Shopify Script #2 - Buy two of X item for $Y

script.rb

# Buy two of X item for $Y

# Applied product types
PRODUCT_TYPES = ["Backpack"]

# Custom message
CHECKOUT_MESSAGE = "Get two for $50"

# Price for pair in dollars
PAIR_PRICE = 50


# === Do not change anything below ===

cart = Input.cart

applied_items = []

pair_item_price = Decimal.new(PAIR_PRICE) / 2.00

# Find products
cart.line_items.each do |line_item|
  product = line_item.variant.product
  # If product is in category and qty > 1
  if PRODUCT_TYPES.collect{|el| el.downcase }.include?(product.product_type.downcase) and
    line_item.quantity > 1
    applied_items.push(line_item)
  end

end


# Exclude non-paired items
applied_items.each_with_index do |item, index|
  if item.quantity % 2 != 0
    non_pair = applied_items[index].split(take: 1) 
    cart.line_items.push(non_pair)
  end
end

  # Apply new price
  applied_items.each do |item|
    new_item_price = Money.new(cents: 100) * pair_item_price
    new_line_price = item.quantity * new_item_price
    if (item.line_price > new_line_price)
      item.change_line_price(new_line_price, message: CHECKOUT_MESSAGE)
    end
  end


Output.cart = Input.cart