/* Copyright (C) 2023 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

//! String-enumeration derive macro

/*
String enumeration allows a compact representation, and ensure that
there is no discrepancy between what is logged, and what can be parser
in signature keywords.

Usage: just derive EnumStringUX with X being the number of bits used in repr

    #[derive(EnumStringU8)]
    #[repr(u8)]
    pub enum ExampleEnum {
        Zero = 0,
        BestValueEver = 42,
    }

Then, get 4 functions to translate from u8 <-> ExampleEnum <-> string
- from_u : takes an unsigned and return an Option<ExampleEnum>
- into_u : takes an ExampleEnum and return an unsigned
- from_str : takes a string and return an Option<ExampleEnum>
- into_str : takes an ExampleEnum and return a string (&'static str)

Case:
snake_case is used by default:
ExampleEnum::BestValueEver.to_str() is "best_value_ever"

Strings parsed to get an enumeration value are case insensitive

Parameters:
The enum can have a suricata attribute, which is a list of named values
- enum_string_style can be:
  - UPPERCASE : uppercase is used for logging and parsing
  - LOG_UPPERCASE : uppercase is only used for logging, snake_case for parsing

With UPPERCASE
ExampleEnum::BestValueEver.to_str() is "BESTVALUEEVER" (without underscores)
*/

extern crate proc_macro;
use super::applayerevent::transform_name;
use proc_macro::TokenStream;
use quote::quote;
use std::str::FromStr;
use syn::{self, parse_macro_input, DeriveInput};

fn get_attr_enum_string_style(attr: &syn::Attribute) -> String {
    let meta = attr.parse_meta().unwrap();
    if let syn::Meta::List(l) = meta {
        for n in l.nested {
            if let syn::NestedMeta::Meta(syn::Meta::NameValue(nv)) = n {
                if nv.path.is_ident("enum_string_style") {
                    if let syn::Lit::Str(s) = nv.lit {
                        return s.value();
                    }
                    panic!("enum_string_style invalid syntax");
                }
            }
        }
        panic!("no enum_string_style");
    }
    panic!("suricata attribute is not a list");
}

pub fn derive_enum_string<T: std::str::FromStr + quote::ToTokens>(
    input: TokenStream, ustr: &str,
) -> TokenStream
where
    <T as FromStr>::Err: std::fmt::Display,
{
    let input = parse_macro_input!(input as DeriveInput);
    let name = input.ident;
    let mut values = Vec::new();
    let mut names = Vec::new();
    let mut names_upper = Vec::new();
    let mut fields = Vec::new();

    let mut enum_string_style = String::from("");

    if let syn::Data::Enum(ref data) = input.data {
        for attr in input.attrs.iter() {
            if attr.path.is_ident("suricata") {
                enum_string_style = get_attr_enum_string_style(attr);
            }
        }
        for v in (&data.variants).into_iter() {
            if let Some((_, val)) = &v.discriminant {
                match &enum_string_style[..] {
                    "UPPERCASE" => {
                        names.push(v.ident.to_string().to_ascii_uppercase());
                        names_upper.push(v.ident.to_string().to_ascii_uppercase());
                    }
                    "LOG_UPPERCASE" => {
                        names.push(v.ident.to_string().to_ascii_uppercase());
                        let fname = transform_name(&v.ident.to_string());
                        let fnameu = fname.to_ascii_uppercase();
                        names_upper.push(fnameu);
                    }
                    "" => {
                        // snake_case
                        let fname = transform_name(&v.ident.to_string());
                        let fnameu = fname.to_ascii_uppercase();
                        names.push(fname);
                        names_upper.push(fnameu);
                    }
                    _ => {
                        panic!("EnumString style unknown {}", enum_string_style);
                    }
                };
                fields.push(v.ident.clone());
                if let syn::Expr::Lit(l) = val {
                    if let syn::Lit::Int(li) = &l.lit {
                        if let Ok(value) = li.base10_parse::<T>() {
                            values.push(value);
                        } else {
                            panic!("EnumString requires explicit {}", ustr);
                        }
                    } else {
                        panic!("EnumString requires explicit literal integer");
                    }
                } else {
                    panic!("EnumString requires explicit literal");
                }
            } else {
                panic!("EnumString requires explicit values");
            }
        }
    } else {
        panic!("EnumString can only be derived for enums");
    }

    let is_suricata = std::env::var("CARGO_PKG_NAME")
        .map(|var| var == "suricata")
        .unwrap_or(false);
    let crate_id = if is_suricata {
        syn::Ident::new("crate", proc_macro2::Span::call_site())
    } else {
        syn::Ident::new("suricata", proc_macro2::Span::call_site())
    };

    let utype_str = syn::Ident::new(ustr, proc_macro2::Span::call_site());

    let expanded = quote! {
        impl #crate_id::detect::EnumString<#utype_str> for #name {
            fn from_u(v: #utype_str) -> Option<Self> {
                match v {
                    #( #values => Some(#name::#fields) ,)*
                    _ => None,
                }
            }
            fn into_u(self) -> #utype_str {
                match self {
                    #( #name::#fields => #values ,)*
                }
            }
            fn to_str(&self) -> &'static str {
                match *self {
                    #( #name::#fields => #names ,)*
                }
            }
            fn from_str(s: &str) -> Option<Self> {
                match s.to_ascii_uppercase().as_str() {
                    #( #names_upper => Some(#name::#fields) ,)*
                    _ => None
                }
            }
        }
    };

    proc_macro::TokenStream::from(expanded)
}