Requirements

Functional Requirements:

• being able to book a spot by license plate
  • customers should have a reserved spot while in the checkout process
• being able to cancel a spot
• administrator can manage spots (when they are out of order for example)
• The system should be able to get feedback from external parking systems when a car with a certain license plate is checked into the spot
• The user only pays for the time actually parked and not the time reserved. So he should pay when checking out

Non-Functional Requirements:

• guarantee that a spot is not double booked

Capacity Estimation

Estimate the scale of the system. Consider daily active users, read/write ratio, storage requirements, bandwidth, and any relevant QPS calculations...

API Design

Following endpoints

• get available spots in a certain timeframe frame. Input is a series of timeslots per half hour.
• get bookings for license plate
• reserve Timeslots for a certain license plate
• cancel reserved timeslots
• Check in we hook which logs it in the CheckInOut table.
• Check out we hook which logs it in the CheckInOut table and propagates the Booking records wether the timeslot is fullfilled. And sends an invoice for the used timeslots.

High-Level Design

We have an api service that accepts updates for our database tables and is able to receive webhooks from the check in / out detection system. The api also exposes all parking spots available within a certain timeframe.

We have a front end or mobile app where users can view and book spots.

We already have an external detection system to track the check in and out times of certain license plates.

Database Design

A relational database like MySQL or Postgres’s.

A table with all spots with a status MAINTENANCE / AVAILABLE.

A table with named bookedSlots with a reference to the spot, the registered license plate and a time slot per half hour. A booking of 2hours would get 4 entries. It has a unique key on the spotId and the slot. This ensures no slots are booked twice in the database. The record also holds a status key with RESERVED, BOOKED and FULLFILLED . Reserved is for when a user has reserved but is still in checkout.

Table with check in and check out times.

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.