feat: update course deadline email cadence and templates

[rjv31]

Summary

This PR updates the automated course deadline email notifications sent to Course Editors and Project Coordinators.

2U ticket - https://2u-internal.atlassian.net/browse/CATALOG-80

Changes

• Updated reminder cadence from:

  • 90 days
  • 30 days
  • 7 days
  • course end

  to:

  • 60 days
  • 30 days
  • 15 days
  • 7 days
  • course end

• Updated email templates (course_deadline.html and course_deadline.txt) to match the new messaging format.

• Updated email subjects according to the new requirements.

• Updated management command to support the new reminder intervals.

• Updated test cases to reflect the new cadence.

Testing

• Verified management command triggers correct email variants.

[ankit-sonata]

Must-fix before merge: there is a logic bug that prevents “course_ended” emails from being sent in common cases, and there’s also a crash risk when there’s no course run.

1) BUG: “course_ended” path is effectively unreachable for courses with any old runs

In send_course_deadline_emails.py, the query selects courses where any course_runs__end matches the deltas:

days_until_end = TruncDate(F('course_runs__end')) - TruncDate(Now())
.filter(days_until_end__in=[timedelta(days=d) for d in EMAIL_DELTA_DAYS])

Because EMAIL_DELTA_DAYS includes -1, any course that has any run that ended “yesterday” will be included.

But then inside the loop, you compute days_until_end using only the advertised run:

advertised_run = course.advertised_course_run
days_until_end = (advertised_run.end.date() - now.date()).days

So if a course has:

• an advertised run ending in 60 days, and
• an older run that ended yesterday

…it will be included by the queryset due to the old run, but days_until_end will be 60 and you’ll send the 60-day email. That’s OK.

However, for courses with no advertised_run, you do:

last_course_run = course.course_runs.last()
days_since_end = (last_course_run.end.date() - now.date()).days
if days_since_end == -1: send course_ended

course.course_runs.last() is not ordered, so “last” is not guaranteed to be the most recently-ended run. If it picks an older run (common if default ordering is by PK asc/desc, or undefined), days_since_end likely won’t be -1, and the course_ended email won’t send, even if there is a run that ended yesterday (which is exactly why the course was selected in the queryset).

Fix required:

• Explicitly choose the correct run for the ended-path, e.g.:
  • order by end and select the most recent ended run (order_by('-end').first()), or
  • compute “ended yesterday” run directly in the queryset and use that run, or
  • remove the -1 from the broad course filter and handle ended runs separately with an explicit query.

2) Crash risk: course.course_runs.last() can be None

Even though the queryset filters course_runs__end__isnull=False, it’s still safer to guard because:

• the queryset is about any run, but prefetch + distinct + iteration can produce edge cases; and
• defensive code is important in management commands.

Right now this will crash if last_course_run is None:

last_course_run = course.course_runs.last()
days_since_end = (last_course_run.end.date() - now.date()).days

Fix required:

• Add a guard:
  • if no runs exist, log and continue.

3) Missing must-have tests for the fixed behavior

The command tests were updated for (60, 30, 15, 7, -1) variants, but there should be an explicit regression test for:

• A course with no advertised run and multiple historic runs, where one ended yesterday: ensure course_ended triggers.
• A course where .last() would pick the wrong run unless ordering is applied.

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[ankit-sonata]

@rjv31 can you tell me the purpose of the following file - course_deadline.txt

[rjv31]

Hi @ankit-sonata ,

The course_deadline.txt file is the plain-text version of the course deadline email template.

It’s used along with the HTML template (course_deadline.html) so that emails are sent as multipart (HTML + text), ensuring compatibility with email clients that don’t support HTML.

Also, this is part of the existing/legacy pattern followed in Discovery from earlier teams, where both .html and .txt templates are maintained for all email notifications.

[rjv31]

@UsamaSadiq , @openedx/committers-course-discovery could anyone please check and help review/merge this PR

[ankit-sonata]

@rjv31 PR can approved by someone who has write access.

[rjv31]

@UsamaSadiq Could you please check and help review/merge this PR