Dave Jarvis' Repositories

See the [detailed documentation](docs/README.md) for information about

using the application.

![GraphViz Diagram Screenshot](docs/images/screenshots/01.png)

![Korean Poem Screenshot](docs/images/screenshots/02.png)

![TeX Equations Screenshot](docs/images/screenshots/03.png)

* [texample.Rmd](texample.Rmd) -- Numerous examples of formulas

    } catch( final NullPointerException ex ) {

import static com.keenwrite.StatusNotifier.clue;

    } catch( final Exception ignored ) {

      clue( STATUS_DEFINITION_BLANK );

    // the user types---if it is a menu mnemonic. This consumes the Alt key

    // event to work around the bug.

    // See: https://bugs.openjdk.java.net/browse/JDK-8090647

      if( lost ) {

        for( final var mnemonics : stage.getScene().getMnemonics().values() ) {

          for( final var mnemonic : mnemonics ) {

            mnemonic.getNode().fireEvent( keyUp( ALT, false ) );

          }

    stage.setScene( (new MainScene( mWorkspace )).getScene() );

import com.keenwrite.editors.definition.DefinitionTabSceneFactory;

import com.keenwrite.editors.definition.TreeTransformer;

import com.keenwrite.editors.definition.yaml.YamlTreeTransformer;

import com.keenwrite.editors.markdown.MarkdownEditor;

import com.keenwrite.io.MediaType;

import com.keenwrite.preferences.Key;

import com.keenwrite.preferences.Workspace;

import com.keenwrite.preview.HtmlPreview;

import com.keenwrite.processors.IdentityProcessor;

import com.keenwrite.processors.Processor;

import com.keenwrite.processors.ProcessorContext;

import com.keenwrite.processors.ProcessorFactory;

import com.keenwrite.processors.markdown.extensions.caret.CaretExtension;

import com.keenwrite.service.events.Notifier;

import com.keenwrite.sigils.RSigilOperator;

import com.keenwrite.sigils.SigilOperator;

import com.keenwrite.sigils.Tokens;

import com.keenwrite.sigils.YamlSigilOperator;

import com.panemu.tiwulfx.control.dock.DetachableTab;

import com.panemu.tiwulfx.control.dock.DetachableTabPane;

import javafx.application.Platform;

import javafx.beans.property.*;

import javafx.collections.ListChangeListener;

import javafx.event.ActionEvent;

import javafx.event.Event;

import javafx.event.EventHandler;

import javafx.scene.Scene;

import javafx.scene.control.SplitPane;

import javafx.scene.control.Tab;

import javafx.scene.control.Tooltip;

import javafx.scene.control.TreeItem.TreeModificationEvent;

import javafx.scene.input.KeyEvent;

import javafx.stage.Stage;

import javafx.stage.Window;

import java.io.File;

import java.nio.file.Path;

import java.util.*;

import java.util.concurrent.atomic.AtomicBoolean;

import java.util.function.Function;

import java.util.stream.Collectors;

import static com.keenwrite.Constants.*;

import static com.keenwrite.ExportFormat.NONE;

import static com.keenwrite.Messages.get;

import static com.keenwrite.StatusNotifier.clue;

import static com.keenwrite.io.MediaType.*;

import static com.keenwrite.preferences.WorkspaceKeys.*;

import static com.keenwrite.processors.ProcessorFactory.createProcessors;

import static com.keenwrite.service.events.Notifier.NO;

import static com.keenwrite.service.events.Notifier.YES;

import static java.util.stream.Collectors.groupingBy;

import static javafx.application.Platform.runLater;

import static javafx.scene.control.TabPane.TabClosingPolicy.ALL_TABS;

import static javafx.scene.input.KeyCode.SPACE;

import static javafx.scene.input.KeyCombination.CONTROL_DOWN;

import static javafx.util.Duration.millis;

import static javax.swing.SwingUtilities.invokeLater;

import static org.fxmisc.wellbehaved.event.EventPattern.keyPressed;

/**

 * Responsible for wiring together the main application components for a

 * particular workspace (project). These include the definition views,

 * text editors, and preview pane along with any corresponding controllers.

 */

public final class MainPane extends SplitPane {

  private static final Notifier sNotifier = Services.load( Notifier.class );

  /**

   * Used when opening files to determine how each file should be binned and

   * therefore what tab pane to be opened within.

   */

  private static final Set<MediaType> PLAIN_TEXT_FORMAT = Set.of(

    TEXT_MARKDOWN, TEXT_R_MARKDOWN, TEXT_R_XML, UNDEFINED

  );

  /**

   * Prevents re-instantiation of processing classes.

   */

  private final Map<TextResource, Processor<String>> mProcessors =

    new HashMap<>();

  private final Workspace mWorkspace;

  /**

   * Groups similar file type tabs together.

   */

  private final Map<MediaType, DetachableTabPane> mTabPanes = new HashMap<>();

  /**

   * Stores definition names and values.

   */

  private final Map<String, String> mResolvedMap =

    new HashMap<>( MAP_SIZE_DEFAULT );

  /**

   * Renders the actively selected plain text editor tab.

   */

  private final HtmlPreview mHtmlPreview;

  /**

   * Changing the active editor fires the value changed event. This allows

   * refreshes to happen when external definitions are modified and need to

   * trigger the processing chain.

   */

  private final ObjectProperty<TextEditor> mActiveTextEditor =

    createActiveTextEditor();

  /**

   * Changing the active definition editor fires the value changed event. This

   * allows refreshes to happen when external definitions are modified and need

   * to trigger the processing chain.

   */

  private final ObjectProperty<TextDefinition> mActiveDefinitionEditor =

    createActiveDefinitionEditor( mActiveTextEditor );

  /**

   * Responsible for creating a new scene when a tab is detached into

   * its own window frame.

   */

  private final DefinitionTabSceneFactory mDefinitionTabSceneFactory =

    createDefinitionTabSceneFactory( mActiveDefinitionEditor );

  /**

   * Tracks the number of detached tab panels opened into their own windows,

   * which allows unique identification of subordinate windows by their title.

   * It is doubtful more than 128 windows, much less 256, will be created.

   */

  private byte mWindowCount;

  /**

   * Called when the definition data is changed.

   */

  private final EventHandler<TreeModificationEvent<Event>> mTreeHandler =

    event -> {

      final var editor = mActiveDefinitionEditor.get();

      resolve( editor );

      process( getActiveTextEditor() );

      save( editor );

    };

  /**

   * Adds all content panels to the main user interface. This will load the

   * configuration settings from the workspace to reproduce the settings from

   * a previous session.

   */

  public MainPane( final Workspace workspace ) {

    mWorkspace = workspace;

    mHtmlPreview = new HtmlPreview( workspace );

    open( bin( getRecentFiles() ) );

    viewPreview();

    setDividerPositions( calculateDividerPositions() );

    // Once the main scene's window regains focus, update the active definition

    // editor to the currently selected tab.

    runLater(

      () -> {

        getWindow().focusedProperty().addListener( ( c, o, n ) -> {

          if( n != null && n ) {

            final var pane = mTabPanes.get( TEXT_YAML );

            final var model = pane.getSelectionModel();

            final var tab = model.getSelectedItem();

            if( tab != null ) {

              final var resource = tab.getContent();

              if( resource instanceof TextDefinition ) {

                mActiveDefinitionEditor.set( (TextDefinition) tab.getContent() );

              }

            }

          }

        } );

        getWindow().setOnCloseRequest( ( event ) -> {

          // Order matters here. We want to close all the tabs to ensure each

          // is saved, but after they are closed, the workspace should still

          // retain the list of files that were open. If this line came after

          // closing, then restarting the application would list no files.

          mWorkspace.save();

          if( closeAll() ) {

            Platform.exit();

            System.exit( 0 );

          }

          else {

            event.consume();

          }

        } );

      }

    );

  }

  /**

   * TODO: Load divider positions from exported settings, see bin() comment.

   */

  private double[] calculateDividerPositions() {

    final var ratio = 100f / getItems().size() / 100;

    final var positions = getDividerPositions();

    for( int i = 0; i < positions.length; i++ ) {

      positions[ i ] = ratio * i;

    }

    return positions;

  }

  /**

   * Opens all the files into the application, provided the paths are unique.

   * This may only be called for any type of files that a user can edit

   * (i.e., update and persist), such as definitions and text files.

   *

   * @param files The list of files to open.

   */

  public void open( final List<File> files ) {

    files.forEach( this::open );

  }

  /**

   * This opens the given file. Since the preview pane is not a file that

   * can be opened, it is safe to add a listener to the detachable pane.

   *

   * @param file The file to open.

   */

  private void open( final File file ) {

    final var tab = createTab( file );

    final var node = tab.getContent();

    final var mediaType = MediaType.valueFrom( file );

    final var tabPane = obtainDetachableTabPane( mediaType );

    final var newTabPane = !getItems().contains( tabPane );

    tab.setTooltip( createTooltip( file ) );

    tabPane.setFocusTraversable( false );

    tabPane.setTabClosingPolicy( ALL_TABS );

    tabPane.getTabs().add( tab );

    if( newTabPane ) {

      var index = getItems().size();

      if( node instanceof TextDefinition ) {

        tabPane.setSceneFactory( mDefinitionTabSceneFactory::create );

        index = 0;

      }

      addTabPane( index, tabPane );

    }

    getRecentFiles().add( file.getAbsolutePath() );

  }

  /**

   * Opens a new text editor document using the default document file name.

   */

  public void newTextEditor() {

    open( DOCUMENT_DEFAULT );

  }

  /**

   * Opens a new definition editor document using the default definition

   * file name.

   */

  public void newDefinitionEditor() {

    open( DEFINITION_DEFAULT );

  }

  /**

   * Iterates over all tab panes to find all {@link TextEditor}s and request

   * that they save themselves.

   */

  public void saveAll() {

    mTabPanes.forEach(

      ( mt, tp ) -> tp.getTabs().forEach( ( tab ) -> {

        final var node = tab.getContent();

        if( node instanceof TextEditor ) {

          save( ((TextEditor) node) );

        }

      } )

    );

  }

  /**

   * Requests that the active {@link TextEditor} saves itself. Don't bother

   * checking if modified first because if the user swaps external media from

   * an external source (e.g., USB thumb drive), save should not second-guess

   * the user: save always re-saves. Also, it's less code.

   */

  public void save() {

    save( getActiveTextEditor() );

  }

  /**

   * Saves the active {@link TextEditor} under a new name.

   *

   * @param file The new active editor {@link File} reference.

   */

  public void saveAs( final File file ) {

    assert file != null;

    final var editor = getActiveTextEditor();

    final var tab = getTab( editor );

    editor.rename( file );

    tab.ifPresent( t -> {

      t.setText( editor.getFilename() );

      t.setTooltip( createTooltip( file ) );

    } );

    save();

  }

  /**

   * Saves the given {@link TextResource} to a file. This is typically used

   * to save either an instance of {@link TextEditor} or {@link TextDefinition}.

   *

   * @param resource The resource to export.

   */

  private void save( final TextResource resource ) {

    try {

      resource.save();

    } catch( final Exception ex ) {

      clue( ex );

      sNotifier.alert(

        getWindow(), resource.getPath(), "TextResource.saveFailed", ex

      );

    }

  }

  /**

   * Closes all open {@link TextEditor}s; all {@link TextDefinition}s stay open.

   *

   * @return {@code true} when all editors, modified or otherwise, were

   * permitted to close; {@code false} when one or more editors were modified

   * and the user requested no closing.

   */

  public boolean closeAll() {

    var closable = true;

    for( final var entry : mTabPanes.entrySet() ) {

      final var tabPane = entry.getValue();

      final var tabIterator = tabPane.getTabs().iterator();

      while( tabIterator.hasNext() ) {

        final var tab = tabIterator.next();

        final var resource = tab.getContent();

        if( !(resource instanceof TextResource) ) {

          continue;

        }

        if( canClose( (TextResource) resource ) ) {

          tabIterator.remove();

          close( tab );

        }

        else {

          closable = false;

        }

      }

    }

    return closable;

  }

  /**

   * Calls the tab's {@link Tab#getOnClosed()} handler to carry out a close

   * event.

   *

   * @param tab The {@link Tab} that was closed.

   */

  private void close( final Tab tab ) {

    final var handler = tab.getOnClosed();

    if( handler != null ) {

      handler.handle( new ActionEvent() );

    }

  }

  /**

   * Closes the active tab; delegates to {@link #canClose(TextResource)}.

   */

  public void close() {

    final var editor = getActiveTextEditor();

    if( canClose( editor ) ) {

      close( editor );

    }

  }

  /**

   * Closes the given {@link TextResource}. This must not be called from within

   * a loop that iterates over the tab panes using {@code forEach}, lest a

   * concurrent modification exception be thrown.

   *

   * @param resource The {@link TextResource} to close, without confirming with

   *                 the user.

   */

  private void close( final TextResource resource ) {

    getTab( resource ).ifPresent(

      ( tab ) -> {

        tab.getTabPane().getTabs().remove( tab );

        close( tab );

      }

    );

  }

  /**

   * Answers whether the given {@link TextResource} may be closed.

   *

   * @param editor The {@link TextResource} to try closing.

   * @return {@code true} when the editor may be closed; {@code false} when

   * the user has requested to keep the editor open.

   */

  private boolean canClose( final TextResource editor ) {

    final var editorTab = getTab( editor );

    final var canClose = new AtomicBoolean( true );

    if( editor.isModified() ) {

      final var filename = new StringBuilder();

      editorTab.ifPresent( ( tab ) -> filename.append( tab.getText() ) );

      final var message = sNotifier.createNotification(

        Messages.get( "Alert.file.close.title" ),

        Messages.get( "Alert.file.close.text" ),

        filename.toString()

      );

      final var dialog = sNotifier.createConfirmation( getWindow(), message );

      dialog.showAndWait().ifPresent(

        save -> canClose.set( save == YES ? editor.save() : save == NO )

      );

    }

    return canClose.get();

  }

  private ObjectProperty<TextEditor> createActiveTextEditor() {

    final var editor = new SimpleObjectProperty<TextEditor>();

    editor.addListener( ( c, o, n ) -> {

      if( n != null ) {

        mHtmlPreview.setBaseUri( n.getPath() );

        process( n );

      }

    } );

    return editor;

  }

  /**

   * Adds the HTML preview tab to its own tab pane. This will only add the

   * preview once.

   */

  public void viewPreview() {

    final var tabPane = obtainDetachableTabPane( TEXT_HTML );

    // Prevent multiple HTML previews because in the end, there can be only one.

    for( final var tab : tabPane.getTabs() ) {

      if( tab.getContent() == mHtmlPreview ) {

        return;

      }

    }

    tabPane.addTab( "HTML", mHtmlPreview );

    addTabPane( tabPane );

  }

  public void viewRefresh() {

    mHtmlPreview.refresh();

  }

  /**

   * Returns the tab that contains the given {@link TextEditor}.

   *

   * @param editor The {@link TextEditor} instance to find amongst the tabs.

   * @return The first tab having content that matches the given tab.

   */

  private Optional<Tab> getTab( final TextResource editor ) {

    return mTabPanes.values()

                    .stream()

                    .flatMap( pane -> pane.getTabs().stream() )

                    .filter( tab -> editor.equals( tab.getContent() ) )

                    .findFirst();

  }

  /**

   * Creates a new {@link DefinitionEditor} wrapped in a listener that

   * is used to detect when the active {@link DefinitionEditor} has changed.

   * Upon changing, the {@link #mResolvedMap} is updated and the active

   * text editor is refreshed.

   *

   * @param editor Text editor to update with the revised resolved map.

   * @return A newly configured property that represents the active

   * {@link DefinitionEditor}, never null.

   */

  private ObjectProperty<TextDefinition> createActiveDefinitionEditor(

    final ObjectProperty<TextEditor> editor ) {

    final var definitions = new SimpleObjectProperty<TextDefinition>();

    definitions.addListener( ( c, o, n ) -> {

      resolve( n == null ? createDefinitionEditor() : n );

      process( editor.get() );

    } );

    return definitions;

  }

  /**

   * Instantiates a factory that's responsible for creating new scenes when

   * a tab is dropped outside of any application window. The definition tabs

   * are fairly complex in that only one may be active at any time. When

   * activated, the {@link #mResolvedMap} must be updated to reflect the

   * hierarchy displayed in the {@link DefinitionEditor}.

   *

   * @param activeDefinitionEditor The current {@link DefinitionEditor}.

   * @return An object that listens to {@link DefinitionEditor} tab focus

   * changes.

   */

  private DefinitionTabSceneFactory createDefinitionTabSceneFactory(

    final ObjectProperty<TextDefinition> activeDefinitionEditor ) {

    return new DefinitionTabSceneFactory( ( tab ) -> {

      assert tab != null;

      var node = tab.getContent();

      if( node instanceof TextDefinition ) {

        activeDefinitionEditor.set( (DefinitionEditor) node );

      }

    } );

  }

  private DetachableTab createTab( final File file ) {

    final var r = createTextResource( file );

    final var tab = new DetachableTab( r.getFilename(), r.getNode() );

    r.modifiedProperty().addListener(

      ( c, o, n ) -> tab.setText( r.getFilename() + (n ? "*" : "") )

    );

    // This is called when either the tab is closed by the user clicking on

    // the tab's close icon or when closing (all) from the file menu.

    tab.setOnClosed(

      ( __ ) -> getRecentFiles().remove( file.getAbsolutePath() )

    );

    return tab;

  }

  /**

   * Creates bins for the different {@link MediaType}s, which eventually are

   * added to the UI as separate tab panes. If ever a general-purpose scene

   * exporter is developed to serialize a scene to an FXML file, this could

   * be replaced by such a class.

   * <p>

   * When binning the files, this makes sure that at least one file exists

   * for every type. If the user has opted to close a particular type (such

   * as the definition pane), the view will suppressed elsewhere.

   * </p>

   * <p>

   * The order that the binned files are returned will be reflected in the

   * order that the corresponding panes are rendered in the UI.

   * </p>

   *

   * @param paths The file paths to bin according to their type.

   * @return An in-order list of files, first by structured definition files,

   * then by plain text documents.

   */

  private List<File> bin( final SetProperty<String> paths ) {

    // Treat all files destined for the text editor as plain text documents

    // so that they are added to the same pane. Grouping by TEXT_PLAIN is a

    // bit arbitrary, but means explicitly capturing TEXT_PLAIN isn't needed.

    final Function<MediaType, MediaType> bin =

      m -> PLAIN_TEXT_FORMAT.contains( m ) ? TEXT_PLAIN : m;

    // Create two groups: YAML files and plain text files.

    final var bins = paths

      .stream()

      .collect(

        groupingBy( path -> bin.apply( MediaType.valueFrom( path ) ) )

      );

    bins.putIfAbsent( TEXT_YAML, List.of( DEFINITION_DEFAULT.toString() ) );

    bins.putIfAbsent( TEXT_PLAIN, List.of( DOCUMENT_DEFAULT.toString() ) );

    final var result = new ArrayList<File>( paths.size() );

    // Ensure that the same types are listed together (keep insertion order).

    bins.forEach( ( mediaType, files ) -> result.addAll(

      files.stream().map( File::new ).collect( Collectors.toList() ) )

    );

    return result;

  }

  /**

   * Uses the given {@link TextDefinition} instance to update the

   * {@link #mResolvedMap}.

   *

   * @param editor A non-null, possibly empty definition editor.

   */

  private void resolve( final TextDefinition editor ) {

    assert editor != null;

    final var tokens = createDefinitionTokens();

    final var operator = new YamlSigilOperator( tokens );

    final var map = new HashMap<String, String>();

    editor.toMap().forEach( ( k, v ) -> map.put( operator.entoken( k ), v ) );

    mResolvedMap.clear();

    mResolvedMap.putAll( editor.interpolate( map, tokens ) );

  }

  /**

   * Force the active editor to update, which will cause the processor

   * to re-evaluate the interpolated definition map thereby updating the

   * preview pane.

   *

   * @param editor Contains the source document to update in the preview pane.

   */

  private void process( final TextEditor editor ) {

    // Ensure that these are run from within the Swing event dispatch thread

    // so that the text editor thread is immediately freed for caret movement.

    // This means that the preview will have a slight delay when catching up

    // to the caret position.

    invokeLater( () -> {

      mProcessors.getOrDefault( editor, IdentityProcessor.IDENTITY )

                 .apply( editor == null ? "" : editor.getText() );

      mHtmlPreview.scrollTo( CARET_ID );

    } );

  }

  /**

   * Lazily creates a {@link DetachableTabPane} configured to handle focus

   * requests by delegating to the selected tab's content. The tab pane is

   * associated with a given media type so that similar files can be grouped

   * together.

   *

   * @param mediaType The media type to associate with the tab pane.

   * @return An instance of {@link DetachableTabPane} that will handle

   * docking of tabs.

   */

  private DetachableTabPane obtainDetachableTabPane(

    final MediaType mediaType ) {

    return mTabPanes.computeIfAbsent(

      mediaType, ( mt ) -> createDetachableTabPane()

    );

  }

  /**

   * Creates an initialized {@link DetachableTabPane} instance.

   *

   * @return A new {@link DetachableTabPane} with all listeners configured.

   */

  private DetachableTabPane createDetachableTabPane() {

    final var tabPane = new DetachableTabPane();

    initStageOwnerFactory( tabPane );

    initTabListener( tabPane );

    initSelectionModelListener( tabPane );

    return tabPane;

  }

  /**

   * When any {@link DetachableTabPane} is detached from the main window,

   * the stage owner factory must be given its parent window, which will

   * own the child window. The parent window is the {@link MainPane}'s

   * {@link Scene}'s {@link Window} instance.

   *

   * <p>

   * This will derives the new title from the main window title, incrementing

   * the window count to help uniquely identify the child windows.

   * </p>

   *

   * @param tabPane A new {@link DetachableTabPane} to configure.

   */

  private void initStageOwnerFactory( final DetachableTabPane tabPane ) {

    tabPane.setStageOwnerFactory( ( stage ) -> {

      final var title = get(

        "Detach.tab.title",

        ((Stage) getWindow()).getTitle(), ++mWindowCount

      );

      stage.setTitle( title );

      return getScene().getWindow();

    } );

  }

  /**

   * Responsible for configuring the content of each {@link DetachableTab} when

   * it is added to the given {@link DetachableTabPane} instance.

   * <p>

   * For {@link TextEditor} contents, an instance of {@link ScrollEventHandler}

   * is initialized to perform synchronized scrolling between the editor and

   * its preview window. Additionally, the last tab in the tab pane's list of

   * tabs is given focus.

   * </p>

   * <p>

   * Note that multiple tabs can be added simultaneously.

   * </p>

   *

   * @param tabPane A new {@link DetachableTabPane} to configure.

   */

  private void initTabListener( final DetachableTabPane tabPane ) {

    tabPane.getTabs().addListener(

      ( final ListChangeListener.Change<? extends Tab> listener ) -> {

        while( listener.next() ) {

          if( listener.wasAdded() ) {

            final var tabs = listener.getAddedSubList();

            tabs.forEach( ( tab ) -> {

              final var node = tab.getContent();

              if( node instanceof TextEditor ) {

                initScrollEventListener( tab );

              }

            } );

            // Select and give focus to the last tab opened.

            final var index = tabs.size() - 1;

            if( index >= 0 ) {

              final var tab = tabs.get( index );

              tabPane.getSelectionModel().select( tab );

              tab.getContent().requestFocus();

            }

          }

        }

      }

    );

  }

  /**

   * Responsible for handling tab change events.

   *

   * @param tabPane A new {@link DetachableTabPane} to configure.

   */

  private void initSelectionModelListener( final DetachableTabPane tabPane ) {

    final var model = tabPane.getSelectionModel();

    model.selectedItemProperty().addListener( ( c, o, n ) -> {

      if( o != null && n == null ) {

        final var node = o.getContent();

        // If the last definition editor in the active pane was closed,

        // clear out the definitions then refresh the text editor.

        if( node instanceof TextDefinition ) {

          mActiveDefinitionEditor.set( createDefinitionEditor() );

        }

      }

      else if( n != null ) {

        final var node = n.getContent();

        if( node instanceof TextEditor ) {

          // Changing the active node will fire an event, which will

          // update the preview panel and grab focus.

          mActiveTextEditor.set( (TextEditor) node );

          runLater( node::requestFocus );

        }

        else if( node instanceof TextDefinition ) {

          mActiveDefinitionEditor.set( (DefinitionEditor) node );

        }

      }

    } );

  }

  /**

   * Synchronizes scrollbar positions between the given {@link Tab} that

   * contains an instance of {@link TextEditor} and {@link HtmlPreview} pane.

   *

   * @param tab The container for an instance of {@link TextEditor}.

   */

  private void initScrollEventListener( final Tab tab ) {

    final var editor = (TextEditor) tab.getContent();

    final var scrollPane = editor.getScrollPane();

    final var scrollBar = mHtmlPreview.getVerticalScrollBar();

    final var handler = new ScrollEventHandler( scrollPane, scrollBar );

    handler.enabledProperty().bind( tab.selectedProperty() );

  }

  private void addTabPane( final int index, final DetachableTabPane tabPane ) {

    final var items = getItems();

    if( !items.contains( tabPane ) ) {

      items.add( index, tabPane );

    }

  }

  private void addTabPane( final DetachableTabPane tabPane ) {