app.py

import numpy as np
import pandas as pd
import gradio as gr

# -------- helpers --------
def month_start(ts):
    """Return the first day of the month as Timestamp."""
    ts = pd.to_datetime(ts)
    return ts.to_period("M").to_timestamp()  # YYYY-MM-01

def prep_monthly_features(df: pd.DataFrame) -> pd.DataFrame:
    """
    Expect columns: date, amount, category, income
    amount: +inflows, -spend
    """
    df = df.copy()
    df["date"] = pd.to_datetime(df["date"], errors="coerce")
    df = df.dropna(subset=["date"])

    # month bucket
    df["month"] = df["date"].apply(month_start)

    # monthly aggregates
    month_agg = (
        df.groupby("month", as_index=False)
          .agg(
              spend=("amount", lambda x: x[x < 0].sum()),
              inflow=("amount", lambda x: x[x > 0].sum()),
              txns=("amount", "count"),
              income=("income", "max"),
          )
    )

    # category counts per month (diversity proxy)
    cats = (
        df.assign(cnt=1)
          .pivot_table(index="month", columns="category", values="cnt",
                       aggfunc="sum", fill_value=0)
          .rename(columns=lambda c: f"cat_{c}")
    )

    out = month_agg.merge(cats, left_on="month", right_index=True, how="left").fillna(0)

    # target & lags
    out = out.sort_values("month").reset_index(drop=True)
    out["target_next_spend"] = out["spend"].shift(-1)

    out["m_num"] = out["month"].dt.month
    out["y_num"] = out["month"].dt.year
    out["spend_lag1"] = out["spend"].shift(1)
    out["spend_lag2"] = out["spend"].shift(2)
    out["inflow_lag1"] = out["inflow"].shift(1)

    out = out.dropna().reset_index(drop=True)
    return out

def train_model(monthly_df: pd.DataFrame):
    from sklearn.linear_model import LinearRegression
    from sklearn.metrics import mean_absolute_error

    y = monthly_df["target_next_spend"].values
    feature_cols = [c for c in monthly_df.columns if c not in ["month", "target_next_spend"]]
    X = monthly_df[feature_cols].copy()

    model = LinearRegression()
    model.fit(X, y)

    if len(monthly_df) >= 4:
        X_hold = X.tail(3)
        y_hold = y[-3:]
        preds = model.predict(X_hold)
        mae = float(mean_absolute_error(y_hold, preds))
    else:
        mae = np.nan

    return model, feature_cols, mae

def predict_next(monthly_df: pd.DataFrame, model, feature_cols):
    last = monthly_df.iloc[[-1]][feature_cols]
    pred = float(model.predict(last)[0])

    # overspend risk (more negative spend = higher spend)
    p10 = float(np.percentile(monthly_df["spend"], 10))
    risk = "High" if pred <= p10 else "Low"

    # next month label
    last_month = monthly_df["month"].iloc[-1]
    next_month = month_start(last_month + pd.offsets.MonthBegin(1)).strftime("%Y-%m")
    return next_month, pred, risk

# -------- app logic --------
def load_or_demo(file, budget):
    # demo data if no file
    if file is None:
        rng = pd.date_range("2024-01-01", periods=365, freq="D")
        cats = ["groceries", "rent", "utilities", "fun", "transport"]
        rows = []
        income = 3500.0
        rng_seed = np.random.default_rng(7)
        for d in rng:
            if d.day == 1:
                rows.append({"date": d, "amount": income, "category": "income", "income": income})
            for _ in range(rng_seed.poisson(2)):
                amt = -float(rng_seed.choice([15, 25, 40, 60, 120, 300], p=[.25, .25, .2, .15, .1, .05]))
                rows.append({"date": d, "amount": amt, "category": rng_seed.choice(cats), "income": income})
        df = pd.DataFrame(rows)
    else:
        df = pd.read_csv(file.name)
        needed = {"date", "amount", "category", "income"}
        miss = needed - set(df.columns)
        if miss:
            raise ValueError(f"CSV is missing columns: {sorted(miss)}")

    m = prep_monthly_features(df)
    if len(m) < 6:
        raise ValueError("Need at least ~6 months of data (the demo provides this).")

    model, feats, mae = train_model(m)
    next_m, spend_pred, risk = predict_next(m, model, feats)

    # budget evaluation
    try:
        budget_val = float(budget) if budget not in (None, "") else 0.0
    except Exception:
        budget_val = 0.0

    if budget_val:
        budget_check = "Over budget" if spend_pred < -abs(budget_val) else "Within budget"
    else:
        budget_check = "No budget set"

    summary = pd.DataFrame({
        "metric": ["Predicted next-month spend", "MAE (last 3 months)", "Overspend risk", "Budget check", "Next month"],
        "value": [round(spend_pred, 2), (None if np.isnan(mae) else round(mae, 2)), risk, budget_check, next_m]
    })

    monthly_view = m[["month", "spend", "inflow", "txns", "income"]].copy()
    monthly_view["month"] = monthly_view["month"].dt.strftime("%Y-%m")

    return summary, monthly_view

def safe_run(file, budget):
    try:
        return load_or_demo(file, budget)
    except Exception as e:
        import traceback
        print("TRACEBACK:\n", traceback.format_exc())
        raise gr.Error(str(e))

# -------- UI --------
with gr.Blocks(title="Retail Finance: Spend Forecast") as demo:
    gr.Markdown(
        "## Retail Finance Spend Forecaster\n"
        "Upload your transactions CSV (columns: `date, amount, category, income`) or use demo data. "
        "The model forecasts **next-month spend** and flags **overspend risk**."
    )
    with gr.Row():
        file = gr.File(label="Upload CSV (optional)")
        budget = gr.Number(value=2500, label="Monthly budget (positive number)")
    btn = gr.Button("Run Forecast")
    summary = gr.Dataframe(label="Summary")
    monthly_table = gr.Dataframe(label="Monthly aggregates used by the model")
    btn.click(safe_run, inputs=[file, budget], outputs=[summary, monthly_table])

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