#!/usr/bin/env python2

from subprocess import call, Popen, PIPE, STDOUT, check_output
import paho.mqtt.client as mqtt
import shlex
import random
from uuid import getnode as get_mac
import ast
import sys, os
import re

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 get_mac_str():
    mac = hex(get_mac())
    m = re.sub('^0x|L$', '', mac)
    return '{:0>12}'.format(m)

def get_hostname():
    return check_output("/bin/hostname", shell=True).strip();

def check_ssh_connection(port):
    command = '/bin/ps aux | /bin/grep -E \'ssh.*' + str(port) + '\' | /bin/grep -v grep | wc -l';
    output = check_output(command, shell=True)
    print 'output: ', output
    if int(output) == 0:
        return False
    else:
        return True

def try_use_rsa():
    pub = os.getenv('HOME') + "/.ssh/id_rsa.pub"
    if not os.path.isfile(pub):
        # generate id_rsa.pub
        command = 'ssh-keygen -b 2048 -t rsa -f ~/.ssh/id_rsa -P ""'
        print command
        print call(command, shell=True)
    # copy id_rsa.pub
    command = 'sshpass -p' + PASSWORD + ' ssh-copy-id -o "StrictHostKeyChecking=no"  -o "UserKnownHostsFile /dev/null" ' + USER + '@' + SSH_SERVER
    print command
    print call(command, shell=True)



def exec_ssh(port):
    print "#### start establish ssh forwarding connection port, ", port
    if port == None:
        raise Exception('Port not avaliable')
    command = 'sshpass -p' + PASSWORD + ' ssh -o "StrictHostKeyChecking=no"  -o "UserKnownHostsFile /dev/null" -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -fCR ' + str(port) +':localhost:22 ' + USER + '@' + SSH_SERVER + ' sleep ' + str(ALIVE_TIME)
    print command
    ret = call(shlex.split(command), shell=False)
    if check_ssh_connection(port):
        return ret
    else: ## if sshpass fails (sometimes when another process has large CPU usage (100%) , no ssh connection, try another, 
        try_use_rsa()
        command = 'ssh -o "PasswordAuthentication=no" -o "StrictHostKeyChecking=no"  -o "UserKnownHostsFile /dev/null" -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -fCR ' + str(port) +':localhost:22 ' + USER + '@' + SSH_SERVER + ' sleep ' + str(ALIVE_TIME)
        print command
        ret = call(shlex.split(command), shell=False)
        return ret

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

def on_message(client, userdata, msg):
    print('Receive topic:' + msg.topic + ' payload: ' +str(msg.payload))
    payload = ast.literal_eval(str(msg.payload))
    from_id = payload['from']
    if payload['type'] == 'request':
        if payload['command'] == 'ssh':
            port = getAvailablePort(SSH_SERVER, PORT_RANGE)
            if exec_ssh(port) == 0:
                print "#### OK, SSH forwarding connection established, port, ", port
                response = {'from': userdata['id'], 'type':'response', 'command':payload['command'], 'data':port}
                client.publish(payload['from'], str(response))
            else:
                raise Exception ('run ssh failed')
        if payload['command'] == 'list':
            response = {'from': userdata['id'], 'type':'response', 'command':payload['command'], 'data': get_hostname()}
            client.publish(payload['from'], str(response))



if __name__ == '__main__':
    id = get_mac_str()
    print 'Mac: ', id
    client = mqtt.Client(userdata={'id':id})
    client.on_connect = on_connect
    client.on_message = on_message
    client.connect(MQTT_SERVER, MQTT_PORT, 60)
    client.loop_forever()