use std::fs;
use std::path::{Path, PathBuf};

fn collect_rs_files(dir: &Path, out: &mut Vec<PathBuf>) {
    if let Ok(entries) = fs::read_dir(dir) {
        for e in entries.flatten() {
            let path = e.path();
            if path.is_dir() {
                collect_rs_files(&path, out);
            } else if path.extension().and_then(|s| s.to_str()) == Some("rs") {
                out.push(path);
            }
        }
    }
}

#[test]
fn backend_must_not_import_pbs() {
    let crate_root = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
    let backend_dir = crate_root.join("src").join("backend");
    if !backend_dir.exists() { return; }

    let mut files = Vec::new();
    collect_rs_files(&backend_dir, &mut files);

    let mut offenders = Vec::new();
    for f in files {
        if let Ok(src) = fs::read_to_string(&f) {
            if src.contains("frontends::pbs") || src.contains("crate::frontends::pbs") {
                offenders.push(f);
            }
        }
    }

    if !offenders.is_empty() {
        let list = offenders
            .iter()
            .map(|p| p.strip_prefix(&crate_root).unwrap_or(p).display().to_string())
            .collect::<Vec<_>>()
            .join("\n  - ");
        panic!(
            "Backend must not import PBS modules (frontends::pbs). Offending files:\n  - {}",
            list
        );
    }
}