#!/usr/bin/env python
# 
# Copyright 2009 Matthew Brush < mbrush AT leftclick DOT ca >
# 
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA 02110-1301, USA.
 
__version__ = "0.1"
__all__ = [ 'get_gps_port', 'test_port' ]
 
import serial
import glob
import re
import platform
 
BAUD_RATE = 4800    # the standard nmea baud rate
TIMEOUT = 2         # time to wait for nmea sentences
 
class NoGpsReceiverError(Exception):
    def __init__(self, value):
        self.value = value
    def __str__(self):
        return repr(self.value)
 
def scan():
    """ Scan for available ports. return a list of device names. """
    if platform.system == 'Windows':
        import scanwin32
        ports = []
        for order, port, desc, hwid in sorted(scanwin32.comports()):
            ports.append(port)
        return ports
    else:
        import scanlinux
        return scanlinux.scan()
 
 
def test_port(port):
    """ Detects whether NMEA GPS sentences can be read from the port. """
    nmea_gps_pattern = '^\$GP[A-Z]{3},'
    gps_detected = False
    try:
        s = serial.Serial(port, BAUD_RATE, timeout=TIMEOUT)
        for i in range(1,10):   # try 10 lines in a row
            line = s.readline().strip()
            m = re.match(nmea_gps_pattern, line)
            if m:
                gps_detected = True
                break
        s.close()
        return gps_detected
    except serial.SerialException:
        return False
 
def get_gps_port():
    """ Looks for GPS data coming in on any serial port and returns the port name. """
    for port in scan():
        if test_port(port):
            return port
    raise NoGpsReceiverError('Unable to locate a suitable GPS receiver.')
 
def main():
    print "Testing ports to find GPS receiver..."
    try:
        if platform.system == 'Windows':
            print "  Warning: gpsdetect not tested in Windows yet."
        for port in scan():
            if test_port(port):
                print "Detected GPS receiver on '" + port + "'."
                found_gps = True
                break
    except NoGpsReceiverError:
        print "No GPS receivers were detected on the system."
 
 
if __name__ == '__main__': main()