Transform a tall dataset into a wide, pivoted view without using any date/time libraries. Input: a list of records (date, store_id, metric, value) where date is an ISO 8601 string YYYY-MM-DD, metric ∈ {"sales", "refunds", "visits"}, and value is a non-negative integer. Output: for each (store_id, date), produce one row with columns [store_id, date, sales, refunds, visits], filling missing metric values with 0 and ordering rows by ascending date within each store. Requirements: ( 1) Implement this in code (any language), but you may not import date/time packages; rely only on string operations for ordering dates. ( 2) Ensure the solution is O(n log n) or better with respect to the number of records n. ( 3) Explain how you would handle malformed dates, duplicate (store_id, date, metric) entries, and very large inputs that do not fit in memory.