# Document Chat Backend

This is the FastAPI backend for the Document Chat application that enables document uploading, processing, and chat-based Q&A functionality.

## Project Structure
```
backend/
├── app/
│   ├── __init__.py
│   ├── main.py          # FastAPI application and route definitions
│   ├── models.py        # Pydantic models for request/response validation
│   ├── services/
│   │   ├── __init__.py
│   │   ├── document_processor.py    # Document processing and chunking
│   │   ├── vector_store.py         # Vector storage and similarity search
│   │   └── chat_service.py         # OpenAI chat completion handling
│   └── dependencies.py   # FastAPI dependencies and shared resources
└── requirements.txt      # Python package dependencies
```

## Setup

1. Create a virtual environment:
```bash
python -m venv .venv
source .venv/bin/activate  # On Windows: .venv\Scripts\activate
```

2. Install dependencies:
```bash
pip install -r requirements.txt
```

3. Create a `.env` file in the root directory with your OpenAI API key:
```
OPENAI_API_KEY=your_api_key_here
```

4. Run the development server:
```bash
uvicorn app.main:app --reload
```

The API will be available at `http://localhost:8000`

## API Endpoints

- `POST /upload`
  - Upload PDF or TXT files for processing
  - Returns a session ID for subsequent chat interactions

- `POST /chat`
  - Send messages to chat with the uploaded document
  - Requires a session ID from a previous upload

## Development

- The `services` directory contains the core business logic:
  - `document_processor.py`: Handles file uploads and text chunking
  - `vector_store.py`: Manages document embeddings and similarity search
  - `chat_service.py`: Interfaces with OpenAI for chat completions

- `models.py` defines the data structures using Pydantic
- `main.py` contains the FastAPI application and route handlers
- `dependencies.py` manages shared resources and dependencies

## Requirements

See `requirements.txt` for a full list of Python dependencies. Key packages include:
- FastAPI
- OpenAI
- PyPDF2
- python-multipart
- python-dotenv
- uvicorn
```

To create the directory structure, you can run these commands:

```bash
mkdir -p backend/app/services
touch backend/app/__init__.py
touch backend/app/main.py
touch backend/app/models.py
touch backend/app/dependencies.py
touch backend/app/services/__init__.py
touch backend/app/services/document_processor.py
touch backend/app/services/vector_store.py
touch backend/app/services/chat_service.py
touch backend/requirements.txt
```

This will create all the necessary files and directories in the structure you specified. The README.md provides a clear overview of the project structure, setup instructions, and key components for developers who will work with the backend.