#!/usr/bin/env python2

# dependencies:
#   1. pip install paho-mqtt
#   2. apt-get install sshpass
#
from subprocess import call, Popen, PIPE, STDOUT
import paho.mqtt.client as mqtt
import shlex
import random
from uuid import getnode as get_mac

MQTT_SERVER = 'mqtt.suanzi.ai'
MQTT_PORT = 1883

# The alive time new ssh session exist. It means if no client connect to this device through ssh tunnel in 5 minutes,
# this new sessin will terminate.
ALIVE_TIME = 60 * 5

SSH_SERVER = 'autossh.suanzi.ai'
PORT_RANGE = (20000, 40000)
USER = 'autossh'
PASSWORD = 'hard2guess'

def getAvailablePort(host, ports):
    while True:
        port = random.randint(ports[0], ports[1])
        command = 'nc -z -v -w3 ' + host + ' ' + str(port)
        p = Popen(command, shell=True, stdout=PIPE, stderr=STDOUT)
        pout = p.communicate()[0].strip()
        if p.returncode == 0:
            continue
        if 'Connection refused' in pout:
            return port
        else:
            print pout

def exec_ssh(port):
    if port == None:
        raise Exception('Port not avaliable')
    command = 'sshpass -p' + PASSWORD + ' ssh -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -fCR ' + str(port) +':localhost:22 ' + USER + '@' + SSH_SERVER + ' sleep ' + str(ALIVE_TIME)
    print command
    return call(shlex.split(command), shell=False)


def on_connect(client, userdata, flags, rc):
    client.subscribe(client.id + '-request')
    print("Connected with result code "+str(rc))

def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))
    if msg.topic == client.id + '-request':
        print str(msg.payload)
        port = getAvailablePort(SSH_SERVER, PORT_RANGE)
        if exec_ssh(port) == 0:
            client.publish(client.id + '-response', port)
        else:
            raise Exception ('run ssh failed')

class MyClient(mqtt.Client):
    def __init__(self, id):
        mqtt.Client.__init__(self)
        self.id = id
        self.on_connect = on_connect
        self.on_message = on_message

if __name__ == '__main__':
    mac = hex(get_mac())
    id = '{:0>12}'.format(mac[2:-1])
    print 'id is: ' , id
    client = MyClient(id)
    client.connect(MQTT_SERVER, MQTT_PORT, 60)
    client.loop_forever()