BOGO w/ Coupons

bogo

PAID_ITEM_COUNT = 1
DISCOUNTED_ITEM_COUNT = 1

def discounted_items_to_find(total_items_seen, discounted_items_seen)
  Integer(total_items_seen / (PAID_ITEM_COUNT + DISCOUNTED_ITEM_COUNT) * DISCOUNTED_ITEM_COUNT) - discounted_items_seen
end

def partition(cart, line_items)
  sorted_items = line_items.sort_by{|line_item| line_item.variant.price}.reverse
  
  discounted_items = []
  total_items_seen = 0
  discounted_items_seen = 0

  sorted_items.each do |line_item|
    total_items_seen += line_item.quantity
    count = discounted_items_to_find(total_items_seen, discounted_items_seen)

    next if count <= 0

    if count >= line_item.quantity
      discounted_items.push(line_item)
      discounted_items_seen += line_item.quantity
    else
      discounted_item = line_item.split(take: count)

      position = cart.line_items.find_index(line_item)
      cart.line_items.insert(position + 1, discounted_item)

      discounted_items.push(discounted_item)
      discounted_items_seen += discounted_item.quantity
    end
  end

  discounted_items
end

eligible_items = Input.cart.line_items.select do |line_item|
  product = line_item.variant.product
  product.tags.include?('BOGO')
end

if Input.cart.discount_code.code == "BOGO"
  discounted_line_items = partition(Input.cart, eligible_items)
  discounted_line_items.each do |line_item|
    line_item.change_line_price(Money.zero, message: "BOGO")
  end
end

Output.cart = Input.cart