app.py

import math
import gradio
import pandas
from transformers import AutoTokenizer, AutoModelForCausalLM, pipeline

# Model
MODEL_ID = "HuggingFaceTB/SmolLM2-135M-Instruct"
tokenizer = AutoTokenizer.from_pretrained(MODEL_ID)
pipe = pipeline(
    task="text-generation",
    model=AutoModelForCausalLM.from_pretrained(MODEL_ID),
    tokenizer=tokenizer
)

# --- Core calculation ---
def conduction_calc(L_m: float, A_m2: float, k_WmK: float, dT_C: float) -> dict:
    '''
    Steady 1D heat conduction through a flat wall.
    Inputs:
      L_m: wall thickness [m]
      A_m2: area [m²]
      k_WmK: thermal conductivity [W/m·K]
      dT_C: temperature difference [°C or K]
    Returns heat transfer rate, heat flux, and thermal resistance.
    '''

    q_W = k_WmK * A_m2 * dT_C / L_m  # Heat transfer rate
    q_flux = k_WmK * dT_C / L_m      # Heat flux
    R = L_m / (k_WmK * A_m2)         # Thermal resistance

    return dict(
        results={
            "q_W": q_W,
            "q_flux": q_flux,
            "R_KperW": R,
        }
    )

# Chat formatting helper
def _format_chat(system_prompt: str, user_prompt: str) -> str:
    messages = [
        {"role": "system", "content": system_prompt},
        {"role": "user", "content": user_prompt},
    ]
    template = getattr(tokenizer, "chat_template", None)
    return tokenizer.apply_chat_template(
        messages, tokenize=False, add_generation_prompt=True
    )

def _llm_generate(prompt: str, max_tokens: int) -> str:
    out = pipe(
        prompt,
        max_new_tokens=max_tokens,
        do_sample=True,
        temperature=0.5,
        return_full_text=False,
    )
    return out[0]["generated_text"]

# --- LLM Explanation ---
def llm_explain(results: dict, inputs: list) -> str:
    L_m, A_m2, k_WmK, dT_C = inputs
    r = results["results"]

    system_prompt = (
        "You explain engineering to a smart 5-year-old. "
        "Use food-based analogies to support the explanation. "
        "Always return CONCISE one-sentence answers."
    )

    user_prompt = (
        f"A wall of thickness {L_m:.3f} m, area {A_m2:.2f} m², "
        f"and thermal conductivity {k_WmK:.2f} W/m·K has a temperature difference of {dT_C:.1f} °C.\n"
        f"The heat transfer rate is {r['q_W']:.2f} W, "
        f"the heat flux is {r['q_flux']:.2f} W/m², "
        f"and the thermal resistance is {r['R_KperW']:.5f} K/W.\n"
        "Explain these results in ONE friendly analogy-based sentence for a non-expert."
    )

    formatted = _format_chat(system_prompt, user_prompt)
    return _llm_generate(formatted, max_tokens=128)

# --- Runner ---
def run_once(L_m, A_m2, k_WmK, dT_C):
    inputs = [L_m, A_m2, k_WmK, dT_C]
    d = conduction_calc(
        L_m=float(L_m),
        A_m2=float(A_m2),
        k_WmK=float(k_WmK),
        dT_C=float(dT_C),
    )

    df = pandas.DataFrame([{
        "q [W]": round(d["results"]["q_W"], 3),
        "q'' [W/m²]": round(d["results"]["q_flux"], 3),
        "R_th [K/W]": round(d["results"]["R_KperW"], 5),
    }])

    narrative = llm_explain(d, inputs).split("\n")[0]
    return df, narrative

# --- UI ---
with gradio.Blocks() as demo:
    gradio.Markdown("# Heat Conduction Calculator")
    gradio.Markdown("This app computes steady heat conduction through a flat wall and explains the results in simple terms.")

    with gradio.Row():
        L_m = gradio.Number(value=0.2, label="Wall thickness [m]")
        A_m2 = gradio.Number(value=1.0, label="Wall area [m²]")
        k_WmK = gradio.Number(value=0.8, label="Thermal conductivity [W/m·K]")
        dT_C = gradio.Number(value=30.0, label="Temperature difference [°C]")

    run_btn = gradio.Button("Compute")

    results_df = gradio.Dataframe(label="Numerical results", interactive=False)
    explain_md = gradio.Markdown(label="Explanation")

    run_btn.click(fn=run_once, inputs=[L_m, A_m2, k_WmK, dT_C], outputs=[results_df, explain_md])

    gradio.Examples(
        examples=[
            [0.2, 1.0, 0.8, 30.0],   # Brick wall
            [0.05, 0.5, 0.04, 20.0], # Styrofoam insulation
            [0.01, 0.2, 205.0, 50.0] # Aluminum sheet
        ],
        inputs=[L_m, A_m2, k_WmK, dT_C],
        label="Representative cases",
        examples_per_page=3,
        cache_examples=False,
    )

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