#!/usr/bin/python

"""
Find the average population density of a set of GPS coordinates.
"""

import sys
import os
import site
import pgdb
from optparse import OptionParser

# Basically, add '../src' to our path.
# Needed for the imports that follow.
site.addsitedir(os.path.dirname(os.path.abspath(sys.argv[0])) + '/../src')

import Configuration.Defaults
import ExitCodes
import GPS
import StringUtils
import SummaryFile1


"""
Parse the command line options. There's some magic involved here;
otherwise, optparse woule like nothing more than to interpret GPS
coordinates such as '-78.000000' as options.
"""
for idx, value in enumerate(sys.argv):
    # Please oh please don't rename this script to something which
    # validates as a negative float.
    if (StringUtils.is_negative_float(value)):
        sys.argv.insert(idx, '--')
        # We have to break here, otherwise the negative argument
        # will get shifted down the list, and we'll hit it again
        # in the next iteration of enumerate(). And then it'll
        # get shifted down the list...
        break
    
usage = '%prog [options] <longitude> <latitude>'

# -h (help) Conflicts with -h HOSTNAME
parser = OptionParser(usage=usage, add_help_option = False)

# Use this module's docstring as the description.
parser.description = __doc__.strip()

parser.add_option('-h',
                  '--host',
                  help='The hostname/address where the database is located.',
                  default=Configuration.Defaults.DATABASE_HOST)

parser.add_option('-d',
                  '--database',
                  help='The database in which the population data are stored.',
                  default=Configuration.Defaults.DATABASE_NAME)

parser.add_option('-U',
                  '--username',
                  help='The username who has access to the database.',
                  default=Configuration.Defaults.DATABASE_USERNAME)

(options, args) = parser.parse_args()

if len(args) < 2:
    print "\nERROR: You must supply a longitude and latitude.\n"
    parser.print_help()
    print '' # Print a newline
    raise SystemExit(ExitCodes.NOT_ENOUGH_ARGS)


coords = GPS.Coordinates()
coords.longitude = float(args[0])
coords.latitude = float(args[1])

conn = pgdb.connect(host=options.host,
                    database=options.database,
                    user=options.username)

cursor = conn.cursor()

###########
# WARNING #
###########
#
# Most GIS software, including PostGIS and the associated libraries,
# store and manipulate GPS coordinates in (longitude, latitude) format
# rather than (latitude, longitude) format.
#

query = """
SELECT population_density
FROM (sf1_blocks INNER JOIN tiger
      ON sf1_blocks.tiger_blkidfp00=tiger.blkidfp00)
WHERE ST_Contains(tiger.the_geom,
                  ST_SetSRID(ST_Point(%.6f, %.6f), 4269));
""" % (coords.longitude, coords.latitude)

cursor.execute(query)
rows = cursor.fetchall()

if len(rows) > 0:
    avg_density = rows[0][0]
    print str(avg_density)
else:
    print 'Error: No rows returned.'
    print 'Did you pass (longitude, latitude) in the correct order?'
    raise SystemExit(ExitCodes.NO_RESULTS)
    
conn.close()