app.py

import gradio as gr
from langchain_community.document_loaders import PyPDFLoader
from langchain_text_splitters import RecursiveCharacterTextSplitter
from langchain_chroma import Chroma
from langchain_huggingface.embeddings import HuggingFaceEmbeddings
from langchain_huggingface import HuggingFaceEndpoint, ChatHuggingFace
from langchain import hub
from langchain_core.output_parsers import StrOutputParser
from langchain_core.runnables import RunnablePassthrough

def initialise_vectorstore(pdf, progress=gr.Progress()):
    progress(0, desc="Reading PDF")

    loader = PyPDFLoader(pdf.name)
    pages = loader.load()
    text_splitter = RecursiveCharacterTextSplitter(chunk_size=1000, chunk_overlap=200)
    splits = text_splitter.split_documents(pages)

    progress(0.5, desc="Initialising Vectorstore")

    vectorstore = Chroma.from_documents(
        splits,
        embedding=HuggingFaceEmbeddings()
    )

    progress(1, desc="Complete")

    return vectorstore, progress

def initialise_chain(llm, vectorstore, progress=gr.Progress()):

    progress(0, desc="Initialising LLM")

    llm = HuggingFaceEndpoint(
        repo_id=llm,
        task="text-generation",
        max_new_tokens=512,
        do_sample=False,
        repetition_penalty=1.03
    )

    chat = ChatHuggingFace(
        llm=llm, 
        verbose=True
    )

    progress(0.5, desc="Initialising RAG Chain")

    retriever = vectorstore.as_retriever()
    prompt = hub.pull("rlm/rag-prompt")
    parser = StrOutputParser()

    rag_chain = {"context": retriever, "question": RunnablePassthrough()} | prompt | chat | parser

    progress(1, desc="Complete")

    return rag_chain, progress

def send(message, rag_chain, chat_history):
    response = rag_chain.invoke(message)
    chat_history.append((message, response))
    return "", chat_history

def restart():
    return f"Restarting"


with gr.Blocks() as demo:

    vectorstore = gr.State()
    rag_chain = gr.State()
    
    gr.Markdown("<H1>Talk to Documents</H1>")
    gr.Markdown("<H3>Upload and ask questions about your PDF files</H3>")
    gr.Markdown("<H6>Note: This project uses LangChain to perform RAG (Retrieval Augmented Generation) on PDF files, allowing users to ask any questions related to their contents. When a PDF file is uploaded, it is embedded and stored in an in-memory Chroma vectorstore, which the chatbot uses as a source of knowledge when aswering user questions.</H6>")

    # Vectorstore Tab
    with gr.Tab("Vectorstore"):
        with gr.Row():
            input_pdf = gr.File()
        with gr.Row():
            with gr.Column(scale=1, min_width=0):
                pass
            with gr.Column(scale=2, min_width=0):
                initialise_vectorstore_btn = gr.Button(
                    "Initialise Vectorstore",
                    variant='primary'
                )
            with gr.Column(scale=1, min_width=0):
                pass
        with gr.Row():
            vectorstore_initialisation_progress = gr.Textbox(value="None", label="Initialization")

    # RAG Chain
    with gr.Tab("RAG Chain"):
        with gr.Row():
            language_model = gr.Radio(["microsoft/Phi-3-mini-4k-instruct", "mistralai/Mistral-7B-Instruct-v0.2", "nvidia/Mistral-NeMo-Minitron-8B-Base"])
        with gr.Row():
            with gr.Column(scale=1, min_width=0):
                pass
            with gr.Column(scale=2, min_width=0):
                initialise_chain_btn = gr.Button(
                    "Initialise RAG Chain",
                    variant='primary'
                )
            with gr.Column(scale=1, min_width=0):
                pass
        with gr.Row():
            chain_initialisation_progress = gr.Textbox(value="None", label="Initialization")

    # Chatbot Tab
    with gr.Tab("Chatbot"):
        with gr.Row():
            chatbot = gr.Chatbot()
        with gr.Accordion("Advanced - Document references", open=False):
            with gr.Row():
                doc_source1 = gr.Textbox(label="Reference 1", lines=2, container=True, scale=20)
                source1_page = gr.Number(label="Page", scale=1)
            with gr.Row():
                doc_source2 = gr.Textbox(label="Reference 2", lines=2, container=True, scale=20)
                source2_page = gr.Number(label="Page", scale=1)
            with gr.Row():
                doc_source3 = gr.Textbox(label="Reference 3", lines=2, container=True, scale=20)
                source3_page = gr.Number(label="Page", scale=1)
        with gr.Row():
            message = gr.Textbox()
        with gr.Row():
            send_btn = gr.Button(
                "Send",
                variant=["primary"]
            )
            restart_btn = gr.Button(
                "Restart",
                variant=["secondary"]
            )

    initialise_vectorstore_btn.click(fn=initialise_vectorstore, inputs=input_pdf, outputs=[vectorstore, vectorstore_initialisation_progress])
    initialise_chain_btn.click(fn=initialise_chain, inputs=[language_model, vectorstore], outputs=[rag_chain, chain_initialisation_progress])
    send_btn.click(fn=send, inputs=[message, rag_chain, chatbot], outputs=[message, chatbot])
    restart_btn.click(fn=restart)

demo.launch()