app.py

import gradio as gr

# ---------- Inventory (ID, Name, Price) ----------
INVENTORY = [
    (101, "Hammer", 120),
    (102, "Screwdriver Set", 350),
    (103, "Drill Machine", 2500),
    (104, "Pliers", 180),
    (105, "Wrench", 220),
]

# Helpers for lookup and display
ID_TO_ITEM = {str(i): (i, name, price) for i, name, price in INVENTORY}

def format_inventory_option(t):
    i, name, price = t
    return f"{i} – {name} (${price})"

INVENTORY_OPTIONS = [(str(i), format_inventory_option((i, n, p))) for i, n, p in INVENTORY]

def cart_to_text(cart):
    if not cart:
        return "Cart is empty."
    lines = []
    for i, name, price in cart:
        lines.append(f"{i} – {name}: ${price}")
    subtotal = sum(p for _, _, p in cart)
    lines.append("-" * 28)
    lines.append(f"Items: {len(cart)}   Subtotal: ${subtotal}")
    return "\n".join(lines)

def cart_remove_choices(cart):
    # return (values, labels) pairs for the remove dropdown
    values = []
    labels = []
    for idx, (i, name, price) in enumerate(cart):
        # value is cart index (as str) so we can remove the specific occurrence
        values.append(str(idx))
        labels.append(f"{i} – {name} (${price})")
    return values, labels

# ---------- Actions ----------
def add_to_cart(add_id, cart):
    cart = list(cart or [])
    if add_id and add_id in ID_TO_ITEM:
        cart.append(ID_TO_ITEM[add_id])
        msg = "Item added."
    else:
        msg = "Select an item to add."

    remove_vals, remove_labels = cart_remove_choices(cart)
    return (
        cart,                                 # state
        cart_to_text(cart),                   # cart display
        gr.Dropdown(choices=list(zip(remove_labels, remove_vals))),  # update remove dropdown
        msg                                   # info message
    )

def remove_from_cart(remove_index, cart):
    cart = list(cart or [])
    if remove_index is None or remove_index == "":
        msg = "Select an item to remove."
    else:
        idx = int(remove_index)
        if 0 <= idx < len(cart):
            removed = cart.pop(idx)
            msg = f"Removed: {removed[1]}."
        else:
            msg = "Invalid selection."

    remove_vals, remove_labels = cart_remove_choices(cart)
    return (
        cart,
        cart_to_text(cart),
        gr.Dropdown(choices=list(zip(remove_labels, remove_vals))),
        msg
    )

def calculate_total(cart):
    cart = list(cart or [])
    total = sum(p for _, _, p in cart)
    return f"${total}"

def clear_cart(_btn, cart):
    cart = []
    remove_vals, remove_labels = cart_remove_choices(cart)
    return (
        cart,
        cart_to_text(cart),
        gr.Dropdown(choices=list(zip(remove_labels, remove_vals))),
        "Cart cleared.",
        "$0"
    )

# ---------- UI ----------
with gr.Blocks(theme="soft") as demo:
    gr.Markdown("# Hardware Store Billing\nAdd / remove tools and calculate the total.")

    cart_state = gr.State([])  # list of tuples (id, name, price)

    with gr.Row():
        add_dd = gr.Dropdown(
            choices=[(label, value) for value, label in INVENTORY_OPTIONS],
            label="Select tool to ADD to cart",
            value=None,
            allow_custom_value=False,
        )
        remove_dd = gr.Dropdown(
            choices=[],
            label="Select tool in cart to REMOVE",
            value=None,
            allow_custom_value=False,
        )

    with gr.Row():
        add_btn = gr.Button("Add Tool", variant="primary")
        remove_btn = gr.Button("Remove Tool", variant="secondary")
        clear_btn = gr.Button("Clear Cart")

    cart_box = gr.Textbox(label="Cart", value="Cart is empty.", lines=10)
    info = gr.Markdown("")  # action feedback

    with gr.Row():
        calc_btn = gr.Button("Calculate Total", variant="primary")
        total_out = gr.Textbox(label="Total", value="$0")

    # Wire events
    add_btn.click(
        add_to_cart,
        inputs=[add_dd, cart_state],
        outputs=[cart_state, cart_box, remove_dd, info],
    )

    remove_btn.click(
        remove_from_cart,
        inputs=[remove_dd, cart_state],
        outputs=[cart_state, cart_box, remove_dd, info],
    )

    clear_btn.click(
        clear_cart,
        inputs=[clear_btn, cart_state],
        outputs=[cart_state, cart_box, remove_dd, info, total_out],
    )

    calc_btn.click(
        calculate_total,
        inputs=[cart_state],
        outputs=[total_out],
    )

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