methods emitted below.
    for adapter in &config.adapters {
        if !matches!(adapter.pattern, AdapterPattern::Streaming) {
            continue;
        }
        if adapter.owner_type.is_none() || adapter.item_type.is_none() {
            continue;
        }
        out.push_str(&gen_adapter_wrapper(adapter, pkg_name, &api.types));
        out.push_str("\n\n");
    }

    // Generate struct methods.
    // Skip static methods that return Named types (e.g., Default() constructors) —
    // these are redundant with the generated New*() functional options constructors,
    // and the opaque handle conversion pipeline is not yet implemented.
    // Streaming adapter methods use a callback-based C signature that CGO can't call directly —
    // they are skipped here and must be implemented via a separate Go-native streaming API.
    // Also skip methods excluded from FFI or using enum types without FFI JSON helpers.
    for typ in api
        .types
        .iter()
        .filter(|typ| !typ.is_trait && !exclude_types.contains(&typ.name))
    {
        // Types that are both opaque and error types are emitted as Go value
        // structs (Code/Message fields) by `gen_go_error_struct` — they have
        // no `ptr` field to dispatch through. Skip method emission here so we
        // do not generate `h.ptr` references that fail to compile against a
        // value-type struct.
        if typ.is_opaque && error_names.contains(typ.name.as_str()) {
            continue;
        }
        for method in &typ.methods {
            // Skip methods named "default" — these are Rust's Default::default() trait impl
            // and should not be emitted as free functions in Go (use struct literals instead).
            if method.name == "default" {
                continue;
            }
            // For opaque types skip static methods that return Named types — the opaque
            // handle conversion pipeline is not implemented for those. For non-opaque DTO
            // types, static preset constructors (e.g. All(), Minimal()) are
            // emitted as package-level free functions via gen_method_wrapper and must not
            // be suppressed.
            if typ.is_opaque && method.is_static && matches!(method.return_type, TypeRef::Named(_)) {
                continue;
            }
            if let Some(item_type) = streaming_methods.get(&(typ.name.clone(), method.name.clone())) {
                // Streaming method: drive the FFI iterator-handle exports and surface a typed
                // Go channel instead of calling the callback-based wrapper directly.
                out.push_str(&gen_streaming_method_wrapper(
                    typ,
                    method,
                    ffi_prefix,
                    item_type,
                    &data_enum_names,
                    &opaque_names,
                    value_only_types,
                ));
                out.push_str("\n\n");
                continue;
            }
            if ffi_exclude_functions.contains(&method.name) {
                continue;
            }
            if signature_references_excluded_type(&method.params, &method.return_type, exclude_types) {
                continue;
            }
            if uses_ffi_enum_type(&method.params, &method.return_type, &ffi_enum_names, &opaque_names) {
                continue;
            }
            out.push_str(&gen_method_wrapper(
                typ,
                method,
                ffi_prefix,
                &opaque_names,
                value_only_types,
            ));
            out.push_str("\n\n");
        }
    }

    out
}

/// Map a Rust FFI type string (as stored in `ConstructorParam.ty`) to its Go equivalent.
///
/// Only the types actually used in `client_constructors` configs are handled here.
/// Unmapped types fall back to `unsafe.Pointer` with a cast so compilation continues even
/// if the caller passes an exotic type — a compile warning rather than a hard stop.
fn ffi_ty_to_go(rust_ty: &str) -> &'static str {
    let normalized = rust_ty.trim();
    // CString params — any pointer-to-char variant.
    if normalized.contains("c_char") || normalized.contains("CStr") {
        return "string";
    }
    // Unsigned integers.
    if matches!(normalized, "u8" | "uint8_t") {
        return "uint8";
    }
    if matches!(normalized, "u16" | "uint16_t") {
        return "uint16";
    }
    if matches!(normalized, "u32" | "uint32_t") {
        return "uint32";
    }
    if matches!(normalized, "u64" | "uint64_t" | "usize") {
        return "uint64";
    }
    // Signed integers.
    if matches!(normalized, "i8" | "int8_t") {
        return "int8";
    }
    if matches!(normalized, "i16" | "int16_t") {
        return "int16";
    }
    if matches!(normalized, "i32" | "int32_t" | "c_int") {
        return "int32";
    }
    if matches!(normalized, "i64" | "int64_t" | "isize") {
        return "int64";
    }
    if matches!(normalized, "bool") {
        return "bool";
    }
    if matches!(normalized, "f32" | "float") {
        return "float32";
    }
    if matches!(normalized, "f64" | "double") {
        return "float64";
    }
    // Fall back: treat as unsafe.Pointer for any exotic pointer type.
    "unsafe.Pointer"
}

/// Emit the CGO conversion for a single constructor param.
///
/// Returns a pair `(c_var_name, setup_lines)` where `c_var_name` is the expression
/// to pass to the C function and `setup_lines` are the Go statements to insert before
/// the call (CString allocation + deferred free, numeric cast, etc.).
fn go_ctor_param_setup(go_name: &str, rust_ty: &str, ffi_prefix: &str) -> (String, String) {
    let normalized = rust_ty.trim();
    let c_name = format!("c{}{}", &go_name[..1].to_uppercase(), &go_name[1..]);

    if normalized.contains("c_char") || normalized.contains("CStr") {
        // String param: allocate a C string + defer free.
        let setup = format!("\t{c_name} := C.CString({go_name})\n\tdefer C.free(unsafe.Pointer({c_name}))\n");
        (c_name, setup)
    } else if matches!(normalized, "bool") {
        let setup = format!("\t{c_name} := C.bool({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "f32" | "float") {
        let setup = format!("\t{c_name} := C.float({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "f64" | "double") {
        let setup = format!("\t{c_name} := C.double({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "u8" | "uint8_t") {
        let setup = format!("\t{c_name} := C.uint8_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "u16" | "uint16_t") {
        let setup = format!("\t{c_name} := C.uint16_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "u32" | "uint32_t") {
        let setup = format!("\t{c_name} := C.uint32_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "u64" | "uint64_t" | "usize") {
        let setup = format!("\t{c_name} := C.uint64_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "i8" | "int8_t") {
        let setup = format!("\t{c_name} := C.int8_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "i16" | "int16_t") {
        let setup = format!("\t{c_name} := C.int16_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "i32" | "int32_t" | "c_int") {
        let setup = format!("\t{c_name} := C.int32_t({go_name})\n");
        (c_name, setup)
    } else if matches!(normalized, "i64" | "int64_t" | "isize") {
        let setup = format!("\t{c_name} := C.int64_t({go_name})\n");
        (c_name, setup)
    } else {
        // Opaque pointer — pass through with a cast.
        let _ = ffi_prefix;
        let setup = format!("\t{c_name} := {go_name}\n");
        (c_name, setup)
    }
}

/// Generate a `func New<TypeName>(params...) (*<TypeName>, error)` constructor that
/// wraps the `C.{ffi_prefix}_{type_snake}_new(...)` FFI symbol emitted by the FFI backend.
fn gen_go_opaque_constructor(typ: &TypeDef, ffi_prefix: &str, ctor: &ClientConstructorConfig) -> String {
    use crate::codegen::naming::go_type_name;
    use heck::ToSnakeCase;

    let go_name = go_type_name(&typ.name);
    let type_snake = typ.name.to_snake_case();
    let upper_prefix = ffi_prefix.to_uppercase();
    let c_type = format!("{upper_prefix}{}", typ.name);

    // Build Go parameter list.
    let go_params: String = ctor
        .params
        .iter()
        .map(|p| format!("{} {}", p.name, ffi_ty_to_go(&p.ty)))
        .collect::<Vec<_>>()
        .join(", ");

    // Build setup code + C argument list.
    let mut setup = String::new();
    let c_args: Vec<String> = ctor
        .params
        .iter()
        .map(|p| {
            let (c_var, lines) = go_ctor_param_setup(&p.name, &p.ty, ffi_prefix);
            setup.push_str(&lines);
            c_var
        })
        .collect();

    let c_call_args = c_args.join(", ");

    format!(
        "// New{go_name} creates a new {go_name} handle via the FFI constructor.\n\
         func New{go_name}({go_params}) (*{go_name}, error) {{\n\
         {setup}\
         \tptr := C.{ffi_prefix}_{type_snake}_new({c_call_args})\n\
         \tif ptr == nil {{\n\
         \t\treturn nil, fmt.Errorf(\"new{go_name}: %s\", C.GoString(C.{ffi_prefix}_last_error_context()))\n\
         \t}}\n\
         \treturn &{go_name}{{ptr: unsafe.Pointer((*C.{c_type})(ptr))}}, nil\n\
         }}"
    )
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::core::config::NewAlefConfig;

    fn resolved_one(toml: &str) -> ResolvedCrateConfig {
        let cfg: NewAlefConfig = toml::from_str(toml).unwrap();
        cfg.resolve().unwrap().remove(0)
    }

    fn make_config() -> ResolvedCrateConfig {
        resolved_one(
            r#"
[workspace]
languages = ["ffi", "go"]
[[crates]]
name = "test-lib"
sources = ["src/lib.rs"]
[crates.ffi]
prefix = "test"
[crates.go]
module = "github.com/test/test-lib"
"#,
        )
    }

    #[test]
    fn test_package_name_extracts_last_segment() {
        assert_eq!(GoBackend::package_name("github.com/org/my-lib"), "mylib");
        assert_eq!(GoBackend::package_name("binding"), "binding");
    }

    #[test]
    fn test_strip_trailing_whitespace_normalizes_lines() {
        let input = "line one   \nline two\n";
        let result = strip_trailing_whitespace(input);
        assert_eq!(result, "line one\nline two\n");
    }

    #[test]
    fn test_is_ffi_enum_type_returns_true_for_known_enum() {
        let mut enum_names = HashSet::new();
        enum_names.insert("Status".to_string());
        assert!(is_ffi_enum_type("Status", &enum_names));
        assert!(!is_ffi_enum_type("Config", &enum_names));
    }

    #[test]
    fn test_generate_bindings_produces_binding_go_file() {
        use crate::core::ir::ApiSurface;
        let config = make_config();
        let api = ApiSurface {
            crate_name: "test-lib".to_string(),
            version: "0.1.0".to_string(),
            types: vec![],
            functions: vec![],
            enums: vec![],
            errors: vec![],
            excluded_type_paths: ::std::collections::HashMap::new(),
            excluded_trait_names: ::std::collections::HashSet::new(),
        };
        let backend = GoBackend;
        let files = backend.generate_bindings(&api, &config).unwrap();
        assert!(!files.is_empty());
        assert!(files[0].path.to_string_lossy().contains("binding.go"));
    }

    #[test]
    fn test_gen_go_opaque_constructor_emits_new_function() {
        use crate::core::config::workspace::{ClientConstructorConfig, ConstructorParam};
        use crate::core::ir::TypeDef;

        let typ = TypeDef {
            name: "TestClient".to_string(),
            rust_path: "test_lib::TestClient".to_string(),
            original_rust_path: "test_lib::TestClient".to_string(),
            fields: vec![],
            methods: vec![],
            is_opaque: true,
            is_clone: false,
            is_copy: false,
            is_trait: false,
            has_default: false,
            has_stripped_cfg_fields: false,
            is_return_type: false,
            serde_rename_all: None,
            has_serde: false,
            super_traits: vec![],
            doc: String::new(),
            cfg: None,
            binding_excluded: false,
            binding_exclusion_reason: None,
        };
        let ctor = ClientConstructorConfig {
            params: vec![ConstructorParam {
                name: "api_key".to_string(),
                ty: "*const std::ffi::c_char".to_string(),
            }],
            body: "TestClient::new(api_key)".to_string(),
            error_type: None,
        };
        let output = gen_go_opaque_constructor(&typ, "test", &ctor);
        assert!(
            output.contains("func NewTestClient("),
            "should contain func NewTestClient"
        );
        assert!(output.contains("api_key string"), "should contain api_key string param");
        assert!(
            output.contains("C.CString(api_key)"),
            "should use C.CString for c_char param"
        );
        assert!(
            output.contains("C.free(unsafe.Pointer("),
            "should defer-free the C string"
        );
        assert!(
            output.contains("C.test_test_client_new("),
            "should call FFI constructor"
        );
        assert!(output.contains("return nil, fmt.Errorf"), "should return error on nil");
        assert!(
            output.contains("return &TestClient{ptr:"),
            "should return handle on success"
        );
    }
}