file.py

from langchain_openai import ChatOpenAI
from langchain.schema import SystemMessage, HumanMessage
from langgraph.checkpoint.memory import MemorySaver
from langgraph.graph import StateGraph, START, MessagesState
import os

os.environ.get("OPENAI_API_KEY")
# Initialize model
model = ChatOpenAI(model="gpt-4o-mini", temperature=0)

# Create graph
builder = StateGraph(state_schema=MessagesState)    

def chat_node(state: MessagesState):
    system_message = SystemMessage(content="You're a kind therapy assistant.")
    history = state["messages"]
    prompt = [system_message] + history

    response = model.invoke(prompt)

    return {"messages": response}

builder.add_node("chat", chat_node)
builder.add_edge(START, "chat")

# Compile graph with MemorySaver
memory = MemorySaver()
chat_app = builder.compile(checkpointer=memory)


thread_id = "1"

while True:
    user_input = input("You: ")
    state_update = {"messages": [HumanMessage(content=user_input)]}
    
    result = chat_app.invoke(
        state_update,
        {"configurable": {"thread_id": thread_id}}
    )
    
    print(result)

    ai_msg = result["messages"][-1]
    print("Bot:", ai_msg.content)