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use procmeta::prelude::*;
use syn::{DeriveInput, LitInt, LitStr};

#[derive(MetaParser)]
pub enum ParsedFieldAttr {
    #[name("api_error")]
    AssignApiError {
        status: LitInt,
        code: LitStr,
        cause: LitStr,
    },

    // code, cause
    #[name("api_error")]
    BusinessError(LitStr, LitStr),

    #[name("api_error")]
    FromError(FromError),
}

#[derive(MetaParser)]
pub enum FromError {
    #[name("from")]
    Item(Expr),

    #[name("from")]
    AssignCauseItem(Expr, LitStr),
}

pub fn expand(input: &DeriveInput) -> Result<TokenStream> {
    let data = &input.data;
    let ty = &input.ident;
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let mut collect_item_token = quote!();
    let mut extend_token = quote!();
    match data {
        syn::Data::Struct(_) => unimplemented!(),
        syn::Data::Enum(data) => {
            for var in &data.variants {
                let attrs = &var.attrs;
                if attrs.is_empty() {
                    let fields = &var.fields;
                    if let syn::Fields::Unnamed(unnamed) = fields {
                        if unnamed.unnamed.len() == 1 {
                            let unnamed_ty = &unnamed.unnamed[0].ty;

                            extend_token = quote! {
                                #extend_token
                                result.extend(<#unnamed_ty as ApiErrors>::api_errors());
                            };
                        }
                    }
                    continue;
                }
                for attr in attrs {
                    let parsed_attr = ParsedFieldAttr::try_from(attr)?;
                    match parsed_attr {
                        ParsedFieldAttr::AssignApiError {
                            status,
                            code,
                            cause,
                        } => {
                            collect_item_token = quote! {
                                #collect_item_token
                                ApiErrorItem {
                                    status: #status,
                                    code: #code.into(),
                                    cause: #cause.into(),
                                },
                            };
                        }
                        ParsedFieldAttr::BusinessError(code, cause) => {
                            collect_item_token = quote! {
                                #collect_item_token
                                ApiErrorItem {
                                    status: 200,
                                    code: #code.into(),
                                    cause: #cause.into(),
                                },
                            };
                        }
                        ParsedFieldAttr::FromError(inner_err) => match inner_err {
                            FromError::Item(item) => {
                                collect_item_token = quote! {
                                    #collect_item_token
                                    #item.into(),
                                };
                            }
                            FromError::AssignCauseItem(item, cause) => {
                                collect_item_token = quote! {
                                    #collect_item_token
                                    {
                                        let item: ApiErrorItem = #item.into();
                                        ApiErrorItem {
                                            status: item.status,
                                            code: item.code,
                                            cause: #cause.into(),
                                        }
                                    },
                                };
                            }
                        },
                    }
                }
            }
        }
        syn::Data::Union(_) => unimplemented!(),
    }
    let body_token = if extend_token.is_empty() {
        quote!(vec![#collect_item_token])
    } else {
        quote! {
            let mut result = vec![#collect_item_token];
            #extend_token
            result
        }
    };
    let result = quote! {
        impl #impl_generics  ApiErrors for #ty #ty_generics #where_clause {
            fn api_errors() -> Vec<ApiErrorItem> {
                #body_token
            }
        }
    };
    Ok(result)
}