"""
This file contains the calendar class wich abstracts the Google gdata API for working with
Google Calendars.
"""
import datetime
import pytz

from django.utils.tzinfo import FixedOffset
from gdata.calendar.service import CalendarService
from gdata.calendar import CalendarEventFeed
from gdata.calendar import CalendarEventEntry
from gdata.calendar import Who
from gdata.calendar import Where
from gdata.calendar import When
from gdata.service import BadAuthentication
import atom

from gcalendar.models import Event


class CalendarError(Exception):
    def __init__(self, msg):
        self.msg = msg

    def __str__(self):
        return repr(self.msg)


class Calendar(object):
    DATE_FMT = '%Y-%m-%d'
    DATE_TIME_FMT = DATE_FMT + 'T%H:%M:%S'
    DATE_TIME_TZ_FMT = DATE_TIME_FMT + '.000Z'

    def __init__(self, email, password, calendar_id='default'): 
        self.client = CalendarService()
        self.client.email = email
        self.client.password = password
        self.client.source = 'Google-Calendar_Python_GCalendar'
        self.insert_feed = '/calendar/feeds/%s/private/full' % calendar_id
        self.batch_feed = '%s/batch' % self.insert_feed
        try:
            self.client.ProgrammaticLogin()
        except BadAuthentication:
            raise CalendarError('Incorrect password')
        except Exception, e:
            raise CalendarError(str(e))

    def sync_events(self, qs):
        request_feed = CalendarEventFeed()
        for model in qs:
            if model.status == Event.NEW_APRV:
                event = CalendarEventEntry()
                request_feed.AddInsert(entry=self._populate_event(model, event))
            elif model.status == Event.EDIT_APRV:
                event = self._retrieve_event(model)
                request_feed.AddUpdate(entry=self._populate_event(model, event))
            elif model.status == Event.DEL_APRV:
                event = self._retrieve_event(model)
                request_feed.AddDelete(entry=event)
            else:
                assert False, 'unexpected status in sync_events'

        try:
            response_feed = self.client.ExecuteBatch(request_feed, self.batch_feed)
        except Exception, e:
            raise CalendarError('ExecuteBatch exception: %s' % e)

        err_msgs = []
        for entry in response_feed.entry:
            i = int(entry.batch_id.text)
            code = int(entry.batch_status.code)

            error = False
            if qs[i].status == Event.NEW_APRV or qs[i].status == Event.EDIT_APRV:
                if (code == 201 and qs[i].status == Event.NEW_APRV) or \
                        (code == 200 and qs[i].status == Event.EDIT_APRV):
                    qs[i].google_id = entry.id.text
                    qs[i].status = Event.ON_CAL
                    qs[i].save()
                else:
                    error = True
            elif qs[i].status == Event.DEL_APRV:
                if code == 200:
                    qs[i].delete()
                else:
                    error = True

            if error:
                err_msgs.append('%s - (%d) %s' % (
                    qs[i].what, code, entry.batch_status.reason))

        if len(err_msgs) > 0:
            raise CalendarError(', '.join(err_msgs))

    def _retrieve_event(self, model):
        try:
            event = self.client.GetCalendarEventEntry(model.google_id)
        except Exception, e:
            raise CalendarError('Could not retrieve event from Google: %s, %s' \
                    % (model.what, e))
        return event

    def _populate_event(self, model, event):
        """Populates a gdata event from an Event model object."""
        event.title = atom.Title(text=model.what)
        event.content = atom.Content(text=model.html)
        event.where = [Where(value_string=model.where)]
        event.who = [Who(name=model.user.username, email=model.user.email)]

        if model.all_day:
            start_time = self._make_time(model.start_date)
            if model.start_date == model.end_date:
                end_time = None
            else:
                end_time = self._make_time(model.end_date)
        else:
            start_time = self._make_time(model.start_date, model.start_time, model.time_zone)
            end_time = self._make_time(model.end_date, model.end_time, model.time_zone)

        event.when = [When(start_time=start_time, end_time=end_time)]
        return event
    
    def _make_time(self, date, time=None, tz_name=None):
        """
        Returns the gdata formatted date/time string given a date, optional time,
        and optional time zone name (e.g. 'US/Pacific'). If the time zone name is None,
        no time zone info will be added to the string.
        """

        if time is not None:
            d = datetime.datetime.combine(date, time)
        else:
            d = datetime.datetime(date.year, date.month, date.day)

        if time is None:
            s = d.strftime(self.DATE_FMT)
        elif tz_name is None:
            s = d.strftime(self.DATE_TIME_FMT)
        else:
            try:
                tz = pytz.timezone(tz_name)
            except pytz.UnknownTimeZoneError:
                raise CalendarError('Invalid time zone: %s' (tz_name,))
            local = tz.localize(d)
            zulu = local.astimezone(FixedOffset(0))
            s = zulu.strftime(self.DATE_TIME_TZ_FMT)

        return s