Bestseller shelf

Choose which products go on a bestseller shelf, keeping every product that ties for the last spot.

A shop logs its sales as strings "name:qty". The quantity is an integer and is negative when the entry records a return. Product names are matched ignoring leading and trailing spaces and ignoring case: " Tea " and "tea" are the same product, reported in lowercase (spaces inside a name are kept). A product's total is the sum of all of its quantities, returns included.

Only products with a total greater than 0 can be on the shelf. Rank the eligible products by total, highest first. The shelf has room for k products, but ties are never split: if the product in position k shares its total with other products, all of them are included. If fewer than k products are eligible, all eligible products are included.

Input: sales, a list of strings in the format above, and k, a positive integer.

Output: a list of [name, total] pairs for the products on the shelf, sorted by total descending and then by name ascending (lexicographic). If no product is eligible, return [].