Technical Challenge

🎯 Objective

Develop a microservice to manage the lifecycle of voice/video calls via real-time events, following call center business rules (e.g., medical interpreter-patient workflows). Focus on code quality, scalability, and integration.

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⚙️ Technologies

Area	Stack
Frontend	Next.js + TypeScript, Socket.io Client
Backend	Express.js/NestJS + TypeScript, PostgreSQL/MongoDB, Socket.io
Testing	Jest (unit), Cypress/Supertest (integration)

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📞 Call Lifecycle & Events

Call Flow

Initiated → Routed → Answered → [Hold/Transfer] → Ended

Key Events (Implement at least 4)

Event	Trigger	Sample Data	Business Rules
call_initiated	Call starts (voice/video).	{ "call_id": "123", "type": "video", "queue_id": "medical_spanish" }	- Validate queue_id exists. - Start SLA timer (30s max wait).
call_routed	Call assigned to agent/interpreter.	{ "agent_id": "agent_55", "routing_time": 15 }	- Re-route if agent doesn’t answer in 15s (call_retransfer).
call_answered	Agent accepts the call.	{ "wait_time": 25 }	- Alert supervisor if wait_time > 30s. - Update agent metrics.
call_hold	Call placed on hold.	{ "hold_duration": 45 }	- Max hold time: 60s. - Notify supervisor if exceeded.
call_ended	Call finishes (success/failure).	{ "end_reason": "completed", "duration": 300 }	- Flag calls with duration < 10s for review. - Send post-call survey.

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📋 Technical Requirements

Backend (Express/NestJS)

1. REST API:

   • POST /api/events: Ingests events (authenticated via API Key header).
   • GET /api/calls?status=active: Lists calls with filters (status, queue).
   • Validation: Use Zod/Class-Validator for event schemas.

2. WebSockets:

   • Broadcast real-time updates via Socket.io.

3. Database:

   // Call Entity
   interface Call {
     id: string;
     status: "waiting" | "active" | "on_hold" | "ended";
     queue_id: string;
     start_time: Date;
     end_time?: Date;
   }
   
   // CallEvent Entity (Audit Log)
   interface CallEvent {
     id: string;
     call_id: string;
     type: string;
     timestamp: Date;
     metadata?: Record<string, any>;
   }

Frontend (Next.js)

1. Dashboard:
   • Real-time table of active/ended calls.
   • Event history view per call.
   • Filters by status/queue.

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🚀 How to Participate

1. Fork this repository.
2. Develop your solution in the fork.
3. Submit a Pull Request with:
   • Functional code in frontend/ and backend/.
   • Clear setup instructions in the README.
   • Unit + integration tests.

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🔍 Evaluation Criteria

• Event Flow: Correct state transitions (e.g., call_initiated → call_ended).
• Code Quality: Clean architecture (DTOs, services), error handling.
• Real-Time: Efficient WebSocket usage (no duplicates).
• Testing: 5+ unit tests, 1 integration test.

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📈 Bonus (Optional)

• Retry failed events (3 attempts).
• Docker setup (docker-compose.yml).

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❗ Note:
Focus on extensibility (e.g., how this module would integrate with CRM/queuing systems). Good luck! 🚀