#!/usr/bin/env python3

# Retrieves the time (and time difference) at a location (can be an address,
# postal code, country name, etc). Uses Google Maps APIs to map locations to
# coordinates, and coordinates to timezones.
#
# Requires: pytz. tzlocal
# Usage: time-in Copenhagen "Toronto, ON" Vancouver

import sys
import os
import json
from base64 import b64encode
from datetime import datetime
from urllib import request

from pytz import timezone
from tzlocal import get_localzone

URL_BASE = "https://maps.googleapis.com/maps/api/"
URL_TZ = URL_BASE + "timezone/json?location={},{}&timestamp={}"
URL_GEOCODE = URL_BASE + "geocode/json?address={}"

CACHE_FILE = "/tmp/time-in"
CACHE = {}


#
def _generate_url(url, *args):
    return url.format(*map(request.quote, map(str, args)))

def _request(url, *args):
    try:
        real_url = url.format(*map(request.quote, map(str, args)))
        resp = request.urlopen(real_url).read()
        result = json.loads(resp.decode('utf-8'))
        if result['status'] == 'OK':
            return result
        elif result['status'] != 'UNKNOWN_ERROR':
            raise Exception(result['error_message'])
    except IOError:
        print("IOError")  # FIXME Better error handling

def get_timezone(lat, lng, timestamp):
    return _request(URL_TZ, lat, lng, timestamp)['timeZoneId']

def get_coords(desc):
    result = _request(URL_GEOCODE, desc)
    if result['results']:
        return {
            "lat": result['results'][0]['geometry']['location']['lat'],
            "lng": result['results'][0]['geometry']['location']['lng'],
            "name": result['results'][0]['formatted_address']
        }

def cache(key, fn, ttl):
    if key in CACHE and CACHE[key]['time'] < CACHE[key]['time'] + ttl:
        return CACHE[key]['value']
    value = fn()
    if value is not None:
        CACHE[key] = {
            'time': datetime.now().timestamp(),
            'value': fn()
        }
    return value

def diff(a, b):
    a = a.replace(tzinfo=None)
    b = b.replace(tzinfo=None)
    return max(a, b) - min(a, b)

def encode(s):
    return str(b64encode(s.encode('ascii')))


#
if __name__ == '__main__':
    if not sys.argv[1:]:
        print("Usage: {} [LOCATION]".format(sys.argv[0]))
        sys.exit(1)

    if os.path.isfile(CACHE_FILE):
        with open(CACHE_FILE, 'r') as f:
            CACHE = json.load(f)

    here = get_localzone().localize(datetime.now())
    for location in sys.argv[1:]:
        d_coords = cache("coords-" + encode(location), lambda: get_coords(location), 86400)
        if d_coords:
            d_tzname = cache(
                "tz-" + encode(location),
                lambda: get_timezone(d_coords['lat'], d_coords['lng'], here.timestamp()),
                1800
            )

            then = here.astimezone(timezone(d_tzname))
            diff = diff(here, then)

            print("{:24} {}\t{} {}".format(
                d_coords['name'],
                then,
                diff,
                "ago" if then < here else "ahead"
            ))
        else:
            print("Couldn't find {}".format(location))

    with open(CACHE_FILE, 'w') as f:
        json.dump(CACHE, f)

    sys.exit(0)