import pandas as pd
import matplotlib.pyplot as plt
import numpy as np


def generate_heatmap(df: pd.DataFrame):
    if df is None or df.empty:
        return None

    heat = np.zeros((20, 30))

    for _, row in df.iterrows():
        a = int(row["Suggested Aisle"])
        r = int(row["Suggested Rack"])
        if 1 <= a <= 20 and 1 <= r <= 30:
            heat[a - 1, r - 1] += 1

    plt.figure(figsize=(6, 4))
    plt.imshow(heat, cmap="hot", interpolation="nearest")
    plt.colorbar()
    plt.title("Warehouse Heatmap")
    img_path = "/tmp/heatmap.png"
    plt.savefig(img_path)
    plt.close()

    return img_path