Requirements

Functional Requirements:

• Allow reservation of a parking spot.
• Process payment for the reservation.
• Enable parking of a car in the reserved spot.
• Support early departure before reservation time expires.
• Gate check-in/out.
• Handle no show.

Non-Functional Requirements:

• latency : the allocation and payment has to be done very quickly and fast
• scalable : it has to handel heavy tracfic
• relable : it has to allocate correctly and avoid overlapping's

API Design

1) post : api/reserveSpot/ -> this end point will create a request for reservation of a parking spot & redirect to payment

2) post : api/payment?userId -> this url handels payment's very securly and returns success to spot allocation

3) post : api/spotAllocation -> this end point will allocate a place for parking the car for the user and also decide the expire time

4) get : api/parkingId -> this end point will bring's coordinates of the parking spot for the car

5) post : api/check-in -> this end point start's timer

6) post : api/notify -> this end point will send's a alert to the user to avocate the parking of care before the time expires.

7) post : api/extendParkingtime: -> this url is used to extend the parking slot expire time by extra payment

8) post : api/check-out : -> this end point will check's weather the user has avocated within the time and also free up the slot for next car

High-Level Design

Client App

|

API Gateway

|

--------------------------

Reservation Service

Payment Service

Allocation Service

Gate Service

Notification Service

--------------------------

|

DB + Cache + Queue

Detailed Component Design

Component 1: Allocation Engine

How does it work?

Possible logic:

Available spots

↓

Filter by:

• vehicle type
• reservation time
• availability
• zone

↓

Choose nearest/optimal.

Possible DS:

• Priority Queue
• HashMap
• Interval Tree

Tradeoff:

Nearest vs load balancing.

Component 2: Reservation Service

How avoid double booking?

Need:

Locking.

Options:

Optimistic Lock

Fast

Retry on conflict.

Pessimistic Lock

Safe

Lower concurrency.

Interview gold topic.

Component 3: Notification / No-show Worker

Background scheduler.

Every minute:

Check expired reservations.

If:

not checked-in

↓

cancel

↓

refund

↓

release spot.

Usually:

Queue + cron worker.