#!/usr/bin/python

##############################################################################
# GCALC - A command-line interface to the Google calculation. Simply passes
#         the command-line arguments to the Google web-site and displays the
#         results.
#
# Published under the GNU Public License: http://www.gnu.org/copyleft/gpl.html
#
# $Id: $

from httplib import HTTPConnection;
import sys, re, urllib, htmlentitydefs


##############################################################################
# HTTP Constants

GoogleServer = 'www.google.co.uk';
RequestBase  = '/search?num=1&q=';
Headers      = { 'User-Agent' : 'Mozilla/4.0' };

##############################################################################
# Regular Expressions

CoarseMatchEx = re.compile ( '.*calc_img\.gif[^>]*>(?P<match>.+)<\/b>', re.DOTALL );
FineMatchEx   = re.compile ( '.*<b>(?P<match>.*)</b></td>' );

PostProcessExs = [ ( re.compile ( pattern ), subst ) for pattern, subst in ( ( '<sup>', '^' ), ( '<[^>]*>', '' ) ) ];

##############################################################################
# Script

# Construct the request string (the path component of the HTTP request)
calculation = ' '.join ( sys.argv [ 1 : ] ).strip ( );
if not calculation:
    sys.exit ( 'Must provide something to calculate!' );
requeststring = RequestBase + urllib.quote ( calculation );

# Connect to the Google server, make the request and retrieve the response
try:
    connection = HTTPConnection ( GoogleServer );
    connection.request ( method = 'GET', url = requeststring, headers = Headers  );
    response = connection.getresponse ( ).read ( ).strip ( );
except Exception, exception:
    sys.exit ( 'Unable to make request "http://%s/%s" - %s' % ( GoogleServer, requeststring, exception ) );

# Process the response and display the Google Calculator response, if any
coarsematch = CoarseMatchEx.match ( response );
if coarsematch:
    finematch = FineMatchEx.match ( coarsematch.group ( 'match' ) );
    if finematch:
        value = finematch.group ( 'match' );
        # Pass the value through the post processing regular expressions
        for regex, subst in PostProcessExs: value = regex.sub ( subst, value );
        # Expand any unicode values to ASCII
        for unicode in htmlentitydefs.codepoint2name:
            if '&#%d;' % unicode in value:
                entity = htmlentitydefs.codepoint2name [ unicode ];
                if entity in htmlentitydefs.entitydefs:
                    value = value.replace ( '&#%d;' % unicode, htmlentitydefs.entitydefs [ entity ] );
                else:
                    value = value.replace ( '&#%d;' % unicode, '' );
        # Expand any entity definitions to ASCII
        for entity in htmlentitydefs.entitydefs:
            if '&%s;' % entity in value:
                value = value.replace ( '&%s;' % entity, htmlentitydefs.entitydefs [ entity ] );
        # Done!
        print value;
    else:
        sys.exit ( 'Warning - Google appears to have changed its page layout, update Fine Match expression' );
else:
    print 'Google Calculator did not understand : %s' % calculation;