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// Do not use this crate. It is only meant for internal use. Use `format-bytes`
// instead.
//
// Copyright 2020, Raphaël Gomès <rgomes@octobus.net>

/// `extern crate` Required even for 2018 edition
extern crate proc_macro;

mod utils;
use crate::utils::{
    extract_formatting_positions, generate_intermediate_bytestrings,
    FormatArgs,
};

use proc_macro2::TokenStream;
use proc_macro_hack::proc_macro_hack;
use quote::quote;
use syn::parse_macro_input;

/// This macro is documented in the main crate.
#[proc_macro_hack]
pub fn format_bytes(
    input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
    let args = parse_macro_input!(input as FormatArgs);
    inner_format_bytes(&args).into()
}

/// This is the unit-testable version using `proc_macro2`
fn inner_format_bytes(args: &FormatArgs) -> TokenStream {
    let format_string = &args.format_string;
    let input = format_string.value();
    let positions = match extract_formatting_positions(&input) {
        Ok(pos) => pos,
        Err(_) => {
            return quote! {compile_error!("unclosed formatting delimiter")}
        }
    };

    if positions.len() > args.positional_args.len() {
        return quote! {compile_error!("not enough arguments for formatting")};
    }
    if positions.len() < args.positional_args.len() {
        return quote! {compile_error!("too many arguments for formatting")};
    }

    if positions.is_empty() {
        return quote! {#format_string.to_vec()};
    }

    let parts = generate_intermediate_bytestrings(args, &input, &positions);

    quote! (
        {
            let mut res: Vec<u8> = vec![];
            #(res.extend(#parts);)*
            res
        }
    )
}