Travel expense conversion

Convert the expenses of a business trip into US dollars for the expense report.

Each entry of rates is "<date> <currency> <rate>": on that date, one unit of the currency was worth rate US dollars. Each entry of expenses is "<date> <currency> <amount>": an amount paid in that currency on that date. Refunds have a negative amount. Dates are YYYY-MM-DD, in no particular order in either list.

To convert an expense in a currency other than USD:

1. Take the rate for that currency with the latest date on or before the expense date. If several rates share that date, the one listed last in rates is used.
2. The rate is only trusted for 7 days: if it is dated more than 7 days before the expense (exactly 7 days is fine), or if no rate for that currency is dated on or before the expense, the expense cannot be converted and is skipped.
3. The value is amount * rate US dollars, converted to whole cents and rounded to the nearest cent, with exact halves rounded away from zero (7.5 cents becomes 8, -7.5 cents becomes -8).

An expense in USD is already in dollars and needs no rate (any USD rates are ignored); its amount is converted to cents exactly. Round every expense separately, then add up the cents.

Input: rates and expenses, lists of strings in the format above.

Output: a list [total_cents, skipped]: the sum, in cents, of all converted expenses, and the number of expenses that could not be converted. For no expenses, return [0, 0].