How to use the khal.utils.to_unix_time function in khal

def fromVEvents(cls, events_list, ref=None, **kwargs):
        """
        :type events: list
        """
        assert isinstance(events_list, list)

        vevents = dict()
        for event in events_list:
            if 'RECURRENCE-ID' in event:
                if invalid_timezone(event['RECURRENCE-ID']):
                    default_timezone = kwargs['locale']['default_timezone']
                    recur_id = default_timezone.localize(event['RECURRENCE-ID'].dt)
                    ident = str(to_unix_time(recur_id))
                else:
                    ident = str(to_unix_time(event['RECURRENCE-ID'].dt))
                vevents[ident] = event
            else:
                vevents['PROTO'] = event

        if ref is None:
            ref = 'PROTO' if ref in vevents.keys() else list(vevents.keys())[0]
        try:
            if type(vevents[ref]['DTSTART'].dt) != type(vevents[ref]['DTEND'].dt):  # noqa: E721
                raise ValueError('DTSTART and DTEND should be of the same type (datetime or date)')
        except KeyError:
            pass

        if kwargs.get('start'):
            instcls = cls._get_type_from_date(kwargs.get('start'))
        else:
            instcls = cls._get_type_from_vDDD(vevents[ref]['DTSTART'])

thisandfuture = (rrange == THISANDFUTURE)
        if thisandfuture:
            start_shift, duration = calc_shift_deltas(vevent)
            start_shift_seconds = start_shift.days * 3600 * 24 + start_shift.seconds
            duration_seconds = duration.days * 3600 * 24 + duration.seconds

        dtstartend = expand_vevent(vevent, href)
        if not dtstartend:
            # Does this event even have dates? Technically it is possible for
            # events to be empty/non-existent by deleting all their recurrences
            # through EXDATE.
            return

        for dtstart, dtend in dtstartend:
            if dtype == EventType.DATE:
                dbstart = utils.to_unix_time(dtstart)
                dbend = utils.to_unix_time(dtend)
            else:
                dbstart = utils.to_unix_time(dtstart)
                dbend = utils.to_unix_time(dtend)

            if rec_id is not None:
                ref = rec_inst = str(utils.to_unix_time(rec_id.dt))
            else:
                rec_inst = str(dbstart)
                ref = PROTO

            if thisandfuture:
                recs_sql_s = (
                    'UPDATE {0} SET dtstart = rec_inst + ?, dtend = rec_inst + ?, ref = ? '
                    'WHERE rec_inst >= ? AND href = ? AND calendar = ?;'.format(recs_table))
                stuple_f = (

def get_floating_calendars(self, start: dt.datetime, end: dt.datetime) -> Iterable[str]:
        assert start.tzinfo is None
        assert end.tzinfo is None
        start_u = utils.to_unix_time(start)
        end_u = utils.to_unix_time(end)
        sql_s = (
            'SELECT events.calendar FROM '
            'recs_float JOIN events ON '
            'recs_float.href = events.href AND '
            'recs_float.calendar = events.calendar WHERE '
            '(dtstart >= ? AND dtstart < ? OR '
            'dtend > ? AND dtend <= ? OR '
            'dtstart <= ? AND dtend > ? ) AND events.calendar in ({0}) '
            'ORDER BY dtstart')
        stuple = tuple(
            [start_u, end_u, start_u, end_u, start_u, end_u] + list(self.calendars))  # type: ignore
        result = self.sql_ex(sql_s.format(','.join(["?"] * len(self.calendars))), stuple)
        for calendar in result:
            yield calendar[0]

def get_floating(self, start, end) \
            -> Iterable[Tuple[str, str, dt.datetime, dt.datetime, str, str, str]]:
        """return floating events between `start` and `end`

        :type start: datetime.datetime
        :type end: datetime.datetime
        """
        assert start.tzinfo is None
        assert end.tzinfo is None
        start_u = utils.to_unix_time(start)
        end_u = utils.to_unix_time(end)
        sql_s = (
            'SELECT item, recs_float.href, dtstart, dtend, ref, etag, dtype, events.calendar '
            'FROM recs_float JOIN events ON '
            'recs_float.href = events.href AND '
            'recs_float.calendar = events.calendar WHERE '
            '(dtstart >= ? AND dtstart < ? OR '
            'dtend > ? AND dtend <= ? OR '
            'dtstart <= ? AND dtend > ? ) AND events.calendar in ({0}) '
            'ORDER BY dtstart')
        stuple = tuple(
            [start_u, end_u, start_u, end_u, start_u, end_u] + list(self.calendars))  # type: ignore
        result = self.sql_ex(sql_s.format(','.join(["?"] * len(self.calendars))), stuple)
        for item, href, start, end, ref, etag, dtype, calendar in result:
            start = dt.datetime.utcfromtimestamp(start)
            end = dt.datetime.utcfromtimestamp(end)
            if dtype == EventType.DATE:

def get_localized(self, start, end) \
            -> Iterable[Tuple[str, str, dt.datetime, dt.datetime, str, str, str]]:
        """returns
        :type start: datetime.datetime
        :type end: datetime.datetime
        :param minimal: if set, we do not return an event but a minimal stand in
        :type minimal: bool
        """
        assert start.tzinfo is not None
        assert end.tzinfo is not None
        start = utils.to_unix_time(start)
        end = utils.to_unix_time(end)
        sql_s = (
            'SELECT item, recs_loc.href, dtstart, dtend, ref, etag, dtype, events.calendar '
            'FROM recs_loc JOIN events ON '
            'recs_loc.href = events.href AND '
            'recs_loc.calendar = events.calendar WHERE '
            '(dtstart >= ? AND dtstart <= ? OR '
            'dtend > ? AND dtend <= ? OR '
            'dtstart <= ? AND dtend >= ?) AND events.calendar in ({0}) '
            'ORDER BY dtstart')
        stuple = tuple([start, end, start, end, start, end] + list(self.calendars))
        result = self.sql_ex(sql_s.format(','.join(["?"] * len(self.calendars))), stuple)
        for item, href, start, end, ref, etag, dtype, calendar in result:
            start = pytz.UTC.localize(dt.datetime.utcfromtimestamp(start))
            end = pytz.UTC.localize(dt.datetime.utcfromtimestamp(end))
            yield item, href, start, end, ref, etag, calendar

def get_localized(self, start, end) \
            -> Iterable[Tuple[str, str, dt.datetime, dt.datetime, str, str, str]]:
        """returns
        :type start: datetime.datetime
        :type end: datetime.datetime
        :param minimal: if set, we do not return an event but a minimal stand in
        :type minimal: bool
        """
        assert start.tzinfo is not None
        assert end.tzinfo is not None
        start = utils.to_unix_time(start)
        end = utils.to_unix_time(end)
        sql_s = (
            'SELECT item, recs_loc.href, dtstart, dtend, ref, etag, dtype, events.calendar '
            'FROM recs_loc JOIN events ON '
            'recs_loc.href = events.href AND '
            'recs_loc.calendar = events.calendar WHERE '
            '(dtstart >= ? AND dtstart <= ? OR '
            'dtend > ? AND dtend <= ? OR '
            'dtstart <= ? AND dtend >= ?) AND events.calendar in ({0}) '
            'ORDER BY dtstart')
        stuple = tuple([start, end, start, end, start, end] + list(self.calendars))
        result = self.sql_ex(sql_s.format(','.join(["?"] * len(self.calendars))), stuple)
        for item, href, start, end, ref, etag, dtype, calendar in result:
            start = pytz.UTC.localize(dt.datetime.utcfromtimestamp(start))
            end = pytz.UTC.localize(dt.datetime.utcfromtimestamp(end))
            yield item, href, start, end, ref, etag, calendar

duration_seconds = duration.days * 3600 * 24 + duration.seconds

        dtstartend = expand_vevent(vevent, href)
        if not dtstartend:
            # Does this event even have dates? Technically it is possible for
            # events to be empty/non-existent by deleting all their recurrences
            # through EXDATE.
            return

        for dtstart, dtend in dtstartend:
            if dtype == EventType.DATE:
                dbstart = utils.to_unix_time(dtstart)
                dbend = utils.to_unix_time(dtend)
            else:
                dbstart = utils.to_unix_time(dtstart)
                dbend = utils.to_unix_time(dtend)

            if rec_id is not None:
                ref = rec_inst = str(utils.to_unix_time(rec_id.dt))
            else:
                rec_inst = str(dbstart)
                ref = PROTO

            if thisandfuture:
                recs_sql_s = (
                    'UPDATE {0} SET dtstart = rec_inst + ?, dtend = rec_inst + ?, ref = ? '
                    'WHERE rec_inst >= ? AND href = ? AND calendar = ?;'.format(recs_table))
                stuple_f = (
                    start_shift_seconds, start_shift_seconds + duration_seconds,
                    ref, rec_inst, href, calendar,
                )
                self.sql_ex(recs_sql_s, stuple_f)

def fromVEvents(cls, events_list, ref=None, **kwargs):
        """
        :type events: list
        """
        assert isinstance(events_list, list)

        vevents = dict()
        for event in events_list:
            if 'RECURRENCE-ID' in event:
                if invalid_timezone(event['RECURRENCE-ID']):
                    default_timezone = kwargs['locale']['default_timezone']
                    recur_id = default_timezone.localize(event['RECURRENCE-ID'].dt)
                    ident = str(to_unix_time(recur_id))
                else:
                    ident = str(to_unix_time(event['RECURRENCE-ID'].dt))
                vevents[ident] = event
            else:
                vevents['PROTO'] = event

        if ref is None:
            ref = 'PROTO' if ref in vevents.keys() else list(vevents.keys())[0]
        try:
            if type(vevents[ref]['DTSTART'].dt) != type(vevents[ref]['DTEND'].dt):  # noqa: E721
                raise ValueError('DTSTART and DTEND should be of the same type (datetime or date)')
        except KeyError:
            pass

        if kwargs.get('start'):
            instcls = cls._get_type_from_date(kwargs.get('start'))

def get_localized_calendars(self, start: dt.datetime, end: dt.datetime) -> Iterable[str]:
        assert start.tzinfo is not None
        assert end.tzinfo is not None
        start_u = utils.to_unix_time(start)
        end_u = utils.to_unix_time(end)
        sql_s = (
            'SELECT events.calendar FROM '
            'recs_loc JOIN events ON '
            'recs_loc.href = events.href AND '
            'recs_loc.calendar = events.calendar WHERE '
            '(dtstart >= ? AND dtstart <= ? OR '
            'dtend > ? AND dtend <= ? OR '
            'dtstart <= ? AND dtend >= ?) AND events.calendar in ({0}) '
            'ORDER BY dtstart')
        stuple = tuple(
            [start_u, end_u, start_u, end_u, start_u, end_u] + list(self.calendars))  # type: ignore
        result = self.sql_ex(sql_s.format(','.join(["?"] * len(self.calendars))), stuple)
        for calendar in result:
            yield calendar[0]  # result is always an iterable, even if getting only one item

if not dtstartend:
            # Does this event even have dates? Technically it is possible for
            # events to be empty/non-existent by deleting all their recurrences
            # through EXDATE.
            return

        for dtstart, dtend in dtstartend:
            if dtype == EventType.DATE:
                dbstart = utils.to_unix_time(dtstart)
                dbend = utils.to_unix_time(dtend)
            else:
                dbstart = utils.to_unix_time(dtstart)
                dbend = utils.to_unix_time(dtend)

            if rec_id is not None:
                ref = rec_inst = str(utils.to_unix_time(rec_id.dt))
            else:
                rec_inst = str(dbstart)
                ref = PROTO

            if thisandfuture:
                recs_sql_s = (
                    'UPDATE {0} SET dtstart = rec_inst + ?, dtend = rec_inst + ?, ref = ? '
                    'WHERE rec_inst >= ? AND href = ? AND calendar = ?;'.format(recs_table))
                stuple_f = (
                    start_shift_seconds, start_shift_seconds + duration_seconds,
                    ref, rec_inst, href, calendar,
                )
                self.sql_ex(recs_sql_s, stuple_f)
            else:
                recs_sql_s = (
                    'INSERT OR REPLACE INTO {0} '