Top Tracks per Country and Globally

Design a system that can return the top N most-played tracks both globally and on a per-country basis. You will receive a continuous stream of play events; each event contains a track ID, a country code, and a timestamp. The system must support two types of queries:

1. Top N tracks in a given country (ranked by total plays in that country).
2. Top N tracks globally (ranked by total plays across all countries).

The same track may appear in many countries. Queries will be executed far more often than new events arrive, so you should pre-compute and cache the ranked lists rather than scan the entire data set on every query.