How can I know which side of a card is being shown?

[Sweeper777]

In my app, I want to have a button on the background view that controls the flipping of cards. When you tap it once, the revealed card gets flipped. When you tap it again, the revealed card is flipped back. To implement this, I need a way of determine whether the revealed card is flipped or not, in order to write code like this:

if revealedCardIsFlipped {
    layout.flipRevealedCardBack()
} else {
    layout.flipRevealedCard(toView: someView)
}

As I mentioned in #17, if I could detect when the card is flipped, I could keep track of the revealed card's state using a variable myself. But since I can't, I don't know what to do.