chain_setup.py

# chain_setup.py

from langchain.chains import ConversationalRetrievalChain
from langchain_community.chat_models import ChatOllama
from langchain.memory import ConversationBufferMemory

def build_conversational_chain(vectorstore):
    """
    Creates a ConversationalRetrievalChain with a ChatOllama LLM and 
    a ConversationBufferMemory for multi-turn Q&A.
    """
    llm = ChatOllama(model="qwen2.5:7b")

    memory = ConversationBufferMemory(
        memory_key="chat_history",
        return_messages=True
    )

    qa_chain = ConversationalRetrievalChain.from_llm(
        llm=llm,
        retriever=vectorstore.as_retriever(search_type="similarity", search_kwargs={"k": 5}),
        memory=memory,
        verbose=True  # optional debug logs
    )

    return qa_chain