from time import time
from socket import socket
from socket import AF_INET
from socket import SOCK_DGRAM
from socket import IPPROTO_UDP
from socket import SOL_SOCKET
from socket import SO_REUSEADDR
from socket import SO_BROADCAST


DISCOVERY_ACK = 'IP_DISCOVERY_ACK'.encode()           # ACK for broadcast
DISCOVERY_OK = 'IP_DISCOVERY_OK'.encode()             # Not used yet
DISCOVERY_RSP_GTW = 'IP_DISCOVERY_RSP_GTW'.encode()   # RSP for gateway
DISCOVERY_RSP_MSH = 'IP_DISCOVERY_RSP_MSH'.encode()   # RSP for mesh
DISCOVERY_TIMEOUT = 0.5
SOCKET_TIMEOUT = 0.2
PORT_SERVER = 9434
PORT_CLIENT = 9435


def start_discovery_client():
  sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)
  sock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
  sock.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
  sock.settimeout(SOCKET_TIMEOUT)
  server_address = ('255.255.255.255', PORT_SERVER)
  start_time_stamp = time()
  delta = round(time() - start_time_stamp, 2)
  discovered_devices = []

  try:
    sock.bind(('', PORT_CLIENT))

    while delta <= DISCOVERY_TIMEOUT:
      delta = round(time() - start_time_stamp, 2)
      sock.sendto(DISCOVERY_ACK, server_address)
      data, addr = sock.recvfrom(4096)

      if str(addr[0]) in discovered_devices: continue
      if data == DISCOVERY_RSP_GTW:
        discovered_devices.append(str(addr[0]))

  except Exception as err:
    print(err)

  finally:
    sock.close()
    return discovered_devices[0]