Refactor lists into class

Author: subhramit

jabgui/src/main/java/org/jabref/gui/LibraryTab.java

@@ -2,7 +2,6 @@
 
 import java.io.IOException;
 import java.nio.file.Path;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
@@ -119,9 +118,7 @@ public class LibraryTab extends Tab implements CommandSelectionTab {
     private final BibEntryTypesManager entryTypesManager;
     private final BooleanProperty changedProperty = new SimpleBooleanProperty(false);
     private final BooleanProperty nonUndoableChangeProperty = new SimpleBooleanProperty(false);
-    private final List<BibEntry> previousEntries = new ArrayList<>();
-    private final List<BibEntry> nextEntries = new ArrayList<>();
-    private BibEntry currentlyShowing;
+    private final NavigationHistory navigationHistory = new NavigationHistory();
     private final BooleanProperty canGoBackProperty = new SimpleBooleanProperty(false);
     private final BooleanProperty canGoForwardProperty = new SimpleBooleanProperty(false);
     private boolean backOrForwardNavigationActionTriggered = false;
@@ -983,56 +980,36 @@ public void resetChangedProperties() {
     }
 
     public void back() {
-        navigateToEntry(previousEntries, nextEntries);
+        navigationHistory.back().ifPresent(this::navigateToEntry);
     }
 
     public void forward() {
-        navigateToEntry(nextEntries, previousEntries);
+        navigationHistory.forward().ifPresent(this::navigateToEntry);
     }
 
-    private void navigateToEntry(List<BibEntry> sourceHistory, List<BibEntry> destinationHistory) {
-        if (!sourceHistory.isEmpty()) {
-            BibEntry toShow = sourceHistory.getLast();
-            sourceHistory.removeLast();
-
-            // add current entry to destination history
-            if (currentlyShowing != null) {
-                destinationHistory.add(currentlyShowing);
-            }
-
-            backOrForwardNavigationActionTriggered = true;
-            clearAndSelect(toShow);
-            updateNavigationState();
-        }
+    private void navigateToEntry(BibEntry entry) {
+        backOrForwardNavigationActionTriggered = true;
+        clearAndSelect(entry);
+        updateNavigationState();
     }
 
     public boolean canGoBack() {
-        return !previousEntries.isEmpty();
+        return navigationHistory.canGoBack();
     }
 
     public boolean canGoForward() {
-        return !nextEntries.isEmpty();
+        return navigationHistory.canGoForward();
     }
 
     private void newEntryShowing(BibEntry entry) {
         // skip history updates if this is from a back/forward operation
         if (backOrForwardNavigationActionTriggered) {
-            currentlyShowing = entry;
             backOrForwardNavigationActionTriggered = false;
-            updateNavigationState();
             return;
         }
 
-        nextEntries.clear(); // clear forward history when new entry selected in existing chronological sequence
-
-        if (!Objects.equals(entry, currentlyShowing)) {
-            // add the entry we are leaving to the history
-            if (currentlyShowing != null) {
-                previousEntries.add(currentlyShowing);
-            }
-            currentlyShowing = entry;
-            updateNavigationState();
-        }
+        navigationHistory.add(entry);
+        updateNavigationState();
     }
 
     /**

jabgui/src/main/java/org/jabref/gui/NavigationHistory.java

@@ -0,0 +1,77 @@
+package org.jabref.gui;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+
+import org.jabref.model.entry.BibEntry;
+
+/**
+ * Manages the navigation history of viewed entries using two stacks.
+ * This class encapsulates the logic of moving back and forward by maintaining a "back" stack for past entries
+ * and a "forward" stack for future entries.
+ */
+public class NavigationHistory {
+    private final List<BibEntry> previousEntries = new ArrayList<>();
+    private final List<BibEntry> nextEntries = new ArrayList<>();
+    private BibEntry currentEntry;
+
+    /**
+     * Sets a new entry as the current one, clearing the forward history.
+     * The previously current entry is moved to the back stack.
+     *
+     * @param entry The BibEntry to add to the history.
+     */
+    public void add(BibEntry entry) {
+        if (Objects.equals(currentEntry, entry)) {
+            return;
+        }
+
+        // a new selection invalidates the forward history
+        nextEntries.clear();
+
+        if (currentEntry != null) {
+            previousEntries.add(currentEntry);
+        }
+        currentEntry = entry;
+    }
+
+    /**
+     * Moves to the previous entry in the history.
+     * The current entry is pushed to the forward stack, and the last entry from the back stack becomes current.
+     *
+     * @return An Optional containing the previous BibEntry, or an empty Optional if there's no history to go back to.
+     */
+    public Optional<BibEntry> back() {
+        if (canGoBack()) {
+            nextEntries.add(currentEntry);
+            currentEntry = previousEntries.removeLast();
+            return Optional.of(currentEntry);
+        }
+        return Optional.empty();
+    }
+
+    /**
+     * Moves to the next entry in the history.
+     * The current entry is pushed to the back stack, and the last entry from the forward stack becomes current.
+     *
+     * @return An Optional containing the next BibEntry, or an empty Optional if there is no "forward" history.
+     */
+    public Optional<BibEntry> forward() {
+        if (canGoForward()) {
+            previousEntries.add(currentEntry);
+            currentEntry = nextEntries.removeLast();
+            return Optional.of(currentEntry);
+        }
+        return Optional.empty();
+    }
+
+    public boolean canGoBack() {
+        return !previousEntries.isEmpty();
+    }
+
+    public boolean canGoForward() {
+        return !nextEntries.isEmpty();
+    }
+}