# 100: E-Commerce Checkout
# Complete checkout flow with payment, consent, and local cart

state cart = load "cart" locally or []
state user = load "user" locally or null
state checkout_step = "cart"  # cart, shipping, payment, confirmation

# Add to cart
add_to_cart(product):
  existing = cart.find(item => item.id == product.id)

  if existing != null:
    existing.quantity = existing.quantity + 1
  else:
    cart.append({ ...product, quantity: 1 })

  store cart locally as "cart"
  show "Added to cart"

# Remove from cart
remove_from_cart(product_id):
  cart = cart.filter(item => item.id != product_id)
  store cart locally as "cart"

# Update quantity
update_quantity(product_id, quantity):
  if quantity <= 0:
    remove_from_cart(product_id)
    return

  cart = cart.map(item => {
    if item.id == product_id:
      { ...item, quantity }
    else:
      item
  })

  store cart locally as "cart"

# Cart totals
computed subtotal = cart.reduce((sum, item) => {
  sum + (item.price * item.quantity)
}, 0)

computed tax = subtotal * 0.08
computed shipping = subtotal > 50 ? 0 : 5.99
computed total = subtotal + tax + shipping

# Checkout flow
checkout_step is:
  "cart": show_cart()
  "shipping": show_shipping_form()
  "payment": show_payment_form()
  "confirmation": show_confirmation()

# Step 1: Cart
show_cart():
  show "Shopping Cart ({cart.length} items)"

  for item in cart:
    show_cart_item:
      name: item.name
      price: "${item.price}"
      quantity: item.quantity
      total: "${(item.price * item.quantity).toFixed(2)}"
      on_update: (qty) => update_quantity(item.id, qty)
      on_remove: () => remove_from_cart(item.id)

  show "Subtotal: ${subtotal.toFixed(2)}"
  show "Tax: ${tax.toFixed(2)}"
  show "Shipping: ${shipping.toFixed(2)}"
  show "Total: ${total.toFixed(2)}"

  if cart.length > 0:
    button "Proceed to Checkout" -> checkout_step = "shipping"

# Step 2: Shipping
show_shipping_form():
  form shipping_address:
    input fullname -> shipping.name
    input address -> shipping.address
    input city -> shipping.city
    select state -> shipping.state
      options: ["CA", "NY", "TX", "FL", "WA"]
    input zipcode -> shipping.zip
      validate: is_zipcode

    button "Continue to Payment" -> {
      store shipping locally as "shipping"
      checkout_step = "payment"
    }

# Step 3: Payment
show_payment_form():
  # Request payment permission
  ask permission for: payment.process
    purpose: "Complete purchase of ${total.toFixed(2)}"

  if granted:
    form payment_method:
      select method -> payment.method
        options: ["Credit Card", "PayPal", "Apple Pay"]

      if payment.method == "Credit Card":
        input card_number -> payment.card_number
          type: "text"
          validate: is_credit_card

        input expiry -> payment.expiry
          placeholder: "MM/YY"

        input cvv -> payment.cvv
          type: "password"
          maxlength: 4

      checkbox save_payment -> payment.save
        label: "Save payment method for future purchases"

      button "Place Order" -> process_payment()

process_payment():
  # Consent to charge
  ask permission for: payment.charge
    amount: total
    purpose: "Complete purchase"

  if granted:
    with consent.record:
      # Process payment
      result = charge_payment(payment, total)

      if result.success:
        # Clear cart
        order_id = result.order_id
        cart = []
        store cart locally as "cart"

        # Save order
        order = {
          id: order_id,
          items: cart,
          total: total,
          shipping: shipping,
          date: now()
        }

        orders = load "orders" locally or []
        orders.append(order)
        store orders locally as "orders"

        checkout_step = "confirmation"
      else:
        show "Payment failed: {result.error}"
  else:
    show "Payment cancelled"

# Step 4: Confirmation
show_confirmation():
  show "✓ Order Confirmed!"
  show "Order ID: {order_id}"
  show "Total: ${total.toFixed(2)}"

  show "A confirmation email has been sent"

  button "Continue Shopping" -> {
    checkout_step = "cart"
  }

  button "View Orders" -> show_order_history()

# Order history
show_order_history():
  orders = load "orders" locally or []

  show "Your Orders ({orders.length})"

  for order in orders:
    show_order_summary:
      id: order.id
      date: format_date(order.date)
      total: "${order.total.toFixed(2)}"
      items: order.items.length

# This example shows:
# - Local-first cart (persists across sessions)
# - Multi-step checkout flow
# - Consent for payment processing
# - Real payment integration
# - Order history
# - All data stored locally
# - Works offline (cart persists)