ChatGPT Pay-As-You-Go Web App

Purpose:

This project provides a self-hosted web interface to use OpenAI's ChatGPT models in a "pay-as-you-go" fashion via the official API. If you want access to all available GPT models without being tied to a fixed monthly subscription, this application is for you. You pay only for what you use, with no time limits or quotas, leveraging your own OpenAI API key. The app is ideal for users who want flexibility, full model availability, and cost control for personal or small-team usage.

See it in action: Interact with ChatGPT models, switch context, and manage conversations — all in one place.

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📁 Project Structure

chatgpt_flask/
│
├── backend/                 # Flask backend (API, DB, business logic)
│   ├── app.py
│   └── chatgpt_api/
│       ├── api/
│       │   ├── contexto.py
│       │   ├── conversacion.py
│       │   ├── mensaje.py
│       │   ├── modelo.py
│       │   └── tools.py
│       ├── db.py
│       ├── db_init/
│       │   ├── add_modelo_a_conversacion_SQL.py
│       │   ├── crear_db.py
│       │   ├── crear_db_con_modelo.py
│       │   └── verificar_db.py
│       ├── models.py
│       └── services/
│           └── openai_service.py
│
├── frontend/                # Static frontend (HTML, JS, CSS, SCSS, images)
│   ├── web/
│   │   ├── chattest.html
│   │   └── static/
│   │       ├── css/
│   │       │   ├── main.css
│   │       │   └── main.min.css
│   │       ├── images/
│   │       │   ├── favicon.ico
│   │       │   └── flaskchat-logo.png
│   │       ├── js/
│   │       │   ├── main.js
│   │       │   └── modules/
│   │       │       ├── api.js
│   │       │       ├── conversation.js
│   │       │       ├── events.js
│   │       │       └── ui.js
│   └── scss/
│
├── docs/                    # Documentation (Doxygen, etc.)
│
└── ...

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🚀 Backend (Flask API)

Requirements

• Python 3.8+
• Virtual environment with dependencies installed (see requirements.txt)
• OpenAI API Key

Setup

1. Clone the repository and enter the backend directory:

   cd chatgpt_flask/backend

2. Create and activate a Python virtual environment:

   python -m venv venv
   source venv/bin/activate  # On Windows: venv\Scripts\activate

3. Install dependencies:

   pip install -r requirements.txt

4. Initialize the SQLite database:

   • Inside chatgpt_api/db_init/ you will find scripts to create or update the DB schema.
   • To initialize the DB:

     cd chatgpt_api/db_init
     python crear_db_con_modelo.py

   • To verify tables:

     python verificar_db.py

   • To add the modelo column if missing:

     python add_modelo_a_conversacion_SQL.py

5. Set the OpenAI API Key:

   • The backend expects the environment variable OPENAI_API_KEY to be set.
   • You can export it manually or use a process manager (see below).

Running as a Service (Recommended for Production)

A sample systemd service file is provided as follows:

Example configuration (/etc/systemd/system/flaskchat.service):

[Unit]
Description=Flask ChatGPT API Service
After=network.target

[Service]
User=youruser
WorkingDirectory=/path/to/chatgpt_flask/backend
ExecStart=/path/to/chatgpt_flask/backend/venv/bin/python /path/to/chatgpt_flask/backend/app.py
Environment=OPENAI_API_KEY=your-openai-api-key
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target

Enable and start the service:

sudo systemctl daemon-reload
sudo systemctl enable flaskchat
sudo systemctl start flaskchat

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🖥️ Frontend (Static Web)

• All frontend files are under frontend/web/ (HTML, JS, CSS, images).
• SCSS sources are in frontend/scss/ and should be compiled to CSS as needed.
• The frontend can be served by any web server (e.g., Apache, Nginx, Caddy, etc).

Reverse Proxy Configuration

The frontend communicates with the Flask API (backend) via HTTP requests.
You must configure your web server as a reverse proxy to forward API calls.

Example (Apache VirtualHost):

# Proxy settings for Flask application
ProxyPass /api/ http://localhost:5000/api/
ProxyPassReverse /api/ http://localhost:5000/api/

Place this inside your relevant <VirtualHost> block.

• Adjust the URL and port (localhost:5000) to match your Flask backend.
• Make sure mod_proxy and mod_proxy_http are enabled in Apache.

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🗄️ Database Initialization

• All scripts for initializing and updating the SQLite database are in backend/chatgpt_api/db_init/.
• See the Backend Setup section for usage.

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📄 Documentation

• Doxygen-generated documentation and other docs are in the docs/ directory.

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🛡️ Security Notes

• Never commit your OpenAI API key or other secrets to the repository.
• Use environment variables or secure secret managers for sensitive information.

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✨ Credits

Developed by Rafael Sanchez, 2025.