//! Guards the lockstep rules: the core must not use anything whose result
//! can differ between machines or between runs.

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

/// Text that must not appear anywhere in the source of the core, and why.
const FORBIDDEN: &[(&str, &str)] = &[
    ("f32", "floating point results can differ between machines"),
    ("f64", "floating point results can differ between machines"),
    (
        "HashMap",
        "iteration order differs between runs; use BTreeMap or Vec",
    ),
    (
        "HashSet",
        "iteration order differs between runs; use BTreeSet or Vec",
    ),
    ("std::time", "the core must not read the clock"),
    ("Instant", "the core must not read the clock"),
    ("SystemTime", "the core must not read the clock"),
    ("std::thread", "the core must stay single-threaded"),
    ("std::env", "the core must not depend on the environment"),
    (
        "std::fs",
        "the core must not touch files; the shell does that",
    ),
    (
        "std::net",
        "the core must not open connections; the shell does that",
    ),
    ("unsafe", "the core forbids unsafe code"),
];

fn rust_files(dir: &Path, out: &mut Vec<PathBuf>) {
    for entry in fs::read_dir(dir).expect("source directory is readable") {
        let path = entry.expect("directory entry is readable").path();
        if path.is_dir() {
            rust_files(&path, out);
        } else if path.extension().is_some_and(|ext| ext == "rs") {
            out.push(path);
        }
    }
}

#[test]
fn core_source_uses_no_forbidden_apis() {
    let src = Path::new(env!("CARGO_MANIFEST_DIR")).join("src");
    let mut files = Vec::new();
    rust_files(&src, &mut files);
    files.sort();
    assert!(
        !files.is_empty(),
        "no source files found in {}",
        src.display()
    );

    let mut problems = Vec::new();
    for file in &files {
        let text = fs::read_to_string(file).expect("source file is readable");
        for (number, line) in text.lines().enumerate() {
            for (needle, reason) in FORBIDDEN {
                if line.contains(needle) {
                    problems.push(format!(
                        "{}:{}: `{needle}`: {reason}",
                        file.display(),
                        number + 1
                    ));
                }
            }
        }
    }
    assert!(
        problems.is_empty(),
        "forbidden APIs in the core:\n{}",
        problems.join("\n")
    );
}