ChatStack

A full‑stack chat application with Google OAuth, conversation history, system prompts, and OpenAI model selection. The backend is built with FastAPI and MongoDB; the frontend is a Next.js app.

Features

• Chat with streaming responses (SSE)
• Conversation history with titles and timestamps
• Per‑user system prompt management
• OpenAI model selection
• CORS and security headers configured for dev/prod
• Google OAuth login with secure HttpOnly cookies and PKCE

Tech Stack

• Backend: FastAPI, Uvicorn, Pydantic, python-jose, Google OAuth, MongoDB (PyMongo)
• AI: LangChain, langchain-openai, langgraph, langchain-community
• Frontend: Next.js 15, React 19, TypeScript, Tailwind CSS 4

Monorepo Layout

• backend/: FastAPI app, services, repositories, schemas
• frontend/: Next.js app, UI, hooks, and services

Prerequisites

• Node.js 20+
• Python 3.10+
• MongoDB (local or hosted)
• Google OAuth 2.0 Client (Web) credentials
• OpenAI API key

Environment Variables

Create .env files in both backend/ and frontend/ (or a shared root .env if you prefer) with the following.

Backend .env (at backend/.env):

• ENVIRONMENT = development | production
• BASE_URL = http://localhost:8000
• FRONTEND_URL = http://localhost:3000
• ALLOWED_ORIGINS = http://localhost:3000
• OPENAI_API_KEY = your_openai_api_key
• GOOGLE_CLIENT_ID = your_google_client_id
• GOOGLE_CLIENT_SECRET = your_google_client_secret
• JWT_SECRET = random_long_secret
• MONGO_URI = mongodb://localhost:27017 (or your Atlas URI)
• MONGO_DB_NAME = chatstack

Frontend .env.local (at frontend/.env.local):

• NEXT_PUBLIC_API_URL = http://localhost:8000

Notes:

• In production, set ENVIRONMENT=production. Cookies will be secure with SameSite=None. Update ALLOWED_ORIGINS to include your web origin(s).
• Ensure BASE_URL and FRONTEND_URL match your actual deployed URLs.

Install and Run (Development)

Backend:

1. Create a Python virtualenv (recommended)
2. Install dependencies
3. Run FastAPI server

Commands:

# from repo root
cd backend
python -m venv venv
# Windows PowerShell
./venv/Scripts/Activate.ps1
pip install -r requirements.txt
uvicorn main:app --reload --host 0.0.0.0 --port 8000

Frontend:

1. Install dependencies
2. Run Next.js dev server

Commands:

# from repo root
cd frontend
npm install
npm run dev

App URLs (dev):

• Frontend: http://localhost:3000
• API: http://localhost:8000/api

Scripts

Frontend:

• npm run dev → Next dev server
• npm run build → Next build
• npm start → Next start

Backend:

• uvicorn main:app --reload → Dev server

License

MIT