def respond(user_message, history):
    if not user_message:
        return "", history

    # ✅ Ensure proper message handling
    try:
        messages = [{"role": "system", "content": INITIAL_PROMPT}]

        for user_text, assistant_text in history:
            if user_text:
                messages.append({"role": "user", "content": user_text})
            if assistant_text:
                messages.append({"role": "assistant", "content": assistant_text})

        # ✅ Handling Method Selection
        method_selection = user_message.lower().strip()
        method_prompt = get_prompt_for_method(method_selection)
        
        if method_prompt != "I didn’t understand your choice. Please type 'Bar Model,' 'Double Number Line,' or 'Equation' to proceed.":
            messages.append({"role": "assistant", "content": method_prompt})
            history.append((user_message, method_prompt))
            return "", history

        messages.append({"role": "user", "content": user_message})

        # ✅ Get AI response
        completion = client.chat.completions.create(
            model="gpt-4o",
            messages=messages,
            max_tokens=512,
            temperature=0.7
        )

        assistant_reply = completion.choices[0].message.content
        history.append((user_message, assistant_reply))

        return "", history

    except Exception as e:
        return f"⚠️ An error occurred: {str(e)}", history