SNAP Scanner — CalHacks 2025

A mobile app that lets you scan a product barcode and instantly see whether it's eligible for SNAP (food stamps) in Idaho. Built at CalHacks 2025.

Note for the team: This is the hackathon prototype. The next version will be a full website supporting 3 states — this repo is a good reference for the backend eligibility logic and barcode lookup approach.

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What the app does

1. You open the app on your phone
2. Tap "Scan with Camera" and point it at a product barcode
3. The app tells you if that product is SNAP-eligible or not, and suggests alternatives if it isn't

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What you need before starting

• A Mac or PC with Node.js installed (version 18 or higher)
• Python 3 installed
• The Expo Go app on your phone — download it free from the App Store (iPhone) or Google Play (Android)
• Your phone and laptop must be on the same WiFi network

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Setup (do this once)

1. Clone the repo

git clone https://github.com/michellesk23/CalHacks2025.git
cd CalHacks2025

2. Install JavaScript dependencies

npm install

3. Install Python dependencies

pip3 install -r requirements.txt

If that fails on a Mac, try:

pip3 install -r requirements.txt --break-system-packages

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Running the app

You need two terminals open at the same time — one for the backend, one for the frontend.

Terminal 1 — Start the backend (Python server)

python3 start_server.py

You should see:

🚀 Starting Barcode Detection API Server...
📡 Server will be available at: http://localhost:8000

Leave this running. If you see Address already in use, the server is already running — skip this step.

Terminal 2 — Start the frontend (Expo)

npx expo start

A QR code will appear in the terminal.

• iPhone: Open the Camera app, point it at the QR code, tap the notification banner
• Android: Open the Expo Go app, tap "Scan QR code"

The app will load on your phone in about 30 seconds.

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IMPORTANT: Update the IP address before running

The app needs to know your laptop's IP address to talk to the backend. Every person on the team has a different IP, and it can change when you switch WiFi networks.

Step 1 — Find your laptop's IP address

On Mac, run this in a terminal:

ipconfig getifaddr en0

You'll get something like 10.43.201.56.

Step 2 — Update App.js

Open App.js and go to line 27. Change the IP to yours:

// Line 27 in App.js
const BASE_URL = Platform.OS === 'android' ? 'http://10.0.2.2:8000' : 'http://YOUR_IP_HERE:8000';

For example, if your IP is 10.43.201.56:

const BASE_URL = Platform.OS === 'android' ? 'http://10.0.2.2:8000' : 'http://10.43.201.56:8000';

Step 3 — Reload the app

In the Expo terminal, press r to reload the app on your phone.

You need to do this every time you switch WiFi networks or use a different laptop.

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Troubleshooting

"API call failed / Server offline" — The IP address is wrong or the Python backend isn't running. Double-check steps in the IP section above and make sure python3 start_server.py is running in a separate terminal.

"Address already in use" when starting the backend — The server is already running from a previous session. You don't need to start it again.

App loads but camera doesn't open — Make sure you granted camera permission to Expo Go when prompted. If you denied it, go to your phone's Settings → Expo Go → Camera, and enable it.

QR code doesn't scan on iPhone — Try opening the Expo Go app directly and entering the URL manually. The URL shows up in the Expo terminal as exp://YOUR_IP:8081.

npx expo start errors about TypeScript — Run this once to fix it:

npx expo install typescript @types/react

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Project structure

CalHacks2025/
├── App.js              # Main mobile app (React Native / Expo)
├── main.py             # Backend API (FastAPI)
├── start_server.py     # Script to start the backend
├── eligibility/        # SNAP eligibility logic per state
├── scripts/            # Barcode lookup scripts (Open Food Facts + FDC)
├── mobile/             # Experimental data layer (not currently used in app)
└── requirements.txt    # Python dependencies

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Branches

• main — latest working version, use this
• feature/databasequery — database/barcode lookup experiments

When in doubt, use main.

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For the next version (website rebuild)

The key reusable pieces from this prototype:

• eligibility/ — contains the SNAP eligibility rules logic, can be adapted for multiple states
• scripts/check_with_python.js — barcode lookup that tries USDA FoodData Central first, then Open Food Facts as fallback
• main.py — the FastAPI backend structure

The FDC API key is stored in scripts/check_with_python.js. You'll want to move it to an environment variable (.env file) before going public.