app.py

import os

import streamlit as st
from dotenv import load_dotenv
from langchain.callbacks.base import BaseCallbackHandler
from langchain.chains import ConversationalRetrievalChain
from langchain.chat_models import ChatOpenAI
from langchain.embeddings import OpenAIEmbeddings
from langchain.memory import ConversationBufferMemory
from langchain.memory.chat_message_histories import StreamlitChatMessageHistory
from langchain.vectorstores import Chroma

load_dotenv()

website_url = os.environ.get('WEBSITE_URL', 'a website')

st.set_page_config(page_title=f'Chat with {website_url}')
st.title('Chat with a website')

@st.cache_resource(ttl='1h')
def get_retriever():
    embeddings = OpenAIEmbeddings()
    vectordb = Chroma(persist_directory='db', embedding_function=embeddings)

    retriever = vectordb.as_retriever(search_type='mmr')

    return retriever

class StreamHandler(BaseCallbackHandler):
    def __init__(self, container: st.delta_generator.DeltaGenerator, initial_text: str = ''):
        self.container = container
        self.text = initial_text

    def on_llm_new_token(self, token: str, **kwargs) -> None:
        self.text += token
        self.container.markdown(self.text)

retriever = get_retriever()

msgs = StreamlitChatMessageHistory()
memory = ConversationBufferMemory(memory_key='chat_history', chat_memory=msgs, return_messages=True)

llm = ChatOpenAI(model_name='gpt-3.5-turbo', temperature=0, streaming=True)
qa_chain = ConversationalRetrievalChain.from_llm(
    llm, retriever=retriever, memory=memory, verbose=False
)

if st.sidebar.button('Clear message history') or len(msgs.messages) == 0:
    msgs.clear()
    msgs.add_ai_message(f'Ask me anything about {website_url}!')

avatars = {'human': 'user', 'ai': 'assistant'}
for msg in msgs.messages:
    st.chat_message(avatars[msg.type]).write(msg.content)

if user_query := st.chat_input(placeholder='Ask me anything!'):
    st.chat_message('user').write(user_query)

    with st.chat_message('assistant'):
        stream_handler = StreamHandler(st.empty())
        response = qa_chain.run(user_query, callbacks=[stream_handler])