use convert_case::Casing;
// Copyright (C) 2025 Emilis Bliūdžius
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.
use quote::{ToTokens, quote};
use syn::{Fields, FieldsNamed, FieldsUnnamed, Ident, spanned::Spanned};
#[allow(unused)]
pub struct RefAndMut {
    name: syn::Ident,
    variants: Vec<(Ident, Fields)>,
}

impl RefAndMut {
    pub fn parse(input: syn::DeriveInput) -> syn::Result<Self> {
        let variants = match input.data {
            syn::Data::Enum(data) => data.variants,
            syn::Data::Struct(_) | syn::Data::Union(_) => {
                return Err(syn::Error::new(
                    input.span(),
                    "RefAndMut can only be used on enums",
                ));
            }
        };

        Ok(Self {
            name: input.ident,
            variants: variants.into_iter().map(|v| (v.ident, v.fields)).collect(),
        })
    }
}

impl ToTokens for RefAndMut {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        for (field, value) in self.variants.iter().cloned() {
            match value {
                Fields::Named(named) => named_fields(self.name.clone(), field, named, tokens),
                Fields::Unnamed(unnamed) => {
                    unnamed_fields(self.name.clone(), field, unnamed, tokens)
                }
                Fields::Unit => continue,
            }
        }
        tokens.extend(quote! {});
    }
}

fn named_fields(
    struct_name: Ident,
    name: Ident,
    fields: FieldsNamed,
    tokens: &mut proc_macro2::TokenStream,
) {
    let base_name = name.to_string().to_case(convert_case::Case::Pascal);
    let name_ref = Ident::new(format!("{base_name}Ref").as_str(), name.span());
    let fn_name_ref = Ident::new(
        format!(
            "{}_ref",
            name.to_string().to_case(convert_case::Case::Snake)
        )
        .as_str(),
        name.span(),
    );
    let fn_name_mut = Ident::new(
        format!(
            "{}_mut",
            name.to_string().to_case(convert_case::Case::Snake)
        )
        .as_str(),
        name.span(),
    );
    let name_mut = Ident::new(format!("{base_name}Mut").as_str(), name.span());
    let struct_fields_ref = fields
        .named
        .iter()
        .map(|c| {
            let name = c.ident.as_ref().expect("this is a named field??");
            let ty = &c.ty;
            quote! {
                pub #name: &'a #ty,
            }
        })
        .collect::<Box<[_]>>();
    let struct_fields_mut = fields
        .named
        .iter()
        .map(|c| {
            let name = c.ident.as_ref().expect("this is a named field??");
            let ty = &c.ty;
            quote! {
                pub #name: &'a mut #ty,
            }
        })
        .collect::<Box<[_]>>();
    let fields_idents = fields
        .named
        .iter()
        .map(|c| c.ident.as_ref().expect("this is a named field??"))
        .collect::<Box<[_]>>();

    let for_character = (struct_name == "Role").then_some(quote!{
		impl crate::character::Character {
			pub fn #fn_name_ref<'a>(&'a self) -> core::result::Result<#name_ref<'a>, crate::error::GameError> {
                let got = self.role_title();
				self.role().#fn_name_ref().ok_or(crate::error::GameError::InvalidRole {
					got,
					expected: RoleTitle::#name,
				})
            }
			pub fn #fn_name_mut<'a>(&'a mut self) -> core::result::Result<#name_mut<'a>, crate::error::GameError> {
                let got = self.role_title();
				self.role_mut().#fn_name_mut().ok_or(crate::error::GameError::InvalidRole {
					got,
					expected: RoleTitle::#name,
				})
            }
		}
	});

    tokens.extend(quote! {
        pub struct #name_ref<'a> {
            #(#struct_fields_ref)*
        }

        pub struct #name_mut<'a> {
            #(#struct_fields_mut)*
        }

        #for_character

        impl #struct_name {
            pub fn #fn_name_ref<'a>(&'a self) -> Option<#name_ref<'a>> {
                match self {
                    Self::#name{ #(#fields_idents),* } => Some(#name_ref {#(#fields_idents),* }),
                    _ => None,
                }
            }
            pub fn #fn_name_mut<'a>(&'a mut self) -> Option<#name_mut<'a>> {
                match self {
                    Self::#name{ #(#fields_idents),* } => Some(#name_mut {#(#fields_idents),* }),
                    _ => None,
                }
            }
        }
    });
}

fn unnamed_fields(
    struct_name: Ident,
    name: Ident,
    fields: FieldsUnnamed,
    tokens: &mut proc_macro2::TokenStream,
) {
    let base_name = name.to_string().to_case(convert_case::Case::Pascal);
    let name_ref = Ident::new(format!("{base_name}Ref").as_str(), name.span());
    let fn_name_ref = Ident::new(
        format!(
            "{}_ref",
            name.to_string().to_case(convert_case::Case::Snake)
        )
        .as_str(),
        name.span(),
    );
    let fn_name_mut = Ident::new(
        format!(
            "{}_mut",
            name.to_string().to_case(convert_case::Case::Snake)
        )
        .as_str(),
        name.span(),
    );
    let name_mut = Ident::new(format!("{base_name}Mut").as_str(), name.span());

    let fields_ref = fields
        .unnamed
        .iter()
        .map(|field| {
            let ty = &field.ty;
            quote! {
                pub &'a #ty
            }
        })
        .collect::<Box<[_]>>();
    let fields_mut = fields
        .unnamed
        .iter()
        .map(|field| {
            let ty = &field.ty;
            quote! {
                pub &'a mut #ty
            }
        })
        .collect::<Box<[_]>>();
    let fields_names = fields
        .unnamed
        .iter()
        .enumerate()
        .map(|(idx, field)| Ident::new(format!("field{idx}").as_str(), field.span()))
        .collect::<Box<[_]>>();
    let for_character = (struct_name == "Role").then_some(quote! {
		impl crate::character::Character {
			pub fn #fn_name_ref<'a>(&'a self) -> core::result::Result<#name_ref<'a>, crate::error::GameError> {
                let got = self.role_title();
				self.role().#fn_name_ref().ok_or(crate::error::GameError::InvalidRole {
					got,
					expected: RoleTitle::#name,
				})
            }
			pub fn #fn_name_mut<'a>(&'a mut self) -> core::result::Result<#name_mut<'a>, crate::error::GameError> {
                let got = self.role_title();
				self.role_mut().#fn_name_mut().ok_or(crate::error::GameError::InvalidRole {
					got,
					expected: RoleTitle::#name,
				})
            }
		}
	});
    tokens.extend(quote! {
        pub struct #name_ref<'a>(#(#fields_ref),*);

        pub struct #name_mut<'a>(#(#fields_mut),*);

        #for_character

        impl #struct_name {
            pub fn #fn_name_ref<'a>(&'a self) -> Option<#name_ref<'a>> {
                match self {
                    Self::#name(#(#fields_names),*) => Some(#name_ref(#(#fields_names),*)),
                    _ => None,
                }
            }
            pub fn #fn_name_mut<'a>(&'a mut self) -> Option<#name_mut<'a>> {
                match self {
                    Self::#name(#(#fields_names),*) => Some(#name_mut(#(#fields_names),*)),
                    _ => None,
                }
            }
        }
    });
}