# Subdirectory Discovery Bug Fix

## Issue Summary

The ETag optimization feature was failing to discover subdirectories during first-time scans, causing it to report "No known subdirectories" and miss thousands of files.

### Root Cause

In `src/services/webdav_service.rs:933-936`, the `check_subdirectories_for_changes` function was returning empty results when no subdirectories were previously tracked in the database:

```rust
// BUGGY CODE (before fix)
if subdirectories.is_empty() {
    info!("📁 No known subdirectories for {}, no changes to process", parent_path);
    return Ok(Vec::new()); // ❌ This was the bug!
}
```

This logic assumed that if a directory's ETag was unchanged, we only needed to check previously-known subdirectories. However, this failed for directories that hadn't been fully scanned before.

### The Fix

Changed the function to fall back to a full recursive scan when no subdirectories are known:

```rust
// FIXED CODE (after fix)
if subdirectories.is_empty() {
    info!("📁 No known subdirectories for {}, performing initial scan to discover structure", parent_path);
    return self.discover_files_in_folder_impl(parent_path).await; // ✅ Fixed!
}
```

### Files Changed

1. **`src/services/webdav_service.rs:933-936`** - Fixed the core logic
2. **`tests/integration_webdav_first_time_scan_tests.rs`** - New integration tests
3. **`tests/unit_webdav_subdirectory_edge_cases_tests.rs`** - New unit tests

### Test Coverage Added

#### Integration Tests (`integration_webdav_first_time_scan_tests.rs`)
- `test_first_time_directory_scan_with_subdirectories()` - Tests the exact bug scenario
- `test_subdirectory_tracking_after_full_scan()` - Verifies proper tracking after discovery
- `test_direct_child_identification_edge_cases()` - Tests path logic with realistic paths
- `test_file_count_accuracy_per_directory()` - Verifies correct file counting
- `test_size_calculation_accuracy()` - Verifies size calculations

#### Unit Tests (`unit_webdav_subdirectory_edge_cases_tests.rs`)
- `test_comprehensive_directory_extraction()` - Tests directory structure extraction
- `test_first_time_scan_scenario_logic()` - Tests the exact bug logic
- `test_directory_etag_mapping_accuracy()` - Tests ETag handling
- `test_direct_file_counting_precision()` - Tests file counting logic
- `test_total_size_calculation_per_directory()` - Tests size calculations
- `test_path_edge_cases_and_normalization()` - Tests path handling edge cases
- `test_bug_scenario_file_count_verification()` - Specifically tests the 7046 files scenario

### Expected Behavior Now

**Before Fix:**
```
📁 No known subdirectories for /FullerDocuments/JonDocuments, no changes to process
Found 0 files in folder /FullerDocuments/JonDocuments
```

**After Fix:**
```
📁 No known subdirectories for /FullerDocuments/JonDocuments, performing initial scan to discover structure
[Performs full recursive scan]
Found 7046 files in folder /FullerDocuments/JonDocuments
```

### Why This Fix is Safe

1. **Performance**: Only affects first-time scans or completely empty directories
2. **Correctness**: Ensures all files are discovered even when ETag optimization is enabled
3. **Backward Compatibility**: Doesn't change behavior for directories with known subdirectories
4. **Robustness**: Falls back to the tried-and-tested full scan method

### Test Verification

The fix has been verified with comprehensive test coverage that includes:
- Real-world directory structures similar to the user's environment
- Edge cases for path handling and file counting
- Integration scenarios that test the full optimization workflow
- Unit tests that isolate the specific logic that was failing

### Summary

This fix ensures that the ETag optimization feature works correctly for first-time directory scans while maintaining all the performance benefits for subsequent scans where subdirectories are already known.