// +build !windows

package fs

import (
	"fmt"
	"os"
	"syscall"
)

// A FileExistsError is returned when an operation cannot be completed due to a
// file already existing.
type FileExistsError struct {
	path string
}

func newFileExistsError(path string) FileExistsError {
	return FileExistsError{path: path}
}

func (e FileExistsError) Error() string {
	return fmt.Sprintf("operation not allowed, file %q exists", e.path)
}

// SyncDir flushes any file renames to the filesystem.
func SyncDir(dirName string) error {
	// fsync the dir to flush the rename
	dir, err := os.OpenFile(dirName, os.O_RDONLY, os.ModeDir)
	if err != nil {
		return err
	}
	defer dir.Close()

	// While we're on unix, we may be running in a Docker container that is
	// pointed at a Windows volume over samba. That doesn't support fsyncs
	// on directories. This shows itself as an EINVAL, so we ignore that
	// error.
	err = dir.Sync()
	if pe, ok := err.(*os.PathError); ok && pe.Err == syscall.EINVAL {
		err = nil
	} else if err != nil {
		return err
	}

	return dir.Close()
}

// RenameFileWithReplacement will replace any existing file at newpath with the contents
// of oldpath.
//
// If no file already exists at newpath, newpath will be created using the contents
// of oldpath. If this function returns successfully, the contents of newpath will
// be identical to oldpath, and oldpath will be removed.
func RenameFileWithReplacement(oldpath, newpath string) error {
	return os.Rename(oldpath, newpath)
}

// RenameFile renames oldpath to newpath, returning an error if newpath already
// exists. If this function returns successfully, the contents of newpath will
// be identical to oldpath, and oldpath will be removed.
func RenameFile(oldpath, newpath string) error {
	if _, err := os.Stat(newpath); err == nil {
		return newFileExistsError(newpath)
	}

	return os.Rename(oldpath, newpath)
}