Script: Buy 2 or more items and get 30% off the least expensive item

DISCOUNT_PERCENT=30
CART_DISCOUNT_MESSAGE="Buy 2 or more items and get 30% off the least expensive item"


eligible_items = Input.cart.line_items.select do |line_item|
  product = line_item.variant.product
  !product.gift_card?
end

# Sort eligible items by price, least exensive first
eligible_items = eligible_items.sort_by{|line_item| line_item.variant.price}

total_items = 0
eligible_items.each do |line_item|
  total_items += line_item.quantity
end

if(total_items >= 2)
  # pull the least exensive item
  line_item = eligible_items.first
  # calculate the discount to be applied
  percent = Decimal.new(DISCOUNT_PERCENT) / 100.0
  
  
  # make sure we don't discount multiple items hiding in a single line item
  if line_item.quantity == 1
    line_discount = line_item.line_price * percent
    puts "line_discount = #{line_discount}"
    # Just discount the item directly
    line_item.change_line_price(line_item.line_price - line_discount, message: CART_DISCOUNT_MESSAGE)
  else
    # If only part of the item must be discounted, split the item
    discounted_item = line_item.split(take: 1)
    # Insert the newly-created item in the cart, right after the original item
    position = Input.cart.line_items.find_index(line_item)
    line_discount = discounted_item.line_price * percent
    puts "line_discount = #{line_discount}"
    Input.cart.line_items.insert(position + 1, discounted_item)
    # Discount the new item
    discounted_item.change_line_price(discounted_item.line_price - line_discount, message: CART_DISCOUNT_MESSAGE)
  end
end


Output.cart = Input.cart