#!/usr/bin/env python3
#
# This script depends on python-dateutil and python-pytz for properly handling
# times and time zones of calendar events.
import datetime
import dateutil.parser
import httplib2
import itertools
import logging
import argparse
import os
import pytz
import sys
import time
from typing import List, Optional, Set, Tuple

from oauth2client import client
from oauth2client.file import Storage
try:
    from googleapiclient import discovery
except ImportError:
    logging.exception('Install google-api-python-client')

sys.path.append(os.path.join(os.path.dirname(__file__), '../../'))
import zulip

SCOPES = 'https://www.googleapis.com/auth/calendar.readonly'
CLIENT_SECRET_FILE = 'client_secret.json'
APPLICATION_NAME = 'Zulip'
HOME_DIR = os.path.expanduser('~')

# Our cached view of the calendar, updated periodically.
events = []  # type: List[Tuple[int, datetime.datetime, str]]

# Unique keys for events we've already sent, so we don't remind twice.
sent = set()  # type: Set[Tuple[int, datetime.datetime]]

sys.path.append(os.path.dirname(__file__))

parser = zulip.add_default_arguments(argparse.ArgumentParser(r"""

google-calendar --calendar calendarID@example.calendar.google.com

    This integration can be used to send yourself reminders, on Zulip, of Google Calendar Events.

    Specify your Zulip API credentials and server in a ~/.zuliprc file or using the options.

    Before running this integration make sure you run the get-google-credentials file to give Zulip
    access to certain aspects of your Google Account.

    This integration should be run on your local machine. Your API key and other information are
    revealed to local users through the command line.

    Depends on: google-api-python-client
"""))


parser.add_argument('--interval',
                    dest='interval',
                    default=30,
                    type=int,
                    action='store',
                    help='Minutes before event for reminder [default: 30]',
                    metavar='MINUTES')

parser.add_argument('--calendar',
                    dest = 'calendarID',
                    default = 'primary',
                    type = str,
                    action = 'store',
                    help = 'Calendar ID for the calendar you want to receive reminders from.')

options = parser.parse_args()

if not (options.zulip_email):
    parser.error('You must specify --user')

zulip_client = zulip.init_from_options(options)

def get_credentials() -> client.Credentials:
    """Gets valid user credentials from storage.

    If nothing has been stored, or if the stored credentials are invalid,
    an exception is thrown and the user is informed to run the script in this directory to get
    credentials.

    Returns:
        Credentials, the obtained credential.
    """
    try:
        credential_path = os.path.join(HOME_DIR,
                                       'google-credentials.json')

        store = Storage(credential_path)
        credentials = store.get()

        return credentials
    except client.Error:
        logging.exception('Error while trying to open the `google-credentials.json` file.')
    except OSError:
        logging.error("Run the get-google-credentials script from this directory first.")


def populate_events() -> Optional[None]:
    global events

    credentials = get_credentials()
    creds = credentials.authorize(httplib2.Http())
    service = discovery.build('calendar', 'v3', http=creds)

    now = datetime.datetime.now(pytz.utc).isoformat()
    feed = service.events().list(calendarId=options.calendarID, timeMin=now, maxResults=5,
                                 singleEvents=True, orderBy='startTime').execute()

    events = []
    for event in feed["items"]:
        try:
            start = dateutil.parser.parse(event["start"]["dateTime"])
            # According to the API documentation, a time zone offset is required
            # for start.dateTime unless a time zone is explicitly specified in
            # start.timeZone.
            if start.tzinfo is None:
                event_timezone = pytz.timezone(event["start"]["timeZone"])
                # pytz timezones include an extra localize method that's not part
                # of the tzinfo base class.
                start = event_timezone.localize(start)
        except KeyError:
            # All-day events can have only a date.
            start_naive = dateutil.parser.parse(event["start"]["date"])

            # All-day events don't have a time zone offset; instead, we use the
            # time zone of the calendar.
            calendar_timezone = pytz.timezone(feed["timeZone"])
            # pytz timezones include an extra localize method that's not part
            # of the tzinfo base class.
            start = calendar_timezone.localize(start_naive)

        try:
            events.append((event["id"], start, event["summary"]))
        except KeyError:
            events.append((event["id"], start, "(No Title)"))


def send_reminders() -> Optional[None]:
    global sent

    messages = []
    keys = set()
    now = datetime.datetime.now(tz=pytz.utc)

    for id, start, summary in events:
        dt = start - now
        if dt.days == 0 and dt.seconds < 60 * options.interval:
            # The unique key includes the start time, because of
            # repeating events.
            key = (id, start)
            if key not in sent:
                if start.hour == 0 and start.minute == 0:
                    line = '%s is today.' % (summary,)
                else:
                    line = '%s starts at %s' % (summary, start.strftime('%H:%M'))
                print('Sending reminder:', line)
                messages.append(line)
                keys.add(key)

    if not messages:
        return

    if len(messages) == 1:
        message = 'Reminder: ' + messages[0]
    else:
        message = 'Reminder:\n\n' + '\n'.join('* ' + m for m in messages)

    zulip_client.send_message(dict(
        type    = 'private',
        to      = options.zulip_email,
        sender  = options.zulip_email,
        content = message))

    sent.update(keys)

# Loop forever
for i in itertools.count():
    try:
        # We check reminders every minute, but only
        # download the calendar every 10 minutes.
        if not i % 10:
            populate_events()
        send_reminders()
    except Exception:
        logging.exception("Couldn't download Google calendar and/or couldn't post to Zulip.")
    time.sleep(60)