/*
    * Tethys: GUI Utilities
    * Copyright 2012-2026. Tony Washer
    *
    * Licensed under the Apache License, Version 2.0 (the "License"); you may not
    * use this file except in compliance with the License.  You may obtain a copy
    * of the License at
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
   * License for the specific language governing permissions and limitations under
   * the License.
   */
  package io.github.tonywasher.joceanus.tethys.javafx.menu;
  
  import io.github.tonywasher.joceanus.oceanus.event.OceanusEventManager;
  import io.github.tonywasher.joceanus.oceanus.event.OceanusEventRegistrar;
  import io.github.tonywasher.joceanus.tethys.api.base.TethysUIConstant;
  import io.github.tonywasher.joceanus.tethys.api.base.TethysUIEvent;
  import io.github.tonywasher.joceanus.tethys.api.base.TethysUIIcon;
  import io.github.tonywasher.joceanus.tethys.api.base.TethysUIIconId;
  import io.github.tonywasher.joceanus.tethys.api.menu.TethysUIScrollIcon;
  import io.github.tonywasher.joceanus.tethys.api.menu.TethysUIScrollItem;
  import io.github.tonywasher.joceanus.tethys.api.menu.TethysUIScrollMenu;
  import io.github.tonywasher.joceanus.tethys.api.menu.TethysUIScrollToggle;
  import io.github.tonywasher.joceanus.tethys.core.menu.TethysUICoreScrollMenu;
  import io.github.tonywasher.joceanus.tethys.javafx.base.TethysUIFXArrowIcon;
  import io.github.tonywasher.joceanus.tethys.javafx.base.TethysUIFXIcon;
  import io.github.tonywasher.joceanus.tethys.javafx.base.TethysUIFXUtils;
  import javafx.animation.KeyFrame;
  import javafx.animation.Timeline;
  import javafx.collections.ObservableList;
  import javafx.event.Event;
  import javafx.event.EventHandler;
  import javafx.event.EventType;
  import javafx.geometry.Dimension2D;
  import javafx.geometry.Insets;
  import javafx.geometry.Point2D;
  import javafx.geometry.Pos;
  import javafx.geometry.Side;
  import javafx.scene.Node;
  import javafx.scene.Scene;
  import javafx.scene.control.ContentDisplay;
  import javafx.scene.control.Label;
  import javafx.scene.input.KeyEvent;
  import javafx.scene.input.MouseEvent;
  import javafx.scene.input.ScrollEvent;
  import javafx.scene.layout.BorderPane;
  import javafx.scene.layout.VBox;
  import javafx.scene.shape.Polygon;
  import javafx.stage.Modality;
  import javafx.stage.Stage;
  import javafx.stage.StageStyle;
  import javafx.util.Duration;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  
  /**
   * Scroll-able version of ContextMenu.
   * <p>
   * Implemented as Stage since ContextMenu does not allow control of individual elements.
   *
   * @param <T> the value type
   */
  public class TethysUIFXScrollMenu<T>
          implements TethysUIScrollMenu<T> {
      /**
       * StyleSheet Name.
       */
      private static final String CSS_STYLE_NAME = "jtethys-javafx-contextmenu.css";
  
      /**
       * StyleSheet.
       */
      private static final String CSS_STYLE = TethysUIFXScrollMenu.class.getResource(CSS_STYLE_NAME).toExternalForm();
  
      /**
       * The menu style.
       */
      private static final String STYLE_MENU = TethysUIFXUtils.CSS_STYLE_BASE + "-context";
  
      /**
       * The item style.
       */
      static final String STYLE_ITEM = STYLE_MENU + "-item";
  
      /**
       * The Event Manager.
       */
      private final OceanusEventManager<TethysUIEvent> theEventManager;
  
      /**
       * List of menu items.
       */
     private final List<TethysUIFXScrollElement> theMenuItems;
 
     /**
      * List of active menu items.
      */
     private final ObservableList<Node> theActiveItems;
 
     /**
      * First item to show in list.
      */
     private int theFirstIndex;
 
     /**
      * Max number of items to display in popUp.
      */
     private int theMaxDisplayItems;
 
     /**
      * The ScrollUp Item.
      */
     private final ScrollControl theUpItem;
 
     /**
      * The ScrollDown Item.
      */
     private final ScrollControl theDownItem;
 
     /**
      * The container box.
      */
     private final BorderPane theContainer;
 
     /**
      * The Parent scrollMenu.
      */
     private final TethysUIFXScrollSubMenu<T> theParentMenu;
 
     /**
      * The Parent contextMenu.
      */
     private final TethysUIFXScrollMenu<T> theParentContext;
 
     /**
      * The Stage.
      */
     private Stage theStage;
 
     /**
      * The Active subMenu.
      */
     private TethysUIFXScrollSubMenu<T> theActiveMenu;
 
     /**
      * The Active item.
      */
     private TethysUIFXScrollItem<T> theActiveItem;
 
     /**
      * The selected value.
      */
     private TethysUIFXScrollItem<T> theSelectedItem;
 
     /**
      * Do we need to close menu on toggle?
      */
     private boolean closeOnToggle;
 
     /**
      * Do we need to reBuild the menu?
      */
     private boolean needReBuild;
 
     /**
      * The size of the menu.
      */
     private Dimension2D theMenuSize;
 
     /**
      * Constructor.
      */
     TethysUIFXScrollMenu() {
         this(TethysUICoreScrollMenu.DEFAULT_ITEMCOUNT);
     }
 
     /**
      * Constructor.
      *
      * @param pMaxDisplayItems the maximum number of items to display
      */
     TethysUIFXScrollMenu(final int pMaxDisplayItems) {
         this(null, pMaxDisplayItems);
     }
 
     /**
      * Constructor.
      *
      * @param pParent the parent scroll menu
      */
     TethysUIFXScrollMenu(final TethysUIFXScrollSubMenu<T> pParent) {
         this(pParent, pParent.getContext().getMaxDisplayItems());
     }
 
     /**
      * Constructor.
      *
      * @param pParent          the parent scroll menu
      * @param pMaxDisplayItems the maximum number of items to display
      */
     private TethysUIFXScrollMenu(final TethysUIFXScrollSubMenu<T> pParent,
                                  final int pMaxDisplayItems) {
         /* Check parameters */
         if (pMaxDisplayItems <= 0) {
             throw new IllegalArgumentException(TethysUICoreScrollMenu.ERROR_MAXITEMS);
         }
 
         /* Create event manager */
         theEventManager = new OceanusEventManager<>();
 
         /* Record parameters */
         theMaxDisplayItems = pMaxDisplayItems;
         theParentMenu = pParent;
         theParentContext = theParentMenu == null
                 ? null
                 : theParentMenu.getContext();
 
         /* Initially need reBuild */
         needReBuild = true;
 
         /* Initially close on toggle */
         closeOnToggle = true;
 
         /* Create the scroll items */
         theUpItem = new ScrollControl(TethysUIFXArrowIcon.UP.getArrow(), -1);
         theDownItem = new ScrollControl(TethysUIFXArrowIcon.DOWN.getArrow(), 1);
 
         /* Allocate the list */
         theMenuItems = new ArrayList<>();
         final VBox myBox = new VBox();
         myBox.setSpacing(2);
         myBox.setPadding(new Insets(2, 2, 2, 2));
         theActiveItems = myBox.getChildren();
 
         /* Create the scene */
         theContainer = new BorderPane();
         theContainer.setCenter(myBox);
         theContainer.getStyleClass().add(STYLE_MENU);
     }
 
     @Override
     public OceanusEventRegistrar<TethysUIEvent> getEventRegistrar() {
         return theEventManager.getEventRegistrar();
     }
 
     /**
      * Ensure the Stage.
      */
     private void ensureStage() {
         if (theStage == null) {
             createStage();
         }
     }
 
     /**
      * Create the Stage.
      */
     private void createStage() {
         /* Non-Modal and undecorated */
         theStage = new Stage(StageStyle.UNDECORATED);
         theStage.initModality(Modality.NONE);
 
         /* Create the scene */
         final Scene myScene = new Scene(theContainer);
         final ObservableList<String> mySheets = myScene.getStylesheets();
         mySheets.add(CSS_STYLE);
         theStage.setScene(myScene);
 
         /* Add listener to shut dialog on loss of focus */
         theStage.focusedProperty().addListener((v, o, n) -> handleFocusChange(n));
 
         /* ensure that escape closes menu */
         myScene.setOnKeyPressed(this::handleKeyPress);
 
         /* Handle scroll events */
         theStage.addEventFilter(ScrollEvent.SCROLL, this::handleScroll);
     }
 
     /**
      * CloseOnFocusLoss.
      */
     private void closeOnFocusLoss() {
         /* Pass call on to parent if it exists */
         if (theParentContext != null) {
             theParentContext.closeOnFocusLoss();
         }
 
         /* Close the menu */
         closeMenu();
     }
 
     @Override
     public TethysUIScrollItem<T> getSelectedItem() {
         return theSelectedItem;
     }
 
     /**
      * Obtain the maximum # of items in the displayed PopUp window.
      *
      * @return the # of items
      */
     public int getMaxDisplayItems() {
         return theMaxDisplayItems;
     }
 
     @Override
     public void setCloseOnToggle(final boolean pCloseOnToggle) {
         /* Set value */
         closeOnToggle = pCloseOnToggle;
     }
 
     /**
      * Is the menu showing?
      *
      * @return true/false
      */
     public boolean isShowing() {
         return theStage != null
                 && theStage.isShowing();
     }
 
     @Override
     public void setMaxDisplayItems(final int pMaxDisplayItems) {
         /* Check parameters */
         if (pMaxDisplayItems <= 0) {
             throw new IllegalArgumentException(TethysUICoreScrollMenu.ERROR_MAXITEMS);
         }
 
         /* Check state */
         if (isShowing()) {
             throw new IllegalStateException();
         }
 
         /* Store parameters */
         theMaxDisplayItems = pMaxDisplayItems;
 
         /* Loop through the children */
         final Iterator<TethysUIFXScrollElement> myIterator = theMenuItems.iterator();
         while (myIterator.hasNext()) {
             final TethysUIFXScrollElement myChild = myIterator.next();
 
             /* If this is a subMenu */
             if (myChild instanceof TethysUIFXScrollSubMenu) {
                 /* Pass call on */
                 final TethysUIFXScrollSubMenu<?> mySubMenu = (TethysUIFXScrollSubMenu<?>) myChild;
                 mySubMenu.setMaxDisplayItems(pMaxDisplayItems);
             }
         }
 
         /* Request reBuild */
         needReBuild = true;
     }
 
     /**
      * Show the menu at position.
      *
      * @param pAnchor the anchor node
      * @param pSide   the side of the anchor node
      */
     public void showMenuAtPosition(final Node pAnchor,
                                    final Side pSide) {
         /* Ensure the stage */
         ensureStage();
 
         /* determine the size of the menu */
         determineSize();
 
         /* If we have elements */
         if (theMenuSize != null) {
             /* determine location to display */
             final Point2D myLocation = TethysUIFXUtils.obtainDisplayPoint(pAnchor, pSide, theMenuSize);
 
             /* Show menu */
             showMenuAtLocation(myLocation);
         }
     }
 
     /**
      * Show the menu at position.
      *
      * @param pAnchor the anchor node
      * @param pX      the relative X position
      * @param pY      the relative Y position
      */
     public void showMenuAtPosition(final Node pAnchor,
                                    final double pX,
                                    final double pY) {
         /* Ensure the stage */
         ensureStage();
 
         /* determine the size of the menu */
         determineSize();
 
         /* If we have elements */
         if (theMenuSize != null) {
             /* determine location to display */
             final Point2D myRequest = new Point2D(pX, pY);
             final Point2D myLocation = TethysUIFXUtils.obtainDisplayPoint(pAnchor, myRequest, theMenuSize);
 
             /* Show menu */
             showMenuAtLocation(myLocation);
         }
     }
 
     /**
      * Show the menu at location.
      *
      * @param pLocation the location
      */
     private void showMenuAtLocation(final Point2D pLocation) {
         /* Record position */
         theStage.setX(pLocation.getX());
         theStage.setY(pLocation.getY());
 
         /* Show menu */
         showMenu();
     }
 
     /**
      * Show the menu.
      */
     private void showMenu() {
         /* Initialise the values */
         theSelectedItem = null;
         theActiveMenu = null;
         theActiveItem = null;
 
         /* show the menu */
         theStage.show();
     }
 
     /**
      * Close non-Modal.
      */
     void closeMenu() {
         /* Close any children */
         closeChildren();
 
         /* Close the menu */
         theStage.close();
     }
 
     /**
      * Clear active Item.
      */
     void clearActiveItem() {
         theActiveItem = null;
     }
 
     /**
      * Set the selected item.
      *
      * @param pItem the selected item
      */
     void setSelectedItem(final TethysUIFXScrollItem<T> pItem) {
         /* If we are a child menu */
         if (theParentContext != null) {
             /* pass call on to parent */
             theParentContext.setSelectedItem(pItem);
 
             /* else we are top-level */
         } else {
             /* We assume that we will close the menu */
             boolean doCloseMenu = true;
 
             /* record selection */
             theSelectedItem = pItem;
             if (theSelectedItem instanceof TethysUIFXScrollToggle) {
                 final TethysUIScrollToggle<?> myItem = (TethysUIScrollToggle<?>) theSelectedItem;
                 myItem.toggleSelected();
                 doCloseMenu = closeOnToggle;
             }
 
             /* Close the menu if requested */
             if (doCloseMenu) {
                 /* Close the menu */
                 closeMenu();
             }
 
             /* fire selection event */
             theEventManager.fireEvent(TethysUIEvent.NEWVALUE, theSelectedItem);
         }
     }
 
     /**
      * Handle escapeKey.
      */
     private void handleEscapeKey() {
         /* If we are a child menu */
         if (theParentContext != null) {
             /* pass call on to parent */
             theParentContext.handleEscapeKey();
 
             /* else we are top-level */
         } else {
             /* fire cancellation event */
             theEventManager.fireEvent(TethysUIEvent.WINDOWCLOSED);
 
             /* Notify the cancel */
             closeMenu();
         }
     }
 
     /**
      * Handle enterKey.
      */
     private void handleEnterKey() {
         /* If we are a child menu */
         if (theActiveItem != null) {
             /* assume item is selected */
             setSelectedItem(theActiveItem);
         }
     }
 
     /**
      * Handle focusChange.
      *
      * @param pState the focus state
      */
     private void handleFocusChange(final boolean pState) {
         /* If we've lost focus to other than the active subMenu */
         if (!pState && theActiveMenu == null) {
             /* fire cancellation event */
             if (theParentMenu == null) {
                 theEventManager.fireEvent(TethysUIEvent.WINDOWCLOSED);
             }
 
             /* Close the menu hierarchy if we are currently showing */
             if (isShowing()) {
                 closeOnFocusLoss();
             }
         }
     }
 
     /**
      * Handle keyPress.
      *
      * @param pEvent the event
      */
     private void handleKeyPress(final KeyEvent pEvent) {
         switch (pEvent.getCode()) {
             case ESCAPE:
                 handleEscapeKey();
                 break;
             case ENTER:
                 handleEnterKey();
                 break;
             default:
                 break;
         }
     }
 
     /**
      * Handle scroll.
      *
      * @param pEvent the event
      */
     private void handleScroll(final ScrollEvent pEvent) {
         /* request the scroll */
         final double myDelta = pEvent.getDeltaY() / pEvent.getMultiplierY();
         requestScroll((int) -myDelta);
 
         /* Consume the event */
         pEvent.consume();
     }
 
     /**
      * Handle activeItem.
      *
      * @param pItem the item
      */
     void handleActiveItem(final TethysUIFXScrollItem<T> pItem) {
         /* Close any children */
         closeChildren();
 
         /* Record that we are the active item */
         theActiveItem = pItem;
     }
 
     /**
      * Handle activeMenu.
      *
      * @param pMenu the menu
      */
     void handleActiveMenu(final TethysUIFXScrollSubMenu<T> pMenu) {
         /* Hide any existing menu that is not us */
         if (theActiveMenu != null
                 && theActiveMenu.getIndex() != pMenu.getIndex()) {
             theActiveMenu.hide();
         }
 
         /* Set no active Item */
         theActiveItem = null;
 
         /* Record active menu */
         theActiveMenu = pMenu;
     }
 
     @Override
     public void removeAllItems() {
         /* Check state */
         if (isShowing()) {
             closeMenu();
         }
 
         /* Clear menuItems */
         theMenuItems.clear();
         theFirstIndex = 0;
         needReBuild = true;
 
         /* Clear state */
         theSelectedItem = null;
     }
 
     @Override
     public boolean isEmpty() {
         /* Obtain count */
         return theMenuItems.isEmpty();
     }
 
     /**
      * Obtain count of menu Items.
      *
      * @return the count
      */
     protected int getItemCount() {
         /* Obtain count */
         return theMenuItems.size();
     }
 
     /**
      * Ensure item at index will be visible when displayed.
      *
      * @param pIndex the index to show
      */
     void scrollToIndex(final int pIndex) {
         /* Show the index */
         showIndex(pIndex);
 
         /* cascade call upwards */
         if (theParentMenu != null) {
             theParentMenu.scrollToMenu();
         }
     }
 
     /**
      * Ensure index shown.
      *
      * @param pIndex the index to show
      */
     private void showIndex(final int pIndex) {
         /* Ignore if index is out of range */
         final int myCount = theMenuItems.size();
         if (pIndex < 0
                 || pIndex >= myCount) {
             return;
         }
 
         /* If index is above window */
         if (pIndex < theFirstIndex) {
             /* Scroll window upwards and return */
             requestScroll(pIndex - theFirstIndex);
             return;
         }
 
         /* If index is beyond last visible index */
         final int myLastIndex = theFirstIndex
                 + theMaxDisplayItems
                 - 1;
         if (myLastIndex < pIndex) {
             /* Scroll window downwards */
             requestScroll(pIndex - myLastIndex);
         }
     }
 
     @Override
     public TethysUIScrollItem<T> addItem(final T pValue) {
         /* Use standard name */
         return addItem(pValue, pValue.toString(), null);
     }
 
     @Override
     public TethysUIScrollItem<T> addItem(final T pValue,
                                          final String pName) {
         /* Use standard name */
         return addItem(pValue, pName, null);
     }
 
     @Override
     public TethysUIScrollItem<T> addItem(final T pValue,
                                          final TethysUIIconId pId) {
         /* Use standard name */
         return addItem(pValue, pValue.toString(), TethysUIFXUtils.getIconAtSize(pId, TethysUICoreScrollMenu.ICON_SIZE));
     }
 
     @Override
     public TethysUIScrollItem<T> addItem(final T pValue,
                                          final TethysUIIcon pGraphic) {
         /* Use standard name */
         return addItem(pValue, pValue.toString(), pGraphic);
     }
 
     @Override
     public TethysUIScrollItem<T> addNullItem(final String pName) {
         /* Use given name */
         return addItem(null, pName, null);
     }
 
     @Override
     public TethysUIScrollItem<T> addNullItem(final String pName,
                                              final TethysUIIcon pGraphic) {
         /* Use given name */
         return addItem(null, pName, pGraphic);
     }
 
     @Override
     public TethysUIScrollItem<T> addItem(final T pValue,
                                          final String pName,
                                          final TethysUIIcon pGraphic) {
         /* Check state */
         if (isShowing()) {
             throw new IllegalStateException();
         }
 
         /* Create element */
         final TethysUIFXScrollItem<T> myItem = new TethysUIFXScrollItem<>(this, pValue, pName, pGraphic);
 
         /* Add to the list of menuItems */
         theMenuItems.add(myItem);
         needReBuild = true;
         return myItem;
     }
 
     @Override
     public TethysUIScrollSubMenu<T> addSubMenu(final String pName) {
         /* Use given name */
         return addSubMenu(pName, null);
     }
 
     @Override
     public TethysUIScrollSubMenu<T> addSubMenu(final String pName,
                                                final TethysUIIcon pGraphic) {
         /* Check state */
         if (isShowing()) {
             throw new IllegalStateException();
         }
 
         /* Create menu */
         final TethysUIFXScrollSubMenu<T> myMenu = new TethysUIFXScrollSubMenu<>(this, pName, pGraphic);
 
         /* Add to the list of menuItems */
         theMenuItems.add(myMenu);
         needReBuild = true;
         return myMenu;
     }
 
     @Override
     public TethysUIScrollToggle<T> addToggleItem(final T pValue) {
         /* Use standard name */
         return addToggleItem(pValue, pValue.toString());
     }
 
     @Override
     public TethysUIScrollToggle<T> addToggleItem(final T pValue,
                                                  final String pName) {
         /* Check state */
         if (isShowing()) {
             throw new IllegalStateException();
         }
 
         /* Create element */
         final TethysUIFXScrollToggle<T> myItem = new TethysUIFXScrollToggle<>(this, pValue, pName);
 
         /* Add to the list of menuItems */
         theMenuItems.add(myItem);
         needReBuild = true;
         return myItem;
     }
 
     /**
      * close child menus.
      */
     void closeChildren() {
         /* Close any active subMenu */
         if (theActiveMenu != null) {
             theActiveMenu.hide();
         }
         theActiveMenu = null;
     }
 
     /**
      * Determine size of menu.
      */
     private void determineSize() {
         /* NoOp if we do not need to reBuild the menu */
         if (!needReBuild) {
             return;
         }
 
         /* If we have items */
         if (!theMenuItems.isEmpty()) {
             /* Access the number of entries and the scroll count */
             final int myCount = theMenuItems.size();
             final int myScroll = Math.min(theMaxDisplayItems, myCount);
 
             /* Remove all items */
             theActiveItems.clear();
 
             /* If we do not need to scroll */
             if (myScroll == myCount) {
                 /* Ensure we have no arrows */
                 theContainer.setTop(null);
                 theContainer.setBottom(null);
 
                 /* Loop through the items to add */
                 for (int i = 0; i < myCount; i++) {
                     /* Add the items */
                     theActiveItems.add(theMenuItems.get(i).getBorderPane());
                 }
 
                 /* Calculate size of menu */
                 theStage.show();
                 theStage.close();
 
                 /* Determine the size */
                 theMenuSize = new Dimension2D(theStage.getWidth(), theStage.getHeight());
 
                 /* else need to set up scroll */
             } else {
                 /* Add the scrolling items */
                 theContainer.setTop(theUpItem.getLabel());
                 theContainer.setBottom(theDownItem.getLabel());
                 theUpItem.setVisible(true);
                 theDownItem.setVisible(true);
 
                 /* Add ALL items */
                 for (final TethysUIFXScrollElement myItem : theMenuItems) {
                     /* Add the items */
                     theActiveItems.add(myItem.getBorderPane());
                 }
 
                 /* Calculate size of menu */
                 theStage.show();
                 theStage.close();
                 final double myWidth = theStage.getWidth();
 
                 /* Remove all items */
                 theActiveItems.clear();
 
                 /* Ensure that the starting index is positive */
                 if (theFirstIndex < 0) {
                     theFirstIndex = 0;
                 }
 
                 /* Ensure that the starting point is not too late */
                 int myMaxIndex = theFirstIndex
                         + myScroll;
                 if (myMaxIndex > myCount) {
                     /* Adjust the first index */
                     theFirstIndex = myCount
                             - myScroll;
                     myMaxIndex = myCount;
                 }
 
                 /* Loop through the items to add */
                 for (int i = theFirstIndex; i < myMaxIndex; i++) {
                     /* Add the items */
                     theActiveItems.add(theMenuItems.get(i).getBorderPane());
                 }
 
                 /* Calculate size of menu */
                 theStage.show();
                 theStage.close();
                 final double myHeight = theStage.getHeight();
 
                 /* Set visibility of scroll items */
                 theUpItem.setVisible(theFirstIndex > 0);
                 theDownItem.setVisible(myMaxIndex < myCount);
 
                 /* Determine the size */
                 theMenuSize = new Dimension2D(myWidth, myHeight);
 
                 /* Fix the width */
                 theStage.setMinWidth(myWidth);
             }
 
             /* else reset the menuSize */
         } else {
             theMenuSize = null;
         }
 
         /* Reset flag */
         needReBuild = false;
     }
 
     /**
      * ScrollPlusOne.
      */
     protected void scrollPlusOne() {
         /* If we are already built */
         if (!needReBuild) {
             /* Access the number of entries */
             final int myCount = theMenuItems.size();
 
             /* Reset the children */
             closeChildren();
 
             /* Ensure Up item is enabled */
             theUpItem.setVisible(true);
 
             /* Remove the first item */
             theActiveItems.remove(0);
 
             /* Add the final item */
             final int myLast = theFirstIndex + theMaxDisplayItems;
             final TethysUIFXScrollElement myItem = theMenuItems.get(myLast);
             theActiveItems.add(myItem.getBorderPane());
 
             /* Adjust down item */
             theDownItem.setVisible(myLast + 1 < myCount);
         }
 
         /* Adjust first index */
         theFirstIndex++;
     }
 
     /**
      * ScrollMinusOne.
      */
     protected void scrollMinusOne() {
         /* If we are already built */
         if (!needReBuild) {
             /* Reset the children */
             closeChildren();
 
             /* Ensure Down item is enabled */
             theDownItem.setVisible(true);
 
             /* Remove the last item */
             theActiveItems.remove(theMaxDisplayItems - 1);
 
             /* Add the initial item */
             final TethysUIFXScrollElement myItem = theMenuItems.get(theFirstIndex - 1);
             theActiveItems.add(0, myItem.getBorderPane());
 
             /* Adjust up item */
             theUpItem.setVisible(theFirstIndex > 1);
         }
 
         /* Adjust first index */
         theFirstIndex--;
     }
 
     /**
      * request scroll.
      *
      * @param pDelta the delta to scroll.
      */
     void requestScroll(final int pDelta) {
         /* If this is a scroll downwards */
         if (pDelta > 0) {
             /* If we can scroll downwards */
             final int myCount = theMenuItems.size();
             final int mySpace = myCount - theFirstIndex - theMaxDisplayItems;
             int myScroll = Math.min(mySpace, pDelta);
 
             /* While we have space */
             while (myScroll-- > 0) {
                 /* Scroll downwards */
                 scrollPlusOne();
             }
 
             /* else scroll upwards if we can */
         } else if (theFirstIndex > 0) {
             /* Determine space */
             int myScroll = Math.min(theFirstIndex, -pDelta);
 
             /* While we have space */
             while (myScroll-- > 0) {
                 /* Scroll upwards */
                 scrollMinusOne();
             }
         }
     }
 
     /**
      * Scroll element.
      */
     public abstract static class TethysUIFXScrollElement {
         /**
          * BorderPane.
          */
         private final BorderPane theBorderPane;
 
         /**
          * The label.
          */
         private final Label theLabel;
 
         /**
          * The icon label.
          */
         private final Label theIcon;
 
         /**
          * Constructor.
          *
          * @param pName    the display name
          * @param pGraphic the icon for the item
          */
         private TethysUIFXScrollElement(final String pName,
                                         final TethysUIIcon pGraphic) {
             /* Create the borderPane */
             theBorderPane = new BorderPane();
 
             /* Create a Label for the name */
             theLabel = new Label();
             theLabel.setText(pName);
             theLabel.setMaxWidth(Double.MAX_VALUE);
 
             /* Create a Label for the graphic */
             theIcon = new Label();
             theIcon.setGraphic(TethysUIFXIcon.getIcon(pGraphic));
             theIcon.setMinWidth(TethysUIConstant.DEFAULT_ICONSIZE);
 
             /* Add the children */
             theBorderPane.setLeft(theIcon);
             theBorderPane.setCenter(theLabel);
 
             /* Set style of item */
             theBorderPane.getStyleClass().add(STYLE_ITEM);
         }
 
         /**
          * Obtain the label.
          *
          * @return the label
          */
         BorderPane getBorderPane() {
             return theBorderPane;
         }
 
         /**
          * Add event filter.
          *
          * @param <T>     the event type
          * @param pEvent  the event
          * @param pFilter the filter
          */
         <T extends Event> void addEventFilter(final EventType<T> pEvent,
                                               final EventHandler<? super T> pFilter) {
             theBorderPane.addEventFilter(pEvent, pFilter);
         }
 
         /**
          * Obtain the text.
          *
          * @return the text
          */
         public String getText() {
             return theLabel.getText();
         }
 
         /**
          * Set the graphic.
          *
          * @param pGraphic the graphic
          */
         protected void setIcon(final TethysUIFXIcon pGraphic) {
             theIcon.setGraphic(TethysUIFXIcon.getIcon(pGraphic));
         }
 
         /**
          * Add Menu icon.
          */
         protected void addMenuIcon() {
             final Label myLabel = new Label();
             myLabel.setGraphic(TethysUIFXArrowIcon.RIGHT.getArrow());
             theBorderPane.setRight(myLabel);
         }
     }
 
     /**
      * Scroll item.
      *
      * @param <T> the value type
      */
     protected static class TethysUIFXScrollItem<T>
             extends TethysUIFXScrollElement
             implements TethysUIScrollItem<T> {
         /**
          * Parent context menu.
          */
         private final TethysUIFXScrollMenu<T> theContext;
 
         /**
          * The index.
          */
         private final int theIndex;
 
         /**
          * Associated value.
          */
         private final T theValue;
 
         /**
          * Constructor.
          *
          * @param pContext the parent context menu
          * @param pValue   the value
          * @param pName    the display name
          * @param pGraphic the icon for the item
          */
         protected TethysUIFXScrollItem(final TethysUIFXScrollMenu<T> pContext,
                                        final T pValue,
                                        final String pName,
                                        final TethysUIIcon pGraphic) {
             /* Call super-constructor */
             super(pName, pGraphic);
 
             /* Record parameters */
             theContext = pContext;
             theValue = pValue;
 
             /* Determine the index */
             theIndex = theContext.getItemCount();
 
             /* Handle removal of subMenus */
             addEventFilter(MouseEvent.MOUSE_ENTERED, e -> theContext.handleActiveItem(this));
 
             /* Handle selection */
             addEventFilter(MouseEvent.MOUSE_CLICKED, e -> theContext.setSelectedItem(this));
         }
 
         @Override
         public T getValue() {
             return theValue;
         }
 
         @Override
         public void scrollToItem() {
             theContext.scrollToIndex(theIndex);
         }
     }
 
     /**
      * Scroll item.
      *
      * @param <T> the value type
      */
     private static final class TethysUIFXScrollToggle<T>
             extends TethysUIFXScrollItem<T>
             implements TethysUIScrollToggle<T> {
         /**
          * Selected state.
          */
         private boolean isSelected;
 
         /**
          * Constructor.
          *
          * @param pContext the parent context menu
          * @param pValue   the value
          * @param pName    the display name
          */
         TethysUIFXScrollToggle(final TethysUIFXScrollMenu<T> pContext,
                                final T pValue,
                                final String pName) {
             /* Call super-constructor */
             super(pContext, pValue, pName, null);
         }
 
         @Override
         public boolean isSelected() {
             return isSelected;
         }
 
         @Override
         public void setSelected(final boolean pSelected) {
             isSelected = pSelected;
             setIcon(isSelected
                     ? TethysUIFXUtils.getIconAtSize(TethysUIScrollIcon.CHECKMARK, TethysUIConstant.DEFAULT_ICONSIZE)
                     : null);
         }
 
         @Override
         public void toggleSelected() {
             setSelected(!isSelected);
         }
     }
 
     /**
      * Scroll menu.
      *
      * @param <T> the value type
      */
     public static final class TethysUIFXScrollSubMenu<T>
             extends TethysUIFXScrollElement
             implements TethysUIScrollSubMenu<T> {
         /**
          * Parent contextMenu.
          */
         private final TethysUIFXScrollMenu<T> theContext;
 
         /**
          * The index.
          */
         private final int theIndex;
 
         /**
          * Associated value.
          */
         private final TethysUIFXScrollMenu<T> theSubMenu;
 
         /**
          * Constructor.
          *
          * @param pContext the parent context menu
          * @param pName    the name
          * @param pGraphic the icon for the menu
          */
         TethysUIFXScrollSubMenu(final TethysUIFXScrollMenu<T> pContext,
                                 final String pName,
                                 final TethysUIIcon pGraphic) {
             /* Call super-constructor */
             super(pName, pGraphic);
 
             /* Record parameters */
             theContext = pContext;
 
             /* Create the subMenu */
             theSubMenu = new TethysUIFXScrollMenu<>(this);
 
             /* Determine the index */
             theIndex = theContext.getItemCount();
 
             /* Set menu icon */
             addMenuIcon();
 
             /* Handle show menu */
             addEventFilter(MouseEvent.MOUSE_ENTERED, e -> {
                 theContext.handleActiveMenu(this);
                 theSubMenu.showMenuAtPosition(getBorderPane(), Side.RIGHT);
             });
         }
 
         /**
          * Obtain the parent.
          *
          * @return the parent
          */
         TethysUIFXScrollMenu<T> getContext() {
             return theContext;
         }
 
         @Override
         public TethysUIFXScrollMenu<T> getSubMenu() {
             return theSubMenu;
         }
 
         /**
          * Obtain the index.
          *
          * @return the index
          */
         int getIndex() {
             return theIndex;
         }
 
         /**
          * Hide the subMenu.
          */
         void hide() {
             theSubMenu.closeMenu();
         }
 
         /**
          * Set the number of items in the scrolling portion of the menu.
          *
          * @param pMaxDisplayItems the maximum number of items to display
          * @throws IllegalArgumentException if pMaxDisplayItems is 0 or negative
          */
         private void setMaxDisplayItems(final int pMaxDisplayItems) {
             /* Pass call to subMenu */
             theSubMenu.setMaxDisplayItems(pMaxDisplayItems);
         }
 
         /**
          * Ensure that this menu is visible immediately the context is displayed.
          */
         void scrollToMenu() {
             theContext.scrollToIndex(theIndex);
         }
     }
 
     /**
      * Scroll control class.
      */
     private final class ScrollControl {
         /**
          * Label.
          */
         private final Label theLabel;
 
         /**
          * Increment.
          */
         private final int theIncrement;
 
         /**
          * KickStart Timer.
          */
         private final Timeline theKickStartTimer;
 
         /**
          * Repeat Timer.
          */
         private final Timeline theRepeatTimer;
 
         /**
          * Constructor.
          *
          * @param pIcon      the icon
          * @param pIncrement the increment
          */
         ScrollControl(final Polygon pIcon,
                       final int pIncrement) {
             /* Create the label */
             theLabel = new Label();
 
             /* Set the icon for the item */
             theLabel.setGraphic(pIcon);
             theLabel.setContentDisplay(ContentDisplay.GRAPHIC_ONLY);
             theLabel.setAlignment(Pos.CENTER);
             theLabel.setMaxWidth(Double.MAX_VALUE);
             theLabel.getStyleClass().add(STYLE_ITEM);
 
             /* Store parameters */
             theIncrement = pIncrement;
 
             /* Handle selection */
             theLabel.addEventFilter(MouseEvent.MOUSE_CLICKED, e -> processScroll());
 
             /* Handle mouse enters */
             theLabel.addEventHandler(MouseEvent.MOUSE_ENTERED, e -> processMouseEnter());
 
             /* Handle mouse exits */
             theLabel.addEventHandler(MouseEvent.MOUSE_EXITED, e -> processMouseExit());
 
             /* Create the timers */
             theKickStartTimer = new Timeline(new KeyFrame(Duration.millis(TethysUICoreScrollMenu.INITIAL_SCROLLDELAY),
                     e -> processScroll()));
             theRepeatTimer = new Timeline(new KeyFrame(Duration.millis(TethysUICoreScrollMenu.REPEAT_SCROLLDELAY),
                     e -> processScroll()));
         }
 
         /**
          * Obtain the label.
          *
          * @return the label
          */
         Label getLabel() {
             return theLabel;
         }
 
         /**
          * Set visibility.
          *
          * @param pVisible true/false
          */
         void setVisible(final boolean pVisible) {
             theLabel.setVisible(pVisible);
         }
 
         /**
          * Process scroll event.
          */
         private void processScroll() {
             /* Request the scroll */
             requestScroll(theIncrement);
             theRepeatTimer.play();
         }
 
         /**
          * Process mouseEnter event.
          */
         private void processMouseEnter() {
             /* Close any children */
             closeChildren();
 
             /* Set no active Item */
             clearActiveItem();
 
             /* Schedule the task */
             theKickStartTimer.play();
         }
 
         /**
          * Process mouseExit event.
          */
         private void processMouseExit() {
             /* Cancel any timer tasks */
             theKickStartTimer.stop();
             theRepeatTimer.stop();
         }
     }
 }