Shopify Scripts: Buy X, Y, and Z products together and get XX% off

combo_discount.rb

ELIGIBLE_PRODUCT_IDS = [111111111, 22222222, 3333333333] # Specify which product IDs create a discount
DISCOUNT_AMOUNT = 0.2 # Set the discount amount here

cart_product_ids = Input.cart.line_items.map { |line_item| line_item.variant.product.id }

if ELIGIBLE_PRODUCT_IDS.all? { |product_id| cart_product_ids.include?(product_id) }
    Input.cart.line_ites.each do |line_item|
        discounted_price = line_item.line_price * (1.0 - DISCOUNT_AMOUNT)
        line_item.change_line_price(discounted_price, message: "#{DISCOUNT_AMOUNT * 100}% off!")
    end
end

Output.cart = Input.cart