Design communication handler and exceptions

Q: Design communication handler and exceptions

This question evaluates object-oriented design, API and state management skills along with exception handling and identity-based reasoning by requiring implementation of a single-connection communication handler and a custom CommunicationException; it belongs to the System Design domain and emphasizes practical implementation details rather than purely conceptual theory. Such questions are commonly asked to assess a candidate's ability to enforce invariants, manage limited resources and error conditions in a mutable service interface, and demonstrate practical coding-level design and testing of runtime behaviors.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a medium difficulty System Design question, commonly asked during Take-home Project rounds at Akuna Capital.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Akuna Capital during technical interviews.

Question

Implement a Communication Handler with Exceptions

Context

You are building a single-line communication handler that can connect exactly two Caller instances at a time. The environment already provides:

Caller: a class with at least a .name attribute (assume implemented elsewhere).
CommsHandlerABC: an abstract base class specifying the interface for a communication handler.

Your task is to implement a concrete CommsHandler subclass that enforces the specified behaviors and to define a custom CommunicationException.

Requirements

Classes to Implement

CommsHandler(CommsHandlerABC)
- Methods to implement:
  - connect(self, user1: Caller, user2: Caller) -> str
  - hangup(self, user1: Caller, user2: Caller) -> str
  - clear_all(self) -> None
- Behavior:
  - connect:
    - If user1 is user2, raise CommunicationException with the exact message: "{user1.name} cannot connect with {user2.name}!"
    - If user1 and user2 are different and the communication line is already in use, raise CommunicationException with: "Connection in use. Please try later"
    - Otherwise, store the two connected users and return: "Connection established between {user1.name} and {user2.name}"
  - hangup:
    - If user1 is user2, raise CommunicationException with: "{user1.name} cannot hangup with {user2.name}"
    - If user1 and user2 are different and are currently communicating, disconnect them and return: "{user1.name} and {user2.name} are disconnected"
    - If they are not communicating, raise CommunicationException with: "{user1.name} and {user2.name} not found in the communication channel"
  - clear_all:
    - Clear the communication channel regardless of current users (no return value).
CommunicationException(Exception)
- Accepts an error message in its constructor and is raised as specified.

Notes

Use identity checks (is) when comparing callers (i.e., same object instance), not name equality.
The handler supports only one active connection at a time.
Provide brief tests or usage examples demonstrating the specified behaviors.

Design communication handler and exceptions

Quick Overview

Design communication handler and exceptions

Implement a Communication Handler with Exceptions

Context

Requirements

Classes to Implement

Notes

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