package fileutil

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

// WriteFileAtomic replaces path only after data has been written and synced.
func WriteFileAtomic(path string, data []byte, perm os.FileMode) (err error) {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return fmt.Errorf("create directory: %w", err)
	}
	if err := os.Chmod(dir, 0o700); err != nil {
		return fmt.Errorf("secure directory: %w", err)
	}
	if info, statErr := os.Stat(path); statErr == nil {
		perm &= info.Mode().Perm()
	} else if !os.IsNotExist(statErr) {
		return fmt.Errorf("inspect existing file: %w", statErr)
	}

	tmp, err := os.CreateTemp(dir, ".tmp-*")
	if err != nil {
		return fmt.Errorf("create temporary file: %w", err)
	}
	tmpPath := tmp.Name()
	defer func() {
		if tmp != nil {
			if closeErr := tmp.Close(); err == nil && closeErr != nil {
				err = fmt.Errorf("close temporary file: %w", closeErr)
			}
		}
		_ = os.Remove(tmpPath)
	}()

	if err = tmp.Chmod(perm); err != nil {
		return fmt.Errorf("set temporary file permissions: %w", err)
	}
	if _, err = tmp.Write(data); err != nil {
		return fmt.Errorf("write temporary file: %w", err)
	}
	if err = tmp.Sync(); err != nil {
		return fmt.Errorf("sync temporary file: %w", err)
	}
	if err = tmp.Close(); err != nil {
		return fmt.Errorf("close temporary file: %w", err)
	}
	tmp = nil
	if err = os.Rename(tmpPath, path); err != nil {
		return fmt.Errorf("replace file: %w", err)
	}

	d, openErr := os.Open(dir)
	if openErr != nil {
		return fmt.Errorf("open parent directory: %w", openErr)
	}
	defer d.Close()
	if err = d.Sync(); err != nil {
		return fmt.Errorf("sync parent directory: %w", err)
	}
	return nil
}