# How to apply discounts to lowest value products first in a buy X get X promotion?

Tourist
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``````TAG_SELECTED = "selecionado"

# Returns the integer amount of items that must be discounted next
# given the amount of items seen
#
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

# Partitions the items and returns the items that are to be discounted.
#
# Arguments
# ---------
#
# * cart
#   The cart to which split items will be added (typically Input.cart).
#
# * line_items
#   The selected items that are applicable for the campaign.
#
def partition(cart, line_items)
# Sort the items by price from high to low
sorted_items = line_items.sort_by{|line_item| line_item.variant.price}.reverse
# Create an array of items to return
discounted_items = []
# Keep counters of items seen and discounted, to avoid having to recalculate on each iteration
total_items_seen = 0
discounted_items_seen = 0

# Loop over all the items and find those to be discounted
sorted_items.each do |line_item|
total_items_seen += line_item.quantity
# After incrementing total_items_seen, see if any items must be discounted
cont = 0
totalitems = total_items_seen
levenumber = total_items_seen
while totalitems > 0 do
if totalitems  >= 8
totalitems = totalitems - 8;
cont = cont + 3
elsif totalitems >= 6
totalitems = totalitems - 6;
cont = cont + 2;
elsif totalitems >= 4
puts totalitems.inspect
totalitems = totalitems - 4;
cont = cont + 1;
else
totalitems = totalitems - 1;
end
pague = levenumber - cont;
brinde = levenumber - pague
PAID_ITEM_COUNT = pague
DISCOUNTED_ITEM_COUNT = brinde
MENSAGE =   "Leve #{levenumber} garrafas, pague #{pague} ";
end
count = discounted_items_to_find(total_items_seen, discounted_items_seen)
# If there are none, skip to the next item
next if count <= 0

if count >= line_item.quantity
# If the full item quantity must be discounted, add it to the items to return
# and increment the count of discounted items
discounted_items.push(line_item)
discounted_items_seen += line_item.quantity
else
# If only part of the item must be discounted, split the item
discounted_item = line_item.split(take: count)
# Insert the newly-created item in the cart, right after the original item
position = cart.line_items.find_index(line_item)
cart.line_items.insert(position + 1, discounted_item)
# Add it to the list of items to return
discounted_items.push(discounted_item)
discounted_items_seen += discounted_item.quantity
end
end

# Return the items to be discounted
discounted_items
end

eligible_items = Input.cart.line_items.select do |line_item|
product = line_item.variant.product
!product.gift_card? && product.tags.include?(TAG_SELECTED)

end

discounted_line_items = partition(Input.cart, eligible_items)
discounted_line_items.each do |line_item|
line_item.change_line_price(Money.zero, message: MENSAGE)
end

Output.cart = Input.cart``````

I'm not able to make this filter, could someone help me, please?

example (wrong)

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