Take a percentage off the product based on vendor

% off vendor

@percent = Decimal.new(20) / 100.0
Input.cart.line_items.each do |line_item|
product = line_item.variant.product
next if product.gift_card?
next unless product.vendor.include?('Nike')
line_discount = line_item.line_price * @percent
line_item.change_line_price(line_item.line_price - line_discount, message: "20% off all Nike products!")
end

Output.cart = Input.cart