#!/usr/bin/env python3
# Protocol:
#   Server sends type, length, username
#   1 byte type is one byte
#   2 bytes username length is two bytes
#   length bytes Actual username
#   Types:  0 - existing login, 1 - new login, 2 - logout

from subprocess import getoutput
from _thread import start_new_thread
from socket import *
from struct import *
from time import sleep

clients = []

def updater():
    user_string = getoutput('who | cut -d " " -f 1 | sort -u')
    while True:
        sleep(1)
        new_user_string = getoutput('who | cut -d " " -f 1 | sort -u')
        if(new_user_string != user_string):
            old_users = user_string.split()
            user_string = new_user_string
            users = user_string.split()
            new_users = [u for u in users if u not in old_users]
            loggedout_users = [u for u in old_users if u not in users]
            if len(new_users):
                for nu in new_users:
                    print("New user:  ", nu)
                    nu_bytes = nu.encode("utf-8")
                    user_message = pack("<BH", 1, len(nu_bytes))
                    for c in clients:
                        try:
                            c.send(user_message)
                            c.send(nu_bytes)
                        except:
                            print("Couldn't send to one client")
            if len(loggedout_users):
                for nu in loggedout_users:
                    print("Logged out user:  ", nu)
                    nu_bytes = nu.encode("utf-8")
                    user_message = pack("<BH", 2, len(nu_bytes))
                    for c in clients:
                        try:
                            c.send(user_message)
                            c.send(nu_bytes)
                        except:
                            print("Couldn't send to one client")
    
start_new_thread(updater, ())

skt = socket(AF_INET, SOCK_STREAM)
skt.bind(("0.0.0.0", 5091))
skt.listen(5)
while True:
    client_socket, client_address = skt.accept()
    print("New connection from:", client_address)
    users = getoutput('who | cut -d " " -f 1 | sort -u').split()
    for u in users:
        byte_username = u.encode("utf-8")
        header = pack("<BH", 0, len(byte_username))
        client_socket.send(header)
        client_socket.send(byte_username)
    clients.append(client_socket)