Parking Lot System

(Object Oriented Design using TypeScript)

Why OOD ?

• I have been looking into TypeScript & thought of building out something which uses TypeScript a lot.
• So, I thought to try out this problem statement. and while solving this, document my thought process, approach & ways to break down the problem

Problem Statement (high level requirements)

In this exercise, we will design an in memory software for a parking system using object oriented programming. these requirements might be intentionally vague, try to resolve ambiguity by asking questions & clarifying things.

Overview

• A parking system consists of n floors, and each floor has m parking spots.
• To enter the premise, driver can press a button which issues a parking ticket.
  • NOTE: No spot is assigned at the time of issuing the ticket.
• To exit the premise, driver can enter his ticket and press a button to exit.
• At entrance, driver can see floor wise availability on signage board: As an example:
  • Floor 1 has 5 out of 30 available
  • Floor 2 has 20 out of 50 available
• At the time of exit, driver can see parking charges associated with the ticket.

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How to approach for solving this problem

Handle Ambiguity:

• As a good developer you should not make assumptions, rather, ask questions to clarify requirements.

After all, a developer who just codes something without understanding what is expected to be build 🤷‍♂️, wastes the company's time & money. Potentially, may create much more serious issues.

Queries in given requirements: 🤷‍♂️

• Q1: What different Vehicle we are planning to be parked ? eg: Bike, Car, Bus ?
  • this gives us idea about size of vehicles being parked
• Q2: How do we know if Vehicle has been parked on a spot ? will that be decided by system while issuing ticket ? or driver can park at any vacant spot ?
  • important because we need to keep track of free/available spots inside ParkingLot
• Q3: when driver exits, How are charges calculated 💵 ? hourly ?
  • gives us idea about what information needs to be recorded when issuing ticket & when Vehicle exits

Step 1: Defining Core Objects (Identify Entities)

Now, lets identify the core objects/entities from the requirement.

• Vehicle 🛵
• Ticket: 🎫 issued for vehicle
• Floor: parking-lot has multiple floors
• ParkingSpot: each Floor has multiple spots for parking
• ParkingLot: contains multiple floors

Step 2: Analyze relationship between core objects/entities

Now, lets analyze

• which objects are member of which other objects ? Composition
• Do any object inherit from other ? Inheritance
• Is the relationship one-to-one or many-to-many ? Cardinality
• how these objects will be communicating with one another. Interfacing (or behaviours)
• Also, think about the key actions that objects will take & how they relate to each other

We can come up with following relationships/associations:

• Ticket is issued for a Vehicle (containment)
• Floor has multiple ParkingSpot (ParkingSpot[] 💡)
• Vehicle is parked at ParkingSpot (containment)
• ParkingLot is located at some Address & has multiple Floors (Floors[])
• ParkingLot has SignageBoard to display availability of spots
• When drives exits he provides parking Ticket & based on that charges are calculated
  • (exitTime - entryTime) * HOURLY_RATE

🧠 think about any design patterns which can be leveraged in these use-cases

Class Diagram

Step 3: Writing implementation code

• All the entities can be found inside src/models directory
• unit tests can be found inside src/models/__test__ directory