Events: notify guests on cancellation and keep cancelled pages visible

CHANGELOG.md

@@ -1,5 +1,19 @@
 # Changelog
 
+## 0.5.6
+
+- Events: cancelling an event now notifies its guests. `cancel_event` is idempotent,
+  skips the event's pending reminders, and after commit dispatches an
+  `events.notify_cancellation` job that sends one `events.event_cancelled` mail per
+  active registration, deduped by registration and `ics_sequence`; inactive
+  registrations are never mailed. The mail context resolves the absolute event URL and
+  a `calendar_cancel_url`: for a cancelled event `calendar.ics` serves a
+  `METHOD:CANCEL` invite, so a guest who opens the link removes the calendar entry.
+  Cancelled events keep their detail page with a Cancelled badge and
+  `schema.org` `EventCancelled` status instead of returning 404, while staying out of
+  public listings; registration remains closed. The reminder send handler skips
+  reminders whose event is no longer upcoming.
+
 ## 0.5.5
 
 - C5.2i: add an optional `homework_steps` app with per-question resumable drafts,

community_base/__init__.py

@@ -1 +1 @@
-__version__ = "0.5.5"
+__version__ = "0.5.6"

community_base/events/jobs.py

@@ -130,6 +130,12 @@ def send_reminder_handler(context: JobContext, payload: JobPayload):
             or registration.status != EventRegistration.Status.CONFIRMED
         ):
             raise PermanentJobError("event_reminder_stale")
+        if registration.event.status != "upcoming":
+            reminder.status = EventReminder.Status.SKIPPED
+            reminder.reason = "event_inactive"
+            reminder.completed_at = timezone.now()
+            reminder.save(update_fields=("status", "reason", "completed_at", "updated_at"))
+            return
         delivery = send(
             "events.reminder",
             registration.normalized_email,
@@ -148,6 +154,39 @@ def send_reminder_handler(context: JobContext, payload: JobPayload):
         complete_reminder(reminder.pk, delivery)
 
 
+@register_handler("events.notify_cancellation")
+def notify_cancellation_handler(context: JobContext, payload: JobPayload):
+    del context
+    event_id = _positive_id(payload.get("event_id"), "invalid_event_cancellation_payload")
+    with transaction.atomic():
+        event = Event.objects.filter(pk=event_id, status="cancelled").first()
+        if event is None:
+            raise PermanentJobError("event_not_cancelled")
+        registrations = event.registrations.filter(
+            status__in=(
+                EventRegistration.Status.PENDING_VERIFICATION,
+                EventRegistration.Status.CONFIRMED,
+            )
+        ).select_related("user")
+        for registration in registrations:
+            send(
+                "events.event_cancelled",
+                registration.normalized_email,
+                {
+                    "registration_id": str(registration.pk),
+                    "registration_version": registration.version,
+                    "event_id": event.pk,
+                    "event_title": event.title,
+                    "event_start": event.start_datetime.isoformat(),
+                    "event_timezone": event.timezone,
+                },
+                f"events.cancellation:{registration.pk}:{event.ics_sequence}",
+                category="events",
+                user=registration.user,
+                related=registration,
+            )
+
+
 @register_handler("events.expire_registration_verifications")
 def expire_registration_verifications_handler(context: JobContext, payload: JobPayload):
     del context

community_base/events/mail_context.py

@@ -1,4 +1,5 @@
 from community_base.events.models import EventRegistration
+from community_base.events.routing import event_url
 from community_base.events.tokens import generate_registration_token
 from community_base.kernel.conf import require
 
@@ -31,4 +32,11 @@ def resolve_delivery_context(*, delivery, context):
             expiry_hours=24 * 365,
         )
         resolved["manage_url"] = f"{site_url}/events/registration/manage/?token={token}"
+    elif delivery.purpose == "events.event_cancelled":
+        site_url = require("SITE_URL").rstrip("/")
+        base_url = f"{site_url}{event_url(registration.event)}"
+        resolved["event_url"] = base_url
+        # For a cancelled event this endpoint serves the METHOD:CANCEL ICS,
+        # so the guest's calendar entry is removed with one click.
+        resolved["calendar_cancel_url"] = f"{base_url}calendar.ics"
     return resolved

community_base/events/services.py

@@ -6,9 +6,15 @@
 from django.utils import timezone
 from django.utils.text import slugify
 
-from community_base.events.models import Event, EventPublicIdSequence, EventSeries
+from community_base.events.models import (
+    Event,
+    EventPublicIdSequence,
+    EventReminder,
+    EventSeries,
+)
 from community_base.events.registration import enroll_series_registrants_in_event
 from community_base.events.signals import event_cancelled, event_published, event_rescheduled
+from community_base.jobs.dispatch import dispatch_after_commit
 from community_base.kernel.access import can_access
 from community_base.kernel.conf import get
 from community_base.kernel.hooks import resolve
@@ -89,9 +95,25 @@ def cancel_event(event, *, reason=""):
     event = Event.objects.select_for_update().get(pk=event.pk)
     if event.status in {"completed", "archived"}:
         raise ValidationError("Completed or archived events cannot be cancelled.")
+    if event.status == "cancelled":
+        return event
     event.status = "cancelled"
     event.ics_sequence += 1
     event.save(update_fields=("status", "ics_sequence", "updated_at"))
+    now = timezone.now()
+    EventReminder.objects.filter(
+        registration__event_id=event.pk, status=EventReminder.Status.PENDING
+    ).update(
+        status=EventReminder.Status.SKIPPED,
+        reason="event_cancelled",
+        completed_at=now,
+        updated_at=now,
+    )
+    dispatch_after_commit(
+        "events.notify_cancellation",
+        f"events.cancellation:{event.pk}:{event.ics_sequence}",
+        {"event_id": event.pk},
+    )
     _after_commit(event_cancelled, event, reason=str(reason)[:500])
     return event
 

community_base/events/templates/events/event_detail.html

@@ -3,9 +3,10 @@
 {% block meta_description %}{{ event.description|striptags|truncatewords:30 }}{% endblock %}
 {% block content %}
 <main class="cb-page cb-event-detail">
+  <script type="application/ld+json">{{ event_schema|safe }}</script>
   <p><a href="{% url 'events_list' %}">All events</a></p>
   <header class="cb-page-header">
-    <p>{{ event.get_kind_display }}</p>
+    <p>{{ event.get_kind_display }}{% if event.status == "cancelled" %} · <span class="cb-event-status">Cancelled</span>{% endif %}</p>
     <h1 class="cb-page-title">{{ event.title }}</h1>
     <p>
       <time datetime="{{ event.start_datetime|date:'c' }}">{{ event.start_datetime }}</time>
@@ -23,7 +24,13 @@ <h1 class="cb-page-title">{{ event.title }}</h1>
 
   <section class="cb-section" id="registration">
     <h2>Registration</h2>
-    {% if registration.is_active %}
+    {% if event.status == "cancelled" %}
+      <p>This event was cancelled.</p>
+      {% if registration.is_active %}
+        <p>You had been registered for this event.</p>
+        <p><a class="cb-button" href="{{ event.get_absolute_url }}calendar.ics">Remove from calendar</a></p>
+      {% endif %}
+    {% elif registration.is_active %}
       <p>You are registered.</p>
       <form method="post" action="{{ event.get_absolute_url }}unregister/">{% csrf_token %}<button class="cb-button" type="submit">Cancel registration</button></form>
       <p><a class="cb-button" href="{{ event.get_absolute_url }}calendar.ics">Add to calendar</a></p>
@@ -46,7 +53,7 @@ <h2>Registration</h2>
     {% endif %}
   </section>
 
-  {% if event.is_past and registration %}
+  {% if event.is_past and event.status != "cancelled" and registration %}
     <section class="cb-section" id="feedback">
       <h2>Feedback</h2>
       <form class="cb-form" method="post" action="{{ event.get_absolute_url }}feedback/">

community_base/events/views.py

@@ -1,5 +1,7 @@
+import json
+
 from django.contrib import messages
-from django.core.exceptions import PermissionDenied, ValidationError
+from django.core.exceptions import ImproperlyConfigured, PermissionDenied, ValidationError
 from django.http import Http404, HttpResponse
 from django.shortcuts import get_object_or_404, redirect, render
 from django.utils.cache import patch_vary_headers
@@ -21,6 +23,10 @@
 from community_base.kernel.conf import get
 
 PUBLIC_STATUSES = ("upcoming", "completed")
+# A cancelled event keeps its own detail page so guests with the link see the
+# cancellation instead of a 404; it disappears from listings, which stay on
+# PUBLIC_STATUSES.
+DETAIL_STATUSES = (*PUBLIC_STATUSES, "cancelled")
 
 
 def _private(response):
@@ -32,7 +38,7 @@ def _private(response):
 
 
 def _lookup_event(*, slug, public_id=None):
-    events = Event.objects.filter(status__in=PUBLIC_STATUSES).select_related("event_series")
+    events = Event.objects.filter(status__in=DETAIL_STATUSES).select_related("event_series")
     if public_id is not None:
         return get_object_or_404(events, public_id=public_id)
     event = events.filter(slug=slug).order_by("-start_datetime", "-pk").first()
@@ -61,6 +67,29 @@ def _registration_for_user(event, user):
     return EventRegistration.objects.filter(event=event, user=user).first()
 
 
+def _event_schema(event):
+    data = {
+        "@context": "https://schema.org",
+        "@type": "Event",
+        "name": event.title,
+        "eventStatus": (
+            "https://schema.org/EventCancelled"
+            if event.status == "cancelled"
+            else "https://schema.org/EventScheduled"
+        ),
+        "startDate": event.start_datetime.isoformat(),
+        "endDate": event.effective_end_datetime.isoformat(),
+    }
+    site_url = get("SITE_URL")
+    if site_url:
+        try:
+            data["url"] = f"{str(site_url).rstrip('/')}{event_url(event)}"
+        except ImproperlyConfigured:
+            pass
+    # Keep the JSON valid while preventing a </script> breakout from user data.
+    return json.dumps(data).replace("</", "<\\/")
+
+
 @require_GET
 def event_list(request):
     events = (
@@ -96,6 +125,7 @@ def event_detail(request, slug, public_id=None):
             "can_register": can_register_for_event(request.user, event),
             "anonymous_form": AnonymousEventRegistrationForm(),
             "feedback": feedback,
+            "event_schema": _event_schema(event),
             "feedback_form": EventFeedbackForm(
                 initial={
                     "rating": getattr(feedback, "rating", None),
@@ -286,8 +316,9 @@ def event_feedback(request, slug, public_id=None):
 def event_calendar(request, slug, public_id=None):
     event = _lookup_event(slug=slug, public_id=public_id)
     attendee_email = request.user.email if request.user.is_authenticated else None
+    method = "CANCEL" if event.status == "cancelled" else "REQUEST"
     response = HttpResponse(
-        generate_ics(event, audience="attendee", attendee_email=attendee_email),
+        generate_ics(event, method=method, audience="attendee", attendee_email=attendee_email),
         content_type="text/calendar; charset=utf-8",
     )
     response["Content-Disposition"] = f'attachment; filename="{event.slug}.ics"'

community_base/kernel/README.md

@@ -196,7 +196,8 @@ is also why the fix could not be "add a Django system check that requires `SITE_
 force every site to set it, including ones with no present use for it, the opposite of the rule.
 A site that sends the mail purposes needing `SITE_URL` (`accounts.verify_email`,
 `accounts.password_reset`, `accounts.email_change_confirm`, `events.verify_registration`,
-`events.registration_confirmed`, `events.guest_invitation`; also required already, unrelated to
+`events.registration_confirmed`, `events.guest_invitation`, `events.event_cancelled`;
+also required already, unrelated to
 this issue, by `events/integrations/calendar.py`, `jobs/relay.py`, `jobs/relay_scheduling.py`)
 must configure it or those specific sends fail loudly, logged and retried by the job runner like
 any other handler error, rather than delivering a mail nobody can act on.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "community-base"
-version = "0.5.5"
+version = "0.5.6"
 description = "Shared Django apps for DataTalks.Club community sites"
 requires-python = ">=3.13"
 dependencies = [

tests/events/test_jobs.py

@@ -13,7 +13,7 @@
     ZoomTemporaryError,
 )
 from community_base.events.models import Event, EventIntegrationAttempt, EventReminder
-from community_base.events.registration import register_for_event
+from community_base.events.registration import register_for_event, unregister_from_event
 from community_base.jobs.models import JobIntent
 from community_base.jobs.registry import JobContext, registered_handler_names, registered_schedules
 from community_base.jobs.runner import PermanentJobError, RetryableJobError, run_intent
@@ -63,6 +63,7 @@ def test_event_handlers_and_schedules_are_registered():
     assert {
         "events.plan_reminders",
         "events.send_reminder",
+        "events.notify_cancellation",
         "events.expire_registration_verifications",
         "events.sync_zoom",
         "events.process_recording",
@@ -113,6 +114,53 @@ def test_suppressed_reminder_is_terminal_without_a_delivery_job(settings):
     assert reminder.delivery.job is None
 
 
+def test_cancellation_notice_reaches_active_registrations_and_is_idempotent():
+    item = event()
+    active = []
+    for email in ("member@example.com", "second@example.com"):
+        user = get_user_model().objects.create_user(email=email)
+        active.append(register_for_event(item, user)[0])
+    departed = get_user_model().objects.create_user(email="departed@example.com")
+    register_for_event(item, departed)
+    unregister_from_event(item, departed)
+    Event.objects.filter(pk=item.pk).update(status="cancelled")
+
+    jobs.notify_cancellation_handler(None, {"event_id": item.pk})
+    jobs.notify_cancellation_handler(None, {"event_id": item.pk})
+
+    deliveries = EmailDelivery.objects.filter(purpose="events.event_cancelled")
+    assert deliveries.count() == 2
+    assert {delivery.recipient_email for delivery in deliveries} == {
+        "member@example.com",
+        "second@example.com",
+    }
+    assert {delivery.idempotency_key for delivery in deliveries} == {
+        f"events.cancellation:{registration.pk}:{item.ics_sequence}" for registration in active
+    }
+
+
+def test_cancellation_notice_requires_a_cancelled_event():
+    item = event()
+
+    with pytest.raises(PermanentJobError, match="event_not_cancelled"):
+        jobs.notify_cancellation_handler(None, {"event_id": item.pk})
+
+
+def test_reminder_for_cancelled_event_is_skipped_without_a_delivery():
+    registration()
+    jobs.plan_reminders_handler(None, {})
+    reminder = EventReminder.objects.get(interval="24h")
+    assert reminder.status == EventReminder.Status.CLAIMED
+
+    Event.objects.filter(pk=reminder.registration.event_id).update(status="cancelled")
+    jobs.send_reminder_handler(None, {"reminder_id": str(reminder.pk)})
+
+    reminder.refresh_from_db()
+    assert reminder.status == EventReminder.Status.SKIPPED
+    assert reminder.reason == "event_inactive"
+    assert not EmailDelivery.objects.filter(purpose="events.reminder").exists()
+
+
 def test_zoom_create_job_persists_result_once(monkeypatch):
     item = event(required_level=0)
     calls = []

tests/events/test_mail_context.py

@@ -2,9 +2,9 @@
 
 Companion to `tests/accounts/test_mail_context.py`: the same rule applied to the
 events half of `mail_context.resolve_delivery_context`. `events.verify_registration`,
-`events.registration_confirmed` and `events.guest_invitation` all compose an absolute
-link and must raise loudly when `SITE_URL` is unset; `events.reminder` does not
-compose a link and must be unaffected.
+`events.registration_confirmed`, `events.guest_invitation` and `events.event_cancelled`
+all compose an absolute link and must raise loudly when `SITE_URL` is unset;
+`events.reminder` does not compose a link and must be unaffected.
 """
 
 from datetime import timedelta
@@ -57,3 +57,35 @@ def test_a_purpose_that_builds_no_link_is_unaffected_by_an_unset_site_url():
         resolved = resolve_delivery_context(delivery=delivery, context=context)
 
     assert resolved == {}
+
+
+def test_event_cancelled_links_compose_absolute_urls():
+    requested = request_anonymous_registration(event(), "person@example.com")
+    registration = requested.registration
+    delivery = SimpleNamespace(purpose="events.event_cancelled")
+    context = {
+        "registration_id": str(registration.pk),
+        "registration_version": registration.version,
+    }
+
+    resolved = resolve_delivery_context(delivery=delivery, context=context)
+
+    assert resolved["event_url"] == "http://testserver/events/open-community-event/"
+    assert (
+        resolved["calendar_cancel_url"]
+        == "http://testserver/events/open-community-event/calendar.ics"
+    )
+
+
+def test_event_cancelled_link_raises_when_site_url_is_unset():
+    requested = request_anonymous_registration(event(), "person@example.com")
+    registration = requested.registration
+    delivery = SimpleNamespace(purpose="events.event_cancelled")
+    context = {
+        "registration_id": str(registration.pk),
+        "registration_version": registration.version,
+    }
+
+    with override_settings(COMMUNITY_BASE={"SITE_URL": ""}):
+        with pytest.raises(ImproperlyConfigured):
+            resolve_delivery_context(delivery=delivery, context=context)