moadim 0.11.2

//! Atomic file writes: write to a temp file in the same directory, then rename into place.
//!
//! `std::fs::write` truncates-then-writes in place, so a crash mid-write leaves a torn file holding
//! neither the old nor the new complete contents. [`atomic_write`] avoids that by writing to a
//! uniquely-named sibling temp file and renaming it over the target, so a concurrent reader always
//! observes one complete version. This mirrors the durability guarantee the daemon already gives
//! `~/.claude.json` (write temp + `os.replace`).

use std::fs::{self, File};
use std::io::{self, Write};
use std::path::{Path, PathBuf};

use uuid::Uuid;

/// Write `bytes` to `path` atomically: a reader sees either the previous contents or the complete
/// new contents, never a partial/torn file.
///
/// Writes to a uniquely-named temporary file in the **same directory** as `path` (so the final
/// rename stays on one filesystem), flushes it to disk, then renames it over `path`. The temp file
/// is removed if any step fails, so a failed write leaves no `.tmp` residue.
pub fn atomic_write(path: &Path, bytes: &[u8]) -> io::Result<()> {
    let tmp = tmp_path(path);
    if let Err(err) = write_tmp(&tmp, bytes) {
        let _ = fs::remove_file(&tmp);
        return Err(err);
    }
    if let Err(err) = fs::rename(&tmp, path) {
        let _ = fs::remove_file(&tmp);
        return Err(err);
    }
    Ok(())
}

/// Path to a unique sibling temp file alongside `path` (same directory, so the rename that follows
/// stays on one filesystem). The random UUID suffix avoids collisions between concurrent writers.
fn tmp_path(path: &Path) -> PathBuf {
    let name = path.file_name().and_then(|n| n.to_str()).unwrap_or("tmp");
    let mut tmp = path.to_path_buf();
    tmp.set_file_name(format!(".{name}.{}.tmp", Uuid::new_v4()));
    tmp
}

/// Create `tmp`, write all of `bytes`, and flush to disk so the rename publishes complete contents.
fn write_tmp(tmp: &Path, bytes: &[u8]) -> io::Result<()> {
    let mut file = File::create(tmp)?;
    file.write_all(bytes)?;
    file.sync_all()?;
    Ok(())
}

#[cfg(test)]
#[path = "atomic_tests.rs"]
mod atomic_tests;