From 78a5b9cc3d9d302b93fa5b8e827c09b992a57504 Mon Sep 17 00:00:00 2001
From: Rhys Lloyd <krakow20@gmail.com>
Date: Fri, 15 May 2026 08:54:07 -0700
Subject: [PATCH] undo

---
 README.md        |  2 +-
 src/card_game.rs | 20 ++++++++++++++++----
 src/klondike.rs  |  4 +++-
 src/test.rs      |  5 ++---
 4 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 3c22084..b79b7e6 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ use card_game::klondike::Klondike;
 // create game session
 let seed = Rng::default();
 let game = Klondike::new(seed.clone(), Default::default());
-let mut session = Session::new(seed, game);
+let mut session = Session::new(game);
 
 // is winnable
 let is_winnable = session.is_winnable().is_some();
diff --git a/src/card_game.rs b/src/card_game.rs
index 02828b9..8341ab5 100644
--- a/src/card_game.rs
+++ b/src/card_game.rs
@@ -165,14 +165,17 @@ impl Pile {
 }
 
 pub struct Session<G: Game> {
-	seed: Rng,
+	seed: G,
 	state: G,
 	history: Vec<G::Instruction>,
 }
-impl<G: Game> Session<G> {
-	pub fn new(seed: Rng, state: G) -> Self {
+impl<G: Game + Clone> Session<G>
+where
+	G::Instruction: Clone,
+{
+	pub fn new(state: G) -> Self {
 		Self {
-			seed,
+			seed: state.clone(),
 			state,
 			history: Vec::new(),
 		}
@@ -183,6 +186,15 @@ impl<G: Game> Session<G> {
 	pub fn is_winnable(&self) -> Option<Vec<G::Instruction>> {
 		None
 	}
+	pub fn undo(&mut self) {
+		// replay the entire history of the game except one move
+		self.history.pop();
+		let mut state = self.seed.clone();
+		for instruction in self.history() {
+			state.process_instruction(instruction.clone());
+		}
+		self.state = state;
+	}
 }
 impl<G: Game> Game for Session<G>
 where
diff --git a/src/klondike.rs b/src/klondike.rs
index a2f225c..a813302 100644
--- a/src/klondike.rs
+++ b/src/klondike.rs
@@ -1,6 +1,7 @@
 use crate::Rng;
 use crate::card_game::{Game, Pile, Stack};
 
+#[derive(Clone, Debug)]
 pub struct KlondikeConfig {}
 impl Default for KlondikeConfig {
 	fn default() -> Self {
@@ -66,7 +67,7 @@ impl KlondikeInstruction {
 	}
 }
 
-#[derive(Clone, Hash)]
+#[derive(Clone, Debug, Hash)]
 struct KlondikeState {
 	piles: [Pile; 13],
 }
@@ -157,6 +158,7 @@ impl Iterator for KlondikeIter {
 	}
 }
 
+#[derive(Clone, Debug)]
 pub struct Klondike {
 	config: KlondikeConfig,
 	state: KlondikeState,
diff --git a/src/test.rs b/src/test.rs
index d05b442..f64f27c 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -5,9 +5,8 @@ fn test_klondike() {
 	use crate::klondike::Klondike;
 
 	// create game session
-	let seed = Rng::default();
-	let game = Klondike::new(seed.clone(), Default::default());
-	let mut session = Session::new(seed, game);
+	let game = Klondike::new(Rng::default(), Default::default());
+	let mut session = Session::new(game);
 
 	// is winnable
 	let is_winnable = session.is_winnable().is_some();