From 0663ea50b5ad4f3da181061980ac1706922e6e17 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lukas=20Br=C3=BCbach?= <Bruebach.Lukas@bdosecurity.de>
Date: Thu, 17 Sep 2026 14:57:44 +0200
Subject: [PATCH] [DeckList] Deduplicate undo/redo state switching

undo() and redo() were mirror images that differed only in
which stack was the source. Both now delegate to a single
restoreAndSwap(source, target, deck) helper, so the save-current-
state, apply-memento and signal-emission logic lives in one place.
---
 .../deck_list/deck_list_history_manager.cpp   | 42 +++++++------------
 .../deck_list/deck_list_history_manager.h     |  7 ++++
 2 files changed, 23 insertions(+), 26 deletions(-)

diff --git a/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.cpp b/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.cpp
index acf4707ab..b6d0687b4 100644
--- a/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.cpp
+++ b/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.cpp
@@ -14,42 +14,32 @@ void DeckListHistoryManager::clear()
     emit undoRedoStateChanged();
 }
 
-void DeckListHistoryManager::undo(DeckList *deck)
+void DeckListHistoryManager::restoreAndSwap(QStack<DeckListMemento> &source,
+                                            QStack<DeckListMemento> &target,
+                                            DeckList *deck)
 {
-    if (undoStack.isEmpty()) {
+    if (source.isEmpty()) {
         return;
     }
 
-    // Peek at the memento we are going to restore
-    const DeckListMemento &mementoToRestore = undoStack.top();
+    // The reason is read before the source is popped.
+    const QString reason = source.top().getReason();
 
-    // Save current state for redo
-    DeckListMemento currentState = deck->createMemento(mementoToRestore.getReason());
-    redoStack.push(currentState);
+    // Save the current state so the opposite direction can return to it.
+    target.push(deck->createMemento(reason));
 
-    // Pop the last state from undo stack and restore it
-    DeckListMemento memento = undoStack.pop();
-    deck->restoreMemento(memento);
+    // Apply the state we are moving to.
+    deck->restoreMemento(source.pop());
 
     emit undoRedoStateChanged();
 }
 
+void DeckListHistoryManager::undo(DeckList *deck)
+{
+    restoreAndSwap(undoStack, redoStack, deck);
+}
+
 void DeckListHistoryManager::redo(DeckList *deck)
 {
-    if (redoStack.isEmpty()) {
-        return;
-    }
-
-    // Peek at the memento we are going to restore
-    const DeckListMemento &mementoToRestore = redoStack.top();
-
-    // Save current state for undo
-    DeckListMemento currentState = deck->createMemento(mementoToRestore.getReason());
-    undoStack.push(currentState);
-
-    // Pop the next state from redo stack and restore it
-    DeckListMemento memento = redoStack.pop();
-    deck->restoreMemento(memento);
-
-    emit undoRedoStateChanged();
+    restoreAndSwap(redoStack, undoStack, deck);
 }
diff --git a/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.h b/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.h
index e6bd27e2d..6acdb199e 100644
--- a/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.h
+++ b/libcockatrice_deck_list/libcockatrice/deck_list/deck_list_history_manager.h
@@ -47,6 +47,13 @@ public:
     }
 
 private:
+    /**
+     * @brief Moves one state from @p source to @p target, applying it to @p deck.
+     *
+     * Used by both undo (undoStack -> redoStack) and redo (redoStack -> undoStack).
+     */
+    void restoreAndSwap(QStack<DeckListMemento> &source, QStack<DeckListMemento> &target, DeckList *deck);
+
     QStack<DeckListMemento> undoStack;
     QStack<DeckListMemento> redoStack;
 };