Design a Parking Lot System

🏁 The Parking Lot Drama We All Know

You’re late for a movie.

You pull into the mall’s parking lot.

You start circling.

1st round: No spot.

2nd round: Still nothing.

3rd round: A glimmer of hope! A car’s pulling out!

But before you reach it — zoom — someone cuts in and parks like they owned the lot 😤

You whisper under your breath:

“Why is this so painful? Can’t someone fix this?”

Spoiler alert: Yes, you can.

You’re about to design a smart, scalable, high-performance Parking Lot System.

Let’s go, architect.

🎯 Step 1: What Should This Parking Lot Do?

Before we build the Batcave, let’s list our gadgets.

✅ Must-Haves (Functional Requirements)

• Park a vehicle
• Unpark a vehicle
• Check if a slot is available
• Assign the nearest right-sized slot
• Track parking time and fees
• Show real-time availability

💎 Nice-to-Haves (Bonus Features)

• Custom slot booking via app
• EV-only spots with charging
• QR-based entry/exit
• Admin dashboard (monitor, control, analyze)

📈 Non-Functional Requirements

• Fast redirections (no lag at gates)
• Scalable (mall one day, airport the next)
• Reliable (no ghost slots 👻)
• Easy to extend (add new floors, slot types later 🛸)

🚗 Step 2: Who's Parking?

You’re not dealing with just cars.

Let’s meet the cast:

• 🛵 Motorcycle
• 🚗 Car/SUV
• 🚌 Bus/Truck
• 🔌 Electric Vehicle (Bonus round!)

Each one needs different slot sizes.

So we’ll also have:

• 🟩 Bike Slot
• ⬜ Compact Slot
• 🟦 Large Slot
• ⚡ EV Charging Slot

🧱 Step 3: Think in Objects (OOP to the rescue!)

This is where it gets fun.

We break things down like LEGO blocks 🧱

🚘 Vehicle (Base Class)

• → Subclasses: Car, Bike, Bus, EV

class Vehicle:

def __init__(self, number, type):

self.number = number

self.type = type

🅿️ Slot

• Knows its size, location, and status.

class Slot:

def __init__(self, id, slot_type):

self.id = id

self.type = slot_type

self.occupied = False

🧭 ParkingFloor

• Holds a collection of slots. Manages them.

class ParkingFloor:

def __init__(self, floor_number):

self.slots = []

🏢 ParkingLot

• The big boss. Manages all floors.

🎫 Ticket

• Keeps track of who parked where and when.

💳 Payment

• Calculates how much to charge (no free rides!).

📊 Step 4: High-Level Architecture — Let’s Zoom Out 🔍

Here's what happens when a vehicle arrives:

1. It reaches the entry gate
2. System finds the nearest valid empty slot
3. Issues a ticket (with time & location)
4. Parks the vehicle
5. On exit, it calculates the time and bill
6. Collects payment & frees the slot

Let’s see the services we need.

🧠 Our System Brain:

• Entry/Exit Gate Services
• Parking Allocation Service
• Slot Management Service
• Ticketing Service
• Payment Gateway
• Notification Service (optional: send SMS/email)
• Admin Dashboard

We’ll also sprinkle in:

• 🔄 Redis: For quick slot lookups
• 🧵 Kafka: For async updates (slot freed, car left)
• 💾 DB: For persistent records (MongoDB or SQL — your call)

🗄️ Step 5: Design the Database

Here’s what our data might look like:

🧠 Step 6: Scale It Like a Pro

If you’re building for 5 vehicles/day, you’re fine.

If you’re building for 50,000/day — you need to scale smart.

Here’s how:

• 🚀 Shard by floor (one DB per floor)
• ⚖️ Load balancers at entry/exit gates
• 💡 Cache hot data (available slots)
• 📩 Async messaging to update dashboards in real-time
• 🧱 Microservices to separate logic and scale independently
• 🧪 Rate limiting to stop bots from reserving slots unfairly

🎁 Step 7: Bonus Features (Level Up!)

1. Mobile App Entry

• Book a slot, get a QR code, skip the line 😎

2. EV Charging Logic

• Reserve ⚡ slots only for EVs
• Notify when charging is done

3. Overstay Fines

• Extra charge if you exceed max hours

4. Analytics Dashboard

• See busiest hours, average time parked, revenue, etc.

🎉 Wrapping It All Up

Let’s recap what you just built:

• ✅ Object-oriented classes to model real-world parking
• 🧠 Scalable services to handle thousands of vehicles
• 💾 Well-structured database
• ⚙️ High-performance features
• 🔌 Bonus functionality to delight users

You just designed a real-world, scalable, modular, and fun-to-build system.

You just designed a real-world, modular, scalable, and fun system.

Give yourself a high-five, architect. 🙌