This is an Irish song attributed to Ruairi Dall O’Cathain, c. 1570-c.1650. There are many lovely renditions on youtube played by ensembles, harpists, various other instrumentalists. There's one guitar arrangement I found but I didn't love it. I'm wondering if anyone has come across an arrangement of this. I am thinking that this should perhaps be my first effort at arranging something. Apparently O’Cathain and O’Carolan were rivals.