#!/usr/bin/env python3
#
# Copyright (C) 2020 VyOS maintainers and contributors
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 or later as
# published by the Free Software Foundation.
#
# This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

import os

from sys import exit
from copy import deepcopy
from jinja2 import Template
from subprocess import Popen, PIPE
from netifaces import interfaces

from vyos.config import Config
from vyos.util import chown_file, chmod_x_file
from vyos import ConfigError

# Please be careful if you edit the template.
config_wwan_tmpl = """### Autogenerated by interfaces-wirelessmodem.py ###
{% if description %}
# {{ description }}
{% endif %}
ifname {{ intf }}
ipparam "{{ intf }} {{ metric }}"
linkname {{ intf }}
{% if name_server -%}
usepeerdns
{%- endif %}
# physical device
/dev/{{ device }}
lcp-echo-failure 0
115200
debug
logfile {{ logfile }}
nodefaultroute
ipcp-max-failure 4
ipcp-accept-local
ipcp-accept-remote
noauth
crtscts
lock
persist
{% if on_demand -%}
demand
{%- endif %}

connect '/usr/sbin/chat -v -t6 -f {{ chat_script }}'

"""

# Please be careful if you edit the template.
chat_wwan_tmpl = """
ABORT 'NO DIAL TONE' ABORT 'NO ANSWER' ABORT 'NO CARRIER' ABORT DELAYED
'' AT
OK ATZ
OK 'AT+CGDCONT=1,"IP","{{ apn }}"'
OK ATD*99#
CONNECT ''

"""

config_wwan_ip_pre_up_tmpl = """#!/bin/sh
# As PPPoE is an "on demand" interface we need to re-configure it when it
# becomes 'up'

ipparam=$6

# device name and metric are received using ipparam
device=`echo "$ipparam"|awk '{ print $1 }'`

if [ "$device" != "{{ intf }}" ]; then
    exit
fi

# add some info to syslog
DIALER_PID=$(cat /var/run/{{ intf }}.pid)
logger -t pppd[$DIALER_PID] "executing $0"

{% if vrf -%}
logger -t pppd[$DIALER_PID] "configuring interface {{ intf }} for VRF {{ vrf }}"
ip link set dev {{ intf }} master {{ vrf }}
{% endif %}

"""

default_config_data = {
    'address': [],
    'apn': '',
    'chat_script': '',
    'deleted': False,
    'description': '',
    'device': 'ttyUSB0',
    'disable': False,
    'disable_link_detect': 1,
    'on_demand': False,
    'logfile': '',
    'metric': '10',
    'mtu': '1500',
    'name_server': True,
    'intf': '',
    'vrf': ''
}

def subprocess_cmd(command):
    p = Popen(command, stdout=PIPE, shell=True)
    p.communicate()

def check_kmod():
    modules = ['option', 'usb_wwan', 'usbserial']
    for module in modules:
        if not os.path.exists(f'/sys/module/{module}'):
            if os.system(f'modprobe {module}') != 0:
                raise ConfigError(f'Loading Kernel module {module} failed')

def get_config():
    wwan = deepcopy(default_config_data)
    conf = Config()

    # determine tagNode instance
    if 'VYOS_TAGNODE_VALUE' not in os.environ:
        raise ConfigError('Interface (VYOS_TAGNODE_VALUE) not specified')

    wwan['intf'] = os.environ['VYOS_TAGNODE_VALUE']
    wwan['logfile'] = f"/var/log/vyatta/ppp_{wwan['intf']}.log"
    wwan['chat_script'] = f"/etc/ppp/peers/chat.{wwan['intf']}"

    # Check if interface has been removed
    if not conf.exists('interfaces wirelessmodem ' + wwan['intf']):
        wwan['deleted'] = True
        return wwan

    # set new configuration level
    conf.set_level('interfaces wirelessmodem ' + wwan['intf'])

    # get metrick for backup default route
    if conf.exists(['apn']):
        wwan['apn'] = conf.return_value(['apn'])

    # get metrick for backup default route
    if conf.exists(['backup', 'distance']):
        wwan['metric'] = conf.return_value(['backup', 'distance'])

    # Retrieve interface description
    if conf.exists(['description']):
        wwan['description'] = conf.return_value(['description'])

    # System device name
    if conf.exists(['device']):
        wwan['device'] = conf.return_value(['device'])

    # disable interface
    if conf.exists('disable'):
        wwan['disable'] = True

    # ignore link state changes
    if conf.exists('disable-link-detect'):
        wwan['disable_link_detect'] = 2

    # Do not use DNS servers provided by the peer
    if conf.exists(['mtu']):
        wwan['mtu'] = conf.return_value(['mtu'])

    # Do not use DNS servers provided by the peer
    if conf.exists(['no-peer-dns']):
        wwan['name_server'] = False

    # Access concentrator name (only connect to this concentrator)
    if conf.exists(['ondemand']):
        wwan['on_demand'] = True

    # retrieve VRF instance
    if conf.exists('vrf'):
        wwan['vrf'] = conf.return_value(['vrf'])

    return wwan

def verify(wwan):
    if wwan['deleted']:
        return None

    if not wwan['apn']:
        raise ConfigError(f"APN for {wwan['intf']} not configured")

    # we can not use isfile() here as Linux device files are no regular files
    # thus the check will return False
    if not os.path.exists(f"/dev/{wwan['device']}"):
        raise ConfigError(f"Device {wwan['device']} does not exist")

    vrf_name = wwan['vrf']
    if vrf_name and vrf_name not in interfaces():
        raise ConfigError(f'VRF {vrf_name} does not exist')

    return None

def generate(wwan):
    config_file_wwan = f"/etc/ppp/peers/{wwan['intf']}"
    config_file_wwan_chat = wwan['chat_script']
    ip_up_script_file = f"/etc/ppp/ip-up.d/9991-vyos-vrf-{wwan['intf']}"

    config_files = [config_file_wwan, config_file_wwan_chat, ip_up_script_file]

    # Ensure directories for config files exist - otherwise create them on demand
    for file in config_files:
        dirname = os.path.dirname(file)
        if not os.path.isdir(dirname):
            os.mkdir(dirname)

    # Always hang-up WWAN connection prior generating new configuration file
    cmd = f"systemctl stop ppp@{wwan['intf']}.service"
    subprocess_cmd(cmd)

    if wwan['deleted']:
        # Delete PPP configuration files
        for file in config_files:
            if os.path.exists(file):
                os.unlink(file)

    else:
        # Create PPP configuration files
        tmpl = Template(config_wwan_tmpl)
        config_text = tmpl.render(wwan)
        with open(config_file_wwan, 'w') as f:
            f.write(config_text)

        # Create PPP chat script
        tmpl = Template(chat_wwan_tmpl)
        config_text = tmpl.render(wwan)
        with open(wwan['chat_script'], 'w') as f:
            f.write(config_text)

        # Create ip-pre-up script
        tmpl = Template(config_wwan_ip_pre_up_tmpl)
        config_text = tmpl.render(wwan)
        with open(ip_up_script_file, 'w') as f:
            f.write(config_text)

        # make generated script file executable
        chmod_x_file(ip_up_script_file)

    return None

def apply(wwan):
    if wwan['deleted']:
        # bail out early
        return None

    if not wwan['disable']:
        # dial WWAN connection
        cmd = f"systemctl start ppp@{wwan['intf']}.service"
        subprocess_cmd(cmd)

        # make logfile owned by root / vyattacfg
        chown_file(wwan['logfile'], 'root', 'vyattacfg')

    return None

if __name__ == '__main__':
    try:
        check_kmod()
        c = get_config()
        verify(c)
        generate(c)
        apply(c)
    except ConfigError as e:
        print(e)
        exit(1)