app.py

import os
import math
from pathlib import Path

import gradio as gr
import pandas as pd

REQUIRED_COLUMNS = [
    "CreditScore",
    "Age",
    "Balance",
    "NumOfProducts",
    "IsActiveMember",
    "EstimatedSalary",
]

def clamp(x, low=0.0, high=1.0):
    return max(low, min(high, x))

def churn_probability(
    credit_score,
    age,
    balance,
    num_products,
    is_active_member,
    estimated_salary,
):
    score = -1.2
    score += max(age - 40, 0) * 0.04
    score += max(650 - credit_score, 0) * 0.003
    score += min(balance / 100000.0, 2.0) * 0.45
    score += 0.35 if int(num_products) <= 1 else -0.15
    score += -0.55 if int(is_active_member) == 1 else 0.35
    score += min(estimated_salary / 200000.0, 1.0) * 0.08
    prob = 1 / (1 + math.exp(-score))
    return clamp(prob)

def risk_label(prob):
    if prob < 0.30:
        return "Low"
    if prob < 0.60:
        return "Medium"
    return "High"

def predict_single(
    credit_score,
    age,
    balance,
    num_products,
    is_active_member,
    estimated_salary,
):
    p = churn_probability(
        float(credit_score),
        float(age),
        float(balance),
        float(num_products),
        int(is_active_member),
        float(estimated_salary),
    )
    label = 1 if p >= 0.5 else 0
    summary = (
        f"### Prediction Result\n\n"
        f"- Churn probability: **{p:.1%}**\n"
        f"- Predicted class: **{label}**\n"
        f"- Risk level: **{risk_label(p)}**"
    )
    table = pd.DataFrame(
        {
            "metric": ["churn_probability", "predicted_class", "risk_level"],
            "value": [round(p, 4), label, risk_label(p)],
        }
    )
    return summary, table

def predict_batch(file):
    if file is None:
        return None, "Please upload a CSV file."
    try:
        df = pd.read_csv(file.name)
    except Exception as e:
        return None, f"Could not read CSV: {e}"

    missing = [c for c in REQUIRED_COLUMNS if c not in df.columns]
    if missing:
        return None, f"Missing required columns: {missing}"

    probs = []
    preds = []
    for _, row in df.iterrows():
        p = churn_probability(
            row["CreditScore"],
            row["Age"],
            row["Balance"],
            row["NumOfProducts"],
            row["IsActiveMember"],
            row["EstimatedSalary"],
        )
        probs.append(round(p, 4))
        preds.append(1 if p >= 0.5 else 0)

    out = df.copy()
    out["churn_probability"] = probs
    out["churn_prediction"] = preds

    output_path = Path("/tmp/bank_churn_predictions.csv")
    out.to_csv(output_path, index=False)
    return str(output_path), f"Done. Processed {len(out)} rows."

def sample_csv():
    df = pd.DataFrame(
        [
            [600, 45, 50000, 1, 0, 70000],
            [720, 31, 12000, 2, 1, 85000],
        ],
        columns=REQUIRED_COLUMNS,
    )
    path = Path("/tmp/sample_bank_churn_input.csv")
    df.to_csv(path, index=False)
    return str(path)

def build_ui():
    with gr.Blocks() as demo:
        gr.Markdown("# 🏦 Bank Churn Simple App")
        gr.Markdown(
            "This is a lightweight version built to reduce Hugging Face startup issues."
        )

        with gr.Tab("Single Prediction"):
            credit_score = gr.Slider(300, 900, value=650, step=1, label="CreditScore")
            age = gr.Slider(18, 100, value=40, step=1, label="Age")
            balance = gr.Number(value=50000, label="Balance")
            num_products = gr.Slider(1, 4, value=2, step=1, label="NumOfProducts")
            is_active_member = gr.Dropdown(
                choices=[0, 1], value=1, label="IsActiveMember"
            )
            estimated_salary = gr.Number(value=80000, label="EstimatedSalary")

            predict_btn = gr.Button("Predict")
            summary_out = gr.Markdown()
            table_out = gr.Dataframe()

            predict_btn.click(
                fn=predict_single,
                inputs=[
                    credit_score,
                    age,
                    balance,
                    num_products,
                    is_active_member,
                    estimated_salary,
                ],
                outputs=[summary_out, table_out],
            )

        with gr.Tab("CSV Batch Prediction"):
            gr.Markdown("Required columns: " + ", ".join(REQUIRED_COLUMNS))
            input_file = gr.File(label="Upload CSV", file_types=[".csv"])
            batch_btn = gr.Button("Run Batch Prediction")
            output_file = gr.File(label="Download Results")
            batch_msg = gr.Markdown()
            sample_btn = gr.Button("Download Sample CSV")

            batch_btn.click(
                fn=predict_batch,
                inputs=[input_file],
                outputs=[output_file, batch_msg],
            )
            sample_btn.click(fn=sample_csv, outputs=[output_file])

    return demo

if __name__ == "__main__":
    demo = build_ui()
    port = int(os.environ.get("PORT", "7860"))
    demo.launch(server_name="0.0.0.0", server_port=port)