feat: Add handleMoveLines method with keystroke support and ActionListeners

- Implement handleMoveLines to manage line movement functionality
- Add keystroke bindings for triggering line movements
- Integrate ActionListeners for responsive UI interactions
- Ensure cross-platform compatibility for macOS and Linux

Author: yehiarasheed

app/src/processing/app/ui/Editor.java

@@ -821,6 +821,17 @@ protected JMenu buildEditMenu() {
     editMenuUpdatable.add(action);
     menu.add(item);
 
+    item = new JMenuItem("Move Selected Lines Up");
+    item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_UP, InputEvent.ALT_DOWN_MASK));
+    item.addActionListener(e -> handleMoveLines(true));
+    menu.add(item);
+
+    item = new JMenuItem("Move Selected Lines Down");
+    item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, InputEvent.ALT_DOWN_MASK));
+    item.addActionListener(e -> handleMoveLines(false));
+    menu.add(item);
+
+
     // Update copy/cut state on selection/de-selection
     menu.addMenuListener(new MenuListener() {
       // UndoAction and RedoAction do this for themselves.
@@ -1865,6 +1876,7 @@ protected void handleCommentUncomment() {
   }
 
 
+
   public void handleIndent() {
     handleIndentOutdent(true);
   }
@@ -1918,6 +1930,84 @@ public void handleIndentOutdent(boolean indent) {
     stopCompoundEdit();
     sketch.setModified(true);
   }
+  /**
+   * Moves the selected lines up or down in the text editor.
+   *
+   * <p>If {@code moveUp} is true, the selected lines are moved up. If false, they move down.</p>
+   * <p>This method ensures proper selection updates and handles edge cases like moving
+   * the first or last line.</p>
+   *
+   * @param moveUp {@code true} to move the selection up, {@code false} to move it down.
+   */
+  public void handleMoveLines(boolean moveUp) {
+    startCompoundEdit();
+
+    int startLine = textarea.getSelectionStartLine();
+    int stopLine = textarea.getSelectionStopLine();
+
+    // Adjust selection if the last line isn't fully selected
+    if (startLine != stopLine &&
+            textarea.getSelectionStop() == textarea.getLineStartOffset(stopLine)) {
+      stopLine--;
+    }
+
+    int replacedLine = moveUp ? startLine - 1 : stopLine + 1;
+    if (replacedLine < 0 || replacedLine >= textarea.getLineCount()) {
+      stopCompoundEdit();
+      return;
+    }
+
+    final String source = textarea.getText();  // Get full text from textarea
+
+    int replaceStart = textarea.getLineStartOffset(replacedLine);
+    int replaceEnd = textarea.getLineStopOffset(replacedLine);
+    if (replaceEnd > source.length()) {
+      replaceEnd = source.length();
+    }
+
+    int selectionStart = textarea.getLineStartOffset(startLine);
+    int selectionEnd = textarea.getLineStopOffset(stopLine);
+    if (selectionEnd > source.length()) {
+      selectionEnd = source.length();
+    }
+
+    String replacedText = source.substring(replaceStart, replaceEnd);
+    String selectedText = source.substring(selectionStart, selectionEnd);
+
+    if (replacedLine == textarea.getLineCount() - 1) {
+      replacedText += "\n";
+      selectedText = selectedText.substring(0, Math.max(0, selectedText.length() - 1));
+    } else if (stopLine == textarea.getLineCount() - 1) {
+      selectedText += "\n";
+      replacedText = replacedText.substring(0, Math.max(0, replacedText.length() - 1));
+    }
+
+    int newSelectionStart, newSelectionEnd;
+    if (moveUp) {
+      textarea.select(selectionStart, selectionEnd);
+      textarea.setSelectedText(replacedText);  // Use setSelectedText()
+
+      textarea.select(replaceStart, replaceEnd);
+      textarea.setSelectedText(selectedText);
+
+      newSelectionStart = textarea.getLineStartOffset(startLine - 1);
+      newSelectionEnd = textarea.getLineStopOffset(stopLine - 1);
+    } else {
+      textarea.select(replaceStart, replaceEnd);
+      textarea.setSelectedText(selectedText);
+
+      textarea.select(selectionStart, selectionEnd);
+      textarea.setSelectedText(replacedText);
+
+      newSelectionStart = textarea.getLineStartOffset(startLine + 1);
+      newSelectionEnd = stopLine + 1 < textarea.getLineCount()
+              ? Math.min(textarea.getLineStopOffset(stopLine + 1), source.length())
+              : textarea.getLineStopOffset(stopLine); // Prevent out-of-bounds
+    }
+
+    textarea.select(newSelectionStart, newSelectionEnd);
+    stopCompoundEdit();
+  }
 
 
   static public boolean checkParen(char[] array, int index, int stop) {