Duplicate Activity Detection Service

This is a high-complexity service with two dependencies — the Contact Chapter Repository and a Cross-Chapter Activity Query component — both of which must be stable before end-to-end integration testing can begin. Because this service runs at submission time, its performance characteristics directly affect the perceived responsiveness of the activity submission flow, making performance testing under realistic data volumes a required QA deliverable. The cross-chapter query scope means test data must include contacts with multiple chapter affiliations, which adds setup complexity to the test environment. Given its shared status, any interface changes will have ripple effects on the Duplicate Activity Warning Dialog and must be versioned carefully.

The service's primary entry point is checkForDuplicate(), which accepts an ActivitySubmission and returns a nullable DuplicateActivityMatch. Internally it calls getActivitiesForContactAcrossChapters() to retrieve all activities for that contact across every affiliated chapter via the Cross-Chapter Activity Query, then iterates the result set calling isDuplicateActivity() — a pure comparison function matching on contact_id, date, and activity_type. A match triggers buildDuplicateMatch() to construct the structured result consumed by the warning dialog. The service runs in both mobile and backend contexts: on mobile it acts as a pre-flight check before network submission; on backend it provides a server-side guard.

Ensure that the date comparison uses normalized UTC values to avoid timezone-related false negatives, and that activity_type comparison is case-insensitive.