app.py

from langchain.chains import LLMChain
from langchain.prompts import PromptTemplate
from langchain.memory import ConversationBufferMemory
from langchain.chat_models import ChatOpenAI
from langchain_community.chat_message_histories import StreamlitChatMessageHistory
import streamlit as st
import os
from dotenv import load_dotenv

load_dotenv()

OPENAI_API_KEY = os.getenv("OPENAI_API_KEY")

# Initialize Streamlit app
st.set_page_config(page_title="LangChain Chatbot with Memory")
st.title("🤖 LangChain Chatbot with Memory")

# Initialize chat message history
history = StreamlitChatMessageHistory(key="chat_messages")

# Display chat history
for msg in history.messages:
    if msg.type == "human":
        st.chat_message("user").write(msg.content)
    else:
        st.chat_message("assistant").write(msg.content)

# Memory
memory = ConversationBufferMemory(
    memory_key="chat_history",
    chat_memory=history,
    return_messages=True
)

# Prompt with system role + instruction
prompt = PromptTemplate(
    input_variables=["chat_history", "input"],
    template="""
You are a friendly and knowledgeable assistant. 
Always reply in a complete sentence using no more than 50 words.

Conversation so far:
{chat_history}

User: {input}
Assistant:"""
)

# LLM and chain
llm = ChatOpenAI(
    openai_api_key=OPENAI_API_KEY,
    model_name="gpt-4o-mini",
    temperature=0.7,
    max_tokens=50
)

conversation = LLMChain(
    llm=llm,
    prompt=prompt,
    memory=memory
)

# Input from user
if prompt_input := st.chat_input("Say something..."):
    st.chat_message("user").write(prompt_input)

    # Let LangChain handle history
    response = conversation.run(input=prompt_input)

    st.chat_message("assistant").write(response)