package main

import (
	"os"
	"path/filepath"
)

// writeFileAtomic writes data to path via a temp file + rename in the
// same directory, so readers never observe a partially written file
// and a crash mid-write cannot corrupt the target.
func writeFileAtomic(path string, data []byte, perm os.FileMode) error {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return err
	}
	tmp, err := os.CreateTemp(dir, filepath.Base(path)+".tmp-*")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName) // no-op after successful rename

	if err := tmp.Chmod(perm); err != nil {
		tmp.Close()
		return err
	}
	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	return os.Rename(tmpName, path)
}