# SharePoint Download Tool - Technical Documentation

A production-ready Python utility for robust synchronization of SharePoint Online folders using Microsoft Graph API.

## Project Overview

*   **Purpose:** Enterprise-grade synchronization tool for local mirroring of SharePoint content.
*   **Technologies:** 
    *   **Microsoft Graph API:** Advanced REST API for SharePoint data.
    *   **MSAL:** Secure authentication using Azure AD Client Credentials.
    *   **Requests:** High-performance HTTP client with streaming and Range header support.
    *   **ThreadPoolExecutor:** Parallel file processing for optimized throughput.

## Core Features (Production Ready)

1.  **Resumable Downloads:** Implements HTTP `Range` headers to resume partially downloaded files, critical for multi-gigabyte assets.
2.  **Reliability:** Includes a custom `retry_request` decorator for Exponential Backoff, handling throttling (429) and transient network errors.
3.  **Concurrency:** Multi-threaded architecture (5 workers) for simultaneous scanning and downloading.
4.  **Pagination:** Full support for OData pagination, ensuring complete folder traversal regardless of item count.
5.  **Self-Healing Sessions:** Automatically detects and resolves 401 Unauthorized errors by refreshing both expiring Microsoft Graph Download URLs and MSAL Access Tokens mid-process.
6.  **Logging & Audit:** Integrated Python `logging` to `sharepoint_download.log` and structured CSV reports for error auditing.

## Building and Running

### Setup
1.  **Dependencies:** `pip install -r requirements.txt`
2.  **Configuration:** Use `connection_info.template.txt` to create `connection_info.txt`.

### Execution
`python download_sharepoint.py`

## Development Conventions

*   **Error Handling:** Always use the `safe_get` (retry-wrapped) method for Graph API calls. For item-specific operations, use `get_fresh_download_url` to handle token/URL expiry.
*   **Authentication:** Use `get_headers(app, force_refresh=True)` when a 401 error is encountered from Graph API to ensure session continuity.
*   **Thread Safety:** Use `report_lock` when updating the shared error list from worker threads.
*   **Logging:** Prefer `logger.info()` or `logger.error()` over `print()` to ensure persistence in `sharepoint_download.log`.
*   **Integrity:** Always verify file integrity using `size` and `quickXorHash` where available.