Implement Call Center Business Logic for VoyceLink

[franco148]

Implemented complete call lifecycle management and business rules for the VoyceLink call-center system as specified in README.md:

Call Lifecycle Events

• call_initiated: Validates queueId, creates call record, sets initial waiting status
• call_routed: Assigns agent ID, updates call to active status, stores routing time
• call_answered: Updates call to active status, records wait time, flags SLA breaches (>30 sec)
• call_hold: Updates call to on_hold status, records hold duration, flags excessive holds (>60 sec)
• call_ended: Marks call as ended, records end reason and duration, flags short calls (<10 sec)

Features Implemented

• Event processing with state transitions
• Persistence layer with PostgreSQL integration
• Real-time event publishing via Redis pub/sub
• Business rule enforcement (SLA times, hold limits, short call detection)
• Input validation (queue IDs, call existence)
• Error handling with specific error types
• Full test coverage (14/14 unit tests passing)

Technical Implementation

• Separated concerns: CallService orchestrates, CallRepository handles persistence, EventHandlers process specific events
• Used Strategy pattern for extensible event handling
• Eliminated magic values through constants and error classes
• Maintained compatibility with existing API endpoints:
  • POST /api/events (event ingestion)
  • GET /api/calls (call listing with filtering)
  • GET /api/calls/:id/events (event history)

This implementation fulfills all business logic requirements for the call-service package, enabling the dashboard to display live calls and event history with accurate state transitions and real-time updates.