MongoDB Aggregation Pipeline — Complex Analytics

## Task
MongoDB Aggregation Pipeline

## Requirements
- Language/Framework: [language/framework]
- Target: [target platform or environment]
- Style: Follow [coding standard] conventions

## Specifications
```
Input: [input description]
Output: [output description]
Constraints: [constraints]
```

## Implementation Notes
1. Use [design pattern] pattern where applicable
2. Include error handling for [error scenarios]
3. Add TypeScript types / type hints where relevant
4. Follow SOLID principles
5. Include inline comments for complex logic

## Testing
- Include [test framework] tests for core functionality
- Cover edge cases: [edge cases]
- Ensure [performance requirement]