lyra-engine/lyra-reflect/lyra-reflect-derive/src/struct_macro.rs

use quote::quote;
use syn::{Token, parenthesized, punctuated::Punctuated};

struct Field {
    name: syn::Ident,
    _eq: Token![=],
    ty: syn::Ident,
}

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

struct SimpleStruct {
    type_path: syn::Path,
    pub generics: syn::Generics,
    fields: Vec<Field>,
}

impl syn::parse::Parse for SimpleStruct {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        //let type_path = syn::Path::parse_mod_style(input)?;
        let type_path: syn::Path = input.parse()?;
        /* let mut generics = input.parse::<syn::Generics>()?;
        generics.where_clause = input.parse()?; */

        let mut fields = vec![];

        // parse fields if a comma is found
        if input.peek(Token![,]) {
            let _: Token![,] = input.parse()?;
            let ident: syn::Ident = input.parse()?;
            let ident_str = ident.to_string();

            match ident_str.as_str() {
                "fields" => {
                    let content;
                    let _parens: syn::token::Paren = parenthesized!(content in input);

                    let f: Punctuated<Field, Token![,]> = content.parse_terminated(Field::parse, Token![,])?;
                    fields = f.into_iter().collect();
                },
                _ => return Err(syn::Error::new(ident.span(), "Unknown macro command, expected `fields`")),
            }
        }

        Ok(Self {
            type_path,
            generics: syn::Generics::default(),
            fields,
        })

    }
}


fn gen_match_field_name_arm(simple: &SimpleStruct, default: &proc_macro2::TokenStream, arm_gen: fn(field: &Field) -> proc_macro2::TokenStream) -> proc_macro2::TokenStream {
    let field_arms_iter = simple.fields.iter().map(|f| {
        let fname = &f.name;
        let arm = arm_gen(f);

        quote! {
            stringify!(#fname) => #arm
        }
    });

    quote! {
        match name {
            #(#field_arms_iter,)*
            _ => #default,
        }
    }
}

fn gen_match_field_index_arm(simple: &SimpleStruct, default: &proc_macro2::TokenStream, arm_gen: fn(field: &Field) -> proc_macro2::TokenStream) -> proc_macro2::TokenStream {
    let field_arms_iter = simple.fields.iter().enumerate().map(|(idx, f)| {
        let arm = arm_gen(f);

        quote! {
            #idx => #arm
        }
    });

    quote! {
        match idx {
            #(#field_arms_iter,)*
            _ => #default,
        }
    }
}

pub(crate) fn impl_reflect_simple_struct(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let simple = syn::parse_macro_input!(input as SimpleStruct);

    let type_path = &simple.type_path;
    let (impl_generics, ty_generics, where_clause) = simple.generics.split_for_impl();
    // convert the type path to a string. This would not create a leading separator
    /* let type_path_str = {
        let idents: Vec<String> = type_path.segments.iter()
            .map(|segment| segment.ident.to_string())
            .collect();
        idents.join("::")
    }; */

    let borrow_fn = |field: &Field| {
        let name = &field.name;
        quote! {
            Some(&self.#name)
        }
    };

    let borrow_mut_fn = |field: &Field| {
        let name = &field.name;
        quote! {
            Some(&mut self.#name)
        }
    };

    let none_default = quote!(None);
    let false_return_default = quote!( { return false; });
    
    let field_count = simple.fields.len();

    let field_fn = gen_match_field_name_arm(&simple, &none_default, borrow_fn);
    let field_mut_fn = gen_match_field_name_arm(&simple, &none_default, borrow_mut_fn);
    let field_at_fn = gen_match_field_index_arm(&simple, &none_default, borrow_fn);
    let field_at_mut_fn = gen_match_field_index_arm(&simple, &none_default, borrow_mut_fn);
    let field_name_at_fn = gen_match_field_index_arm(&simple, &none_default, |f| {
        let name = &f.name;
        quote! {
            Some(stringify!(#name))
        }
    });

    let set_field_arm = |f: &Field| {
        let name = &f.name;
        let ty = &f.ty;
        quote! {
            self.#name = any_val.downcast_ref::<#ty>()
                .expect(&format!("Cannot set struct's field of {} type to the provided type of {}", stringify!(#name), val.name()))
                .clone() //Some(&#mut_tkn self.#field_ident)
        }
    };

    let set_field_fn = gen_match_field_name_arm(&simple, &false_return_default, set_field_arm);
    let set_field_at_fn = gen_match_field_index_arm(&simple, &false_return_default, set_field_arm);

    let get_field_ty_arm = |f: &Field| {
        let fty = &f.ty;
        quote! {
            Some(stringify!(#fty))
        }
    };
    let field_type_fn = gen_match_field_name_arm(&simple, &none_default, get_field_ty_arm);
    let field_type_at_fn = gen_match_field_index_arm(&simple, &none_default, get_field_ty_arm);

    proc_macro::TokenStream::from(quote! {
        impl #impl_generics lyra_engine::reflect::Reflect for #type_path #ty_generics #where_clause {
            fn name(&self) -> ::std::string::String {
                stringify!(#type_path).to_string()
            }
        
            fn type_id(&self) -> std::any::TypeId {
                std::any::TypeId::of::<#type_path #ty_generics>()
            }
        
            fn as_any(&self) -> &dyn std::any::Any {
                self
            }
        
            fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
                self
            }
        
            fn apply(&mut self, val: &dyn lyra_engine::reflect::Reflect) {
                let val = val.as_any().downcast_ref::<Self>()
                    .expect("The type of `val` is not the same as `self`");
                *self = val.clone();
            }

            fn clone_inner(&self) -> Box<dyn lyra_engine::reflect::Reflect> {
                Box::new(self.clone())
            }

            fn reflect_ref(&self) -> lyra_engine::reflect::ReflectRef {
                lyra_engine::reflect::ReflectRef::Value(self)
            }

            fn reflect_mut(&mut self) -> lyra_engine::reflect::ReflectMut {
                lyra_engine::reflect::ReflectMut::Value(self)
            }

            fn reflect_val(&self) -> &dyn lyra_engine::reflect::Reflect {
                self
            }

            fn reflect_val_mut(&mut self) -> &mut dyn lyra_engine::reflect::Reflect {
                self
            }
        }

        impl #impl_generics lyra_engine::reflect::Struct for #type_path #ty_generics #where_clause {
            fn field(&self, name: &str) -> Option<&dyn Reflect> {
                #field_fn
            }

            fn field_mut(&mut self, name: &str) -> Option<&mut dyn Reflect> {
                #field_mut_fn
            }

            fn fields_len(&self) -> usize {
                #field_count
            }

            fn field_at(&self, idx: usize) -> Option<&dyn Reflect> {
                #field_at_fn
            }

            fn field_at_mut(&mut self, idx: usize) -> Option<&mut dyn Reflect> {
                #field_at_mut_fn
            }

            fn field_name_at(&self, idx: usize) -> Option<&str> {
                #field_name_at_fn
            }

            fn set_field(&mut self, name: &str, val: &dyn Reflect) -> bool {
                let any_val = val.as_any();

                #set_field_fn

                true
            }

            fn set_field_at(&mut self, idx: usize, val: &dyn Reflect) -> bool {
                let any_val = val.as_any();

                #set_field_at_fn

                true
            }

            fn field_type(&self, name: &str) -> Option<&'static str> {
                #field_type_fn
            }

            fn field_type_at(&self, idx: usize) -> Option<&'static str> {
                #field_type_at_fn
            }

            fn method(&self, name: &str) -> Option<&Method> {
                unimplemented!()
            }
            
            fn method_at(&self, idx: usize) -> Option<&Method> {
                unimplemented!()
            }

            fn methods_len(&self) -> usize {
                unimplemented!()
            }
        }
    })
}