plusplus-macros 0.2.0

use proc_macro_crate::{FoundCrate, crate_name};
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote};
use syn::parse::{Parse, ParseStream};
use syn::spanned::Spanned;
use syn::token::Brace;
use syn::{
    AngleBracketedGenericArguments, AttrStyle, CapturedParam, Error, GenericArgument, GenericParam,
    Lifetime, LifetimeParam, MacroDelimiter, Meta, Path, PathArguments, ReturnType, Signature,
    Token, TypeParamBound, parse2,
};
use syn::{
    Attribute, Field, FnArg, Ident, ImplItemFn, Pat, Type, Visibility, braced, parse_macro_input,
    parse_quote,
};

mod kw {
    syn::custom_keyword!(class);
}

#[derive(Debug, Clone)]
struct OverrideItem {
    _override_token: Token![override],
    override_class: Type,
    _brace_token: Brace,
    items: Vec<ImplItemFn>,
}

fn correct_priv_vis(vis: Visibility) -> Visibility {
    match vis {
        Visibility::Public(p) => Visibility::Public(p),
        Visibility::Restricted(mut restricted) => {
            if restricted.path.segments.get(0) != Some(&parse_quote!(crate)) {
                restricted.path.segments.insert(0, parse_quote!(super));
            }
            Visibility::Restricted(restricted)
        }
        Visibility::Inherited => {
            parse_quote!(pub(super))
        }
    }
}

impl Parse for OverrideItem {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let content;
        let override_token = input.parse()?;
        let override_class = input.parse()?;
        let brace_token = braced!(content in input);
        let mut items = Vec::new();
        while !content.is_empty() {
            let mut item: ImplItemFn = content.parse()?;
            item.vis = correct_priv_vis(item.vis);
            items.push(item);
        }

        Ok(OverrideItem {
            _override_token: override_token,
            override_class,
            _brace_token: brace_token,
            items,
        })
    }
}

#[derive(Debug, Clone)]
enum ClassItem {
    Field {
        field: Field,
        _semi_token: Token![;],
    },
    ImplItemFn(ImplItemFn),
    OverrideItem(OverrideItem),
}

impl Parse for ClassItem {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let lookahead = input.lookahead1();
        if lookahead.peek(Token![override]) {
            return Ok(ClassItem::OverrideItem(OverrideItem::parse(input)?));
        }

        let begin = input.fork();
        let _attrs = input.call(Attribute::parse_outer)?;
        let _vis: Visibility = begin.parse()?;
        let lookahead = begin.lookahead1();
        if lookahead.peek(Token![fn])
            || lookahead.peek(Token![unsafe])
            || lookahead.peek(Token![async])
        {
            return Ok(ClassItem::ImplItemFn(ImplItemFn::parse(input)?));
        }

        let mut field = Field::parse_named(input)?;
        field.vis = correct_priv_vis(field.vis);
        let semi_token = input.parse()?;
        Ok(ClassItem::Field {
            field,
            _semi_token: semi_token,
        })
    }
}

#[derive(Debug, Clone)]
struct SuperclassInput {
    _colon_token: Token![:],
    ty: Type,
}

impl Parse for SuperclassInput {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        Ok(SuperclassInput {
            _colon_token: input.parse()?,
            ty: input.parse()?,
        })
    }
}

#[derive(Debug, Clone)]
struct ClassInput {
    attrs: Vec<Attribute>,
    vis: Visibility,
    _class_token: kw::class,
    ident: Ident,
    superclass: Option<SuperclassInput>,
    _brace_token: Brace,
    items: Vec<ClassItem>,
}

impl Parse for ClassInput {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let attrs = input.call(Attribute::parse_outer)?;
        let content;
        let vis = input.parse()?;
        let class_token = input.parse()?;
        let ident = input.parse()?;

        let lookahead = input.lookahead1();
        let superclass = if lookahead.peek(Token![:]) {
            Some(input.parse()?)
        } else {
            None
        };

        let brace_token = braced!(content in input);
        let mut items = Vec::new();
        while !content.is_empty() {
            items.push(content.parse()?);
        }
        Ok(ClassInput {
            attrs,
            vis,
            _class_token: class_token,
            ident,
            superclass,
            _brace_token: brace_token,
            items,
        })
    }
}

#[derive(Debug, Clone)]
struct CrateAlias {
    _crate_token: Token![crate],
    _as_token: Token![as],
    ident: Ident,
    _semi_token: Token![;],
}

impl Parse for CrateAlias {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        Ok(CrateAlias {
            _crate_token: input.parse()?,
            _as_token: input.parse()?,
            ident: input.parse()?,
            _semi_token: input.parse()?,
        })
    }
}

struct ClassInputs {
    crate_alias: Option<CrateAlias>,
    inputs: Vec<ClassInput>,
}

impl Parse for ClassInputs {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let lookahead = input.lookahead1();
        let crate_alias = if lookahead.peek(Token![crate]) {
            Some(input.parse()?)
        } else {
            None
        };

        let mut inputs = Vec::new();
        while !input.is_empty() {
            inputs.push(input.parse()?);
        }

        Ok(ClassInputs {
            crate_alias,
            inputs,
        })
    }
}

fn plusplus() -> proc_macro2::TokenStream {
    let found_crate = crate_name("plusplus").expect("plusplus is present in `Cargo.toml`");
    match found_crate {
        FoundCrate::Itself => quote!(crate),
        FoundCrate::Name(name) => {
            let ident = Ident::new(&name, Span::call_site());
            quote!( #ident )
        }
    }
}

fn cast_class_ptr(
    plusplus: &proc_macro2::TokenStream,
    from: &Type,
    to: &Type,
    expr: impl Into<proc_macro2::TokenStream>,
) -> proc_macro2::TokenStream {
    let expr = expr.into();
    quote! {{
        let t: &#from = #expr;
        let self_size = std::mem::size_of_val(t);
        let target_size = std::mem::size_of::<#to<#plusplus::InConstruction>>();
        assert!(self_size >= target_size);
        let array_size = self_size - target_size;
        let target_ptr = std::ptr::slice_from_raw_parts(t as *const #from as *const u8, array_size);
        let target_ref = &*(target_ptr as *const #to);
        assert_eq!(self_size, std::mem::size_of_val(target_ref));
        target_ref
    }}
}

fn cast_class_ptr_mut(
    plusplus: &TokenStream,
    from: &Type,
    to: &Type,
    expr: impl Into<TokenStream>,
) -> TokenStream {
    let expr = expr.into();
    quote! {{
        let t: &mut #from = #expr;
        let self_size = std::mem::size_of_val(t);
        let target_size = std::mem::size_of::<#to<#plusplus::InConstruction>>();
        assert!(self_size >= target_size);
        let array_size = self_size - target_size;
        let target_ptr = std::ptr::slice_from_raw_parts_mut(t as *mut #from as *mut u8, array_size);
        let target_ref = &mut *(target_ptr as *mut #to);
        assert_eq!(self_size, std::mem::size_of_val(target_ref));
        target_ref
    }}
}

fn set_arg_blank_lifetime(arg: &mut FnArg, lifetime: &Lifetime, lifetime_set: &mut bool) {
    match arg {
        FnArg::Receiver(rx) => {
            if let Some((_, lt)) = &mut rx.reference {
                maybe_set_lifetime_opt(lt, lifetime, lifetime_set);
            }
        }
        FnArg::Typed(ty) => {
            set_blank_type_lifetimes(&mut ty.ty, lifetime, lifetime_set);
        }
    }
}

fn set_blank_type_lifetimes(ty: &mut Type, lifetime: &Lifetime, lifetime_set: &mut bool) {
    match ty {
        Type::Array(arr) => set_blank_type_lifetimes(&mut arr.elem, lifetime, lifetime_set),
        Type::BareFn(_) => {}
        Type::Group(group) => set_blank_type_lifetimes(&mut group.elem, lifetime, lifetime_set),
        Type::ImplTrait(_) => {} // technically we should implement this but it doesn't come up in our use
        Type::Infer(_) => {}
        Type::Macro(_) => {}
        Type::Never(_) => {}
        Type::Paren(paren) => set_blank_type_lifetimes(&mut paren.elem, lifetime, lifetime_set),
        Type::Path(path) => {
            if let Some(qself) = &mut path.qself {
                set_blank_type_lifetimes(&mut qself.ty, lifetime, lifetime_set);
            }
            set_blank_path_lifetimes(&mut path.path, lifetime, lifetime_set);
        }
        Type::Ptr(ptr) => set_blank_type_lifetimes(&mut ptr.elem, lifetime, lifetime_set),
        Type::Reference(refer) => {
            maybe_set_lifetime_opt(&mut refer.lifetime, lifetime, lifetime_set);
            set_blank_type_lifetimes(&mut refer.elem, lifetime, lifetime_set)
        }
        Type::Slice(slice) => set_blank_type_lifetimes(&mut slice.elem, lifetime, lifetime_set),
        Type::TraitObject(obj) => {
            set_blank_type_param_bounds(&mut obj.bounds, lifetime, lifetime_set)
        }
        Type::Tuple(tup) => {
            for ty in &mut tup.elems {
                set_blank_type_lifetimes(ty, lifetime, lifetime_set);
            }
        }
        Type::Verbatim(_) => {}
        _ => (),
    }
}

fn set_blank_path_lifetimes(path: &mut Path, lifetime: &Lifetime, lifetime_set: &mut bool) {
    for path_args in path.segments.iter_mut().map(|seg| &mut seg.arguments) {
        match path_args {
            PathArguments::None => {}
            PathArguments::AngleBracketed(angle_args) => {
                set_blank_angle_bracket_lifetimes(angle_args, lifetime, lifetime_set)
            }
            PathArguments::Parenthesized(paren_args) => {
                for ty in &mut paren_args.inputs {
                    set_blank_type_lifetimes(ty, lifetime, lifetime_set);
                }
                if let ReturnType::Type(_, ty) = &mut paren_args.output {
                    set_blank_type_lifetimes(ty, lifetime, lifetime_set);
                }
            }
        }
    }
}

fn set_blank_angle_bracket_lifetimes(
    angle: &mut AngleBracketedGenericArguments,
    lifetime: &Lifetime,
    lifetime_set: &mut bool,
) {
    for arg in &mut angle.args {
        set_blank_generic_lifetimes(arg, lifetime, lifetime_set);
    }
}

fn maybe_set_lifetime(set: &mut Lifetime, to: &Lifetime, lifetime_set: &mut bool) {
    if set.ident == format_ident!("_") {
        *set = to.clone();
        *lifetime_set = true;
    }
}
fn maybe_set_lifetime_opt(set: &mut Option<Lifetime>, to: &Lifetime, lifetime_set: &mut bool) {
    match set {
        Some(lt) => maybe_set_lifetime(lt, to, lifetime_set),
        None => {
            *set = Some(to.clone());
            *lifetime_set = true;
        }
    }
}

fn set_blank_type_param_bounds<'a>(
    bounds: impl IntoIterator<Item = &'a mut TypeParamBound>,
    lifetime: &Lifetime,
    lifetime_set: &mut bool,
) {
    for bound in bounds {
        match bound {
            TypeParamBound::Trait(trait_bound) => {
                set_blank_path_lifetimes(&mut trait_bound.path, lifetime, lifetime_set)
            }
            TypeParamBound::Lifetime(lt) => maybe_set_lifetime(lt, lifetime, lifetime_set),
            TypeParamBound::PreciseCapture(cap) => {
                for p in &mut cap.params {
                    match p {
                        CapturedParam::Lifetime(lt) => {
                            maybe_set_lifetime(lt, lifetime, lifetime_set)
                        }
                        CapturedParam::Ident(_) => {}
                        _ => (),
                    }
                }
            }
            TypeParamBound::Verbatim(_) => {}
            _ => (),
        }
    }
}
fn set_blank_generic_lifetimes(
    arg: &mut GenericArgument,
    lifetime: &Lifetime,
    lifetime_set: &mut bool,
) {
    match arg {
        GenericArgument::Lifetime(lt) => maybe_set_lifetime(lt, lifetime, lifetime_set),
        GenericArgument::Type(ty) => set_blank_type_lifetimes(ty, lifetime, lifetime_set),
        GenericArgument::Const(_) => {}
        GenericArgument::AssocType(ty) => {
            if let Some(args) = &mut ty.generics {
                set_blank_angle_bracket_lifetimes(args, lifetime, lifetime_set);
            }
            set_blank_type_lifetimes(&mut ty.ty, lifetime, lifetime_set);
        }
        GenericArgument::AssocConst(_) => {}
        GenericArgument::Constraint(constraint) => {
            if let Some(args) = &mut constraint.generics {
                set_blank_angle_bracket_lifetimes(args, lifetime, lifetime_set);
            }

            set_blank_type_param_bounds(&mut constraint.bounds, lifetime, lifetime_set);
        }
        _ => (),
    }
}

#[derive(Debug, Clone)]
struct FuncInfo {
    func: ImplItemFn,
    name: Ident,
    vtbl_name: Ident,
    lifetime_bounds: Option<TokenStream>,
    vtbl_sig: TokenStream,
    args: Vec<Box<Pat>>,
    mut_self: bool,
}

fn get_func_sig(class_name: &Type, f: &ImplItemFn) -> FuncInfo {
    let func_name = &f.sig.ident;
    let is_async = f.sig.asyncness.is_some();

    let mut inputs = f.sig.inputs.clone();
    let mut mut_self = false;
    if let Some(FnArg::Receiver(rx)) = &f.sig.inputs.get(0) {
        let receiver = &mut inputs[0];
        if let Some((_, rx_lifetime)) = &rx.reference {
            if rx.mutability.is_some() {
                *receiver = FnArg::Typed(parse_quote!(this: & #rx_lifetime mut #class_name));
            } else {
                *receiver = FnArg::Typed(parse_quote!(this: & #rx_lifetime #class_name));
            }
        }
        mut_self = rx.mutability.is_some();
    };

    let mut lifetimes: Vec<LifetimeParam> = Vec::new();
    let future_fallback_lt: Lifetime = parse_quote!('rpp_future);
    let mut using_future_lifetime = false;
    let mut vtbl_inputs = inputs.clone();
    // eprintln!("inputs = {:#?}", vtbl_inputs);
    if is_async {
        for arg in &mut vtbl_inputs {
            set_arg_blank_lifetime(arg, &future_fallback_lt, &mut using_future_lifetime);
        }
        if using_future_lifetime {
            lifetimes.push(parse_quote!(#future_fallback_lt));
        }
    }
    for generic in &f.sig.generics.params {
        match generic {
            GenericParam::Lifetime(lt) => {
                let mut lt = lt.clone();
                if using_future_lifetime {
                    lt.bounds.push(future_fallback_lt.clone());
                }
                lifetimes.push(lt)
                // if using_future_lifetime {
                //     lifetimes.push(parse_quote!(#lt: #future_fallback_lt));
                // } else {
                //     lifetimes.push(parse_quote!(#lt));
                // }
            }
            GenericParam::Type(_) => {}
            GenericParam::Const(_) => {}
        }
    }

    let lifetime_bounds = if lifetimes.len() > 0 {
        Some(quote!(<#(#lifetimes),*>))
    } else {
        None
    };

    let mut output = f.sig.output.clone();
    if is_async {
        let future_output = match output {
            ReturnType::Default => quote!(()),
            ReturnType::Type(_, ty) => quote!(#ty),
        };
        let future_lifetimes = if using_future_lifetime {
            future_fallback_lt
        } else {
            assert!(lifetimes.len() > 0);
            lifetimes[0].lifetime.clone()
        };
        output = parse_quote!(-> std::pin::Pin<Box<dyn #future_lifetimes + Future<Output=#future_output>>>);
    }
    let vtbl_name = format_ident!("fn_{func_name}");
    let vtbl_sig = quote! {
        (#vtbl_inputs) #output
    };

    let func_args = inputs
        .into_iter()
        .skip(1)
        .map(|arg| match arg {
            FnArg::Receiver(_) => unreachable!(),
            FnArg::Typed(arg) => arg.pat,
        })
        .collect::<Vec<_>>();

    FuncInfo {
        func: f.clone(),
        name: func_name.clone(),
        vtbl_name,
        lifetime_bounds,
        vtbl_sig,
        args: func_args,
        mut_self,
    }
}

#[derive(Debug, Clone, Copy)]
struct Derives {
    clone: bool,
}

impl Derives {
    fn from_attributes(attrs: impl Iterator<Item = Attribute>) -> syn::Result<Derives> {
        let mut clone = false;
        for attr in attrs {
            if let AttrStyle::Inner(_) = attr.style {
                return Err(Error::new(
                    attr.span(),
                    "did not expect inner attribute in class macro",
                ));
            }

            let derive_tokens = match attr.meta {
                Meta::List(list) if list.path == parse_quote!(derive) => {
                    if !matches!(list.delimiter, MacroDelimiter::Paren(_)) {
                        return Err(Error::new(
                            list.delimiter.span().open(),
                            "derive attribute must have parenthesis",
                        ));
                    }
                    list.tokens
                }
                _ => return Err(Error::new(attr.span(), "unsupported attribute on class")),
            };

            let derive_path: Path = parse2(derive_tokens)?;
            if derive_path == parse_quote!(Clone) {
                if clone {
                    return Err(Error::new(
                        derive_path.span(),
                        "Clone derive already specified",
                    ));
                }
                clone = true;
            }
        }

        Ok(Derives { clone })
    }

    fn has_any_derives(&self) -> bool {
        self.clone
    }
}

struct ClassData {
    plusplus: TokenStream,
    class_name: Ident,
    class_type: Type,
    class_mod_name: Ident,
    vtbl_ident: Ident,
    class_vis: Visibility,
    fields: Vec<Field>,
    constructors: Vec<FuncInfo>,
    member_funcs: Vec<FuncInfo>,
    overrides: Vec<OverrideItem>,
    override_funcs: Vec<FuncInfo>,
    superclass_type: Option<Type>,
    mod_superclass_type: Option<Type>,
    derives: Derives,
}

impl ClassData {
    fn from_input(input: ClassInput, crate_alias: Option<&CrateAlias>) -> syn::Result<ClassData> {
        let ClassInput {
            attrs,
            vis: class_vis,
            _class_token: _,
            ident: class_name,
            superclass,
            _brace_token: _,
            items: class_items,
        } = input;

        let mut fields = Vec::new();
        let mut constructors = Vec::new();
        let mut member_funcs = Vec::new();
        let mut overrides = Vec::new();
        let mut override_funcs = Vec::new();

        let class_type: Type = parse_quote!(#class_name);

        for item in class_items {
            match item {
                ClassItem::Field { field, .. } => fields.push(field),
                ClassItem::ImplItemFn(func) => {
                    if let Some(FnArg::Receiver(_)) = func.sig.inputs.get(0) {
                        member_funcs.push(get_func_sig(&class_type, &func))
                    } else {
                        constructors.push(get_func_sig(&class_type, &func));
                    }
                }
                ClassItem::OverrideItem(override_item) => {
                    override_funcs.extend(
                        override_item
                            .items
                            .iter()
                            .map(|f| get_func_sig(&class_type, &f)),
                    );
                    overrides.push(override_item);
                }
            }
        }

        let class_mod_name =
            format_ident!("plusplus__class_{}", class_name.to_string().to_lowercase());

        let plusplus = if let Some(alias) = crate_alias {
            let alias = &alias.ident;
            quote!(#alias)
        } else {
            plusplus()
        };

        let superclass_type = superclass.map(|sc| sc.ty);
        let mod_superclass_type = match superclass_type.clone() {
            Some(Type::Path(mut type_path)) => {
                if type_path.path.segments.get(0) != Some(&parse_quote!(crate)) {
                    type_path.path.segments.insert(0, parse_quote!(super));
                }
                Some(Type::Path(type_path))
            }
            ty => ty,
        };

        let derives = Derives::from_attributes(attrs.into_iter())?;

        Ok(ClassData {
            plusplus,
            vtbl_ident: format_ident!("{}Vtbl", class_name),
            class_vis,
            class_name,
            class_type,
            class_mod_name,
            fields,
            constructors,
            member_funcs,
            overrides,
            override_funcs,
            superclass_type,
            mod_superclass_type,
            derives,
        })
    }

    fn has_superclass(&self) -> bool {
        self.superclass_type.is_some()
    }

    fn gen_mod_vtbl_struct(&self) -> TokenStream {
        // create vtbl
        let vtbl_ident = &self.vtbl_ident;
        let class_name = &self.class_name;
        let plusplus = &self.plusplus;

        let mut vtbl_func_names = Vec::new();
        let mut vtbl_sigs = Vec::new();
        let mut my_func_names = Vec::new();
        let mut async_func_impls = Vec::new();
        let mut func_setters = Vec::new();
        let mut vtbl_fors = Vec::new();
        let mut vtbl_unsafes = Vec::new();

        for f in self.member_funcs.iter() {
            let FuncInfo {
                func:
                    ImplItemFn {
                        sig:
                            Signature {
                                asyncness,
                                unsafety,
                                ..
                            },
                        ..
                    },
                name: func_name,
                vtbl_name: vtbl_func_name,
                lifetime_bounds,
                vtbl_sig,
                args,
                mut_self: _,
            } = f;
            let my_func_name = format_ident!("my_{func_name}");
            let vtbl_for = lifetime_bounds.as_ref().map(|bounds| quote!(for #bounds));
            vtbl_fors.push(vtbl_for.clone());
            vtbl_unsafes.push(unsafety);

            if asyncness.is_some() {
                async_func_impls.push(quote!{
                    // fn #my_func_name #func_sig {
                    let #my_func_name: #vtbl_for #unsafety fn #vtbl_sig = |this, #(#args)*| #unsafety {
                        Box::pin(#class_name::#my_func_name(this, #(#args)*))
                    };
                });
                func_setters.push(quote! {
                    #vtbl_func_name: #my_func_name,
                })
            } else {
                func_setters.push(quote! {
                     #vtbl_func_name: #class_name::#my_func_name,
                })
            }

            my_func_names.push(my_func_name);
            vtbl_func_names.push(vtbl_func_name);
            vtbl_sigs.push(vtbl_sig);
        }

        let vtbl_drop_field: Option<_>;
        let vtbl_drop_func: Option<_>;
        let vtbl_drop_set: Option<_>;
        if !self.has_superclass() {
            vtbl_drop_field = Some(quote! {
                pub manually_drop: unsafe fn(*mut #class_name),
            });
            vtbl_drop_func = Some(quote! {
                unsafe fn manually_drop(this: *mut #class_name) {
                    unsafe{ std::ptr::drop_in_place(this) }
                }
            });
            vtbl_drop_set = Some(quote! {
                manually_drop,
            });
        } else {
            vtbl_drop_field = None;
            vtbl_drop_func = None;
            vtbl_drop_set = None;
        };

        let mut vtbl_trait_fields = None;
        let mut vtbl_trait_impls = None;
        let mut vtbl_trait_setters = None;
        if self.derives.has_any_derives() && !self.has_superclass() {
            let Derives { clone } = self.derives;
            let clone_field = clone.then(|| {
                quote! {
                    class_clone: fn(&#class_name) -> #plusplus::ClassBox<#class_name>,
                }
            });
            let clone_impl = clone.then(|| {
                quote! {
                    fn class_clone(this: &#class_name) -> #plusplus::ClassBox<#class_name> {
                        use #plusplus::{Class, ClassInConstruction};
                        let in_construction = unsafe{ this.as_in_construction() };
                        in_construction.clone().finish()
                    }
                }
            });
            let clone_set = clone.then(|| {
                quote! {
                    class_clone,
                }
            });
            vtbl_trait_fields = Some(quote! {
                #clone_field
            });
            vtbl_trait_impls = Some(quote! {
                #clone_impl
            });
            vtbl_trait_setters = Some(quote! {
                #clone_set
            })
        };

        quote! {
            #[doc(hidden)]
            #[derive(Clone, Copy)]
            pub struct #vtbl_ident {
                #vtbl_drop_field
                #vtbl_trait_fields
                #(pub #vtbl_func_names: #vtbl_fors #vtbl_unsafes fn #vtbl_sigs,)*
            }

            impl #vtbl_ident {
                const BASE: Self = {
                    #vtbl_drop_func
                    #vtbl_trait_impls
                    #(#async_func_impls)*

                    Self {
                        #vtbl_drop_set
                        #vtbl_trait_setters
                        #(#func_setters)*
                    }
                };
            }
        }
    }

    fn gen_fn_set_vtbls(&self) -> TokenStream {
        let plusplus = &self.plusplus;
        let class_name = &self.class_name;

        let set_vtbls = self.overrides.iter().map(|ovr| {
            let ovr_class = &ovr.override_class;
            let ovr_class = match ovr_class.clone() {
                Type::Path(mut type_path) => {
                    type_path.path.segments.insert(0, parse_quote!(super));
                    Type::Path(type_path)
                }
                ty => ty,
            };

            let mut ol_func_names = Vec::new();
            let mut ol_func_sigs = Vec::new();
            let mut ol_func_self_call_impls = Vec::new();
            let mut ol_lifetime_bounds = Vec::new();
            for f in &ovr.items {
                let FuncInfo {
                    func:
                        ImplItemFn {
                            sig:
                                Signature {
                                    asyncness,
                                    unsafety,
                                    ..
                                },
                            ..
                        },
                    name: func_name,
                    vtbl_name,
                    lifetime_bounds,
                    vtbl_sig: func_sig,
                    args: func_args,
                    mut_self,
                } = get_func_sig(&ovr_class, f);
                ol_func_names.push(vtbl_name);
                ol_func_sigs.push(func_sig);
                ol_lifetime_bounds.push(lifetime_bounds);

                let func_name = format_ident!("my_{}", func_name);
                let make_this = if mut_self {
                    quote! {
                        let this: &mut #class_name = unsafe{ #class_name::from_root_class_mut(this.root_class_mut()) };
                    }
                } else {
                    quote! {
                        let this: &#class_name = unsafe{ #class_name::from_root_class_ref(this.root_class()) };
                    }
                };
                let self_call = if asyncness.is_some() {
                    quote! {
                        #make_this
                        #unsafety { Box::pin(this.#func_name(#(#func_args,)*)) }
                    }
                } else {
                    quote! {
                        #make_this
                        #unsafety { this.#func_name(#(#func_args,)*) }
                    }
                };
                ol_func_self_call_impls.push(self_call);
            }

            quote! {{
                let this: &mut #ovr_class = &mut *(unsafe{ self.to_constructed() });
                #(
                    fn #ol_func_names #ol_lifetime_bounds #ol_func_sigs {
                        #ol_func_self_call_impls
                    }
                    unsafe{ this.plusplus__vtbl_mut().#ol_func_names = #ol_func_names };
                )*
            }}
        });

        let root_type: Type = parse_quote!(<#class_name as #plusplus::Class>::RootClass);
        let root_type = &root_type;

        let set_subclass = self.has_superclass().then(|| quote!{
            use #plusplus::Class as _;
            unsafe{ self.superclass.plusplus__set_subclass(<#class_name as #plusplus::Class>::TYPE_ID) };

            {
                unsafe fn manually_drop(this: *mut #root_type) {
                    let this = unsafe{ #class_name::from_root_class_mut(&mut *this) };
                    unsafe{ std::ptr::drop_in_place(this) };
                }
                let root_vtbl = unsafe{ <#class_name as #plusplus::Class>::root_class_mut(self.to_constructed()).plusplus__vtbl_mut() };
                root_vtbl.manually_drop = manually_drop;
            }
        });

        let mut set_trait_vtbls = None;
        if !self.has_superclass() {
            let mut derive_trait_bounds = None;
            let mut derive_trait_impls = None;
            if self.derives.has_any_derives() {
                let Derives { clone } = self.derives;
                let clone_trait_bound = clone.then(|| quote!(Clone));
                let clone_impl = clone.then(|| quote!{
                    let class_clone = |this: &#class_name| -> #plusplus::ClassBox<#class_name> {
                        use #plusplus::{Class as _, ClassBox, ClassInConstruction};
                        let child_class = unsafe{ Class::from_root_class_ref(this).as_in_construction() };
                        let cloned = child_class.clone().finish();
                        unsafe{ ClassBox::from_raw(ClassBox::leak(cloned).root_class_mut()) }
                    };
                    self.vtbl.class_clone = class_clone;
                });
                derive_trait_bounds =
                    Some(quote! {where Class::InConstruction: #clone_trait_bound});
                derive_trait_impls = Some(quote! {
                    #clone_impl
                });
            }

            set_trait_vtbls = Some(quote! {
                #[doc(hidden)]
                pub fn plusplus__set_trait_vtbls<Class: ?Sized + #plusplus::Class<RootClass=#class_name>>(&mut self)
                #derive_trait_bounds
                {
                    #derive_trait_impls
                }
            });
        }

        quote! {
            fn plusplus__set_vtbls(&mut self) {
                #set_subclass
                #(#set_vtbls)*
            }

            #set_trait_vtbls
        }
    }

    fn gen_mod_class_struct(&self) -> TokenStream {
        let plusplus = &self.plusplus;

        let superclass_field = self.mod_superclass_type.as_ref().map(|sc_type| {
            quote! {
                superclass: #sc_type<#plusplus::InConstruction>,
            }
        });
        let superclass_field = superclass_field.as_ref();
        let superclass_bound = self.mod_superclass_type.as_ref().map(|sc_ident| {
            quote! {
                where #sc_ident: #plusplus::Class
            }
        });

        let class_struct_vis = correct_priv_vis(self.class_vis.clone());
        let vtbl_ident = &self.vtbl_ident;
        let class_name = &self.class_name;
        let fields = &self.fields;
        let init_superclass_field = superclass_field.map(|f| quote!(pub #f));
        let init_fields = self.fields.iter().cloned().map(|f| Field {
            vis: Visibility::Public(parse_quote!(pub)),
            ..f
        });

        let derives = self.derives.has_any_derives().then(|| {
            let Derives { clone } = self.derives;
            let clone = clone.then(|| quote!(Clone,));
            quote!(#[derive(#clone)])
        });

        quote! {
            #[repr(C)]
            #derives
            #class_struct_vis struct #class_name<C: ?Sized + #plusplus::ClassMemory = #plusplus::Constructed>
                #superclass_bound
            {
                #superclass_field
                vtbl: #vtbl_ident,
                // we store a reference to a type ID instead of a type ID as a size optimization;
                // an Option<TypeId> is 24 bytes, while an Option<&TypeId> is 8 bytes
                subclass_id: Option<&'static std::any::TypeId>,
                #(#fields,)*
                memory: C,
            }

            pub struct PlusPlus__InitClass {
                #init_superclass_field
                #(#init_fields,)*
            }
        }
    }

    fn gen_mod_trait_impls(&self) -> TokenStream {
        let plusplus = &self.plusplus;
        let class_name = &self.class_name;

        let Derives { clone } = self.derives;

        let clone_impl = clone.then(|| {
            if self.has_superclass() {
                quote! {
                    impl #plusplus::ClassClone for #class_name {
                        fn class_clone(&self) -> #plusplus::ClassBox<Self> {
                            use #plusplus::{ClassBox, Class, ClassClone};
                            let root_ref: &mut _ = ClassBox::leak(self.root_class().class_clone());
                            let self_ref = unsafe{ Self::from_root_class_mut(root_ref) };
                            unsafe{ ClassBox::from_raw(self_ref) }
                        }
                    }
                }
            } else {
                quote! {
                    impl #plusplus::ClassClone for #class_name {
                        fn class_clone(&self) -> #plusplus::ClassBox<Self> {
                            (self.vtbl.class_clone)(self)
                        }
                    }
                }
            }
        });

        quote! {
            #clone_impl
        }
    }

    fn gen_superclass_casters(&self) -> Option<TokenStream> {
        let Some(sc_type) = self.superclass_type.as_ref() else {
            return None;
        };
        let class_name = &self.class_name;

        let deref_upcast = cast_class_ptr(&self.plusplus, &self.class_type, sc_type, quote! {self});
        let deref_upcast_mut =
            cast_class_ptr_mut(&self.plusplus, &self.class_type, sc_type, quote! {self});
        let ref_downcast = cast_class_ptr(&self.plusplus, sc_type, &self.class_type, quote! {self});
        let ref_downcast_mut =
            cast_class_ptr_mut(&self.plusplus, sc_type, &self.class_type, quote! {self});

        let plusplus = &self.plusplus;
        Some(quote! {
            impl std::ops::Deref for #class_name {
                type Target = #sc_type;

                fn deref(&self) -> &Self::Target {
                    unsafe { #deref_upcast }
                }
            }

            impl std::ops::DerefMut for #class_name {
                fn deref_mut(&mut self) -> &mut Self::Target {
                    unsafe { #deref_upcast_mut }
                }
            }

            impl<'a> #plusplus::Downcast<#class_name> for &'a #sc_type {
                type Wrapped = &'a #class_name;
                fn downcast(self) -> Result<&'a #class_name, Self> {
                    use #plusplus::Class;
                    let subclass_type_id = <#class_name as #plusplus::Class>::TYPE_ID;
                    if self.subclass_id() == Some(subclass_type_id) {
                        Ok(unsafe{ #ref_downcast })
                    } else {
                        Err(self)
                    }
                }
            }

            impl<'a> #plusplus::Downcast<#class_name> for &'a mut #sc_type {
                type Wrapped = &'a mut #class_name;
                fn downcast(self) -> Result<&'a mut #class_name, Self> {
                    use #plusplus::Class;
                    let subclass_type_id = <#class_name as #plusplus::Class>::TYPE_ID;
                    if self.subclass_id() == Some(subclass_type_id) {
                        Ok(unsafe{ #ref_downcast_mut })
                    } else {
                        Err(self)
                    }
                }
            }
        })
    }

    fn gen_mod_impl_class_trait(&self) -> TokenStream {
        let plusplus = &self.plusplus;
        let class_name = &self.class_name;
        let root_class = self
            .mod_superclass_type
            .as_ref()
            .map(|sc_ident| quote! { <#sc_ident as #plusplus::Class>::RootClass })
            .unwrap_or_else(|| quote! { #class_name });

        let from_root_class_ref = cast_class_ptr(
            plusplus,
            &parse_quote!(#root_class),
            &parse_quote!(#class_name),
            quote!(root),
        );
        let from_root_class_mut = cast_class_ptr_mut(
            plusplus,
            &parse_quote!(#root_class),
            &parse_quote!(#class_name),
            quote!(root),
        );


        quote! {
            unsafe impl #plusplus::Class for #class_name {
                const TYPE_ID: &'static std::any::TypeId = &std::any::TypeId::of::<#class_name>();

                type RootClass = #root_class;
                type InConstruction = #class_name<#plusplus::InConstruction>;

                fn subclass_id(&self) -> Option<&'static std::any::TypeId> {
                    self.subclass_id
                }

                fn root_class(&self) -> &Self::RootClass {
                    self
                }

                fn root_class_mut(&mut self) -> &mut Self::RootClass {
                    self
                }

                unsafe fn manually_drop(slot: &mut std::mem::ManuallyDrop<Self>) {
                    let as_root_class = slot.root_class_mut();
                    let manual_drop_fn = unsafe{ as_root_class.plusplus__vtbl_mut().manually_drop };
                    unsafe{ manual_drop_fn(as_root_class); }
                }
                unsafe fn as_in_construction(&self) -> &#class_name<#plusplus::InConstruction> {
                    unsafe{ &*(self as *const Self as *const #class_name<#plusplus::InConstruction>) }
                }
                unsafe fn as_in_construction_mut(&mut self) -> &mut #class_name<#plusplus::InConstruction> {
                    unsafe{ &mut *(self as *mut Self as *mut #class_name<#plusplus::InConstruction>) }
                }
                unsafe fn from_root_class_ref(root: &Self::RootClass) -> &Self {
                    unsafe{ #from_root_class_ref }
                }
                unsafe fn from_root_class_mut(root: &mut Self::RootClass) -> &mut Self {
                    unsafe{ #from_root_class_mut }
                }
            }

            impl #plusplus::ClassInConstruction for #class_name<#plusplus::InConstruction> {
                type Class = #class_name;

                /// Finish constructing this by moving it to the heap placing it in a `ClassBox`.
                ///
                /// Downcasting, upcasting, and deref coersions will work properly after calling this!
                fn finish(self) -> #plusplus::ClassBox<#class_name> {
                    let boxed = Box::new(self);
                    let leaked = Box::leak(boxed);
                    let constructed = unsafe{ leaked.to_constructed() };
                    unsafe{ #plusplus::ClassBox::from_raw(constructed) }
                }
            }
        }
    }

    fn gen_mod_class_impl(&self) -> TokenStream {
        let class_name = &self.class_name;
        let vtbl_ident = &self.vtbl_ident;

        let mut call_vtbl_impls = Vec::new();
        for f in self.member_funcs.iter() {
            let FuncInfo {
                func: ImplItemFn { vis, sig, .. },
                name: _,
                vtbl_name,
                lifetime_bounds: _,
                vtbl_sig: _,
                args: func_args,
                mut_self: _,
            } = f;

            let vis = correct_priv_vis(vis.clone());
            let do_await = sig.asyncness.is_some().then(|| quote!(.await));
            let call_vtbl = quote! {
                #vis #sig {
                    (self.vtbl.#vtbl_name)(self, #(#func_args,)*) #do_await
                }
            };
            call_vtbl_impls.push(call_vtbl);
        }

        let mut my_func_impls = Vec::new();
        let mut super_func_impls = Vec::new();

        for (f, is_override) in self
            .member_funcs
            .iter()
            .cloned()
            .map(|f| (f, false))
            .chain(self.override_funcs.iter().cloned().map(|f| (f, true)))
        {
            let FuncInfo {
                func:
                    ImplItemFn {
                        attrs: _,
                        vis,
                        defaultness: _,
                        sig,
                        block,
                    },
                name: func_name,
                vtbl_name: _,
                lifetime_bounds: _,
                vtbl_sig: _,
                args: func_args,
                mut_self,
            } = f;

            let my_impl_name = format_ident!("my_{}", func_name);
            let mut my_impl_sig = sig.clone();
            my_impl_sig.ident = my_impl_name.clone();
            my_func_impls.push(quote! {
                #vis #my_impl_sig {
                    #block
                }
            });

            if is_override {
                let super_impl_name = format_ident!("super_{}", func_name);
                let mut super_impl_sig = sig.clone();
                super_impl_sig.ident = super_impl_name.clone();
                let get_super = if mut_self {
                    quote! {
                        self.plusplus__super_mut()
                    }
                } else {
                    quote! {
                        self.plusplus__super_ref()
                    }
                };
                let super_impl_block = if sig.asyncness.is_some() {
                    quote! { #get_super.#my_impl_name(#(#func_args,)*).await }
                } else {
                    quote! { #get_super.#my_impl_name(#(#func_args,)*) }
                };

                super_func_impls.push(quote! {
                    #vis #super_impl_sig {
                        #super_impl_block
                    }
                });
            }
        }

        let superclass_getters = self.mod_superclass_type.as_ref().map(|sc_ident| {
            quote! {
                fn plusplus__super_ref(&self) -> &#sc_ident {
                    self
                }

                fn plusplus__super_mut(&mut self) -> &mut #sc_ident {
                    self
                }
            }
        });

        quote! {
            impl #class_name {
                #(#call_vtbl_impls)*
                #(#super_func_impls)*

                #superclass_getters

                #[doc(hidden)]
                pub unsafe fn plusplus__vtbl_mut(&mut self) -> &mut #vtbl_ident {
                    &mut self.vtbl
                }
            }
        }
    }

    fn gen_mod_in_construction_class_impl(&self) -> TokenStream {
        let plusplus = &self.plusplus;
        let class_name = &self.class_name;
        let vtbl_ident = &self.vtbl_ident;

        let set_vtbl_func = self.gen_fn_set_vtbls();

        let superclass_field = self
            .has_superclass()
            .then(|| quote! {superclass: init.superclass,});
        let fields = self.fields.iter().map(|f| &f.ident).collect::<Vec<_>>();

        quote! {
            impl #class_name<#plusplus::InConstruction> {
                #set_vtbl_func

                pub(super) fn plusplus__new_from_init(init: PlusPlus__InitClass) -> Self {
                    use #plusplus::Class;
                    let mut this = Self {
                        vtbl: #vtbl_ident::BASE,
                        memory: #plusplus::InConstruction::default(),
                        subclass_id: None,
                        #superclass_field
                        #(#fields: init.#fields,)*
                    };

                    this.plusplus__set_vtbls();
                    unsafe{ this.to_constructed().root_class_mut().as_in_construction_mut() }.plusplus__set_trait_vtbls::<#class_name>();

                    this
                }

                #[doc(hidden)]
                pub unsafe fn plusplus__set_subclass(&mut self, subclass_id: &'static std::any::TypeId) {
                    self.subclass_id = Some(subclass_id);
                }

                /// Unsafe because caller must guarantee that vtbl doesn't contain any
                /// subclass methods
                pub unsafe fn to_constructed(&mut self) -> &mut #class_name {
                    unsafe{ &mut *(std::ptr::slice_from_raw_parts_mut::<u8>(self as *mut _ as *mut u8, 0) as *mut #class_name) }
                }
            }
        }
    }

    fn gen_init_class_macro(&self) -> TokenStream {
        let plusplus = &self.plusplus;
        let class_name = &self.class_name;
        let class_mod_name = &self.class_mod_name;

        quote! {
            macro_rules! init_class {
                ($($tt:tt)*) => {{
                    #class_name::<#plusplus::InConstruction>::plusplus__new_from_init(#class_mod_name::PlusPlus__InitClass {
                        $($tt)*
                    })
                }}
            }
        }
    }

    fn gen_class_impl(&self) -> TokenStream {
        let class_name = &self.class_name;
        let mut my_func_impls = Vec::new();
        for f in self
            .member_funcs
            .iter()
            .cloned()
            .chain(self.override_funcs.iter().cloned())
        {
            let FuncInfo {
                func:
                    ImplItemFn {
                        attrs: _,
                        vis,
                        defaultness: _,
                        sig,
                        block,
                    },
                name: func_name,
                vtbl_name: _,
                lifetime_bounds: _,
                vtbl_sig: _,
                args: _,
                mut_self: _,
            } = f;

            let my_impl_name = format_ident!("my_{}", func_name);
            let mut my_impl_sig = sig.clone();
            my_impl_sig.ident = my_impl_name.clone();
            my_func_impls.push(quote! {
                #vis #my_impl_sig {
                    #block
                }
            });
        }

        let init_class_macro = self.gen_init_class_macro();
        let mut constructor_impls = Vec::new();
        for c in self.constructors.iter() {
            let ImplItemFn {
                attrs,
                vis,
                defaultness,
                sig,
                block,
            } = &c.func;

            let vis = correct_priv_vis(vis.clone());
            constructor_impls.push(quote! {
                #(#attrs)* #vis #defaultness #sig {
                    #init_class_macro
                    #block
                }
            });
        }

        quote! {
            impl #class_name {
                #(#constructor_impls)*
                #(#my_func_impls)*
            }
        }
    }

    fn gen_class(&self) -> TokenStream {
        let class_vis = &self.class_vis;
        let class_name = &self.class_name;
        let class_mod_name = &self.class_mod_name;
        let mod_vtbl_struct = self.gen_mod_vtbl_struct();
        let mod_class_struct = self.gen_mod_class_struct();
        let mod_impl_class_trait = self.gen_mod_impl_class_trait();
        let mod_trait_impls = self.gen_mod_trait_impls();
        let superclass_cast = self.gen_superclass_casters();
        let mod_class_impl = self.gen_mod_class_impl();
        let mod_in_construction_class_impl = self.gen_mod_in_construction_class_impl();
        let class_impl = self.gen_class_impl();

        quote! {
            #class_vis use #class_mod_name::#class_name;
            mod #class_mod_name {
                use super::*;
                #mod_vtbl_struct
                #mod_class_struct

                #mod_class_impl

                #mod_impl_class_trait

                #mod_in_construction_class_impl

                #mod_trait_impls
            }

            #class_impl

            #superclass_cast
        }
    }
}

fn do_class(inputs: ClassInputs) -> syn::Result<TokenStream> {
    let class_data = inputs
        .inputs
        .into_iter()
        .map(|input| Ok(ClassData::from_input(input, inputs.crate_alias.as_ref())?.gen_class()))
        .collect::<Result<Vec<_>, syn::Error>>()?;

    Ok(quote! {
        #(#class_data)*
    })
}

/// The whole point.
#[proc_macro]
pub fn class(tokens: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let inputs = parse_macro_input!(tokens as ClassInputs);
    do_class(inputs)
        .unwrap_or_else(syn::Error::into_compile_error)
        .into()
}