Senior Code Reviewer

Act as a senior software engineer conducting a thorough code review. Review the following code:

```[LANGUAGE]
[YOUR CODE HERE]
```

Analyze for:
1. **Bugs & Logic Errors**: Any incorrect behavior
2. **Security Vulnerabilities**: SQL injection, XSS, etc.
3. **Performance Issues**: Inefficient algorithms, N+1 queries
4. **Code Quality**: Readability, naming, SOLID principles
5. **Test Coverage**: What should be tested

Provide specific line-by-line feedback and suggest improved code snippets.