Shopify Script #5 - Buy anything from collection A and get anything from collection B with X% discount

script.rb

# Buy anything from collection A and get anything from collection B with X% discount,
# if discount code XYZ is applied

# Custom Message
CHECKOUT_MESSAGE = "Get a 50% off"

# Discount code which should me appled
DISCOUNT_CODE = "GET50OFF"

COLLECTION_A = ["BACKPACKS"]

COLLECTION_B = ["SHIRTS"]

# DISCOUNT VALUE (WITHOUT "%")
DISCOUNT_VALUE = 50


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

cart = Input.cart

discounted_items_qty = 0
discount_percent = Decimal.new(DISCOUNT_VALUE) / 100.0


# Calculate eligible discounted items (X <= ITEMS FROM A COLLECTION)
cart.line_items.each do |line_item|
  product = line_item.variant.product
  if COLLECTION_A.collect{|el| el.downcase }.include?(product.product_type.downcase)
    discounted_items_qty += line_item.quantity
  end
end



subtotal = cart.subtotal_price_was

is_free_item_applied = false

if cart.discount_code
  if cart.discount_code.code == DISCOUNT_CODE
      cart.line_items.each do |line_item|
        product = line_item.variant.product
        if COLLECTION_B.collect{|el| el.downcase }.include?(product.product_type.downcase) and
          discounted_items_qty > 0
          
          if(discounted_items_qty < line_item.quantity)
            free_item = line_item.split(take: discounted_items_qty) 
            cart.line_items.push(free_item)
          else
            free_item = line_item
          end
          
          new_price = line_item.line_price - (line_item.line_price * discount_percent)
          
          free_item.change_line_price(new_price, message: CHECKOUT_MESSAGE)
          discounted_items_qty -= free_item.quantity
        end
      end
  end
end

Output.cart = Input.cart