Quantity Breaks

quantity_breaks.rb

DISCOUNTS_BY_QUANTITY = {
  100 => 20,
  50 => 15,
  25 => 10,
  10 => 5,
}

Input.cart.line_items.each do |line_item|
  next if line_item.variant.product.gift_card?

  quantity, discount = DISCOUNTS_BY_QUANTITY.find do |quantity, _|
    line_item.quantity >= quantity
  end
  next unless discount

  message = "#{discount}% off when you buy #{quantity} items."
  line_item.change_line_price(
    line_item.line_price * (Decimal.new(1) - discount.to_d / 100),
    message: message,
  )
end

Output.cart = Input.cart