NexusAI - Intelligent Conversational AI Platform

NexusAI is a full-stack, state-of-the-art conversational AI platform built with the MERN stack (MongoDB, Express, React, Node.js) and TypeScript. It features a resilient Multi-LLM Fallback Architecture that seamlessly routes chat completions across Groq (Llama 3.3 70B), Google Gemini (Gemini 1.5 Flash), and OpenAI (GPT-3.5 / GPT-4).

Live Demo: NexusAI

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Screenshots

User Experience

Chat Studio & Syntax Highlighting

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Key Features

• Multi-LLM Fallback Engine: Automatic failover across Groq, Google Gemini, and OpenAI to ensure 99.9% uptime and prevent vendor rate-limiting disruptions.
• Persistent Chat History: Fast MongoDB-backed conversation storage per user with full markdown and syntax-highlighted code blocks.
• One-Click Code Copy: Developer-first syntax highlighter with instant copy-to-clipboard buttons and feedback.
• Secure Authentication: Cookie-based JWT sessions with signed HTTP-only cookies and bcrypt password hashing.
• Modern Responsive UI: Premium cyberpunk-styled interface crafted with React, Material-UI, and smooth micro-animations.
• Smart Session Recovery: Clean 200 OK guest state handling for seamless client-side authentication checks.

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Multi-LLM Architecture

User Prompt ──► [Express API Layer] ──► [Token Auth & Validation]
                                              │
                                              ▼
                             [Multi-Provider Fallback Chain]
                                              │
              ┌───────────────────────────────┼───────────────────────────────┐
              ▼                               ▼                               ▼
       [Primary: Groq]             [Secondary: Gemini]             [Tertiary: OpenAI]
    (Llama 3.3 70B / 8B)            (Gemini 1.5 Flash)             (GPT-3.5 / GPT-4)

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Tech Stack

Frontend

• React 19 with TypeScript & Vite
• Material-UI (MUI) & Custom CSS Design System
• React Router v7
• React Syntax Highlighter (Prism theme with custom styling)
• React Hot Toast (custom notifications)
• Axios (configured for cross-origin credentials)

Backend

• Node.js & Express 5 (TypeScript)
• MongoDB with Mongoose ODM
• OpenAI SDK v4 (OpenAI-compatible multi-provider routing)
• JSON Web Tokens (JWT) & cookie-parser
• express-validator & bcrypt

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Setup & Installation

Prerequisites

• Node.js (v18 or higher)
• MongoDB Atlas cluster or local MongoDB instance
• At least one API key from Groq, Google AI Studio, or OpenAI

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1. Clone the Repository

git clone https://github.com/Anshr23/NexusAI.git
cd NexusAI

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2. Backend Configuration & Startup

cd backend
npm install

Create a .env file in the backend/ directory:

PORT=5001
NODE_ENV=development
MONGODB_URL=your_mongodb_connection_string
JWT_SECRET=your_super_secret_jwt_key
COOKIE_NAME=auth_token
COOKIE_SECRET=your_cookie_signature_secret
FRONTEND_URL=http://localhost:5173

# AI Providers (add one or all for automatic fallback)
GROQ_API_KEY=your_groq_api_key
GEMINI_API_KEY=your_google_gemini_api_key
OPEN_AI_SECRET=your_openai_api_key

Run the backend server:

npm run dev

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3. Frontend Configuration & Startup

In a new terminal:

cd frontend
npm install
npm run dev

The application will start at http://localhost:5173.

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API Endpoints

User Routes (/api/v1/user)

• POST /signup — Register a new user account
• POST /login — Authenticate and issue signed session cookie
• GET /auth-status — Verify active session (returns 200 OK with isAuthenticated)
• GET /logout — Invalidate session and clear auth cookie

Chat Routes (/api/v1/chat)

• POST /new — Send message and receive AI completion (with multi-provider fallback)
• GET /all-chats — Retrieve conversation history for current user
• DELETE /delete — Clear all chat messages for current user

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License

Distributed under the ISC License.