fix ace to foundation

src/card_game.rs

@@ -29,6 +29,19 @@ impl Suit {
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct CardValue(u8);
 impl CardValue {
+	pub const ACE: Self = CardValue(1);
+	pub const TWO: Self = CardValue(2);
+	pub const THREE: Self = CardValue(3);
+	pub const FOUR: Self = CardValue(4);
+	pub const FIVE: Self = CardValue(5);
+	pub const SIX: Self = CardValue(6);
+	pub const SEVEN: Self = CardValue(7);
+	pub const EIGHT: Self = CardValue(8);
+	pub const NINE: Self = CardValue(9);
+	pub const TEN: Self = CardValue(10);
+	pub const JACK: Self = CardValue(11);
+	pub const QUEEN: Self = CardValue(12);
+	pub const KING: Self = CardValue(13);
 	pub fn checked_add(self, offset: u8) -> Option<CardValue> {
 		let new_value = self.0.checked_add(offset)?;
 		if 13 < new_value {

src/klondike.rs

@@ -1,5 +1,5 @@
 use crate::Rng;
-use crate::card_game::{Game, Pile, Stack};
+use crate::card_game::{CardValue, Game, Pile, Stack};
 
 #[derive(Clone, Debug)]
 pub struct KlondikeConfig {}
@@ -106,14 +106,18 @@ impl KlondikeState {
 				) =>
 			{
 				// get the top cards
-				if let Some(src_card) = self.pile(src).face_up().last()
-					&& let Some(dst_card) = self.pile(dst).face_up().last()
-					// suit matches?
-					&& src_card.suit() == dst_card.suit()
-					// value is +1?
-					&& dst_card.value().checked_add(1) == Some(src_card.value())
-				{
-					true
+				if let Some(src_card) = self.pile(src).face_up().last() {
+					match self.pile(dst).face_up().last() {
+						// destination card exists
+						Some(dst_card) => {
+							// suit matches?
+							src_card.suit() == dst_card.suit()
+							// value is +1?
+							&& dst_card.value().checked_add(1) == Some(src_card.value())
+						}
+						// only ace is allowed to go onto empty foundation
+						None => src_card.value() == CardValue::ACE,
+					}
 				} else {
 					false
 				}