Design and implement a communications handler to manage a one-at-a-time conversation channel between exactly two distinct users. Specifications: ( 1) Define a custom exception type ConnectionException that accepts a single error-message string. ( 2) Define an abstract base CommsHandlerABC with three abstract methods: connect(user1: Caller, user2: Caller) -> str to establish a call or raise ConnectionException; hangup(user1: Caller, user2: Caller) -> str to end the call or raise ConnectionException; clear_all() -> None to force-clear any existing call. ( 3) Implement a concrete CommsHandler that tracks the current active call and enforces: only one active call at a time; a user cannot connect with themselves; while a call is active, any new connect attempt fails with an appropriate error; hangup succeeds only for the currently connected pair; clear_all resets state immediately. Caller has a unique name field (name: str). Process the following commands and produce the exact outputs shown. Sample Input: connect Alice Bob; connect Carol Dave; hangup Alice Bob; connect Carol Dave; hangup Carol Dave; connect Eve Eve; hangup Alice Bob. Expected Output: Success: Connection established between Alice and Bob; Error: Connection in use. Please try later; Success: Alice and Bob are disconnected; Success: Connection established between Carol and Dave; Success: Carol and Dave are disconnected; Error: Eve cannot connect with Eve; Error: Alice and Bob not found in the communication channel.

This question evaluates skills in stateful resource management, API and abstraction design, custom exception handling, and input validation for enforcing a single-active connection between two users.

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Implement a two-user communications handler | Akuna Capital Interview Question

One-at-a-time Two-User Communications Handler

Context

Design and implement a communications handler that supports exactly one active conversation at a time between two distinct users. Each user is represented by a Caller with a unique name.

Requirements

Define a custom exception type:
- ConnectionException that accepts a single error-message string.
Define an abstract base class CommsHandlerABC with these abstract methods:
- connect(user1: Caller, user2: Caller) -> str
  - Establish a call and return a success message, or raise ConnectionException.
- hangup(user1: Caller, user2: Caller) -> str
  - End the call and return a success message, or raise ConnectionException.
- clear_all() -> None
  - Force-clear any existing call and reset state.
Implement a concrete CommsHandler that enforces:
- Only one active call at any time.
- A user cannot connect with themselves.
- While a call is active, any new connect attempt fails with error: "Connection in use. Please try later".
- hangup succeeds only for the currently connected pair (order-agnostic). Otherwise raise: "{A} and {B} not found in the communication channel." (note trailing period).
- clear_all resets the state immediately.

I/O Behavior

Commands to support (semicolon-separated in a single line or as separate lines):
- connect <user1> <user2>
- hangup <user1> <user2>
- clear_all
Output:
- On success: prefix with "Success: " and include the handler's returned message.
- On error: prefix with "Error: " and include the exception's message.

Sample

Sample Input:
- connect Alice Bob; connect Carol Dave; hangup Alice Bob; connect Carol Dave; hangup Carol Dave; connect Eve Eve; hangup Alice Bob
Expected Output:
- Success: Connection established between Alice and Bob; Error: Connection in use. Please try later; Success: Alice and Bob are disconnected; Success: Connection established between Carol and Dave; Success: Carol and Dave are disconnected; Error: Eve cannot connect with Eve; Error: Alice and Bob not found in the communication channel.

Requirements

Define a custom exception type:

ConnectionException that accepts a single error-message string.

Define an abstract base class CommsHandlerABC with these abstract methods:

connect(user1: Caller, user2: Caller) -> str
- Establish a call and return a success message, or raise ConnectionException.
hangup(user1: Caller, user2: Caller) -> str
- End the call and return a success message, or raise ConnectionException.
clear_all() -> None
- Force-clear any existing call and reset state.

Implement a concrete CommsHandler that enforces:

Only one active call at any time.
A user cannot connect with themselves.
While a call is active, any new connect attempt fails with error: "Connection in use. Please try later".
hangup succeeds only for the currently connected pair (order-agnostic). Otherwise raise: "{A} and {B} not found in the communication channel." (note trailing period).
clear_all resets the state immediately.

I/O Behavior

Commands to support (semicolon-separated in a single line or as separate lines):

connect <user1> <user2>
hangup <user1> <user2>
clear_all

Output:

On success: prefix with "Success: " and include the handler's returned message.
On error: prefix with "Error: " and include the exception's message.

Sample

Sample Input:

connect Alice Bob; connect Carol Dave; hangup Alice Bob; connect Carol Dave; hangup Carol Dave; connect Eve Eve; hangup Alice Bob

Expected Output:

Success: Connection established between Alice and Bob; Error: Connection in use. Please try later; Success: Alice and Bob are disconnected; Success: Connection established between Carol and Dave; Success: Carol and Dave are disconnected; Error: Eve cannot connect with Eve; Error: Alice and Bob not found in the communication channel.

Implement a two-user communications handler

Quick Overview

One-at-a-time Two-User Communications Handler

Context

Requirements

I/O Behavior

Sample

Solution

Comments (0)

Implement a two-user communications handler

Quick Overview

One-at-a-time Two-User Communications Handler

Context

Requirements

I/O Behavior

Sample

Solution

Comments (0)