Langchain & GPTIndex chatbot

We are looking for a talented web developer to create a web-based chatbot application for answering questions from a database of texts. This chatbot will use GPTIndex to create a vector database of texts stored in Notion. You should be able to enable adding custom texts to the database. Additionally, you will use Langchain/GPTIndex to integrate multiple sources for the Q&A and summarization, including large language models. Additionally, you should be able to implement the langchain 'memory' concept so that each question remembers the chat history. Finally, you should be able to implement streaming so that the user can see the words appear dynamically instead of waiting until the full answer is synthesized.