Sleepy visitor

We found this lovely creature resting indoors.  It was flapping its wings in a half-hearted way.  I was afraid it was dying so I gave it some sugar water which it lapped up, then put it in a box to let it hibernate over the winter.  I hope this is the right thing to do, I read up on it on the internet so I'm hoping it will survive the cold weather.  I had no idea that butterflies lived so long to be honest.