code/breadcrumb/client/tracking.py

   1 # -*- coding: utf8 -*-
   2 """Tracking code for Breadcrumb. Mainly glue between other components."""
   3
   4 # Copyright (C) 2008 Laurens Van Houtven <lvh at laurensvh.be>
   5 # This program is free software: you can redistribute it and/or modify
   6 # it under the terms of the GNU General Public License as published by
   7 # the Free Software Foundation, either version 3 of the License, or
   8 # (at your option) any later version.
   9 #
  10 # This program is distributed in the hope that it will be useful,
  11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 # GNU General Public License for more details.
  14 #
  15 # You should have received a copy of the GNU General Public License
  16 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17
  18 import net
  19 import logging
  20 import collections
  21
  22 class Tracker:
  23     """The central class for handling GPS tracking."""
  24     def __init__(self, host = None, port = None):
  25         self.network_interface = net.UDPClient(host = host, port = port)
  26         self.gps = None # See connect_to_gps()
  27         self.messages = collections.deque()
  28         self.last_point = None
  29
  30     def start(self):
  31         """Starts the main tracking cycle.
  32
  33         This iterates over the gps attribute, which produces points.
  34         """
  35         for new_point in self.gps:
  36             if new_point is not None: # new point
  37                 if self.last_point is None:
  38                     self.last_point = new_point
  39
  40                 elif self.last_point < new_point:
  41                     self.last_point.update(new_point)
  42
  43                 else:
  44                     continue
  45
  46                 self.send_point()
  47
  48         logging.debug("No more data from the GPS! Fake device?")
  49
  50     def send_point(self):
  51         """Sends the tracker's current point.
  52
  53         Also tries to send a handler message together with the point, unless
  54         that point already has one. In that case, a second crumb is sent
  55         immediately afterwards that has nothing but the handler message. This
  56         prevents clients that send a handler message with *every* point from
  57         blocking all other handler messages permanently.
  58         """
  59         delayed = False
  60         if self.messages:
  61             if not has_message(self.last_point):
  62                 next_message(point)
  63             else:
  64                 delayed = True
  65
  66         self.network_interface.send_point(self.last_point)
  67         self.last_point.clear_message()
  68
  69         if delayed:
  70             point = self.next_message()
  71             self.networkinterface.sendpoint(point)
  72
  73     def next_message(self, point = {}):
  74         """Gets the next handler message from the queue and adds it to a point.
  75
  76         Uses an empty dict if no point is provided.
  77
  78         The point is always returned. This is useful if no point was provided.
  79         """
  80         if self.messages:
  81             id, msg = self.messages.popleft()
  82             point.update({'handlerid': id, 'handlermessage': msg})
  83
  84         return point
  85
  86 def has_message(point):
  87     """Returns True if the point has a handler message, False otherwise."""
  88     for attr in ('handlerid', 'handlermessage'):
  89         if attr not in point:
  90             return False
  91     return True