# coding: utf-8

# shells.py - functions for validating user shells

#

# Copyright (C) 2013 Arthur de Jong

#

# This library is free software; you can redistribute it and/or

# modify it under the terms of the GNU Lesser General Public

# License as published by the Free Software Foundation; either

# version 2.1 of the License, or (at your option) any later version.

#

# This library 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

# Lesser General Public License for more details.

#

# You should have received a copy of the GNU Lesser General Public

# License along with this library; if not, write to the Free Software

# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

# 02110-1301 USA

import ctypes

import ctypes.util

import os

import sys

def list_shells():

    """List the shells from /etc/shells."""

    libc = ctypes.CDLL(ctypes.util.find_library("c"))

    libc.setusershell()

    while True:

        shell = ctypes.c_char_p(libc.getusershell()).value

        if not shell:

            break

        yield shell

    libc.endusershell()

def shellexists(shell):

    """Check if the provided shell exists and is executable."""

    return os.path.isfile(shell) and os.access(shell, os.X_OK)

def check(shell, asroot=False):

    """Check if the specified shell is valid and exit if it isn't."""

    # if the shell is listed in /etc/shells, everything should be OK

    if shell in list_shells():

        return

    # if we are not root, bail out

    if not asroot:

        if not shell:

            # FIXME: print to stderr

            print('%s: empty shell not allowed' % sys.argv[0])

        else:

            # FIXME: print to stderr

            print('%s: %s is an invalid shell' % (sys.argv[0], shell))

        sys.exit(1)

    # warn if something seems wrong

    if not shell:

        # FIXME: print to stderr

        print('%s: Warning: setting empty shell' % sys.argv[0])

    elif not shellexists(shell):

        print('%s: Warning: %s does not exist' % (sys.argv[0], shell))