Elevator Control System Design (N floors, M elevators)

Context

You are designing a multi-elevator control system for a building with N floors (1..N) and M elevators. Users generate two types of requests:

• Hall calls: from a floor, pressing Up or Down to request pickup.
• Car calls: inside an elevator, pressing a destination floor for dropoff.

Assume each elevator has sensors for door state, weight/load, current floor/position, and fault signals.

Requirements

1. Model core classes and entities:
   • Elevator, Door, Floor, Request (HallCall, CarCall), Controller, Scheduler.
2. Define key methods and interfaces:
   • requestPickup(floor, direction)
   • requestDropoff(floor)
   • step()/tick()
   • getStatus()
3. Choose and justify a scheduling strategy (e.g., nearest-car, SCAN/LOOK/collective-control, hybrid).
4. Describe state machines and transitions for elevator and door.
5. Handle concurrency and multiple simultaneous requests.
6. Address priority and fairness (avoid starvation, balance load).
7. Error handling and safety (overload, door obstruction, stuck elevator, out-of-service).
8. Extensibility and service modes (e.g., VIP, fire service, maintenance).
9. Provide class interfaces or language-agnostic pseudocode for main operations.