app.py

import torch
import gradio as gr
from transformers import AutoTokenizer, AutoModelForSeq2SeqLM, pipeline

# ---------------- CONFIG ----------------
MODEL_NAME = "google/flan-t5-base"   # ✅ CPU-friendly model
SYSTEM_PROMPT_DEFAULT = (
    "You are a formal and polite AI assistant. "
    "Always respond appropriately depending on the selected explanation style."
)

MAX_NEW_TOKENS_DEFAULT = 256
TEMP_DEFAULT = 0.7
TOP_P_DEFAULT = 0.9

# ---------------- LOAD MODEL ----------------
tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)

model = AutoModelForSeq2SeqLM.from_pretrained(
    MODEL_NAME,
    torch_dtype=torch.float32   # ✅ safe for CPU
)

generator = pipeline(
    "text2text-generation",   # ✅ T5 models use this, not causal LM
    model=model,
    tokenizer=tokenizer,
    device=-1   # ✅ force CPU
)

# ---------------- HELPERS ----------------
def format_prompt(chat_history, user_message, system_message, response_style):
    # Start with system message
    prompt = system_message + "\n\n"
    
    # Append previous conversation content only
    for turn in chat_history:
        prompt += f"{turn['content']}\n"
    
    # Append the new user message
    prompt += user_message
    
    # Optional: add response style instruction
    if response_style == "No explanation":
        prompt += " Provide only the answer."
    elif response_style == "Short explanation":
        prompt += " Provide a short one-sentence explanation."
    elif response_style == "Detailed explanation":
        prompt += " Provide a detailed explanation."
    
    return prompt

# ---------------- CHAT FUNCTION ----------------
def chat(user_message, chat_history, system_message, max_tokens, temperature, top_p, response_style):
    chat_history = chat_history or []
    prompt = format_prompt(chat_history, user_message, system_message, response_style)
    
    output = generator(
        prompt,
        max_new_tokens=max_tokens,
        do_sample=True,
        temperature=temperature,
        top_p=top_p,
    )[0]['generated_text']
    
    # Sometimes Flan-T5 outputs the question in the result, so strip it
    response = output.replace(prompt, "").strip()
    
    # Save user and assistant content without labels
    chat_history.append({"role": "user", "content": user_message})
    chat_history.append({"role": "assistant", "content": response})
    
    return "", chat_history

# ---------------- UI ----------------
with gr.Blocks(theme=gr.themes.Soft(primary_hue="violet", secondary_hue="pink")) as demo:
    gr.Markdown("# 🧠 FLAN-T5-Base Chat Assistant (CPU-safe)")

    chatbot = gr.Chatbot(type="messages", height=500, show_copy_button=True)

    with gr.Row():
        msg = gr.Textbox(label="💬 Your Message", placeholder="Type here…", scale=6)
        send_btn = gr.Button("🚀 Send", variant="primary", scale=1)
        clear_btn = gr.Button("🧹 Clear Chat", scale=1)

    with gr.Accordion("⚙️ Advanced Settings", open=False):
        system_prompt = gr.Textbox(label="System Prompt", value=SYSTEM_PROMPT_DEFAULT, lines=3)
        response_style = gr.Dropdown(
            ["No explanation", "Short explanation", "Detailed explanation"],
            value="Detailed explanation",
            label="Response Style"
        )
        temperature = gr.Slider(0.1, 1.5, value=TEMP_DEFAULT, step=0.1, label="Temperature")
        top_p = gr.Slider(0.1, 1.0, value=TOP_P_DEFAULT, step=0.05, label="Top-p")
        max_tokens = gr.Slider(32, 512, value=MAX_NEW_TOKENS_DEFAULT, step=16, label="Max new tokens")

    send_btn.click(
        chat,
        [msg, chatbot, system_prompt, max_tokens, temperature, top_p, response_style],
        [msg, chatbot]
    )
    msg.submit(
        chat,
        [msg, chatbot, system_prompt, max_tokens, temperature, top_p, response_style],
        [msg, chatbot]
    )
    clear_btn.click(lambda: [], None, chatbot, queue=False)

if __name__ == "__main__":
    demo.launch()