package main

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
)

// writeFileAtomic replaces the file at path with data through a temporary file
// and a rename. A reader or a crash of the process sees the old file or the new
// file, never a part of one.
func writeFileAtomic(path string, data []byte) error {
	file, err := os.CreateTemp(filepath.Dir(path), "."+filepath.Base(path)+".*")
	if err != nil {
		return fmt.Errorf("create temporary file: %w", err)
	}

	_, err = file.Write(data)
	err = errors.Join(err, file.Close())
	if err == nil {
		err = os.Rename(file.Name(), path)
	}

	if err != nil {
		return errors.Join(fmt.Errorf("replace file: %w", err), os.Remove(file.Name()))
	}

	return nil
}