extern crate proc_macro;

use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, DeriveInput};

#[proc_macro_derive(NoneGuard)]
pub fn none_guard(input: TokenStream) -> TokenStream {
    let ast = parse_macro_input!(input as DeriveInput);
    let struct_name = &ast.ident;

    if let syn::Data::Struct(s) = &ast.data {
        let field_checks = s.fields.iter().map(|field| {
            let name = &field.ident;
            if let syn::Type::Path(type_path) = &field.ty {
                if type_path.path.segments.len() == 1 {
                    let segment = &type_path.path.segments.iter().next().unwrap();
                    if segment.ident != "Option" {
                        return quote! {
                            compile_error!("All fields must be of type Option!");
                        };
                    }
                } else {
                    return quote! {
                        compile_error!("All fields must be of type Option!");
                    };
                }
            } else {
                return quote! {
                    compile_error!("All fields must be of type Option!");
                };
            }

            quote! { self.#name.is_some() }
        });

        let is_some_checks = field_checks
            .clone()
            .reduce(|acc, e| {
                dbg!(&acc, &e);

                quote! { #acc && #e }
            })
            .unwrap();

        let is_none_checks = field_checks
            .map(|tok| quote! { !(#tok) })
            .reduce(|acc, e| {
                dbg!(&acc, &e);

                quote! { #acc && #e }
            })
            .unwrap();

        quote! {
            impl #struct_name {
                pub fn is_all_some(&self) -> bool {
                    #is_some_checks
                }

                pub fn is_all_none(&self) -> bool {
                    #is_none_checks
                }
            }
        }
        .into()
    } else {
        quote! {
            compile_error!("CheckAllNone macro can only be used with structs!");
        }
        .into()
    }
}