Haystack/LangChain Backend Development

I'm looking for an expert in Haystack or LangChain to help me enhance an already developed document and chat analysis application. The frontend is built on JavaScript, and we now need a robust backend that leverages the capabilities Haystack offers.

Key Requirements:
- Support for chat and document analysis
- Backend integration with existing JS frontend
- Functionality for:
- Sentiment analysis
- Keyword extraction
- Entity recognition

Ideal Skills:
- Proficiency in Haystack and or LangChain
- Strong backend development skills
- Experience with text data processing and analysis

Your expertise will help bring this project to fruition. Please share relevant experience and approach.