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use std::str::FromStr;

use proc_macro2::TokenStream;
use quote::quote;
use syn::{Data, DeriveInput, Generics, Meta};

use super::{
    super::TraitHandler,
    models::{FieldAttributeBuilder, TypeAttributeBuilder},
};
use crate::Trait;

pub struct PartialEqStructHandler;

impl TraitHandler for PartialEqStructHandler {
    fn trait_meta_handler(
        ast: &DeriveInput,
        tokens: &mut TokenStream,
        traits: &[Trait],
        meta: &Meta,
    ) {
        let type_attribute = TypeAttributeBuilder {
            enable_flag: true, enable_bound: true
        }
        .from_partial_eq_meta(meta);

        let bound = type_attribute
            .bound
            .into_punctuated_where_predicates_by_generic_parameters(&ast.generics.params);

        let mut comparer_tokens = TokenStream::new();

        if let Data::Struct(data) = &ast.data {
            for (index, field) in data.fields.iter().enumerate() {
                let field_attribute = FieldAttributeBuilder {
                    enable_ignore: true,
                    enable_impl:   true,
                }
                .from_attributes(&field.attrs, traits);

                if field_attribute.ignore {
                    continue;
                }

                let compare_trait = field_attribute.compare_trait;
                let compare_method = field_attribute.compare_method;

                let field_name = if let Some(ident) = field.ident.as_ref() {
                    ident.to_string()
                } else {
                    format!("{}", index)
                };

                match compare_trait {
                    Some(compare_trait) => {
                        let compare_method = compare_method.unwrap();

                        let statement = format!(
                            "if !{compare_trait}::{compare_method}(&self.{field_name}, \
                             &other.{field_name}) {{ return false }}",
                            compare_trait = compare_trait,
                            compare_method = compare_method,
                            field_name = field_name
                        );

                        comparer_tokens.extend(TokenStream::from_str(&statement).unwrap());
                    },
                    None => match compare_method {
                        Some(compare_method) => {
                            let statement = format!(
                                "if !{compare_method}(&self.{field_name}, &other.{field_name}) {{ \
                                 return false; }}",
                                compare_method = compare_method,
                                field_name = field_name
                            );

                            comparer_tokens.extend(TokenStream::from_str(&statement).unwrap());
                        },
                        None => {
                            let statement = format!(
                                "if core::cmp::PartialEq::ne(&self.{field_name}, \
                                 &other.{field_name}) {{ return false; }}",
                                field_name = field_name
                            );

                            comparer_tokens.extend(TokenStream::from_str(&statement).unwrap());
                        },
                    },
                }
            }
        }

        let ident = &ast.ident;

        let mut generics_cloned: Generics = ast.generics.clone();

        let where_clause = generics_cloned.make_where_clause();

        for where_predicate in bound {
            where_clause.predicates.push(where_predicate);
        }

        let (impl_generics, ty_generics, where_clause) = generics_cloned.split_for_impl();

        let compare_impl = quote! {
            impl #impl_generics core::cmp::PartialEq for #ident #ty_generics #where_clause {
                #[inline]
                fn eq(&self, other: &Self) -> bool {
                    #comparer_tokens

                    true
                }
            }
        };

        tokens.extend(compare_impl);
    }
}