# 059: Custom Events
# Create your own event system

# Shopping cart events
state cart = []

add_to_cart(item):
  cart.append(item)
  emit event "cart.item_added" with { item, cart_size: cart.length }

remove_from_cart(item_id):
  cart = cart.filter((item) => item.id != item_id)
  emit event "cart.item_removed" with { item_id, cart_size: cart.length }

clear_cart():
  cart = []
  emit event "cart.cleared"

# Cart listeners
on event "cart.item_added":
  show "Added: {event.data.item.name}"
  show "Cart size: {event.data.cart_size}"

on event "cart.item_removed":
  show "Removed item {event.data.item_id}"
  show "Cart size: {event.data.cart_size}"

on event "cart.cleared":
  show "Cart is now empty"

# Usage
button "Add Apple" -> add_to_cart({ id: 1, name: "Apple", price: 1.50 })
button "Add Banana" -> add_to_cart({ id: 2, name: "Banana", price: 0.75 })
button "Remove Apple" -> remove_from_cart(1)
button "Clear Cart" -> clear_cart()

# Events decouple components - cart logic doesn't need to know
# about UI updates, analytics, etc. They just listen for events.