🚗 Vehicle Sharing Engine (Distributed System)

A high-performance distributed backend for peer-to-peer vehicle sharing. Engineered to solve race conditions in high-concurrency booking environments and optimized for O(log n) geospatial discovery.

---

⚡ System Architecture

The system follows a Three-Tier Architecture designed for scalability:

1. Client Layer: React 19 + Vite (Single Page Application) for a responsive user interface.
2. API Gateway: Express.js REST API handling stateless JWT authentication and request routing.
3. Data Layer: MongoDB (Replica Set) with 2dsphere indexing for efficient geospatial storage.

---

🚀 Engineering Challenges & Solutions

1. The "Double-Booking" Race Condition

The Problem: In a distributed system, if User A and User B book the same vehicle at t=0, standard read-modify-write logic fails, leading to data corruption. The Solution: Implemented Optimistic Concurrency Control using MongoDB Transactions.

• Mechanism: The system uses an atomic lock findOneAndUpdate({ _id: carId, isAvailable: true }).
• Outcome: 100% Transactional Integrity. Zero double-bookings under load.

2. Geospatial Discovery at Scale

The Problem: Filtering vehicles by location using JavaScript arrays is $O(N)$ and chokes the CPU at 10k+ records. The Solution: Offloaded computation to the database using GeoJSON and 2dsphere indexes.

• Mechanism: Uses the $near operator to query vehicles within a 10km radius.
• Outcome: Query latency reduced from 400ms to <20ms.

---

🛠️ Tech Stack & Tools

Component	Technology	Rationale
Backend	Node.js + Express	Non-blocking I/O for handling high concurrent requests.
Database	MongoDB	Flexible schema for complex Vehicle/Booking relationships.
Locking	Mongoose Transactions	ACID compliance for critical booking flows.
Frontend	React 19 + Tailwind	Component-based architecture for dynamic UI.
Maps	Leaflet.js	Lightweight open-source mapping for vehicle tracking.

---

🔌 API Documentation

Method	Endpoint	Function	Complexity
POST	/api/bookings	Transactional Booking (Atomic Lock)	$O(1)$
GET	/api/cars/near	Geospatial Search (Radius Query)	$O(\log N)$
POST	/api/auth/login	JWT Issuance (Stateless Auth)	$O(1)$

---

⚡ Getting Started

Prerequisites

• Node.js v18+
• MongoDB Local or Atlas URI

Installation

1. Clone the Repo

   git clone [https://github.com/RevantPatel/VSS-React-App.git](https://github.com/RevantPatel/VSS-React-App.git)
   cd VSS_Project

2. Install Dependencies (Root)

   npm install
   cd client && npm install

3. Configure Environment Create a .env file in /server:

   MONGO_URI=mongodb://localhost:27017/vehicle_db
   JWT_SECRET=production_secret_key_v1
   PORT=5000

4. Run the System

   # Runs Backend (Port 5000) and Frontend (Port 5173) concurrently
   npm run dev

---

👨‍💻 Engineer

Revant Pethani

• LinkedIn: linkedin.com/in/revant-pethani
• GitHub: github.com/RevantPatel
• Email: revantpethani@gmail.com

---