////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 1996-2024 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Octave is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
//
////////////////////////////////////////////////////////////////////////

#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif

#include <cstdlib>
#include <locale>
#include <codecvt>

#include "dir-ops.h"
#include "file-ops.h"
#include "file-stat.h"
#include "lo-error.h"
#include "lo-sysdep.h"
#include "localcharset-wrapper.h"
#include "putenv-wrapper.h"
#include "unistd-wrappers.h"
#include "unsetenv-wrapper.h"

#if defined (OCTAVE_USE_WINDOWS_API)
#  include <windows.h>
#  include <wchar.h>

#  include "filepos-wrappers.h"
#  include "lo-hash.h"
#  include "oct-locbuf.h"
#  include "uniconv-wrappers.h"
#  include "unwind-prot.h"
#endif

OCTAVE_BEGIN_NAMESPACE(octave)

OCTAVE_BEGIN_NAMESPACE(sys)

int
system (const std::string& cmd_str)
{
#if defined (OCTAVE_USE_WINDOWS_API)
  const std::wstring wcmd_str =  u8_to_wstring (cmd_str);

  return _wsystem (wcmd_str.c_str ());
#else
  return ::system (cmd_str.c_str ());
#endif
}

std::string
getcwd ()
{
  std::string retval;

#if defined (OCTAVE_USE_WINDOWS_API)
  wchar_t *tmp = _wgetcwd (nullptr, 0);

  if (! tmp)
    (*current_liboctave_error_handler) ("unable to find current directory");

  std::wstring tmp_wstr (tmp);
  free (tmp);

  std::string tmp_str = u8_from_wstring (tmp_wstr);

  retval = tmp_str;

#else
  // Using octave_getcwd_wrapper ensures that we have a getcwd that
  // will allocate a buffer as large as necessary if buf and size are
  // both 0.

  char *tmp = octave_getcwd_wrapper (nullptr, 0);

  if (! tmp)
    (*current_liboctave_error_handler) ("unable to find current directory");

  retval = tmp;
  free (tmp);
#endif

  return retval;
}

int
chdir (const std::string& path_arg)
{
  std::string path = sys::file_ops::tilde_expand (path_arg);

#if defined (OCTAVE_USE_WINDOWS_API)
  if (path.length () == 2 && path[1] == ':')
    path += '\\';
#endif

  return octave_chdir_wrapper (path.c_str ());
}

bool
get_dirlist (const std::string& dirname, string_vector& dirlist,
             std::string& msg)
{
  dirlist = "";
  msg = "";
#if defined (OCTAVE_USE_WINDOWS_API)
  _WIN32_FIND_DATAW ffd;

  std::string path_name (dirname);
  if (path_name.empty ())
    return true;

  if (path_name.back () == '\\' || path_name.back () == '/')
    path_name.push_back ('*');
  else
    path_name.append (R"(\*)");

  // Find first file in directory.
  std::wstring wpath_name = u8_to_wstring (path_name);
  HANDLE hFind = FindFirstFileW (wpath_name.c_str (), &ffd);
  if (INVALID_HANDLE_VALUE == hFind)
    {
      DWORD errCode = GetLastError ();
      char *errorText = nullptr;
      FormatMessageA (FORMAT_MESSAGE_FROM_SYSTEM |
                      FORMAT_MESSAGE_ALLOCATE_BUFFER |
                      FORMAT_MESSAGE_IGNORE_INSERTS,
                      nullptr, errCode,
                      MAKELANGID (LANG_NEUTRAL, SUBLANG_DEFAULT),
                      reinterpret_cast <char *> (&errorText), 0, nullptr);
      if (errorText != nullptr)
        {
          msg = std::string (errorText);
          LocalFree (errorText);
        }
      return false;
    }

  std::list<std::string> dirlist_str;
  do
    dirlist_str.push_back (u8_from_wstring (ffd.cFileName));
  while (FindNextFileW (hFind, &ffd) != 0);

  FindClose(hFind);

  dirlist = string_vector (dirlist_str);

#else

  dir_entry dir (dirname);

  if (! dir)
    {
      msg = dir.error ();
      return false;
    }

  dirlist = dir.read ();

  dir.close ();
#endif

  return true;
}

#if defined (OCTAVE_USE_WINDOWS_API)

static bool
check_fseek_ftell_workaround_needed (bool set_nonbuffered_mode)
{
  // To check whether the workaround is needed:
  //
  //   * Create a tmp file with LF line endings only.
  //
  //   * Open that file for reading in text mode.
  //
  //   * Read a line.
  //
  //   * Use ftello to record the position of the beginning of the
  //     second line.
  //
  //   * Read and save the contents of the second line.
  //
  //   * Use fseeko to return to the saved position.
  //
  //   * Read the second line again and compare to the previously
  //     saved text.
  //
  //   * If the lines are different, we need to set non-buffered
  //     input mode for files opened in text mode.

  std::string tmpname = sys::tempnam ("", "oct-");

  if (tmpname.empty ())
    {
      (*current_liboctave_warning_handler)
        ("fseek/ftell bug check failed (tmp name creation)!");
      return false;
    }

  std::FILE *fptr = std::fopen (tmpname.c_str (), "wb");

  if (! fptr)
    {
      (*current_liboctave_warning_handler)
        ("fseek/ftell bug check failed (opening tmp file for writing)!");
      return false;
    }

  fprintf (fptr, "%s", "foo\nbar\nbaz\n");

  std::fclose (fptr);

  fptr = std::fopen (tmpname.c_str (), "rt");

  if (! fptr)
    {
      (*current_liboctave_warning_handler)
        ("fseek/ftell bug check failed (opening tmp file for reading)!");
      return false;
    }

  unwind_action act ([] ()
  {
    std::fclose (fptr);
    sys::unlink (tmpname);
  });

  if (set_nonbuffered_mode)
    ::setvbuf (fptr, nullptr, _IONBF, 0);

  while (true)
    {
      int c = fgetc (fptr);

      if (c == EOF)
        {
          (*current_liboctave_warning_handler)
            ("fseek/ftell bug check failed (skipping first line)!");
          return false;
        }

      if (c == '\n')
        break;
    }

  off_t pos = octave_ftello_wrapper (fptr);

  char buf1[8];
  int i = 0;
  while (true)
    {
      int c = fgetc (fptr);

      if (c == EOF)
        {
          (*current_liboctave_warning_handler)
            ("fseek/ftell bug check failed (reading second line)!");
          return false;
        }

      if (c == '\n')
        break;

      buf1[i++] = static_cast<char> (c);
    }
  buf1[i] = '\0';

  octave_fseeko_wrapper (fptr, pos, SEEK_SET);

  char buf2[8];
  i = 0;
  while (true)
    {
      int c = fgetc (fptr);

      if (c == EOF)
        {
          (*current_liboctave_warning_handler)
            ("fseek/ftell bug check failed (reading after repositioning)!");
          return false;
        }

      if (c == '\n')
        break;

      buf2[i++] = static_cast<char> (c);
    }
  buf2[i] = '\0';

  return strcmp (buf1, buf2);
}

static std::string
get_formatted_last_error ()
{
  std::string msg = "";

  DWORD last_error = GetLastError ();

  wchar_t *error_text = nullptr;
  FormatMessageW (FORMAT_MESSAGE_FROM_SYSTEM |
                  FORMAT_MESSAGE_ALLOCATE_BUFFER |
                  FORMAT_MESSAGE_IGNORE_INSERTS,
                  nullptr, last_error,
                  MAKELANGID (LANG_NEUTRAL, SUBLANG_DEFAULT),
                  reinterpret_cast <wchar_t *> (&error_text), 0, nullptr);

  if (error_text != nullptr)
    {
      msg = u8_from_wstring (error_text);
      LocalFree (error_text);
    }
  else
    msg = "Unknown error.";

  return msg;
}
#endif

bool
file_exists (const std::string& filename, bool is_dir)
{
  // Check if a file with the given name exists on the file system.  If is_dir
  // is true (the default), also return true if filename refers to a directory.
#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring w_fn = u8_to_wstring (filename);

  DWORD f_attr = GetFileAttributesW (w_fn.c_str ());

  return ((f_attr != INVALID_FILE_ATTRIBUTES)
          && (is_dir || ! (f_attr & FILE_ATTRIBUTE_DIRECTORY)));

#else
  file_stat fs (filename);

  return (fs && (fs.is_reg () || (is_dir && fs.is_dir ())));

#endif
}

bool
file_exists (const std::string& filename, bool is_dir, std::string& msg)
{
  // Check if a file with the given name exists on the file system.  If is_dir
  // is true (the default), also return true if filename refers to a directory.
#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring w_fn = u8_to_wstring (filename);

  DWORD f_attr = GetFileAttributesW (w_fn.c_str ());

  if (f_attr == INVALID_FILE_ATTRIBUTES)
    msg = get_formatted_last_error ();

  return ((f_attr != INVALID_FILE_ATTRIBUTES)
          && (is_dir || ! (f_attr & FILE_ATTRIBUTE_DIRECTORY)));

#else
  file_stat fs (filename);

  if (! fs)
    msg = fs.error ();

  return (fs && (fs.is_reg () || (is_dir && fs.is_dir ())));

#endif
}

bool
dir_exists (const std::string& dirname)
{
  // Check if a directory with the given name exists on the file system.
#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring w_dn = u8_to_wstring (dirname);

  DWORD f_attr = GetFileAttributesW (w_dn.c_str ());

  return ((f_attr != INVALID_FILE_ATTRIBUTES)
          && (f_attr & FILE_ATTRIBUTE_DIRECTORY));

#else
  file_stat fs (dirname);

  return (fs && fs.is_dir ());

#endif
}

bool
dir_exists (const std::string& dirname, std::string& msg)
{
  // Check if a directory with the given name exists on the file system.
#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring w_dn = u8_to_wstring (dirname);

  DWORD f_attr = GetFileAttributesW (w_dn.c_str ());

  if (f_attr == INVALID_FILE_ATTRIBUTES)
    msg = get_formatted_last_error ();

  return ((f_attr != INVALID_FILE_ATTRIBUTES)
          && (f_attr & FILE_ATTRIBUTE_DIRECTORY));

#else
  file_stat fs (dirname);

  if (! fs)
    msg = fs.error ();

  return (fs && fs.is_dir ());

#endif
}

// Return TRUE if FILE1 and FILE2 refer to the same (physical) file.

bool
same_file (const std::string& file1, const std::string& file2)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  // FIXME: When Octave switches to C++17, consider replacing this function
  //        by https://en.cppreference.com/w/cpp/filesystem/equivalent.

  bool retval = false;

  std::wstring file1w = sys::u8_to_wstring (file1);
  std::wstring file2w = sys::u8_to_wstring (file2);
  const wchar_t *f1 = file1w.c_str ();
  const wchar_t *f2 = file2w.c_str ();

  bool f1_is_dir = GetFileAttributesW (f1) & FILE_ATTRIBUTE_DIRECTORY;
  bool f2_is_dir = GetFileAttributesW (f2) & FILE_ATTRIBUTE_DIRECTORY;

  // Windows native code
  // Reference: http://msdn2.microsoft.com/en-us/library/aa363788.aspx

  DWORD share = FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE;

  HANDLE hfile1
    = CreateFileW (f1, 0, share, 0, OPEN_EXISTING,
                   f1_is_dir ? FILE_FLAG_BACKUP_SEMANTICS : 0, 0);

  if (hfile1 != INVALID_HANDLE_VALUE)
    {
      HANDLE hfile2
        = CreateFileW (f2, 0, share, 0, OPEN_EXISTING,
                       f2_is_dir ? FILE_FLAG_BACKUP_SEMANTICS : 0, 0);

      if (hfile2 != INVALID_HANDLE_VALUE)
        {
          BY_HANDLE_FILE_INFORMATION hfi1;
          BY_HANDLE_FILE_INFORMATION hfi2;

          if (GetFileInformationByHandle (hfile1, &hfi1)
              && GetFileInformationByHandle (hfile2, &hfi2))
            {
              retval = (hfi1.dwVolumeSerialNumber == hfi2.dwVolumeSerialNumber
                        && hfi1.nFileIndexHigh == hfi2.nFileIndexHigh
                        && hfi1.nFileIndexLow == hfi2.nFileIndexLow
                        && hfi1.nFileSizeHigh == hfi2.nFileSizeHigh
                        && hfi1.nFileSizeLow == hfi2.nFileSizeLow
                        && hfi1.ftLastWriteTime.dwLowDateTime
                        == hfi2.ftLastWriteTime.dwLowDateTime
                        && hfi1.ftLastWriteTime.dwHighDateTime
                        == hfi2.ftLastWriteTime.dwHighDateTime);
            }

          CloseHandle (hfile2);
        }

      CloseHandle (hfile1);
    }

  return retval;

#else

  // POSIX Code

  sys::file_stat fs_file1 (file1);
  sys::file_stat fs_file2 (file2);

  return (fs_file1 && fs_file2
          && fs_file1.ino () == fs_file2.ino ()
          && fs_file1.dev () == fs_file2.dev ());

#endif
}

std::FILE *
fopen (const std::string& filename, const std::string& mode)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  std::wstring wfilename = u8_to_wstring (filename);
  std::wstring wmode = u8_to_wstring (mode);

  std::FILE *fptr = _wfopen (wfilename.c_str (), wmode.c_str ());

  static bool fseek_ftell_bug_workaround_needed = false;
  static bool fseek_ftell_bug_checked = false;

  if (! fseek_ftell_bug_checked && mode.find ('t') != std::string::npos)
    {
      // FIXME: Is the following workaround needed for all files
      // opened in text mode, or only for files opened for reading?

      // Try to avoid fseek/ftell bug on Windows systems by setting
      // non-buffered input mode for files opened in text mode, but
      // only if it appears that the workaround is needed.  See
      // Octave bug #58055.

      // To check whether the workaround is needed:
      //
      //   * Create a tmp file with LF line endings only.
      //
      //   * Open that file for reading in text mode.
      //
      //   * Read a line.
      //
      //   * Use ftello to record the position of the beginning of
      //     the second line.
      //
      //   * Read and save the contents of the second line.
      //
      //   * Use fseeko to return to the saved position.
      //
      //   * Read the second line again and compare to the
      //     previously saved text.
      //
      //   * If the lines are different, we need to set non-buffered
      //     input mode for files opened in text mode.
      //
      //   * To verify that the workaround solves the problem,
      //     repeat the above test with non-buffered input mode.  If
      //     that fails, warn that there may be trouble with
      //     ftell/fseek when reading files opened in text mode.

      if (check_fseek_ftell_workaround_needed (false))
        {
          if (check_fseek_ftell_workaround_needed (true))
            (*current_liboctave_warning_handler)
              ("fseek/ftell may fail for files opened in text mode");
          else
            fseek_ftell_bug_workaround_needed = true;
        }

      fseek_ftell_bug_checked = true;
    }

  if (fseek_ftell_bug_workaround_needed
      && mode.find ('t') != std::string::npos)
    ::setvbuf (fptr, nullptr, _IONBF, 0);

  return fptr;

#else
  return std::fopen (filename.c_str (), mode.c_str ());
#endif
}

std::FILE *
fopen_tmp (const std::string& name, const std::string& mode)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  // Append "D" to the mode string to indicate that this is a temporary
  // file that should be deleted when the last open handle is closed.
  std::string tmp_mode = mode + "D";

  return std::fopen (name.c_str (), tmp_mode.c_str ());

#else

  std::FILE *fptr = std::fopen (name.c_str (), mode.c_str ());

  // From gnulib: This relies on the Unix semantics that a file is not
  // really removed until it is closed.
  octave_unlink_wrapper (name.c_str ());

  return fptr;

#endif
}

std::fstream
fstream (const std::string& filename, const std::ios::openmode mode)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  std::wstring wfilename = u8_to_wstring (filename);

  return std::fstream (wfilename.c_str (), mode);

#else
  return std::fstream (filename.c_str (), mode);
#endif
}

std::ifstream
ifstream (const std::string& filename, const std::ios::openmode mode)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  std::wstring wfilename = u8_to_wstring (filename);

  return std::ifstream (wfilename.c_str (), mode);

#else
  return std::ifstream (filename.c_str (), mode);
#endif
}

std::ofstream
ofstream (const std::string& filename, const std::ios::openmode mode)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  std::wstring wfilename = u8_to_wstring (filename);

  return std::ofstream (wfilename.c_str (), mode);

#else
  return std::ofstream (filename.c_str (), mode);
#endif
}

void
putenv_wrapper (const std::string& name, const std::string& value)
{
  std::string new_env = name + "=" + value;

  // FIXME: The malloc leaks memory, but so would a call to setenv.
  // Short of extreme measures to track memory, altering the environment
  // always leaks memory, but the saving grace is that the leaks are small.

  // As far as I can see there's no way to distinguish between the
  // various errors; putenv doesn't have errno values.

#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring new_wenv = u8_to_wstring (new_env);

  int len = (new_wenv.length () + 1) * sizeof (wchar_t);

  wchar_t *new_item = static_cast<wchar_t *> (std::malloc (len));

  wcscpy (new_item, new_wenv.c_str());

  if (_wputenv (new_item) < 0)
    (*current_liboctave_error_handler)
      ("putenv (%s) failed", new_env.c_str());
#else
  int len = new_env.length () + 1;

  char *new_item = static_cast<char *> (std::malloc (len));

  std::strcpy (new_item, new_env.c_str());

  if (octave_putenv_wrapper (new_item) < 0)
    (*current_liboctave_error_handler) ("putenv (%s) failed", new_item);
#endif
}

std::string
getenv_wrapper (const std::string& name)
{
#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring wname = u8_to_wstring (name);
  wchar_t *env = _wgetenv (wname.c_str ());
  return env ? u8_from_wstring (env) : "";
#else
  char *env = ::getenv (name.c_str ());
  return env ? env : "";
#endif
}

int
unsetenv_wrapper (const std::string& name)
{
#if defined (OCTAVE_USE_WINDOWS_API)
  putenv_wrapper (name, "");

  std::wstring wname = u8_to_wstring (name);
  return (SetEnvironmentVariableW (wname.c_str (), nullptr) ? 0 : -1);
#else
  return octave_unsetenv_wrapper (name.c_str ());
#endif
}

bool
isenv_wrapper (const std::string& name)
{
#if defined (OCTAVE_USE_WINDOWS_API)
  std::wstring wname = u8_to_wstring (name);
  wchar_t *env = _wgetenv (wname.c_str ());
#else
  char *env = ::getenv (name.c_str ());
#endif
  return env != 0;
}

std::wstring
u8_to_wstring (const std::string& utf8_string)
{
  // convert multibyte UTF-8 string to wide character string
  static std::wstring_convert<std::codecvt_utf8<wchar_t>, wchar_t>
  wchar_conv;

  std::wstring retval = L"";

  try
    {
      retval = wchar_conv.from_bytes (utf8_string);
    }
  catch (const std::range_error& e)
    {
      // What to do in case of error?
      // error ("u8_to_wstring: converting from UTF-8 to wchar_t: %s",
      //        e.what ());
    }

  return retval;
}

std::string
u8_from_wstring (const std::wstring& wchar_string)
{
  // convert wide character string to multibyte UTF-8 string
  static std::wstring_convert<std::codecvt_utf8<wchar_t>, wchar_t>
  wchar_conv;

  std::string retval = "";

  try
    {
      retval = wchar_conv.to_bytes (wchar_string);
    }
  catch (const std::range_error& e)
    {
      // What to do in case of error?
      // error ("u8_from_wstring: converting from wchar_t to UTF-8: %s",
      //        e.what ());
    }

  return retval;
}

// At quite a few places in the code we are passing file names as
// char arrays to external library functions.

// When these functions try to locate the corresponding file on the
// disc, they need to use the wide character API on Windows to
// correctly open files with non-ASCII characters.

// But they have no way of knowing which encoding we are using for
// the passed string.  So they have no way of reliably converting to
// a wchar_t array.  (I.e. there is no possible fix for these
// functions with current C or C++.)

// To solve the dilemma, the function "get_ASCII_filename" first
// checks whether there are any non-ASCII characters in the passed
// file name.  If there are not, it returns the original name.

// Otherwise, it optionally tries to convert the file name to the locale
// charset.

// If the file name contains characters that cannot be converted to the
// locale charset (or that step is skipped), it tries to obtain the short
// file name (8.3 naming scheme) which only consists of ASCII characters
// and are safe to pass.  However, short file names can be disabled for
// performance reasons on the file system level with NTFS and they are not
// stored on other file systems (e.g. ExFAT).  So there is no guarantee
// that these exist.

// If short file names are not stored, a hard link to the file is
// created.  For this the path to the file is split at the deepest
// possible level that doesn't contain non-ASCII characters.  At
// that level a hidden folder is created that holds the hard links.
// That means we need to have write access on that location.  A path
// to that hard link is returned.

// If the file system is FAT32, there are no hard links.  But FAT32
// always stores short file names.  So we are safe.

// ExFAT that is occasionally used on USB sticks and SD cards stores
// neither short file names nor does it support hard links.  So for
// exFAT with this function, there is (currently) no way to generate
// a file name that is stripped from non-ASCII characters but still
// is valid.

// For Unixy systems, this function does nothing.

std::string
get_ASCII_filename (const std::string& orig_file_name,
                    const bool allow_locale)
{
#if defined (OCTAVE_USE_WINDOWS_API)

  // Return file name that only contains ASCII characters that can
  // be used to access the file orig_file_name.  The original file
  // must exist in the file system before calling this function.
  // This is useful for passing file names to functions that are not
  // aware of the character encoding we are using.

  // 0. Check whether filename contains non-ASCII (UTF-8) characters.

  std::string::const_iterator first_non_ASCII
    = std::find_if (orig_file_name.begin (), orig_file_name.end (),
  [](char c) { return (c < 0 || c >= 128); });

  if (first_non_ASCII == orig_file_name.end ())
    return orig_file_name;

  // 1. Optionally, check if all characters in the path can be successfully
  // converted to the locale charset
  if (allow_locale)
    {
      const char *locale = octave_locale_charset_wrapper ();
      if (locale)
        {
          const uint8_t *name_u8 = reinterpret_cast<const uint8_t *>
                                   (orig_file_name.c_str ());
          std::size_t length = 0;
          char *name_locale = octave_u8_conv_to_encoding_strict
                              (locale, name_u8,
                               orig_file_name.length () + 1, &length);
          if (name_locale)
            {
              std::string file_name_locale (name_locale, length);
              free (name_locale);
              return file_name_locale;
            }
        }
    }

  // 2. Check if file system stores short filenames (might be ASCII-only).

  std::wstring w_orig_file_name_str = u8_to_wstring (orig_file_name);
  const wchar_t *w_orig_file_name = w_orig_file_name_str.c_str ();

  // Get full path to file
  wchar_t w_full_file_name[_MAX_PATH];
  if (_wfullpath (w_full_file_name, w_orig_file_name, _MAX_PATH) == nullptr)
    return orig_file_name;

  std::wstring w_full_file_name_str = w_full_file_name;

  // Get short filename (8.3) from UTF-16 filename.

  long length = GetShortPathNameW (w_full_file_name, nullptr, 0);

  if (length > 0)
    {
      // Dynamically allocate the correct size (terminating null char
      // was included in length).

      OCTAVE_LOCAL_BUFFER (wchar_t, w_short_file_name, length);
      GetShortPathNameW (w_full_file_name, w_short_file_name, length);

      std::wstring w_short_file_name_str
        = std::wstring (w_short_file_name, length);

      if (w_short_file_name_str.compare (0, length-1, w_full_file_name_str) != 0)
        {
          // Check whether short file name contains non-ASCII characters
          std::string short_file_name
            = u8_from_wstring (w_short_file_name_str);
          first_non_ASCII
            = std::find_if (short_file_name.begin (),
                            short_file_name.end (),
          [](char c) { return (c < 0 || c >= 128); });
          if (first_non_ASCII == short_file_name.end ())
            return short_file_name;
        }
    }

  // 3. Create hard link with only-ASCII characters.
  // Get longest possible part of path that only contains ASCII chars.

  std::wstring::iterator w_first_non_ASCII
    = std::find_if (w_full_file_name_str.begin (), w_full_file_name_str.end (),
  [](wchar_t c) { return (c < 0 || c >= 128); });
  std::wstring tmp_substr
    = std::wstring (w_full_file_name_str.begin (), w_first_non_ASCII);

  std::size_t pos
    = tmp_substr.find_last_of (u8_to_wstring (file_ops::dir_sep_chars ()));

  std::string par_dir
    = u8_from_wstring (w_full_file_name_str.substr (0, pos+1));

  // Create .oct_ascii directory.
  // FIXME: We need to have write permission in this location.

  std::string oct_ascii_dir = par_dir + ".oct_ascii";
  std::string test_dir = canonicalize_file_name (oct_ascii_dir);

  if (test_dir.empty ())
    {
      std::string msg;
      int status = sys::mkdir (oct_ascii_dir, 0777, msg);

      if (status < 0)
        return orig_file_name;

      // Set hidden property.
      SetFileAttributesA (oct_ascii_dir.c_str (), FILE_ATTRIBUTE_HIDDEN);
    }

  // Create file from hash of full filename.
  std::string filename_hash
    = (oct_ascii_dir + file_ops::dir_sep_str ()
       + crypto::hash ("SHA1", orig_file_name));

  // FIXME: This is just to check if the file exists.  Use a more efficient
  // method.
  std::string abs_filename_hash = canonicalize_file_name (filename_hash);

  if (! abs_filename_hash.empty ())
    sys::unlink (filename_hash);

  // At this point, we know that we have only ASCII characters.
  // So instead of converting, just copy the characters to std::wstring.
  std::wstring w_filename_hash (filename_hash.begin (),
                                filename_hash.end ());

  if (CreateHardLinkW (w_filename_hash.c_str (), w_orig_file_name, nullptr))
    return filename_hash;

#else

  octave_unused_parameter (allow_locale);

#endif

  return orig_file_name;
}

OCTAVE_END_NAMESPACE(sys)
OCTAVE_END_NAMESPACE(octave)