coding-tools 0.8.8

// SPDX-License-Identifier: Apache-2.0
// Copyright 2026 Jonathan Shook

//! Atomic sibling-file publication, including replace-existing semantics on
//! Windows where `std::fs::rename` does not provide it.

use std::path::Path;
use std::sync::atomic::{AtomicU64, Ordering};

static NEXT: AtomicU64 = AtomicU64::new(0);

pub fn write(path: &Path, bytes: impl AsRef<[u8]>) -> Result<(), String> {
    let parent = path
        .parent()
        .ok_or_else(|| format!("{} has no parent", path.display()))?;
    std::fs::create_dir_all(parent).map_err(|e| format!("{}: {e}", parent.display()))?;
    let tmp = parent.join(format!(
        ".{}.tmp-{}-{}",
        path.file_name().and_then(|s| s.to_str()).unwrap_or("state"),
        std::process::id(),
        NEXT.fetch_add(1, Ordering::Relaxed)
    ));
    std::fs::write(&tmp, bytes).map_err(|e| format!("{}: {e}", tmp.display()))?;
    replace(&tmp, path).map_err(|e| format!("{} -> {}: {e}", tmp.display(), path.display()))
}

#[cfg(not(windows))]
fn replace(from: &Path, to: &Path) -> std::io::Result<()> {
    std::fs::rename(from, to)
}

#[cfg(windows)]
fn replace(from: &Path, to: &Path) -> std::io::Result<()> {
    use std::os::windows::ffi::OsStrExt;
    use windows_sys::Win32::Storage::FileSystem::{
        MOVEFILE_REPLACE_EXISTING, MOVEFILE_WRITE_THROUGH, MoveFileExW,
    };

    let from: Vec<u16> = from.as_os_str().encode_wide().chain(Some(0)).collect();
    let to: Vec<u16> = to.as_os_str().encode_wide().chain(Some(0)).collect();
    // SAFETY: both buffers are NUL-terminated and live for the duration of the
    // call; MoveFileExW does not retain their pointers.
    let ok = unsafe {
        MoveFileExW(
            from.as_ptr(),
            to.as_ptr(),
            MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH,
        )
    };
    if ok == 0 {
        Err(std::io::Error::last_os_error())
    } else {
        Ok(())
    }
}