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

use crate::helpers::{non_enum_error, HasStrumVariantProperties, HasTypeProperties};

fn get_arms(ast: &DeriveInput) -> syn::Result<Vec<TokenStream>> {
    let name = &ast.ident;
    let mut arms = Vec::new();
    let variants = match &ast.data {
        Data::Enum(v) => &v.variants,
        _ => return Err(non_enum_error()),
    };

    let type_properties = ast.get_type_properties()?;

    for variant in variants {
        use syn::Fields::*;
        let ident = &variant.ident;
        let variant_properties = variant.get_variant_properties()?;

        if variant_properties.disabled.is_some() {
            continue;
        }

        // Look at all the serialize attributes.
        // Use `to_string` attribute (not `as_ref_str` or something) to keep things consistent
        // (i.e. always `enum.as_ref().to_string() == enum.to_string()`).
        let output = variant_properties.get_preferred_name(type_properties.case_style);
        let params = match variant.fields {
            Unit => quote! {},
            Unnamed(..) => quote! { (..) },
            Named(..) => quote! { {..} },
        };

        arms.push(quote! { #name::#ident #params => #output });
    }

    if arms.len() < variants.len() {
        arms.push(quote! {
            _ => panic!(
                "AsRef::<str>::as_ref() or AsStaticRef::<str>::as_static() \
                 called on disabled variant.",
            )
        });
    }

    Ok(arms)
}

pub fn as_ref_str_inner(ast: &DeriveInput) -> syn::Result<TokenStream> {
    let name = &ast.ident;
    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
    let arms = get_arms(ast)?;
    Ok(quote! {
        impl #impl_generics ::core::convert::AsRef<str> for #name #ty_generics #where_clause {
            fn as_ref(&self) -> &str {
                match *self {
                    #(#arms),*
                }
            }
        }
    })
}

pub enum GenerateTraitVariant {
    AsStaticStr,
    From,
}

pub fn as_static_str_inner(
    ast: &DeriveInput,
    trait_variant: GenerateTraitVariant,
) -> syn::Result<TokenStream> {
    let name = &ast.ident;
    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
    let arms = get_arms(ast)?;
    let type_properties = ast.get_type_properties()?;
    let strum_module_path = type_properties.crate_module_path();

    let mut generics = ast.generics.clone();
    generics
        .params
        .push(syn::GenericParam::Lifetime(syn::LifetimeDef::new(
            parse_quote!('_derivative_strum),
        )));
    let (impl_generics2, _, _) = generics.split_for_impl();
    let arms2 = arms.clone();
    let arms3 = arms.clone();

    Ok(match trait_variant {
        GenerateTraitVariant::AsStaticStr => quote! {
            impl #impl_generics #strum_module_path::AsStaticRef<str> for #name #ty_generics #where_clause {
                fn as_static(&self) -> &'static str {
                    match *self {
                        #(#arms),*
                    }
                }
            }
        },
        GenerateTraitVariant::From => quote! {
            impl #impl_generics ::core::convert::From<#name #ty_generics> for &'static str #where_clause {
                fn from(x: #name #ty_generics) -> &'static str {
                    match x {
                        #(#arms2),*
                    }
                }
            }
            impl #impl_generics2 ::core::convert::From<&'_derivative_strum #name #ty_generics> for &'static str #where_clause {
                fn from(x: &'_derivative_strum #name #ty_generics) -> &'static str {
                    match *x {
                        #(#arms3),*
                    }
                }
            }
        },
    })
}