use crate::rust::{to_rust_ident, to_rust_upper_camel_case, RustGenerator, TypeMode};
use crate::types::{TypeInfo, Types};
use anyhow::{anyhow, bail, Context};
use heck::*;
use indexmap::{IndexMap, IndexSet};
use std::collections::{BTreeMap, HashMap, HashSet};
use std::fmt::Write as _;
use std::io::{Read, Write};
use std::mem;
use std::process::{Command, Stdio};
use wit_parser::*;

macro_rules! uwrite {
    ($dst:expr, $($arg:tt)*) => {
        write!($dst, $($arg)*).unwrap()
    };
}

macro_rules! uwriteln {
    ($dst:expr, $($arg:tt)*) => {
        writeln!($dst, $($arg)*).unwrap()
    };
}

mod rust;
mod source;
mod types;
use source::Source;

#[derive(Clone)]
enum InterfaceName {
    /// This interface was remapped using `with` to some other Rust code.
    Remapped {
        name_at_root: String,
        local_path: Vec<String>,
    },
    /// This interface is generated in the module hierarchy specified.
    Path(Vec<String>),
}

#[derive(Default)]
struct Wasmtime {
    src: Source,
    opts: Opts,
    import_interfaces: Vec<(String, InterfaceName)>,
    import_functions: Vec<ImportFunction>,
    exports: Exports,
    types: Types,
    sizes: SizeAlign,
    interface_names: HashMap<InterfaceId, InterfaceName>,
    with_name_counter: usize,
    interface_last_seen_as_import: HashMap<InterfaceId, bool>,
    trappable_errors: IndexMap<TypeId, String>,
}

struct ImportFunction {
    add_to_linker: String,
    sig: String,
}

#[derive(Default)]
struct Exports {
    fields: BTreeMap<String, (String, String)>,
    modules: Vec<(String, InterfaceName)>,
    funcs: Vec<String>,
}

#[derive(Default, Debug, Clone, Copy)]
pub enum Ownership {
    /// Generated types will be composed entirely of owning fields, regardless
    /// of whether they are used as parameters to guest exports or not.
    #[default]
    Owning,

    /// Generated types used as parameters to guest exports will be "deeply
    /// borrowing", i.e. contain references rather than owned values when
    /// applicable.
    Borrowing {
        /// Whether or not to generate "duplicate" type definitions for a single
        /// WIT type if necessary, for example if it's used as both an import
        /// and an export, or if it's used both as a parameter to an export and
        /// a return value from an export.
        duplicate_if_necessary: bool,
    },
}

#[derive(Default, Debug, Clone)]
pub struct Opts {
    /// Whether or not `rustfmt` is executed to format generated code.
    pub rustfmt: bool,

    /// Whether or not to emit `tracing` macro calls on function entry/exit.
    pub tracing: bool,

    /// Whether or not to use async rust functions and traits.
    pub async_: AsyncConfig,

    /// A list of "trappable errors" which are used to replace the `E` in
    /// `result<T, E>` found in WIT.
    pub trappable_error_type: Vec<TrappableError>,

    /// Whether to generate owning or borrowing type definitions.
    pub ownership: Ownership,

    /// Whether or not to generate code for only the interfaces of this wit file or not.
    pub only_interfaces: bool,

    /// Remapping of interface names to rust module names.
    /// TODO: is there a better type to use for the value of this map?
    pub with: HashMap<String, String>,
}

#[derive(Debug, Clone)]
pub struct TrappableError {
    /// Full path to the error, such as `wasi:io/streams/error`.
    pub wit_path: String,

    /// The name, in Rust, of the error type to generate.
    pub rust_type_name: String,
}

#[derive(Default, Debug, Clone)]
pub enum AsyncConfig {
    /// No functions are `async`.
    #[default]
    None,
    /// All generated functions should be `async`.
    All,
    /// These imported functions should not be async, but everything else is.
    AllExceptImports(HashSet<String>),
    /// These functions are the only imports that are async, all other imports
    /// are sync.
    ///
    /// Note that all exports are still async in this situation.
    OnlyImports(HashSet<String>),
}

impl AsyncConfig {
    pub fn is_import_async(&self, f: &str) -> bool {
        match self {
            AsyncConfig::None => false,
            AsyncConfig::All => true,
            AsyncConfig::AllExceptImports(set) => !set.contains(f),
            AsyncConfig::OnlyImports(set) => set.contains(f),
        }
    }

    pub fn maybe_async(&self) -> bool {
        match self {
            AsyncConfig::None => false,
            AsyncConfig::All | AsyncConfig::AllExceptImports(_) | AsyncConfig::OnlyImports(_) => {
                true
            }
        }
    }
}

impl Opts {
    pub fn generate(&self, resolve: &Resolve, world: WorldId) -> String {
        let mut r = Wasmtime::default();
        r.sizes.fill(resolve);
        r.opts = self.clone();
        r.generate(resolve, world)
    }
}

impl Wasmtime {
    fn name_interface(
        &mut self,
        resolve: &Resolve,
        id: InterfaceId,
        name: &WorldKey,
        is_export: bool,
    ) -> bool {
        let mut path = Vec::new();
        if is_export {
            path.push("exports".to_string());
        }
        match name {
            WorldKey::Name(name) => {
                path.push(name.to_snake_case());
            }
            WorldKey::Interface(_) => {
                let iface = &resolve.interfaces[id];
                let pkgname = &resolve.packages[iface.package.unwrap()].name;
                path.push(pkgname.namespace.to_snake_case());
                path.push(self.name_package_module(resolve, iface.package.unwrap()));
                path.push(iface.name.as_ref().unwrap().to_snake_case());
            }
        }
        let entry = if let Some(remapped_path) = self.lookup_replacement(resolve, name, None) {
            let remapped_path = remapped_path.to_string();
            let name = format!("__with_name{}", self.with_name_counter);
            self.with_name_counter += 1;
            uwriteln!(self.src, "use {remapped_path} as {name};");
            InterfaceName::Remapped {
                name_at_root: name,
                local_path: path,
            }
        } else {
            InterfaceName::Path(path)
        };

        let remapped = matches!(entry, InterfaceName::Remapped { .. });
        self.interface_names.insert(id, entry);
        remapped
    }

    /// If the package `id` is the only package with its namespace/name combo
    /// then pass through the name unmodified. If, however, there are multiple
    /// versions of this package then the package module is going to get version
    /// information.
    fn name_package_module(&self, resolve: &Resolve, id: PackageId) -> String {
        let pkg = &resolve.packages[id];
        let versions_with_same_name = resolve
            .packages
            .iter()
            .filter_map(|(_, p)| {
                if p.name.namespace == pkg.name.namespace && p.name.name == pkg.name.name {
                    Some(&p.name.version)
                } else {
                    None
                }
            })
            .collect::<Vec<_>>();
        let base = pkg.name.name.to_snake_case();
        if versions_with_same_name.len() == 1 {
            return base;
        }

        let version = match &pkg.name.version {
            Some(version) => version,
            // If this package didn't have a version then don't mangle its name
            // and other packages with the same name but with versions present
            // will have their names mangled.
            None => return base,
        };

        // Here there's multiple packages with the same name that differ only in
        // version, so the version needs to be mangled into the Rust module name
        // that we're generating. This in theory could look at all of
        // `versions_with_same_name` and produce a minimal diff, e.g. for 0.1.0
        // and 0.2.0 this could generate "foo1" and "foo2", but for now
        // a simpler path is chosen to generate "foo0_1_0" and "foo0_2_0".
        let version = version
            .to_string()
            .replace('.', "_")
            .replace('-', "_")
            .replace('+', "_")
            .to_snake_case();
        format!("{base}{version}")
    }

    fn generate(&mut self, resolve: &Resolve, id: WorldId) -> String {
        self.types.analyze(resolve, id);
        for (i, te) in self.opts.trappable_error_type.iter().enumerate() {
            let id = resolve_type_in_package(resolve, &te.wit_path)
                .context(format!("resolving {:?}", te))
                .unwrap();
            let name = format!("_TrappableError{i}");
            uwriteln!(self.src, "type {name} = {};", te.rust_type_name);
            let prev = self.trappable_errors.insert(id, name);
            assert!(prev.is_none());
        }

        let world = &resolve.worlds[id];
        for (name, import) in world.imports.iter() {
            if !self.opts.only_interfaces || matches!(import, WorldItem::Interface(_)) {
                self.import(resolve, id, name, import);
            }
        }

        for (name, export) in world.exports.iter() {
            if !self.opts.only_interfaces || matches!(export, WorldItem::Interface(_)) {
                self.export(resolve, name, export);
            }
        }
        self.finish(resolve, id)
    }

    fn import(&mut self, resolve: &Resolve, world: WorldId, name: &WorldKey, item: &WorldItem) {
        let mut gen = InterfaceGenerator::new(self, resolve);
        match item {
            WorldItem::Function(func) => {
                // Only generate a trait signature for free functions since
                // resource-related functions get their trait signatures
                // during `type_resource`.
                if let FunctionKind::Freestanding = func.kind {
                    gen.generate_function_trait_sig(func);
                }
                let sig = mem::take(&mut gen.src).into();
                gen.generate_add_function_to_linker(TypeOwner::World(world), func, "linker");
                let add_to_linker = gen.src.into();
                self.import_functions
                    .push(ImportFunction { sig, add_to_linker });
            }
            WorldItem::Interface(id) => {
                gen.gen.interface_last_seen_as_import.insert(*id, true);
                if gen.gen.name_interface(resolve, *id, name, false) {
                    return;
                }
                gen.current_interface = Some((*id, name, false));
                gen.types(*id);
                let key_name = resolve.name_world_key(name);

                gen.generate_add_to_linker(*id, &key_name);

                let module = &gen.src[..];

                let snake = match name {
                    WorldKey::Name(s) => s.to_snake_case(),
                    WorldKey::Interface(id) => resolve.interfaces[*id]
                        .name
                        .as_ref()
                        .unwrap()
                        .to_snake_case(),
                };
                let module = format!(
                    "
                        #[allow(clippy::all)]
                        pub mod {snake} {{
                            #[allow(unused_imports)]
                            use wasmtime::component::__internal::anyhow;

                            {module}
                        }}
                    "
                );
                self.import_interfaces
                    .push((module, self.interface_names[id].clone()));
            }
            WorldItem::Type(ty) => {
                let name = match name {
                    WorldKey::Name(name) => name,
                    WorldKey::Interface(_) => unreachable!(),
                };
                gen.define_type(name, *ty);
                let body = mem::take(&mut gen.src);
                self.src.push_str(&body);
            }
        };
    }

    fn export(&mut self, resolve: &Resolve, name: &WorldKey, item: &WorldItem) {
        let mut gen = InterfaceGenerator::new(self, resolve);
        let (field, ty, getter) = match item {
            WorldItem::Function(func) => {
                gen.define_rust_guest_export(resolve, None, func);
                let body = mem::take(&mut gen.src).into();
                let (_name, getter) = gen.extract_typed_function(func);
                assert!(gen.src.is_empty());
                self.exports.funcs.push(body);
                (
                    func_field_name(resolve, func),
                    "wasmtime::component::Func".to_string(),
                    getter,
                )
            }
            WorldItem::Type(_) => unreachable!(),
            WorldItem::Interface(id) => {
                gen.gen.interface_last_seen_as_import.insert(*id, false);
                gen.gen.name_interface(resolve, *id, name, true);
                gen.current_interface = Some((*id, name, true));
                gen.types(*id);
                let iface = &resolve.interfaces[*id];
                let iface_name = match name {
                    WorldKey::Name(name) => name,
                    WorldKey::Interface(_) => iface.name.as_ref().unwrap(),
                };
                let camel = to_rust_upper_camel_case(iface_name);
                uwriteln!(gen.src, "pub struct {camel} {{");
                for (_, func) in iface.functions.iter() {
                    uwriteln!(
                        gen.src,
                        "{}: wasmtime::component::Func,",
                        func_field_name(resolve, func)
                    );
                }
                uwriteln!(gen.src, "}}");

                uwriteln!(gen.src, "impl {camel} {{");
                uwrite!(
                    gen.src,
                    "
                        pub fn new(
                            __exports: &mut wasmtime::component::ExportInstance<'_, '_>,
                        ) -> wasmtime::Result<{camel}> {{
                    "
                );
                let mut fields = Vec::new();
                for (_, func) in iface.functions.iter() {
                    let (name, getter) = gen.extract_typed_function(func);
                    uwriteln!(gen.src, "let {name} = {getter};");
                    fields.push(name);
                }
                uwriteln!(gen.src, "Ok({camel} {{");
                for name in fields {
                    uwriteln!(gen.src, "{name},");
                }
                uwriteln!(gen.src, "}})");
                uwriteln!(gen.src, "}}");

                let mut resource_methods = IndexMap::new();

                for (_, func) in iface.functions.iter() {
                    match func.kind {
                        FunctionKind::Freestanding => {
                            gen.define_rust_guest_export(resolve, Some(name), func);
                        }
                        FunctionKind::Method(id)
                        | FunctionKind::Constructor(id)
                        | FunctionKind::Static(id) => {
                            resource_methods.entry(id).or_insert(Vec::new()).push(func);
                        }
                    }
                }

                for (id, _) in resource_methods.iter() {
                    let name = resolve.types[*id].name.as_ref().unwrap();
                    let snake = name.to_snake_case();
                    let camel = name.to_upper_camel_case();
                    uwriteln!(
                        gen.src,
                        "pub fn {snake}(&self) -> Guest{camel}<'_> {{
                            Guest{camel} {{ funcs: self }}
                        }}"
                    );
                }

                uwriteln!(gen.src, "}}");

                for (id, methods) in resource_methods {
                    let resource_name = resolve.types[id].name.as_ref().unwrap();
                    let camel = resource_name.to_upper_camel_case();
                    uwriteln!(gen.src, "impl Guest{camel}<'_> {{");
                    for method in methods {
                        gen.define_rust_guest_export(resolve, Some(name), method);
                    }
                    uwriteln!(gen.src, "}}");
                }

                let module = &gen.src[..];
                let snake = iface_name.to_snake_case();

                let module = format!(
                    "
                        #[allow(clippy::all)]
                        pub mod {snake} {{
                            #[allow(unused_imports)]
                            use wasmtime::component::__internal::anyhow;

                            {module}
                        }}
                    "
                );
                let pkgname = match name {
                    WorldKey::Name(_) => None,
                    WorldKey::Interface(_) => {
                        Some(resolve.packages[iface.package.unwrap()].name.clone())
                    }
                };
                self.exports
                    .modules
                    .push((module, self.interface_names[id].clone()));

                let name = resolve.name_world_key(name);
                let (path, method_name) = match pkgname {
                    Some(pkgname) => (
                        format!(
                            "exports::{}::{}::{snake}::{camel}",
                            pkgname.namespace.to_snake_case(),
                            self.name_package_module(resolve, iface.package.unwrap()),
                        ),
                        format!(
                            "{}_{}_{snake}",
                            pkgname.namespace.to_snake_case(),
                            self.name_package_module(resolve, iface.package.unwrap())
                        ),
                    ),
                    None => (format!("exports::{snake}::{camel}"), snake.clone()),
                };
                let getter = format!(
                    "\
                        {path}::new(
                            &mut __exports.instance(\"{name}\")
                                .ok_or_else(|| anyhow::anyhow!(\"exported instance `{name}` not present\"))?
                        )?\
                    "
                );
                let field = format!("interface{}", self.exports.fields.len());
                self.exports.funcs.push(format!(
                    "
                        pub fn {method_name}(&self) -> &{path} {{
                            &self.{field}
                        }}
                    ",
                ));
                (field, path, getter)
            }
        };
        let prev = self.exports.fields.insert(field, (ty, getter));
        assert!(prev.is_none());
    }

    fn build_struct(&mut self, resolve: &Resolve, world: WorldId) {
        let camel = to_rust_upper_camel_case(&resolve.worlds[world].name);
        uwriteln!(self.src, "pub struct {camel} {{");
        for (name, (ty, _)) in self.exports.fields.iter() {
            uwriteln!(self.src, "{name}: {ty},");
        }
        self.src.push_str("}\n");

        let (async_, async__, send, await_) = if self.opts.async_.maybe_async() {
            ("async", "_async", ":Send", ".await")
        } else {
            ("", "", "", "")
        };

        self.toplevel_import_trait(resolve, world);

        uwriteln!(self.src, "const _: () = {{");
        uwriteln!(self.src, "use wasmtime::component::__internal::anyhow;");

        uwriteln!(self.src, "impl {camel} {{");
        self.toplevel_add_to_linker(resolve, world);
        uwriteln!(
            self.src,
            "
                /// Instantiates the provided `module` using the specified
                /// parameters, wrapping up the result in a structure that
                /// translates between wasm and the host.
                pub {async_} fn instantiate{async__}<T {send}>(
                    mut store: impl wasmtime::AsContextMut<Data = T>,
                    component: &wasmtime::component::Component,
                    linker: &wasmtime::component::Linker<T>,
                ) -> wasmtime::Result<(Self, wasmtime::component::Instance)> {{
                    let instance = linker.instantiate{async__}(&mut store, component){await_}?;
                    Ok((Self::new(store, &instance)?, instance))
                }}

                /// Instantiates a pre-instantiated module using the specified
                /// parameters, wrapping up the result in a structure that
                /// translates between wasm and the host.
                pub {async_} fn instantiate_pre<T {send}>(
                    mut store: impl wasmtime::AsContextMut<Data = T>,
                    instance_pre: &wasmtime::component::InstancePre<T>,
                ) -> wasmtime::Result<(Self, wasmtime::component::Instance)> {{
                    let instance = instance_pre.instantiate{async__}(&mut store){await_}?;
                    Ok((Self::new(store, &instance)?, instance))
                }}

                /// Low-level creation wrapper for wrapping up the exports
                /// of the `instance` provided in this structure of wasm
                /// exports.
                ///
                /// This function will extract exports from the `instance`
                /// defined within `store` and wrap them all up in the
                /// returned structure which can be used to interact with
                /// the wasm module.
                pub fn new(
                    mut store: impl wasmtime::AsContextMut,
                    instance: &wasmtime::component::Instance,
                ) -> wasmtime::Result<Self> {{
                    let mut store = store.as_context_mut();
                    let mut exports = instance.exports(&mut store);
                    let mut __exports = exports.root();
            ",
        );
        for (name, (_, get)) in self.exports.fields.iter() {
            uwriteln!(self.src, "let {name} = {get};");
        }
        uwriteln!(self.src, "Ok({camel} {{");
        for (name, _) in self.exports.fields.iter() {
            uwriteln!(self.src, "{name},");
        }
        uwriteln!(self.src, "}})");
        uwriteln!(self.src, "}}"); // close `fn new`

        for func in self.exports.funcs.iter() {
            self.src.push_str(func);
        }

        uwriteln!(self.src, "}}"); // close `impl {camel}`

        uwriteln!(self.src, "}};"); // close `const _: () = ...
    }

    fn finish(&mut self, resolve: &Resolve, world: WorldId) -> String {
        if !self.opts.only_interfaces {
            self.build_struct(resolve, world)
        }

        let imports = mem::take(&mut self.import_interfaces);
        self.emit_modules(imports);

        let exports = mem::take(&mut self.exports.modules);
        self.emit_modules(exports);

        let mut src = mem::take(&mut self.src);
        if self.opts.rustfmt {
            let mut child = Command::new("rustfmt")
                .arg("--edition=2018")
                .stdin(Stdio::piped())
                .stdout(Stdio::piped())
                .spawn()
                .expect("failed to spawn `rustfmt`");
            child
                .stdin
                .take()
                .unwrap()
                .write_all(src.as_bytes())
                .unwrap();
            src.as_mut_string().truncate(0);
            child
                .stdout
                .take()
                .unwrap()
                .read_to_string(src.as_mut_string())
                .unwrap();
            let status = child.wait().unwrap();
            assert!(status.success());
        }

        src.into()
    }

    fn emit_modules(&mut self, modules: Vec<(String, InterfaceName)>) {
        #[derive(Default)]
        struct Module {
            submodules: BTreeMap<String, Module>,
            contents: Vec<String>,
        }
        let mut map = Module::default();
        for (module, name) in modules {
            let path = match name {
                InterfaceName::Remapped { local_path, .. } => local_path,
                InterfaceName::Path(path) => path,
            };
            let mut cur = &mut map;
            for name in path[..path.len() - 1].iter() {
                cur = cur
                    .submodules
                    .entry(name.clone())
                    .or_insert(Module::default());
            }
            cur.contents.push(module);
        }

        emit(&mut self.src, map);

        fn emit(me: &mut Source, module: Module) {
            for (name, submodule) in module.submodules {
                uwriteln!(me, "pub mod {name} {{");
                emit(me, submodule);
                uwriteln!(me, "}}");
            }
            for submodule in module.contents {
                uwriteln!(me, "{submodule}");
            }
        }
    }

    fn lookup_replacement(
        &self,
        resolve: &Resolve,
        key: &WorldKey,
        item: Option<&str>,
    ) -> Option<&str> {
        // First try to lookup the exact name of the interface as specified
        // via `name_world_key`.
        let name = resolve.name_world_key(key);
        let candidate1 = match item {
            Some(item) => format!("{name}/{item}"),
            None => name.clone(),
        };
        if let Some(ret) = self.opts.with.get(&candidate1) {
            return Some(ret);
        }

        // .. if the above failed allow omitting the `@...` version information
        // and see if there's a `with` key for that.
        //
        // NB: this means that in a scenario where there's packages with the
        // same name/namespace where one has a version and one doesn't there's
        // no way to use `with` to specify just one and not the other. That
        // should be ok for now, but this should ideally detect a situation like
        // that and omit this fallback in such a situation.
        let version_start = name.find('@')?;
        let name = &name[..version_start];
        let candidate2 = match item {
            Some(item) => format!("{name}/{item}"),
            None => name.to_string(),
        };
        if let Some(ret) = self.opts.with.get(&candidate2) {
            return Some(ret);
        }

        None
    }
}

impl Wasmtime {
    fn has_world_trait(&self, resolve: &Resolve, world: WorldId) -> bool {
        !self.import_functions.is_empty() || get_world_resources(resolve, world).count() > 0
    }

    fn toplevel_import_trait(&mut self, resolve: &Resolve, world: WorldId) {
        if !self.has_world_trait(resolve, world) {
            return;
        }

        let world_camel = to_rust_upper_camel_case(&resolve.worlds[world].name);
        if self.opts.async_.maybe_async() {
            uwriteln!(self.src, "#[wasmtime::component::__internal::async_trait]")
        }
        uwrite!(self.src, "pub trait {world_camel}Imports");
        for (i, resource) in get_world_resources(resolve, world).enumerate() {
            if i == 0 {
                uwrite!(self.src, ": ");
            } else {
                uwrite!(self.src, " + ");
            }
            uwrite!(self.src, "Host{}", resource.to_upper_camel_case());
        }
        uwriteln!(self.src, " {{");
        for f in self.import_functions.iter() {
            self.src.push_str(&f.sig);
            self.src.push_str("\n");
        }
        uwriteln!(self.src, "}}");
    }

    fn toplevel_add_to_linker(&mut self, resolve: &Resolve, world: WorldId) {
        let has_world_trait = self.has_world_trait(resolve, world);
        if self.import_interfaces.is_empty() && !has_world_trait {
            return;
        }
        let mut interfaces = Vec::new();
        for (_, name) in self.import_interfaces.iter() {
            let path = match name {
                InterfaceName::Remapped { .. } => unreachable!("imported a remapped module"),
                InterfaceName::Path(path) => path,
            };
            interfaces.push(path.join("::"));
        }

        uwrite!(
            self.src,
            "
                pub fn add_to_linker<T, U>(
                    linker: &mut wasmtime::component::Linker<T>,
                    get: impl Fn(&mut T) -> &mut U + Send + Sync + Copy + 'static,
                ) -> wasmtime::Result<()>
                    where U: \
            "
        );
        let world_camel = to_rust_upper_camel_case(&resolve.worlds[world].name);
        let world_trait = format!("{world_camel}Imports");
        for (i, name) in interfaces
            .iter()
            .map(|n| format!("{n}::Host"))
            .chain(if has_world_trait {
                Some(world_trait.clone())
            } else {
                None
            })
            .enumerate()
        {
            if i > 0 {
                self.src.push_str(" + ");
            }
            self.src.push_str(&name);
        }

        let maybe_send = if self.opts.async_.maybe_async() {
            " + Send, T: Send"
        } else {
            ""
        };

        self.src.push_str(maybe_send);
        self.src.push_str(",\n{\n");
        for name in interfaces.iter() {
            uwriteln!(self.src, "{name}::add_to_linker(linker, get)?;");
        }
        if has_world_trait {
            uwriteln!(self.src, "Self::add_root_to_linker(linker, get)?;");
        }
        uwriteln!(self.src, "Ok(())\n}}");
        if !has_world_trait {
            return;
        }

        uwrite!(
            self.src,
            "
                pub fn add_root_to_linker<T, U>(
                    linker: &mut wasmtime::component::Linker<T>,
                    get: impl Fn(&mut T) -> &mut U + Send + Sync + Copy + 'static,
                ) -> wasmtime::Result<()>
                    where U: {world_trait}{maybe_send}
                {{
                    let mut linker = linker.root();
            ",
        );
        for name in get_world_resources(resolve, world) {
            let camel = name.to_upper_camel_case();
            uwriteln!(
                self.src,
                "linker.resource(
                    \"{name}\",
                    wasmtime::component::ResourceType::host::<{camel}>(),
                    move |mut store, rep| -> wasmtime::Result<()> {{
                        Host{camel}::drop(get(store.data_mut()), wasmtime::component::Resource::new_own(rep))
                    }},
                )?;"
            )
        }

        for f in self.import_functions.iter() {
            self.src.push_str(&f.add_to_linker);
            self.src.push_str("\n");
        }
        uwriteln!(self.src, "Ok(())\n}}");
    }
}

fn resolve_type_in_package(resolve: &Resolve, wit_path: &str) -> anyhow::Result<TypeId> {
    // Build a map, `packages_to_omit_version`, where that package can be
    // uniquely identified by its name/namespace combo and as such version
    // information is not required.
    let mut packages_with_same_name = HashMap::new();
    for (id, pkg) in resolve.packages.iter() {
        packages_with_same_name
            .entry(PackageName {
                version: None,
                ..pkg.name.clone()
            })
            .or_insert(Vec::new())
            .push(id)
    }
    let packages_to_omit_version = packages_with_same_name
        .iter()
        .filter_map(
            |(_name, list)| {
                if list.len() == 1 {
                    Some(list)
                } else {
                    None
                }
            },
        )
        .flat_map(|l| l)
        .collect::<HashSet<_>>();

    // Look for an interface whose assigned prefix starts `wit_path`. Not
    // exactly the most efficient thing ever but is sufficient for now.
    for (id, interface) in resolve.interfaces.iter() {
        let iface_name = match &interface.name {
            Some(name) => name,
            None => continue,
        };
        let pkgid = interface.package.unwrap();
        let pkgname = &resolve.packages[pkgid].name;
        let prefix = if packages_to_omit_version.contains(&pkgid) {
            let mut name = pkgname.clone();
            name.version = None;
            format!("{name}/{iface_name}")
        } else {
            resolve.id_of(id).unwrap()
        };
        let wit_path = match wit_path.strip_prefix(&prefix) {
            Some(rest) => rest,
            None => continue,
        };
        let wit_path = wit_path
            .strip_prefix('/')
            .ok_or_else(|| anyhow!("expected `/` after interface name"))?;

        return interface
            .types
            .get(wit_path)
            .copied()
            .ok_or_else(|| anyhow!("no types found to match `{wit_path}` in interface"));
    }

    bail!("no package/interface found to match `{wit_path}`")
}

struct InterfaceGenerator<'a> {
    src: Source,
    gen: &'a mut Wasmtime,
    resolve: &'a Resolve,
    current_interface: Option<(InterfaceId, &'a WorldKey, bool)>,
}

impl<'a> InterfaceGenerator<'a> {
    fn new(gen: &'a mut Wasmtime, resolve: &'a Resolve) -> InterfaceGenerator<'a> {
        InterfaceGenerator {
            src: Source::default(),
            gen,
            resolve,
            current_interface: None,
        }
    }

    fn types_imported(&self) -> bool {
        match self.current_interface {
            Some((_, _, is_export)) => !is_export,
            None => true,
        }
    }

    fn types(&mut self, id: InterfaceId) {
        for (name, id) in self.resolve.interfaces[id].types.iter() {
            self.define_type(name, *id);
        }
    }

    fn define_type(&mut self, name: &str, id: TypeId) {
        let ty = &self.resolve.types[id];
        match &ty.kind {
            TypeDefKind::Record(record) => self.type_record(id, name, record, &ty.docs),
            TypeDefKind::Flags(flags) => self.type_flags(id, name, flags, &ty.docs),
            TypeDefKind::Tuple(tuple) => self.type_tuple(id, name, tuple, &ty.docs),
            TypeDefKind::Enum(enum_) => self.type_enum(id, name, enum_, &ty.docs),
            TypeDefKind::Variant(variant) => self.type_variant(id, name, variant, &ty.docs),
            TypeDefKind::Option(t) => self.type_option(id, name, t, &ty.docs),
            TypeDefKind::Result(r) => self.type_result(id, name, r, &ty.docs),
            TypeDefKind::List(t) => self.type_list(id, name, t, &ty.docs),
            TypeDefKind::Type(t) => self.type_alias(id, name, t, &ty.docs),
            TypeDefKind::Future(_) => todo!("generate for future"),
            TypeDefKind::Stream(_) => todo!("generate for stream"),
            TypeDefKind::Handle(handle) => self.type_handle(id, name, handle, &ty.docs),
            TypeDefKind::Resource => self.type_resource(id, name, ty, &ty.docs),
            TypeDefKind::Unknown => unreachable!(),
        }
    }

    fn type_handle(&mut self, id: TypeId, name: &str, handle: &Handle, docs: &Docs) {
        self.rustdoc(docs);
        let name = name.to_upper_camel_case();
        uwriteln!(self.src, "pub type {name} = ");
        self.print_handle(handle);
        self.push_str(";\n");
        self.assert_type(id, &name);
    }

    fn type_resource(&mut self, id: TypeId, name: &str, resource: &TypeDef, docs: &Docs) {
        let camel = name.to_upper_camel_case();

        if self.types_imported() {
            self.rustdoc(docs);

            let replacement = match self.current_interface {
                Some((_, key, _)) => self.gen.lookup_replacement(self.resolve, key, Some(name)),
                None => self.gen.opts.with.get(name).map(|s| s.as_str()),
            };
            match replacement {
                Some(path) => {
                    uwriteln!(
                        self.src,
                        "pub use {}{path} as {camel};",
                        self.path_to_root()
                    );
                }
                None => {
                    uwriteln!(self.src, "pub enum {camel} {{}}");
                }
            }

            if self.gen.opts.async_.maybe_async() {
                uwriteln!(self.src, "#[wasmtime::component::__internal::async_trait]")
            }

            uwriteln!(self.src, "pub trait Host{camel} {{");

            let functions = match resource.owner {
                TypeOwner::World(id) => self.resolve.worlds[id]
                    .imports
                    .values()
                    .filter_map(|item| match item {
                        WorldItem::Function(f) => Some(f),
                        _ => None,
                    })
                    .collect(),
                TypeOwner::Interface(id) => self.resolve.interfaces[id]
                    .functions
                    .values()
                    .collect::<Vec<_>>(),
                TypeOwner::None => {
                    panic!("A resource must be owned by a world or interface");
                }
            };

            for func in functions {
                match func.kind {
                    FunctionKind::Method(resource)
                    | FunctionKind::Static(resource)
                    | FunctionKind::Constructor(resource)
                        if id == resource => {}
                    _ => continue,
                }

                self.generate_function_trait_sig(func);
            }

            uwrite!(
                self.src,
                "fn drop(&mut self, rep: wasmtime::component::Resource<{camel}>) -> wasmtime::Result<()>;");

            uwriteln!(self.src, "}}");
        } else {
            let iface_name = match self.current_interface.unwrap().1 {
                WorldKey::Name(name) => name.to_upper_camel_case(),
                WorldKey::Interface(i) => self.resolve.interfaces[*i]
                    .name
                    .as_ref()
                    .unwrap()
                    .to_upper_camel_case(),
            };
            self.rustdoc(docs);
            uwriteln!(
                self.src,
                "
                    pub type {camel} = wasmtime::component::ResourceAny;

                    pub struct Guest{camel}<'a> {{
                        funcs: &'a {iface_name},
                    }}
                "
            );
        }
    }

    fn type_record(&mut self, id: TypeId, _name: &str, record: &Record, docs: &Docs) {
        let info = self.info(id);
        for (name, mode) in self.modes_of(id) {
            let lt = self.lifetime_for(&info, mode);
            self.rustdoc(docs);

            self.push_str("#[derive(wasmtime::component::ComponentType)]\n");
            if lt.is_none() {
                self.push_str("#[derive(wasmtime::component::Lift)]\n");
            }
            self.push_str("#[derive(wasmtime::component::Lower)]\n");
            self.push_str("#[component(record)]\n");

            if info.is_copy() {
                self.push_str("#[derive(Copy, Clone)]\n");
            } else if info.is_clone() {
                self.push_str("#[derive(Clone)]\n");
            }
            self.push_str(&format!("pub struct {}", name));
            self.print_generics(lt);
            self.push_str(" {\n");
            for field in record.fields.iter() {
                self.rustdoc(&field.docs);
                self.push_str(&format!("#[component(name = \"{}\")]\n", field.name));
                self.push_str("pub ");
                self.push_str(&to_rust_ident(&field.name));
                self.push_str(": ");
                self.print_ty(&field.ty, mode);
                self.push_str(",\n");
            }
            self.push_str("}\n");

            self.push_str("impl");
            self.print_generics(lt);
            self.push_str(" core::fmt::Debug for ");
            self.push_str(&name);
            self.print_generics(lt);
            self.push_str(" {\n");
            self.push_str(
                "fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {\n",
            );
            self.push_str(&format!("f.debug_struct(\"{}\")", name));
            for field in record.fields.iter() {
                self.push_str(&format!(
                    ".field(\"{}\", &self.{})",
                    field.name,
                    to_rust_ident(&field.name)
                ));
            }
            self.push_str(".finish()\n");
            self.push_str("}\n");
            self.push_str("}\n");

            if info.error {
                self.push_str("impl");
                self.print_generics(lt);
                self.push_str(" core::fmt::Display for ");
                self.push_str(&name);
                self.print_generics(lt);
                self.push_str(" {\n");
                self.push_str(
                    "fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {\n",
                );
                self.push_str("write!(f, \"{:?}\", self)\n");
                self.push_str("}\n");
                self.push_str("}\n");
                self.push_str("impl std::error::Error for ");
                self.push_str(&name);
                self.push_str("{}\n");
            }
            self.assert_type(id, &name);
        }
    }

    fn type_tuple(&mut self, id: TypeId, _name: &str, tuple: &Tuple, docs: &Docs) {
        let info = self.info(id);
        for (name, mode) in self.modes_of(id) {
            let lt = self.lifetime_for(&info, mode);
            self.rustdoc(docs);
            self.push_str(&format!("pub type {}", name));
            self.print_generics(lt);
            self.push_str(" = (");
            for ty in tuple.types.iter() {
                self.print_ty(ty, mode);
                self.push_str(",");
            }
            self.push_str(");\n");
            self.assert_type(id, &name);
        }
    }

    fn type_flags(&mut self, id: TypeId, name: &str, flags: &Flags, docs: &Docs) {
        self.rustdoc(docs);
        let rust_name = to_rust_upper_camel_case(name);
        self.src.push_str("wasmtime::component::flags!(\n");
        self.src.push_str(&format!("{rust_name} {{\n"));
        for flag in flags.flags.iter() {
            // TODO wasmtime-component-macro doesnt support docs for flags rn
            uwrite!(
                self.src,
                "#[component(name=\"{}\")] const {};\n",
                flag.name,
                flag.name.to_shouty_snake_case()
            );
        }
        self.src.push_str("}\n");
        self.src.push_str(");\n\n");
        self.assert_type(id, &rust_name);
    }

    fn type_variant(&mut self, id: TypeId, _name: &str, variant: &Variant, docs: &Docs) {
        self.print_rust_enum(
            id,
            variant.cases.iter().map(|c| {
                (
                    c.name.to_upper_camel_case(),
                    Some(c.name.clone()),
                    &c.docs,
                    c.ty.as_ref(),
                )
            }),
            docs,
            "variant",
        );
    }

    fn type_option(&mut self, id: TypeId, _name: &str, payload: &Type, docs: &Docs) {
        let info = self.info(id);

        for (name, mode) in self.modes_of(id) {
            self.rustdoc(docs);
            let lt = self.lifetime_for(&info, mode);
            self.push_str(&format!("pub type {}", name));
            self.print_generics(lt);
            self.push_str("= Option<");
            self.print_ty(payload, mode);
            self.push_str(">;\n");
            self.assert_type(id, &name);
        }
    }

    // Emit a double-check that the wit-parser-understood size of a type agrees
    // with the Wasmtime-understood size of a type.
    fn assert_type(&mut self, id: TypeId, name: &str) {
        self.push_str("const _: () = {\n");
        uwriteln!(
            self.src,
            "assert!({} == <{name} as wasmtime::component::ComponentType>::SIZE32);",
            self.gen.sizes.size(&Type::Id(id)),
        );
        uwriteln!(
            self.src,
            "assert!({} == <{name} as wasmtime::component::ComponentType>::ALIGN32);",
            self.gen.sizes.align(&Type::Id(id)),
        );
        self.push_str("};\n");
    }

    fn print_rust_enum<'b>(
        &mut self,
        id: TypeId,
        cases: impl IntoIterator<Item = (String, Option<String>, &'b Docs, Option<&'b Type>)> + Clone,
        docs: &Docs,
        derive_component: &str,
    ) where
        Self: Sized,
    {
        let info = self.info(id);

        for (name, mode) in self.modes_of(id) {
            let name = to_rust_upper_camel_case(&name);

            self.rustdoc(docs);
            let lt = self.lifetime_for(&info, mode);
            self.push_str("#[derive(wasmtime::component::ComponentType)]\n");
            if lt.is_none() {
                self.push_str("#[derive(wasmtime::component::Lift)]\n");
            }
            self.push_str("#[derive(wasmtime::component::Lower)]\n");
            self.push_str(&format!("#[component({})]\n", derive_component));
            if info.is_copy() {
                self.push_str("#[derive(Copy, Clone)]\n");
            } else if info.is_clone() {
                self.push_str("#[derive(Clone)]\n");
            }
            self.push_str(&format!("pub enum {name}"));
            self.print_generics(lt);
            self.push_str("{\n");
            for (case_name, component_name, docs, payload) in cases.clone() {
                self.rustdoc(docs);
                if let Some(n) = component_name {
                    self.push_str(&format!("#[component(name = \"{}\")] ", n));
                }
                self.push_str(&case_name);
                if let Some(ty) = payload {
                    self.push_str("(");
                    self.print_ty(ty, mode);
                    self.push_str(")")
                }
                self.push_str(",\n");
            }
            self.push_str("}\n");

            self.print_rust_enum_debug(
                id,
                mode,
                &name,
                cases
                    .clone()
                    .into_iter()
                    .map(|(name, _attr, _docs, ty)| (name, ty)),
            );

            if info.error {
                self.push_str("impl");
                self.print_generics(lt);
                self.push_str(" core::fmt::Display for ");
                self.push_str(&name);
                self.print_generics(lt);
                self.push_str(" {\n");
                self.push_str(
                    "fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {\n",
                );
                self.push_str("write!(f, \"{:?}\", self)");
                self.push_str("}\n");
                self.push_str("}\n");
                self.push_str("\n");

                self.push_str("impl");
                self.print_generics(lt);
                self.push_str(" std::error::Error for ");
                self.push_str(&name);
                self.print_generics(lt);
                self.push_str(" {}\n");
            }

            self.assert_type(id, &name);
        }
    }

    fn print_rust_enum_debug<'b>(
        &mut self,
        id: TypeId,
        mode: TypeMode,
        name: &str,
        cases: impl IntoIterator<Item = (String, Option<&'b Type>)>,
    ) where
        Self: Sized,
    {
        let info = self.info(id);
        let lt = self.lifetime_for(&info, mode);
        self.push_str("impl");
        self.print_generics(lt);
        self.push_str(" core::fmt::Debug for ");
        self.push_str(name);
        self.print_generics(lt);
        self.push_str(" {\n");
        self.push_str("fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {\n");
        self.push_str("match self {\n");
        for (case_name, payload) in cases {
            self.push_str(name);
            self.push_str("::");
            self.push_str(&case_name);
            if payload.is_some() {
                self.push_str("(e)");
            }
            self.push_str(" => {\n");
            self.push_str(&format!("f.debug_tuple(\"{}::{}\")", name, case_name));
            if payload.is_some() {
                self.push_str(".field(e)");
            }
            self.push_str(".finish()\n");
            self.push_str("}\n");
        }
        self.push_str("}\n");
        self.push_str("}\n");
        self.push_str("}\n");
    }

    fn type_result(&mut self, id: TypeId, _name: &str, result: &Result_, docs: &Docs) {
        let info = self.info(id);

        for (name, mode) in self.modes_of(id) {
            self.rustdoc(docs);
            let lt = self.lifetime_for(&info, mode);
            self.push_str(&format!("pub type {}", name));
            self.print_generics(lt);
            self.push_str("= Result<");
            self.print_optional_ty(result.ok.as_ref(), mode);
            self.push_str(",");
            self.print_optional_ty(result.err.as_ref(), mode);
            self.push_str(">;\n");
            self.assert_type(id, &name);
        }
    }

    fn type_enum(&mut self, id: TypeId, name: &str, enum_: &Enum, docs: &Docs) {
        let info = self.info(id);

        let name = to_rust_upper_camel_case(name);
        self.rustdoc(docs);
        self.push_str("#[derive(wasmtime::component::ComponentType)]\n");
        self.push_str("#[derive(wasmtime::component::Lift)]\n");
        self.push_str("#[derive(wasmtime::component::Lower)]\n");
        self.push_str("#[component(enum)]\n");
        self.push_str("#[derive(Clone, Copy, PartialEq, Eq)]\n");
        self.push_str(&format!("pub enum {} {{\n", name));
        for case in enum_.cases.iter() {
            self.rustdoc(&case.docs);
            self.push_str(&format!("#[component(name = \"{}\")]", case.name));
            self.push_str(&case.name.to_upper_camel_case());
            self.push_str(",\n");
        }
        self.push_str("}\n");

        // Auto-synthesize an implementation of the standard `Error` trait for
        // error-looking types based on their name.
        if info.error {
            self.push_str("impl ");
            self.push_str(&name);
            self.push_str("{\n");

            self.push_str("pub fn name(&self) -> &'static str {\n");
            self.push_str("match self {\n");
            for case in enum_.cases.iter() {
                self.push_str(&name);
                self.push_str("::");
                self.push_str(&case.name.to_upper_camel_case());
                self.push_str(" => \"");
                self.push_str(case.name.as_str());
                self.push_str("\",\n");
            }
            self.push_str("}\n");
            self.push_str("}\n");

            self.push_str("pub fn message(&self) -> &'static str {\n");
            self.push_str("match self {\n");
            for case in enum_.cases.iter() {
                self.push_str(&name);
                self.push_str("::");
                self.push_str(&case.name.to_upper_camel_case());
                self.push_str(" => \"");
                if let Some(contents) = &case.docs.contents {
                    self.push_str(contents.trim());
                }
                self.push_str("\",\n");
            }
            self.push_str("}\n");
            self.push_str("}\n");

            self.push_str("}\n");

            self.push_str("impl core::fmt::Debug for ");
            self.push_str(&name);
            self.push_str(
                "{\nfn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {\n",
            );
            self.push_str("f.debug_struct(\"");
            self.push_str(&name);
            self.push_str("\")\n");
            self.push_str(".field(\"code\", &(*self as i32))\n");
            self.push_str(".field(\"name\", &self.name())\n");
            self.push_str(".field(\"message\", &self.message())\n");
            self.push_str(".finish()\n");
            self.push_str("}\n");
            self.push_str("}\n");

            self.push_str("impl core::fmt::Display for ");
            self.push_str(&name);
            self.push_str(
                "{\nfn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {\n",
            );
            self.push_str("write!(f, \"{} (error {})\", self.name(), *self as i32)");
            self.push_str("}\n");
            self.push_str("}\n");
            self.push_str("\n");
            self.push_str("impl std::error::Error for ");
            self.push_str(&name);
            self.push_str("{}\n");
        } else {
            self.print_rust_enum_debug(
                id,
                TypeMode::Owned,
                &name,
                enum_
                    .cases
                    .iter()
                    .map(|c| (c.name.to_upper_camel_case(), None)),
            )
        }
        self.assert_type(id, &name);
    }

    fn type_alias(&mut self, id: TypeId, _name: &str, ty: &Type, docs: &Docs) {
        let info = self.info(id);
        for (name, mode) in self.modes_of(id) {
            self.rustdoc(docs);
            self.push_str(&format!("pub type {}", name));
            let lt = self.lifetime_for(&info, mode);
            self.print_generics(lt);
            self.push_str(" = ");
            self.print_ty(ty, mode);
            self.push_str(";\n");
            let def_id = resolve_type_definition_id(self.resolve, id);
            if !matches!(self.resolve().types[def_id].kind, TypeDefKind::Resource) {
                self.assert_type(id, &name);
            }
        }
    }

    fn type_list(&mut self, id: TypeId, _name: &str, ty: &Type, docs: &Docs) {
        let info = self.info(id);
        for (name, mode) in self.modes_of(id) {
            let lt = self.lifetime_for(&info, mode);
            self.rustdoc(docs);
            self.push_str(&format!("pub type {}", name));
            self.print_generics(lt);
            self.push_str(" = ");
            self.print_list(ty, mode);
            self.push_str(";\n");
            self.assert_type(id, &name);
        }
    }

    fn print_result_ty(&mut self, results: &Results, mode: TypeMode) {
        match results {
            Results::Named(rs) => match rs.len() {
                0 => self.push_str("()"),
                1 => self.print_ty(&rs[0].1, mode),
                _ => {
                    self.push_str("(");
                    for (i, (_, ty)) in rs.iter().enumerate() {
                        if i > 0 {
                            self.push_str(", ")
                        }
                        self.print_ty(ty, mode)
                    }
                    self.push_str(")");
                }
            },
            Results::Anon(ty) => self.print_ty(ty, mode),
        }
    }

    fn special_case_trappable_error(
        &self,
        results: &Results,
    ) -> Option<(&'a Result_, TypeId, String)> {
        // We fillin a special trappable error type in the case when a function has just one
        // result, which is itself a `result<a, e>`, and the `e` is *not* a primitive
        // (i.e. defined in std) type, and matches the typename given by the user.
        let mut i = results.iter_types();
        let id = match i.next()? {
            Type::Id(id) => id,
            _ => return None,
        };
        if i.next().is_some() {
            return None;
        }
        let result = match &self.resolve.types[*id].kind {
            TypeDefKind::Result(r) => r,
            _ => return None,
        };
        let error_typeid = match result.err? {
            Type::Id(id) => resolve_type_definition_id(&self.resolve, id),
            _ => return None,
        };

        let name = self.gen.trappable_errors.get(&error_typeid)?;

        let mut path = self.path_to_root();
        uwrite!(path, "{name}");
        Some((result, error_typeid, path))
    }

    fn generate_add_to_linker(&mut self, id: InterfaceId, name: &str) {
        let iface = &self.resolve.interfaces[id];
        let owner = TypeOwner::Interface(id);

        if self.gen.opts.async_.maybe_async() {
            uwriteln!(self.src, "#[wasmtime::component::__internal::async_trait]")
        }
        // Generate the `pub trait` which represents the host functionality for
        // this import which additionally inherits from all resource traits
        // for this interface defined by `type_resource`.
        uwrite!(self.src, "pub trait Host");
        for (i, resource) in get_resources(self.resolve, id).enumerate() {
            if i == 0 {
                uwrite!(self.src, ": ");
            } else {
                uwrite!(self.src, " + ");
            }
            uwrite!(self.src, "Host{}", resource.to_upper_camel_case());
        }
        uwriteln!(self.src, " {{");
        for (_, func) in iface.functions.iter() {
            match func.kind {
                FunctionKind::Freestanding => {}
                _ => continue,
            }
            self.generate_function_trait_sig(func);
        }

        // Generate `convert_*` functions to convert custom trappable errors
        // into the representation required by Wasmtime's component API.
        let mut required_conversion_traits = IndexSet::new();
        let mut errors_converted = IndexSet::new();
        let my_error_types = iface
            .types
            .iter()
            .filter(|(_, id)| self.gen.trappable_errors.contains_key(*id))
            .map(|(_, id)| *id);
        let used_error_types = iface
            .functions
            .iter()
            .filter_map(|(_, func)| self.special_case_trappable_error(&func.results))
            .map(|(_, id, _)| id);
        for err in my_error_types.chain(used_error_types).collect::<Vec<_>>() {
            let custom_name = &self.gen.trappable_errors[&err];
            let err = &self.resolve.types[resolve_type_definition_id(self.resolve, err)];
            let err_name = err.name.as_ref().unwrap();
            let err_snake = err_name.to_snake_case();
            let err_camel = err_name.to_upper_camel_case();
            let owner = match err.owner {
                TypeOwner::Interface(i) => i,
                _ => unimplemented!(),
            };
            match self.path_to_interface(owner) {
                Some(path) => {
                    required_conversion_traits.insert(format!("{path}::Host"));
                }
                None => {
                    if errors_converted.insert(err_name) {
                        let root = self.path_to_root();
                        uwriteln!(
                            self.src,
                            "fn convert_{err_snake}(&mut self, err: {root}{custom_name}) -> wasmtime::Result<{err_camel}>;"
                        );
                    }
                }
            }
        }
        uwriteln!(self.src, "}}");

        let mut where_clause = if self.gen.opts.async_.maybe_async() {
            "T: Send, U: Host + Send".to_string()
        } else {
            "U: Host".to_string()
        };

        for t in required_conversion_traits {
            where_clause.push_str(" + ");
            where_clause.push_str(&t);
        }

        uwriteln!(
            self.src,
            "
                pub fn add_to_linker<T, U>(
                    linker: &mut wasmtime::component::Linker<T>,
                    get: impl Fn(&mut T) -> &mut U + Send + Sync + Copy + 'static,
                ) -> wasmtime::Result<()>
                    where {where_clause}
                {{
            "
        );
        uwriteln!(self.src, "let mut inst = linker.instance(\"{name}\")?;");

        for name in get_resources(self.resolve, id) {
            let camel = name.to_upper_camel_case();
            uwriteln!(
                self.src,
                "inst.resource(
                    \"{name}\",
                    wasmtime::component::ResourceType::host::<{camel}>(),
                    move |mut store, rep| -> wasmtime::Result<()> {{
                        Host{camel}::drop(get(store.data_mut()), wasmtime::component::Resource::new_own(rep))
                    }},
                )?;"
            )
        }

        for (_, func) in iface.functions.iter() {
            self.generate_add_function_to_linker(owner, func, "inst");
        }
        uwriteln!(self.src, "Ok(())");
        uwriteln!(self.src, "}}");
    }

    fn generate_add_function_to_linker(&mut self, owner: TypeOwner, func: &Function, linker: &str) {
        uwrite!(
            self.src,
            "{linker}.{}(\"{}\", ",
            if self.gen.opts.async_.is_import_async(&func.name) {
                "func_wrap_async"
            } else {
                "func_wrap"
            },
            func.name
        );
        self.generate_guest_import_closure(owner, func);
        uwriteln!(self.src, ")?;")
    }

    fn generate_guest_import_closure(&mut self, owner: TypeOwner, func: &Function) {
        // Generate the closure that's passed to a `Linker`, the final piece of
        // codegen here.

        self.src
            .push_str("move |mut caller: wasmtime::StoreContextMut<'_, T>, (");
        for (i, _param) in func.params.iter().enumerate() {
            uwrite!(self.src, "arg{},", i);
        }
        self.src.push_str(") : (");

        for (_, ty) in func.params.iter() {
            // Lift is required to be impled for this type, so we can't use
            // a borrowed type:
            self.print_ty(ty, TypeMode::Owned);
            self.src.push_str(", ");
        }
        self.src.push_str(") |");
        if self.gen.opts.async_.is_import_async(&func.name) {
            self.src.push_str(" Box::new(async move { \n");
        } else {
            self.src.push_str(" { \n");
        }

        if self.gen.opts.tracing {
            uwrite!(
                self.src,
                "
                   let span = tracing::span!(
                       tracing::Level::TRACE,
                       \"wit-bindgen import\",
                       module = \"{}\",
                       function = \"{}\",
                   );
                   let _enter = span.enter();
               ",
                match owner {
                    TypeOwner::Interface(id) => self.resolve.interfaces[id]
                        .name
                        .as_deref()
                        .unwrap_or("<no module>"),
                    TypeOwner::World(id) => &self.resolve.worlds[id].name,
                    TypeOwner::None => "<no owner>",
                },
                func.name,
            );
            let mut event_fields = func
                .params
                .iter()
                .enumerate()
                .map(|(i, (name, _ty))| {
                    let name = to_rust_ident(&name);
                    format!("{name} = tracing::field::debug(&arg{i})")
                })
                .collect::<Vec<String>>();
            event_fields.push(format!("\"call\""));
            uwrite!(
                self.src,
                "tracing::event!(tracing::Level::TRACE, {});\n",
                event_fields.join(", ")
            );
        }

        self.src.push_str("let host = get(caller.data_mut());\n");
        let func_name = rust_function_name(func);
        let host_trait = match func.kind {
            FunctionKind::Freestanding => match owner {
                TypeOwner::World(id) => format!(
                    "{}Imports",
                    self.resolve.worlds[id].name.to_upper_camel_case()
                ),
                _ => "Host".to_string(),
            },
            FunctionKind::Method(id) | FunctionKind::Static(id) | FunctionKind::Constructor(id) => {
                let resource = self.resolve.types[id]
                    .name
                    .as_ref()
                    .unwrap()
                    .to_upper_camel_case();
                format!("Host{resource}")
            }
        };
        uwrite!(self.src, "let r = {host_trait}::{func_name}(host, ");

        for (i, _) in func.params.iter().enumerate() {
            uwrite!(self.src, "arg{},", i);
        }
        if self.gen.opts.async_.is_import_async(&func.name) {
            uwrite!(self.src, ").await;\n");
        } else {
            uwrite!(self.src, ");\n");
        }

        if self.gen.opts.tracing {
            uwrite!(
                self.src,
                "tracing::event!(tracing::Level::TRACE, result = tracing::field::debug(&r), \"return\");"
            );
        }

        if let Some((_, err, _)) = self.special_case_trappable_error(&func.results) {
            let err = &self.resolve.types[resolve_type_definition_id(self.resolve, err)];
            let err_name = err.name.as_ref().unwrap();
            let owner = match err.owner {
                TypeOwner::Interface(i) => i,
                _ => unimplemented!(),
            };
            let convert_trait = match self.path_to_interface(owner) {
                Some(path) => format!("{path}::Host"),
                None => format!("Host"),
            };
            let convert = format!("{}::convert_{}", convert_trait, err_name.to_snake_case());
            uwrite!(
                self.src,
                "Ok((match r {{
                    Ok(a) => Ok(a),
                    Err(e) => Err({convert}(host, e)?),
                }},))"
            );
        } else if func.results.iter_types().len() == 1 {
            uwrite!(self.src, "Ok((r?,))\n");
        } else {
            uwrite!(self.src, "r\n");
        }

        if self.gen.opts.async_.is_import_async(&func.name) {
            // Need to close Box::new and async block
            self.src.push_str("})");
        } else {
            self.src.push_str("}");
        }
    }

    fn generate_function_trait_sig(&mut self, func: &Function) {
        self.rustdoc(&func.docs);

        if self.gen.opts.async_.is_import_async(&func.name) {
            self.push_str("async ");
        }
        self.push_str("fn ");
        self.push_str(&rust_function_name(func));
        self.push_str("(&mut self, ");
        for (name, param) in func.params.iter() {
            let name = to_rust_ident(name);
            self.push_str(&name);
            self.push_str(": ");
            self.print_ty(param, TypeMode::Owned);
            self.push_str(",");
        }
        self.push_str(")");
        self.push_str(" -> ");

        if let Some((r, _id, error_typename)) = self.special_case_trappable_error(&func.results) {
            // Functions which have a single result `result<ok,err>` get special
            // cased to use the host_wasmtime_rust::Error<err>, making it possible
            // for them to trap or use `?` to propogate their errors
            self.push_str("Result<");
            if let Some(ok) = r.ok {
                self.print_ty(&ok, TypeMode::Owned);
            } else {
                self.push_str("()");
            }
            self.push_str(",");
            self.push_str(&error_typename);
            self.push_str(">");
        } else {
            // All other functions get their return values wrapped in an wasmtime::Result.
            // Returning the anyhow::Error case can be used to trap.
            self.push_str("wasmtime::Result<");
            self.print_result_ty(&func.results, TypeMode::Owned);
            self.push_str(">");
        }

        self.push_str(";\n");
    }

    fn extract_typed_function(&mut self, func: &Function) -> (String, String) {
        let prev = mem::take(&mut self.src);
        let snake = func_field_name(self.resolve, func);
        uwrite!(self.src, "*__exports.typed_func::<(");
        for (_, ty) in func.params.iter() {
            self.print_ty(ty, TypeMode::AllBorrowed("'_"));
            self.push_str(", ");
        }
        self.src.push_str("), (");
        for ty in func.results.iter_types() {
            self.print_ty(ty, TypeMode::Owned);
            self.push_str(", ");
        }
        self.src.push_str(")>(\"");
        self.src.push_str(&func.name);
        self.src.push_str("\")?.func()");

        let ret = (snake, mem::take(&mut self.src).to_string());
        self.src = prev;
        ret
    }

    fn define_rust_guest_export(
        &mut self,
        resolve: &Resolve,
        ns: Option<&WorldKey>,
        func: &Function,
    ) {
        // Exports must be async if anything could be async, it's just imports
        // that get to be optionally async/sync.
        let is_async = self.gen.opts.async_.maybe_async();

        let (async_, async__, await_) = if is_async {
            ("async", "_async", ".await")
        } else {
            ("", "", "")
        };

        self.rustdoc(&func.docs);

        uwrite!(
            self.src,
            "pub {async_} fn call_{}<S: wasmtime::AsContextMut>(&self, mut store: S, ",
            func.item_name().to_snake_case(),
        );

        for (i, param) in func.params.iter().enumerate() {
            uwrite!(self.src, "arg{}: ", i);
            self.print_ty(&param.1, TypeMode::AllBorrowed("'_"));
            self.push_str(",");
        }

        self.src.push_str(") -> wasmtime::Result<");
        self.print_result_ty(&func.results, TypeMode::Owned);

        if is_async {
            self.src
                .push_str("> where <S as wasmtime::AsContext>::Data: Send {\n");
        } else {
            self.src.push_str("> {\n");
        }

        if self.gen.opts.tracing {
            let ns = match ns {
                Some(key) => resolve.name_world_key(key),
                None => "default".to_string(),
            };
            self.src.push_str(&format!(
                "
                   let span = tracing::span!(
                       tracing::Level::TRACE,
                       \"wit-bindgen export\",
                       module = \"{ns}\",
                       function = \"{}\",
                   );
                   let _enter = span.enter();
               ",
                func.name,
            ));
        }

        self.src.push_str("let callee = unsafe {\n");
        self.src.push_str("wasmtime::component::TypedFunc::<(");
        for (_, ty) in func.params.iter() {
            self.print_ty(ty, TypeMode::AllBorrowed("'_"));
            self.push_str(", ");
        }
        self.src.push_str("), (");
        for ty in func.results.iter_types() {
            self.print_ty(ty, TypeMode::Owned);
            self.push_str(", ");
        }
        let projection_to_func = match &func.kind {
            FunctionKind::Freestanding => "",
            _ => ".funcs",
        };
        uwriteln!(
            self.src,
            ")>::new_unchecked(self{projection_to_func}.{})",
            func_field_name(self.resolve, func),
        );
        self.src.push_str("};\n");
        self.src.push_str("let (");
        for (i, _) in func.results.iter_types().enumerate() {
            uwrite!(self.src, "ret{},", i);
        }
        uwrite!(
            self.src,
            ") = callee.call{async__}(store.as_context_mut(), ("
        );
        for (i, _) in func.params.iter().enumerate() {
            uwrite!(self.src, "arg{}, ", i);
        }
        uwriteln!(self.src, ")){await_}?;");

        uwriteln!(
            self.src,
            "callee.post_return{async__}(store.as_context_mut()){await_}?;"
        );

        self.src.push_str("Ok(");
        if func.results.iter_types().len() == 1 {
            self.src.push_str("ret0");
        } else {
            self.src.push_str("(");
            for (i, _) in func.results.iter_types().enumerate() {
                uwrite!(self.src, "ret{},", i);
            }
            self.src.push_str(")");
        }
        self.src.push_str(")\n");

        // End function body
        self.src.push_str("}\n");
    }

    fn rustdoc(&mut self, docs: &Docs) {
        let docs = match &docs.contents {
            Some(docs) => docs,
            None => return,
        };
        for line in docs.trim().lines() {
            self.push_str("/// ");
            self.push_str(line);
            self.push_str("\n");
        }
    }

    fn path_to_root(&self) -> String {
        let mut path_to_root = String::new();
        if let Some((_, key, is_export)) = self.current_interface {
            match key {
                WorldKey::Name(_) => {
                    path_to_root.push_str("super::");
                }
                WorldKey::Interface(_) => {
                    path_to_root.push_str("super::super::super::");
                }
            }
            if is_export {
                path_to_root.push_str("super::");
            }
        }
        path_to_root
    }
}

impl<'a> RustGenerator<'a> for InterfaceGenerator<'a> {
    fn resolve(&self) -> &'a Resolve {
        self.resolve
    }

    fn ownership(&self) -> Ownership {
        self.gen.opts.ownership
    }

    fn path_to_interface(&self, interface: InterfaceId) -> Option<String> {
        if let Some((cur, _, _)) = self.current_interface {
            if cur == interface {
                return None;
            }
        }
        let mut path_to_root = self.path_to_root();
        match &self.gen.interface_names[&interface] {
            InterfaceName::Remapped { name_at_root, .. } => path_to_root.push_str(name_at_root),
            InterfaceName::Path(path) => {
                for (i, name) in path.iter().enumerate() {
                    if i > 0 {
                        path_to_root.push_str("::");
                    }
                    path_to_root.push_str(name);
                }
            }
        }
        Some(path_to_root)
    }

    fn push_str(&mut self, s: &str) {
        self.src.push_str(s);
    }

    fn info(&self, ty: TypeId) -> TypeInfo {
        self.gen.types.get(ty)
    }

    fn is_imported_interface(&self, interface: InterfaceId) -> bool {
        self.gen.interface_last_seen_as_import[&interface]
    }
}

/// When an interface `use`s a type from another interface, it creates a new TypeId
/// referring to the definition TypeId. Chase this chain of references down to
/// a TypeId for type's definition.
fn resolve_type_definition_id(resolve: &Resolve, mut id: TypeId) -> TypeId {
    loop {
        match resolve.types[id].kind {
            TypeDefKind::Type(Type::Id(def_id)) => id = def_id,
            _ => return id,
        }
    }
}

fn rust_function_name(func: &Function) -> String {
    match func.kind {
        FunctionKind::Method(_) | FunctionKind::Static(_) => to_rust_ident(func.item_name()),
        FunctionKind::Constructor(_) => "new".to_string(),
        FunctionKind::Freestanding => to_rust_ident(&func.name),
    }
}

fn func_field_name(resolve: &Resolve, func: &Function) -> String {
    let mut name = String::new();
    match func.kind {
        FunctionKind::Method(id) => {
            name.push_str("method-");
            name.push_str(resolve.types[id].name.as_ref().unwrap());
            name.push_str("-");
        }
        FunctionKind::Static(id) => {
            name.push_str("static-");
            name.push_str(resolve.types[id].name.as_ref().unwrap());
            name.push_str("-");
        }
        FunctionKind::Constructor(id) => {
            name.push_str("constructor-");
            name.push_str(resolve.types[id].name.as_ref().unwrap());
            name.push_str("-");
        }
        FunctionKind::Freestanding => {}
    }
    name.push_str(func.item_name());
    name.to_snake_case()
}

fn get_resources<'a>(resolve: &'a Resolve, id: InterfaceId) -> impl Iterator<Item = &'a str> + 'a {
    resolve.interfaces[id]
        .types
        .iter()
        .filter_map(move |(name, ty)| match resolve.types[*ty].kind {
            TypeDefKind::Resource => Some(name.as_str()),
            _ => None,
        })
}

fn get_world_resources<'a>(
    resolve: &'a Resolve,
    id: WorldId,
) -> impl Iterator<Item = &'a str> + 'a {
    resolve.worlds[id]
        .imports
        .iter()
        .filter_map(move |(name, item)| match item {
            WorldItem::Type(id) => match resolve.types[*id].kind {
                TypeDefKind::Resource => Some(match name {
                    WorldKey::Name(s) => s.as_str(),
                    WorldKey::Interface(_) => unreachable!(),
                }),
                _ => None,
            },
            _ => None,
        })
}