app.py

import os
import gradio as gr
from langchain_openai import ChatOpenAI
from langchain_core.messages import HumanMessage
from langgraph.checkpoint.memory import MemorySaver
from langgraph.graph import START, MessagesState, StateGraph

def create_chat_app(api_key):
    # Initialize the chat model
    llm = ChatOpenAI(
        model="gpt-4o-mini",
        api_key=api_key,
        temperature=0
    )[1]

    # Define the graph
    workflow = StateGraph(state_schema=MessagesState)

    # Define the function that calls the model
    def call_model(state: MessagesState):
        response = llm.invoke(state["messages"])
        return {"messages": response}[1]

    # Add node and edge to graph
    workflow.add_edge(START, "model")
    workflow.add_node("model", call_model)[1]

    # Add memory
    memory = MemorySaver()
    return workflow.compile(checkpointer=memory)[1]

def chat(message, history, api_key, thread_id):
    if not api_key:
        return "Please enter your OpenAI API key first."
    
    try:
        # Create chat application if not exists
        app = create_chat_app(api_key)
        
        # Configure thread
        config = {"configurable": {"thread_id": thread_id}}[1]
        
        # Prepare input message
        input_messages = [HumanMessage(message)]
        
        # Get response
        output = app.invoke({"messages": input_messages}, config)[1]
        
        return output["messages"][-1].content
    except Exception as e:
        return f"Error: {str(e)}"

# Create Gradio interface
with gr.Blocks() as demo:
    gr.Markdown("# LangChain Chat with Message History")
    
    with gr.Row():
        api_key = gr.Textbox(
            label="OpenAI API Key", 
            placeholder="Enter your OpenAI API key",
            type="password"
        )
        thread_id = gr.Textbox(
            label="Thread ID",
            value="default_thread",
            placeholder="Enter a unique thread ID"
        )
    
    chatbot = gr.ChatInterface(
        fn=lambda message, history: chat(message, history, api_key.value, thread_id.value),
        title="Chat with GPT-4o-mini"
    )[2]

# Launch the application
demo.launch()