clean history

card_game/src/lib.rs

@@ -424,6 +424,33 @@ where
 				state.undo();
 			}
 		}
+
+		// history includes cycles
+		let mut state_index: std::collections::HashMap<_, _> = state
+			.history()
+			.iter()
+			.enumerate()
+			.map(|(i, snapshot)| (snapshot.state().clone(), i))
+			.collect();
+
+		// find the longest range where the start and end are the same state
+		while let Some(longest_range) = state
+			.history()
+			.iter()
+			.enumerate()
+			.filter_map(|(index, snapshot)| {
+				let &last_index = state_index.get(snapshot.state())?;
+				let longness = last_index - index;
+				(longness != 0).then_some(index..last_index)
+			})
+			.max_by_key(|range| range.len())
+		{
+			state.state.history.drain(longest_range);
+			for (i, snapshot) in state.history().iter().enumerate() {
+				state_index.insert(snapshot.state().clone(), i);
+			}
+		}
+
 		Some(state.state.history)
 	}
 }