feat: [FC-7879] implement get_user_dates() method to get all user dates for a course#326

[kyrylo-kh]

NOTE: Depends on #343

Description

This PR adds a new API function get_user_dates(course_id, user_id) to return a comprehensive map of dates for a given course and user.

Functionality

• Returns a dictionary where keys are (block_key, field) tuples and values are datetime objects.

• Prioritizes user-specific overrides (UserDate) over default content dates (ContentDate with DatePolicy).

• Supports optional filtering by:

  • block_types (e.g., sequential, vertical)
  • block_keys (UsageKey or string list)
  • date_types (due, start, etc.)

Features

• Handles missing schedules and skips invalid or inactive dates gracefully.
• Fully supports both string and object inputs for course and block keys.
• Optimized with prefetching to minimize query overhead.

Testing

Extensive test suite verifies:

• Correct merging of user and default dates
• All filtering options
• Multiple overrides with the latest one selected
• Handling of edge cases like empty datasets or missing metadata

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[e0d]

I notice that this call is without arguments, compared to this:

edx-when/edx_when/api.py

Line 251 in ab2ee71

dates[key] = cdate.policy.actual_date(schedule, end_datetime, cutoff_datetime)

Has this been tested with self-paced courses?

[kyrylo-kh]

Currently get_user_dates only resolves absolute policy dates here. Relative dates are skipped (MissingScheduleError is caught). So self-paced (relative) policy dates aren’t returned by this API

[e0d]

I'm trying to grok how this function and [get_dates_for_course()](https://github.com/openedx/edx-when/blob/ab2ee71af64ee6ef720083586eb26e1f58a748d9/edx_when/api.py#L163) relate. Given that there is some repeated code, is there a cleaner refactoring that's possible?

[kyrylo-kh]

get_user_dates is a narrow, filterable API for one user. get_dates_for_cours is the full path with caching, subsection filtering, and relative dates. The shared part is that loop that turns content dates into policy dates and applies user overrides. A cleaner approach would be to extract that into a small helper and have both call it (and pass schedule/end/cutoff from the helper so self-paced works in both). Would you like to have such helper function in this PR?