/*
** Wrapper around the access() system call.
*/
int file_access(const char *zFilename, int flags){
#ifdef _WIN32
  SECURITY_DESCRIPTOR *sdPtr = NULL;
  unsigned long size;
  PSID pSid = 0;
  BOOL SidDefaulted;
  SID_IDENTIFIER_AUTHORITY samba_unmapped = {{0, 0, 0, 0, 0, 22}};
  GENERIC_MAPPING genMap;
  HANDLE hToken = NULL;
  DWORD desiredAccess = 0, grantedAccess = 0;
  BOOL accessYesNo = FALSE;
  PRIVILEGE_SET privSet;
  DWORD privSetSize = sizeof(PRIVILEGE_SET);
  int rc = 0;
  DWORD attr;
  wchar_t *zMbcs = fossil_utf8_to_filename(zFilename);

  attr = GetFileAttributesW(zMbcs);

  if( attr==INVALID_FILE_ATTRIBUTES ){
    /*
     * File might not exist.
     */

    if( GetLastError()!=ERROR_SHARING_VIOLATION ){
      fossil_filename_free(zMbcs);
      return -1;
    }
  }

  if( flags==F_OK ){
    /*
     * File exists, nothing else to check.
     */

    fossil_filename_free(zMbcs);
    return 0;
  }

  if( (flags & W_OK)
      && (attr & FILE_ATTRIBUTE_READONLY)
      && !(attr & FILE_ATTRIBUTE_DIRECTORY) ){
    /*
     * The attributes say the file is not writable.     If the file is a
     * regular file (i.e., not a directory), then the file is not
     * writable, full stop.     For directories, the read-only bit is
     * (mostly) ignored by Windows, so we can't ascertain anything about
     * directory access from the attrib data.  However, if we have the
     * advanced 'getFileSecurityProc', then more robust ACL checks
     * will be done below.
     */

    fossil_filename_free(zMbcs);
    return -1;
  }

  /*
   * It looks as if the permissions are ok, but if we are on NT, 2000 or XP,
   * we have a more complex permissions structure so we try to check that.
   * The code below is remarkably complex for such a simple thing as finding
   * what permissions the OS has set for a file.
   */

  /*
   * First find out how big the buffer needs to be.
   */

  size = 0;
  GetFileSecurityW(zMbcs,
      OWNER_SECURITY_INFORMATION | GROUP_SECURITY_INFORMATION
      | DACL_SECURITY_INFORMATION | LABEL_SECURITY_INFORMATION,
      0, 0, &size);

  /*
   * Should have failed with ERROR_INSUFFICIENT_BUFFER
   */

  if( GetLastError()!=ERROR_INSUFFICIENT_BUFFER ){
    /*
     * Most likely case is ERROR_ACCESS_DENIED, which we will convert
     * to EACCES - just what we want!
     */

    fossil_filename_free(zMbcs);
    return -1;
  }

  /*
   * Now size contains the size of buffer needed.
   */

  sdPtr = (SECURITY_DESCRIPTOR *) HeapAlloc(GetProcessHeap(), 0, size);

  if( sdPtr == NULL ){
    goto accessError;
  }

  /*
   * Call GetFileSecurity() for real.
   */

  if( !GetFileSecurityW(zMbcs,
      OWNER_SECURITY_INFORMATION | GROUP_SECURITY_INFORMATION
      | DACL_SECURITY_INFORMATION | LABEL_SECURITY_INFORMATION,
      sdPtr, size, &size) ){
    /*
     * Error getting owner SD
     */

    goto accessError;
  }

  /*
   * As of Samba 3.0.23 (10-Jul-2006), unmapped users and groups are
   * assigned to SID domains S-1-22-1 and S-1-22-2, where "22" is the
   * top-level authority.     If the file owner and group is unmapped then
   * the ACL access check below will only test against world access,
   * which is likely to be more restrictive than the actual access
   * restrictions.  Since the ACL tests are more likely wrong than
   * right, skip them.  Moreover, the unix owner access permissions are
   * usually mapped to the Windows attributes, so if the user is the
   * file owner then the attrib checks above are correct (as far as they
   * go).
   */

  if( !GetSecurityDescriptorOwner(sdPtr,&pSid,&SidDefaulted) ||
      memcmp(GetSidIdentifierAuthority(pSid),&samba_unmapped,
        sizeof(SID_IDENTIFIER_AUTHORITY))==0 ){
    HeapFree(GetProcessHeap(), 0, sdPtr);
    fossil_filename_free(zMbcs);
    return 0; /* Attrib tests say access allowed. */
  }

  /*
   * Perform security impersonation of the user and open the resulting
   * thread token.
   */

  if( !ImpersonateSelf(SecurityImpersonation) ){
    /*
     * Unable to perform security impersonation.
     */

    goto accessError;
  }
  if( !OpenThreadToken(GetCurrentThread(),
      TOKEN_DUPLICATE | TOKEN_QUERY, FALSE, &hToken) ){
    /*
     * Unable to get current thread's token.
     */

    goto accessError;
  }

  RevertToSelf();

  /*
   * Setup desiredAccess according to the access priveleges we are
   * checking.
   */

  if( flags & R_OK ){
    desiredAccess |= FILE_GENERIC_READ;
  }
  if( flags & W_OK){
    desiredAccess |= FILE_GENERIC_WRITE;
  }

  memset(&genMap, 0x0, sizeof(GENERIC_MAPPING));
  genMap.GenericRead = FILE_GENERIC_READ;
  genMap.GenericWrite = FILE_GENERIC_WRITE;
  genMap.GenericExecute = FILE_GENERIC_EXECUTE;
  genMap.GenericAll = FILE_ALL_ACCESS;

  /*
   * Perform access check using the token.
   */

  if( !AccessCheck(sdPtr, hToken, desiredAccess,
      &genMap, &privSet, &privSetSize, &grantedAccess,
      &accessYesNo) ){
    /*
     * Unable to perform access check.
     */

  accessError:
    if( sdPtr != NULL ){
      HeapFree(GetProcessHeap(), 0, sdPtr);
    }
    if( hToken != NULL ){
      CloseHandle(hToken);
    }
    fossil_filename_free(zMbcs);
    return -1;
  }

  /*
   * Clean up.
   */

  HeapFree(GetProcessHeap(), 0, sdPtr);
  CloseHandle(hToken);
  if( !accessYesNo ){
    rc = -1;
  }
#else
  char *zMbcs = fossil_utf8_to_filename(zFilename);
  int rc = access(zMbcs, flags);
#endif
  fossil_filename_free(zMbcs);
  return rc;
}