Sending logic

tasks.py

# ...

def send_facilitator_survey(study_group):
    """ send survey to all facilitators two days before their second to last meeting """
    now = timezone.now()
    end_of_window = now.replace(minute=0, second=0, microsecond=0)
    start_of_window = end_of_window - datetime.timedelta(hours=1)

    last_two_meetings = study_group.meeting_set.active().order_by('-meeting_date', '-meeting_time')[:2]
    time_to_send = None
    if last_two_meetings.count() == 2:
        penultimate_meeting = last_two_meetings[1]
        time_to_send = penultimate_meeting.meeting_datetime() - datetime.timedelta(days=2, hours=1)

    if time_to_send and time_to_send > start_of_window and time_to_send <= end_of_window:
        facilitator_name = study_group.facilitator.first_name
        path = reverse('studygroups_facilitator_survey', kwargs={'study_group_id': study_group.id})
        base_url = f'{settings.PROTOCOL}://{settings.DOMAIN}'
        survey_url = base_url + path
        
# ...

This will send an ~hour later than intended. The time_to_send will be in the period before the period we're currently in.

• time_to_send - this is when we want to send
• now.replace(minute=0, second=0, microsecond=0) is the start of the period we are currently in

The reasonable condition to satisfy is

start_of_window < now <= end_of_window
start_of_window < time_to_send <= end_of_window

Iow, trigger the event in the same period than the intended time to trigger the event.