app.py

from operator import itemgetter

from langchain.chat_models import ChatOpenAI
from langchain.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain.schema.output_parser import StrOutputParser
from langchain.schema.runnable import Runnable, RunnablePassthrough, RunnableLambda
from langchain.schema.runnable.config import RunnableConfig
from langchain.memory import ConversationBufferMemory

from chainlit.client.base import ConversationDict

import chainlit as cl


def setup_runnable():
    memory = cl.user_session.get("memory")  # type: ConversationBufferMemory
    model = ChatOpenAI(streaming=True)
    prompt = ChatPromptTemplate.from_messages(
        [
            ("system", "You are a helpful chatbot"),
            MessagesPlaceholder(variable_name="history"),
            ("human", "{question}"),
        ]
    )

    runnable = (
        RunnablePassthrough.assign(
            history=RunnableLambda(memory.load_memory_variables) | itemgetter("history")
        )
        | prompt
        | model
        | StrOutputParser()
    )
    cl.user_session.set("runnable", runnable)


@cl.on_chat_start
async def on_chat_start():
    await cl.Avatar(
        name="Chatbot",
        path="icon/chainlit.png"
        ).send()
    
    await cl.Avatar(
        name="User",
        path="icon/avatar.png",
    ).send()
    cl.user_session.set("memory", ConversationBufferMemory(return_messages=True))
    setup_runnable()


@cl.on_chat_resume
async def on_chat_resume(conversation: ConversationDict):
    memory = ConversationBufferMemory(return_messages=True)
    root_messages = [m for m in conversation["messages"] if m["parentId"] == None]
    for message in root_messages:
        if message["authorIsUser"]:
            memory.chat_memory.add_user_message(message["content"])
        else:
            memory.chat_memory.add_ai_message(message["content"])

    cl.user_session.set("memory", memory)

    setup_runnable()


@cl.on_message
async def on_message(message: cl.Message):
    memory = cl.user_session.get("memory")  # type: ConversationBufferMemory

    runnable = cl.user_session.get("runnable")  # type: Runnable

    res = cl.Message(content="")

    async for chunk in runnable.astream(
        {"question": message.content},
        config=RunnableConfig(callbacks=[cl.LangchainCallbackHandler()]),
    ):
        await res.stream_token(chunk)

    await res.send()

    memory.chat_memory.add_user_message(message.content)
    memory.chat_memory.add_ai_message(res.content)