# -*- coding: utf-8 -*-

import sys

# Convert latitude and longitude to Maidenhead grid locators.
#
# Arguments are in signed decimal latitude and longitude. For example,
# the location of my QTH Palo Alto, CA is: 37.429167, -122.138056 or
# in degrees, minutes, and seconds: 37° 24' 49" N 122° 6' 26" W
#
# written by Walter Underwood K6WRU
# Found on https://ham.stackexchange.com/questions/221/how-can-one-convert-from-lat-long-to-grid-square
# 

upper = 'ABCDEFGHIJKLMNOPQRSTUVWX'
lower = 'abcdefghijklmnopqrstuvwx'

def to_grid(dec_lat, dec_lon):
    if not (-180<=dec_lon<180):
        sys.stderr.write('longitude must be -180<=lon<180, given %f\n'%dec_lon)
        sys.exit(32)
    if not (-90<=dec_lat<90):
        sys.stderr.write('latitude must be -90<=lat<90, given %f\n'%dec_lat)
        sys.exit(33) # can't handle north pole, sorry, [A-R]

    adj_lat = dec_lat + 90.0
    adj_lon = dec_lon + 180.0

    grid_lat_sq = upper[int(adj_lat/10)];
    grid_lon_sq = upper[int(adj_lon/20)];

    grid_lat_field = str(int(adj_lat%10))
    grid_lon_field = str(int((adj_lon/2)%10))

    adj_lat_remainder = (adj_lat - int(adj_lat)) * 60
    adj_lon_remainder = ((adj_lon) - int(adj_lon/2)*2) * 60

    grid_lat_subsq = lower[int(adj_lat_remainder/2.5)]
    grid_lon_subsq = lower[int(adj_lon_remainder/5)]

    return grid_lon_sq + grid_lat_sq + grid_lon_field + grid_lat_field + grid_lon_subsq + grid_lat_subsq

def usage():
    print 'This script takes two arguments, decimal latitude and longitude.'
    print 'Example for Newington, Connecticut (W1AW):'
    print 'python maidenhead.py 41.714775 -72.727260'
    print 'returns: FN31pr'

def test():
    # First four test examples are from "Conversion Between Geodetic and Grid Locator Systems",
    # by Edmund T. Tyson N5JTY QST January 1989
    test_data = (
        ('Munich', (48.14666,11.60833), 'JN58td'),
        ('Montevideo', (-34.91,-56.21166), 'GF15vc'),
        ('Washington, DC', (38.92,-77.065), 'FM18lw'),
        ('Wellington', (-41.28333,174.745), 'RE78ir'),
        ('Newington, CT (W1AW)', (41.714775,-72.727260), 'FN31pr'),
        ('Palo Alto (K6WRU)', (37.413708,-122.1073236), 'CM87wj'),
    )
    print 'Running self test\n'
    passed = True
    for name,latlon,grid in test_data:
        print 'Testing %s at %f %f:'%(name,latlon[0],latlon[1])
        test_grid = to_grid(latlon[0], latlon[1])
        if test_grid != grid:
            print 'Failed '+test_grid+' should be '+grid
            passed = False
        else:
            print 'Passed '+test_grid
    print ''
    if passed: print 'Passed!'
    else: print 'Failed!'

def main(argv=None):
    if argv is None: argv = sys.argv
    if len(argv) != 3:
        usage()
        print ''
        test()
    else:
        print to_grid(float(argv[1]),float(argv[2]))

main()