Let's dive into designing a Torrent service. Imagine you're tasked with creating the core engine that powers a BitTorrent client. This isn't about building the UI or network discovery aspects, but rather the heart of the system – the mechanism that efficiently downloads and uploads pieces of a file based on metadata from a .torrent file. We'll focus on how the client manages file pieces, verifies their integrity, and handles concurrent access from multiple peers.

The system will simulate a simplified torrent client downloading a single file. We need to manage the pieces of the file, request them from peers, verify their integrity using hash checks, and assemble the complete file. Concurrency is crucial since multiple peers will be sending pieces simultaneously.

This problem requires a deep understanding of how to translate real-world requirements into a robust and scalable object-oriented design. We'll be scrutinizing your choices around data structures, synchronization mechanisms, and adherence to SOLID principles. We'll pay close attention to how you structure your code for testability and future extensibility (e.g., adding support for different piece selection strategies or handling multiple torrents concurrently).

Requirements