#!/usr/bin/python

import socket, struct
import time
import math
import random, re, thread

class DummyNMEAServer:
  """ This is a fake NMEA Sentence server. """

  HOST = ''
  PORT = 12345

  def __init__(self):
    self.socket = socket.socket()
    self.c = None
    self.stop = False

  def stop_listener(self):
    while True:
      s = self.c.recv(1024)
      try:
        if s=="stop":
          self.stop=True
          break
      except socket.error:
        pass

  def checksum(self, sentence):
    """ Source: http://code.activestate.com/recipes/576789-nmea-sentence-checksum/ """
    if re.search("\n$", sentence):
        sentence = sentence[:-1]

    calc_cksum = 0
    for s in sentence:
        calc_cksum ^= ord(s)

    """ Return the nmeadata, the checksum from
        sentence, and the calculated checksum
    """
    return format(calc_cksum, 'x')



  def run(self):
    """ Sends dummy location info of coordinates moving around (0, 0)
      in circular pattern """
    s = self.socket
    s.bind((DummyNMEAServer.HOST, DummyNMEAServer.PORT))
    s.listen(5)
    while True:
      c, addr = s.accept()
      self.c = c
      
      print 'Got connection from', addr
      lat = lon = 0
      cy = cx = 0.0
      r = 4.3
      t = 0
      latS = lonS = ""
      # thread.start_new_thread (self.stop_listener, ())
      while True:
        for i in range(360):
          lat = cx + math.cos(i / 180.0 * math.pi) * r
          lon = cy + math.sin(i / 180.0 * math.pi) * r

          t = time.strftime("%H%M%S", time.gmtime(time.time()))

          latS = 'N' if lat >= 0 else 'S'
          lonS = 'E' if lon >= 0 else 'W'

          print t
          gga = "$GPGGA,%s,%02d%06.3f,%s,%03d%06.3f,%s,1,08,0.9,545.4,M,46.9,M,," % (
            t, abs(lat), abs((lat-int(lat))*60), latS, abs(lon), abs((lon-int(lon))*60), lonS)
          gga = gga + "*" + str(self.checksum(gga))
          size = struct.pack("!L",len(gga))
          c.send(size)
          print(len(gga))
          print gga
          c.send(gga)
          time.sleep(random.randint(1,10))
    c.close()       

app = DummyNMEAServer();
app.run();