launcher/src/bench_io.rs

//! Bench I/O helpers: the output pump (tee the child's stdout/stderr to the
//! console + the log file) and the newest-report lookup.

use std::io::{Read, Write};
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};
use std::time::SystemTime;

use crate::ansi::strip_ansi_step;

/// Tee one output pipe to the console and the log file.
///
/// The console copy keeps the child's ANSI colors; the file copy is
/// stripped (state machine below) so the saved .log stays readable in
/// `sm121 report` and under grep/less.
///
/// The read buffer must not be empty: `read()` on a zero-length slice
/// returns 0 (interpreted as EOF), so an empty `Vec` would silently sever
/// the pipe — the child then dies on its first stderr write with EPIPE
/// (silent exit 120 in CPython).
pub fn pump<R: Read>(mut reader: R, to_console: bool, file: Arc<Mutex<std::fs::File>>) {
    let mut buf = vec![0u8; 8192];
    let mut carry = Vec::new(); // trailing partial escape across chunks
    let mut clean = Vec::new();
    loop {
        let n = match reader.read(&mut buf) {
            Ok(n) => n,
            Err(e) if e.kind() == std::io::ErrorKind::Interrupted => continue,
            Err(e) => panic!("reading bench output pipe: {e}"),
        };
        if n == 0 {
            break;
        }
        if to_console {
            std::io::stdout().write_all(&buf[..n]).ok();
        }
        carry.extend_from_slice(&buf[..n]);
        strip_ansi_step(&mut carry, &mut clean);
        if !clean.is_empty() {
            if let Ok(mut f) = file.lock() {
                f.write_all(&clean).ok();
            }
            clean.clear();
        }
    }
}

/// Newest `.md` under `scratch/runs/` (the tool's `runs/<date>/<run>.md`).
pub fn latest_md(scratch: &Path) -> Option<PathBuf> {
    let runs = scratch.join("runs");
    let mut best: Option<(SystemTime, PathBuf)> = None;
    let mut stack = vec![runs];
    while let Some(dir) = stack.pop() {
        let entries = std::fs::read_dir(dir).ok()?;
        for e in entries.flatten() {
            let p = e.path();
            if p.is_dir() {
                stack.push(p);
            } else if p.extension().is_some_and(|x| x == "md") {
                let t = e
                    .metadata()
                    .and_then(|m| m.modified())
                    .ok()
                    .unwrap_or(SystemTime::UNIX_EPOCH);
                if best.as_ref().is_none_or(|(bt, _)| t > *bt) {
                    best = Some((t, p));
                }
            }
        }
    }
    best.map(|(_, p)| p)
}