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//! rustnim — Rust -> Nim transpiler.
//!
//! Usage: rustnim <input.rs> [-o <output.nim>]

mod fmt;
mod lower;
mod ty;

use std::path::PathBuf;
use std::process::ExitCode;

fn main() -> ExitCode {
    match run() {
        Ok(()) => ExitCode::SUCCESS,
        Err(e) => {
            eprintln!("rustnim: {e}");
            // Exiting non-zero on any failure is load-bearing: the entire
            // point of this project is that a transpiler must never report
            // success for work it did not do.
            ExitCode::FAILURE
        }
    }
}

fn run() -> Result<(), String> {
    let mut args = std::env::args_os().skip(1);
    let mut input: Option<PathBuf> = None;
    let mut output: Option<PathBuf> = None;

    while let Some(a) = args.next() {
        match a.to_string_lossy().as_ref() {
            "-o" | "--output" => {
                output = Some(
                    args.next()
                        .ok_or("`-o` needs a path")?
                        .into(),
                );
            }
            "-h" | "--help" => {
                println!("usage: rustnim <input.rs> [-o <output.nim>]");
                return Ok(());
            }
            s if s.starts_with('-') => return Err(format!("unknown flag `{s}`")),
            _ => {
                if input.is_some() {
                    return Err("more than one input file given".into());
                }
                input = Some(a.into());
            }
        }
    }

    let input = input.ok_or("no input file; usage: rustnim <input.rs> [-o <output.nim>]")?;
    let src = std::fs::read_to_string(&input)
        .map_err(|e| format!("cannot read {}: {e}", input.display()))?;

    let file: syn::File = syn::parse_file(&src)
        .map_err(|e| format!("{}: parse error: {e}", input.display()))?;

    let nim = lower::Lowerer::new().lower_file(&file)?;

    match output {
        Some(p) => std::fs::write(&p, nim)
            .map_err(|e| format!("cannot write {}: {e}", p.display()))?,
        None => print!("{nim}"),
    }
    Ok(())
}