From 82b5020da476bfb096e8566e172cf8935fcd9568 Mon Sep 17 00:00:00 2001
From: Rhys Lloyd <krakow20@gmail.com>
Date: Fri, 15 May 2026 09:10:52 -0700
Subject: [PATCH] implement is_winnable

---
 src/card_game.rs | 25 ++++++++++++++++++++-----
 src/klondike.rs  |  6 +++---
 src/test.rs      |  4 ++--
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/src/card_game.rs b/src/card_game.rs
index 23f4d66..ad165fb 100644
--- a/src/card_game.rs
+++ b/src/card_game.rs
@@ -97,7 +97,7 @@ impl Card {
 	}
 }
 
-#[derive(Clone, Debug, Hash)]
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct Stack(Vec<Card>);
 impl Stack {
 	pub fn new() -> Self {
@@ -131,7 +131,7 @@ impl std::ops::DerefMut for Stack {
 	}
 }
 
-#[derive(Clone, Debug, Hash)]
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct Pile {
 	face_down: Stack,
 	face_up: Stack,
@@ -175,14 +175,15 @@ impl Pile {
 	}
 }
 
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct Session<G: Game> {
 	seed: G,
 	state: G,
 	history: Vec<G::Instruction>,
 }
-impl<G: Game + Clone> Session<G>
+impl<G: Game + Clone + Eq + core::hash::Hash> Session<G>
 where
-	G::Instruction: Clone,
+	G::Instruction: Clone + Eq + core::hash::Hash,
 {
 	pub fn new(state: G) -> Self {
 		Self {
@@ -195,7 +196,21 @@ where
 		&self.history
 	}
 	pub fn is_winnable(&self) -> Option<Vec<G::Instruction>> {
-		None
+		let mut observed_states = std::collections::HashSet::new();
+		let mut state = self.clone();
+		'outer: while !state.is_win() {
+			observed_states.insert(state.clone());
+			for instruction in state.possible_instructions() {
+				let mut next_state = state.clone();
+				next_state.process_instruction(instruction);
+				if !observed_states.contains(&next_state) {
+					state = next_state;
+					continue 'outer;
+				}
+			}
+			return None;
+		}
+		Some(state.history)
 	}
 	pub fn undo(&mut self) {
 		// replay the entire history of the game except one move
diff --git a/src/klondike.rs b/src/klondike.rs
index 4b4720e..b5ada92 100644
--- a/src/klondike.rs
+++ b/src/klondike.rs
@@ -1,7 +1,7 @@
 use crate::Rng;
 use crate::card_game::{CardValue, Game, Pile, Stack};
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct KlondikeConfig {}
 impl Default for KlondikeConfig {
 	fn default() -> Self {
@@ -67,7 +67,7 @@ impl KlondikeInstruction {
 	}
 }
 
-#[derive(Clone, Debug, Hash)]
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 struct KlondikeState {
 	piles: [Pile; 13],
 }
@@ -163,7 +163,7 @@ impl Iterator for KlondikeIter {
 	}
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct Klondike {
 	config: KlondikeConfig,
 	state: KlondikeState,
diff --git a/src/test.rs b/src/test.rs
index 14aee24..bedeae0 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -8,7 +8,8 @@ fn test_klondike() {
 	let mut session = Session::new(game);
 
 	// is winnable
-	let is_winnable = session.is_winnable().is_some();
+	let is_winnable = session.is_winnable();
+	println!("is_winnable = {is_winnable:?}");
 
 	// play game
 	while let Some(instruction) = session.possible_instructions().next() {
@@ -23,6 +24,5 @@ fn test_klondike() {
 		println!("move {i} = {instruction:?}");
 	}
 
-	println!("is_winnable = {is_winnable}");
 	println!("is_win = {is_win}");
 }