# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

A Python utility that synchronizes SharePoint Online folders to local storage using the Microsoft Graph API. Offers both a CLI (`download_sharepoint.py`) and a modern GUI (`sharepoint_gui.py`).

## Running the Tool

```bash
# Install dependencies
pip install -r requirements.txt

# GUI mode (recommended for interactive use)
python sharepoint_gui.py

# CLI mode (for automation/scripting)
python download_sharepoint.py
```

Configuration is read from `connection_info.txt` (gitignored — copy from `connection_info.template.txt` and fill in credentials).

## Architecture

Two-file structure with clear separation of concerns:

**`download_sharepoint.py`** — Core engine with four logical layers:
1. **Authentication** — MSAL `ConfidentialClientApplication` using OAuth 2.0 Client Credentials flow. Tokens are refreshed via `force_refresh=True` when a 401 is received.
2. **Graph API navigation** — `get_site_id()` → `get_drive_id()` → `process_item_list()` (recursive, handles `@odata.nextLink` pagination).
3. **Download & resilience** — `download_single_file()` with Range header support for resumable downloads. `get_fresh_download_url()` handles expired pre-signed URLs. The `@retry_request` decorator provides exponential backoff (up to 5 retries, 2^n seconds) for 429s and network errors.
4. **Concurrency** — `ThreadPoolExecutor` (max 5 workers). A `report_lock` guards the shared error list. A `stop_event` allows the GUI stop button to cancel in-flight work.

**`sharepoint_gui.py`** — CustomTkinter wrapper that:
- Persists settings to a local JSON file
- Spawns the core engine in a background thread
- Patches `requests.get` to route through the GUI's log display
- Provides a folder browser for `LOCAL_PATH`

## Key Behaviors to Preserve

- **Self-healing sessions**: On 401, the code refreshes both the MSAL access token *and* the pre-signed Graph download URL before retrying — these are two separate expiry mechanisms.
- **Resumable downloads**: Files are downloaded in 1 MB chunks using HTTP Range headers. Existing files are skipped if their size matches; partial files are resumed from the last byte.
- **Stop signal**: `stop_event.is_set()` is checked in the download loop and recursive traversal — any new code that loops must respect this.

## Output

- `sharepoint_download.log` — Full operation log
- `download_report_YYYYMMDD_HHMMSS.csv` — Per-run error report (gitignored)