app.py

import streamlit as st
import os
from dotenv import load_dotenv
load_dotenv()

os.environ["LANGCHAIN_API_KEY"] = os.getenv("LANGCHAIN_API_KEY")    
os.environ["LANGCHAIN_TRACING_V2"] = "true"
os.environ["LANGCHAIN_PROJECT"]= "RAG Document Q&A"
os.environ["HUGGINGFACEHUB_API_TOKEN"] = os.getenv("HUGGINGFACEHUB_API_TOKEN")

from langchain_groq import ChatGroq
from langchain_openai import ChatOpenAI, OpenAIEmbeddings
from langchain_huggingface import HuggingFaceEmbeddings
from langchain.text_splitter import RecursiveCharacterTextSplitter
from langchain_core.prompts import ChatPromptTemplate, PromptTemplate, MessagesPlaceholder
from langchain.chains.combine_documents import create_stuff_documents_chain
from langchain.document_loaders import PyPDFLoader

from langchain.vectorstores import FAISS
from langchain.chains import create_retrieval_chain, create_history_aware_retriever
from langchain_core.chat_history import BaseChatMessageHistory
from langchain_community.chat_message_histories import ChatMessageHistory
from langchain_core.runnables.history import RunnableWithMessageHistory



st.title("Conversational RAG With PDF uploads and chat history")
st.write("Upload PDFs and chat with their content")

api_key = st.text_input("Enter your Groq API key:", type="password")

if api_key:
    llm=ChatGroq(groq_api_key=api_key, model_name="openai/gpt-oss-20b")

    session_id= st.text_input("Session ID", value="default_session")

    if 'store' not in st.session_state:
        st.session_state.store={}

    uploaded_files=st.file_uploader("Choose A PDF file", type="pdf", accept_multiple_files=True)

    if uploaded_files:
        documents=[]
        for uploaded_file in uploaded_files:
            tempdf=f"./temp.pdf"
            with open(tempdf, "wb") as file:
                file.write(uploaded_file.getvalue())
                file_name = uploaded_file.name
            
            loader= PyPDFLoader(tempdf)
            docs = loader.load()
            documents.extend(docs)

        text_splitter = RecursiveCharacterTextSplitter(chunk_size=5000, chunk_overlap=500)
        splits = text_splitter.split_documents(documents)
        vectorstore =  FAISS.from_documents(documents=splits, embedding=OpenAIEmbeddings())
        retriever = vectorstore.as_retriever()

        contextualize_q_system_prompt=(
            "Given a chat history and the latest user question"
            "which might reference context in the chat history, "
            "formulate a standalone question which can be understood "
            "without the chat history. Do NOT answer the question, "
            "just reformulate it if needed and otherwise return it as is."
        )

        contextualize_q_prompt = ChatPromptTemplate.from_messages(
                [
                    ("system", contextualize_q_system_prompt),
                    MessagesPlaceholder("chat_history"),
                    ("human", "{input}"),
                ]
            )
        
        history_aware_retriever= create_history_aware_retriever(llm, retriever, contextualize_q_prompt)

        ## Answer question

        # Answer question
        system_prompt = (
                "You are an assistant for question-answering tasks. "
                "Use the following pieces of retrieved context to answer "
                "the question. If you don't know the answer, say that you "
                "don't know. Use three sentences maximum and keep the "
                "answer concise."
                "\n\n"
                "{context}"
            )
        qa_prompt = ChatPromptTemplate.from_messages(
                [
                    ("system", system_prompt),
                    MessagesPlaceholder("chat_history"),
                    ("human", "{input}"),
                ]
            )
        
        question_answer_chain = create_stuff_documents_chain(llm, qa_prompt)

        rag_chain=create_retrieval_chain(history_aware_retriever, question_answer_chain)

        def get_session_history(session:str)->BaseChatMessageHistory:
            if session_id not in st.session_state.store:
                st.session_state.store[session_id]=ChatMessageHistory()
            return st.session_state.store[session_id]
        

        conversational_rag_chain = RunnableWithMessageHistory(
            rag_chain, get_session_history,
            input_messages_key="input",
            history_messages_key="chat_history",
            output_messages_key="answer"
        )
        user_input = st.text_input("Enter your questions:")
        if user_input:
            session_history=get_session_history(session_id)
            response = conversational_rag_chain.invoke(
                {"input": user_input},
                config={
                    "configurable": {"session_id":session_id}
                },  # constructs a key "abc123" in `store`.
            )
            #st.write(st.session_state.store)
            st.write("Assistant:", response['answer'])
            #st.write("Chat History:", session_history.messages)
else:
    st.warning("Please enter the GRoq API Key")