Requirements

Functional Requirements:

• Allow reservation of a parking spot.
• Process payment for the reservation.
• payment model (monthly, daily, yearly) or support cash or mobile pay.
• Enable parking of a car in the reserved spot.
• Support early departure before reservation time expires.
• Gate check-in/out.(type of checking license or tickets or mobile app )
• Handle no show.
• real-time availability display
• vehicles supported
• shows strict if it is reserved for whole day

Non-Functional Requirements:

• slow latency
• high performance
• fault tolerance
• race condition/concurrency ( keep in mind that multiple cars might reserve at the same time)
• scalability

API Design

# 1. Check availability (Real-time)

GET /api/v1/lots/{lotId}/availability?vehicleType=CAR&start=2026-04-01T10:00:00Z&end=2026-04-01T14:00:00Z

Response: {

"availableSpots": 12,

"spots": [{"id": "A-101", "type": "COMPACT", "price": 15.00}],

"dynamicPricing": {"surgeMultiplier": 1.2}

}

# 2. Hold spot (Pre-reservation lock)

POST /api/v1/reservations/hold

Body: {"lotId": "lot-123", "spotId": "A-101", "start": "...", "end": "..."}

Response: {

"holdId": "hold-uuid-789",

"expiresAt": "2026-04-01T09:15:00Z", # 15 min to pay

"paymentIntent": "pi_123456"

}

# 3. Confirm reservation (After payment)

POST /api/v1/reservations/confirm

Body: {"holdId": "hold-uuid-789", "paymentMethod": "card_123"}

Response: {

"reservationId": "res-456",

"qrCode": "base64encoded",

"licensePlate": "ABC-123"

}

# Gate checks if vehicle can enter

POST /api/v1/gate/validate

Body: {

"gateId": "gate-south-1",

"licensePlate": "ABC-123", # OR "qrCode": "..."

"timestamp": "2026-04-01T09:58:00Z"

}

Response: {

"allowed": true,

"reservationId": "res-456",

"spotId": "A-101",

"action": "OPEN_GATE"

}

High-Level Design

Describe the overall system architecture. Identify the main components needed to solve the problem end-to-end. Use the diagramming tool to create a block diagram.

Detailed Component Design

Deep dive into 2-3 key components. Explain how they work, how they scale, discuss tradeoffs, capacity, and any relevant algorithms or data structures.