def secure_filename(filename):
    r"""Borrowed from :mod:`werkzeug.utils`, under the BSD 3-clause license.

    Pass it a filename and it will return a secure version of it.  This
    filename can then safely be stored on a regular file system and passed
    to :func:`os.path.join`.  The filename returned is an ASCII only string
    for maximum portability.

    On windows systems the function also makes sure that the file is not
    named after one of the special device files.

    >>> secure_filename("My cool movie.mov")
    'My_cool_movie.mov'
    >>> secure_filename("../../../etc/passwd")
    'etc_passwd'
    >>> secure_filename(u'i contain cool \xfcml\xe4uts.txt')
    'i_contain_cool_umlauts.txt'

    The function might return an empty filename.  It's your responsibility
    to ensure that the filename is unique and that you generate random
    filename if the function returned an empty one.

    :param filename: the filename to secure
    """
    _filename_ascii_strip_re = re.compile(r'[^A-Za-z0-9_.-]')
    _windows_device_files = ('CON', 'AUX', 'COM1', 'COM2', 'COM3', 'COM4',
                             'LPT1', 'LPT2', 'LPT3', 'PRN', 'NUL')
    if isinstance(filename, text_type):
        from unicodedata import normalize
        filename = normalize('NFKD', filename).encode('ascii', 'ignore')
        if not PY2:
            filename = filename.decode('ascii')
    for sep in os.path.sep, os.path.altsep:
        if sep:
            filename = filename.replace(sep, ' ')
    filename = str(_filename_ascii_strip_re.sub('', '_'.join(
                   filename.split()))).strip('._')

    # on nt a couple of special files are present in each folder.  We
    # have to ensure that the target file is not such a filename.  In
    # this case we prepend an underline
    if os.name == 'nt' and filename and \
       filename.split('.')[0].upper() in _windows_device_files:
        filename = '_' + filename

    return filename
def ban_user(user_id=None):
    if not Permission(CanBanUser, identity=current_user):
        flash(_("You do not have the permissions to ban this user."), "danger")
        return redirect(url_for("management.overview"))

    # ajax request
    if request.is_xhr:
        ids = request.get_json()["ids"]

        data = []
        users = User.query.filter(User.id.in_(ids)).all()
        for user in users:
            # don't let a user ban himself and do not allow a moderator to ban
            # a admin user
            if (
                current_user.id == user.id or
                Permission(IsAdmin, identity=user) and
                Permission(Not(IsAdmin), current_user)
            ):
                continue

            elif user.ban():
                data.append({
                    "id": user.id,
                    "type": "ban",
                    "reverse": "unban",
                    "reverse_name": _("Unban"),
                    "reverse_url": url_for("management.unban_user",
                                           user_id=user.id)
                })

        return jsonify(
            message="{} users banned.".format(len(data)),
            category="success",
            data=data,
            status=200
        )

    user = User.query.filter_by(id=user_id).first_or_404()

    # Do not allow moderators to ban admins
    if Permission(IsAdmin, identity=user) and \
       Permission(Not(IsAdmin), identity=current_user):

        flash(_("A moderator cannot ban an admin user."), "danger")
        return redirect(url_for("management.overview"))

    if not current_user.id == user.id and user.ban():
        flash(_("User is now banned."), "success")
    else:
        flash(_("Could not ban user."), "danger")

    return redirect(url_for("management.banned_users"))