Fixes #25

app/src/main/java/sudoku/structure/StateManager.java

@@ -15,27 +15,35 @@ public class StateManager {
 		this.doku = doku;
 	}
 
-	public void pushState() {
-		states.add(new HashMap<>());
-		saveState();
+	public Map<Cell, Integer> pushState() {
+		states.add(saveState());
+		return states.getLast();
 	}
 
 	public void popState() {
 		assert (states.size() > 0);
-		restoreState();
-		states.pop();
+		restoreState(states.pop());
 	}
 
-	private void restoreState() {
-		for (var entry : this.states.getLast().entrySet()) {
+	public Map<Cell, Integer> popAndGetState() {
+		assert (states.size() > 0);
+		var currentState = saveState();
+		restoreState(states.pop());
+		return currentState;
+	}
+
+	private void restoreState(Map<Cell, Integer> state) {
+		for (var entry : state.entrySet()) {
 			entry.getKey().setSymbolIndex(entry.getValue());
 		}
 	}
 
-	private void saveState() {
+	private Map<Cell, Integer> saveState() {
+		Map<Cell, Integer> state = new HashMap<>();
 		for (Cell cell : this.doku.getCells()) {
-			states.getLast().put(cell, cell.getSymbolIndex());
+			state.put(cell, cell.getSymbolIndex());
 		}
+		return state;
 	}
 
 }