Happy St. Patrick's day!
I learned this morning that the saying, "Top of the morning", is not an old saying from Ireland. It orginated in America among the Irish living here and may have come from an old movie and some say a book.
The common response to this greeting would have been, "And the rest of the day to you."
If you google it you will find differences of opinion on where it originates.
"And the rest of the day to you my friends!"