vaadin-framework/server/src/main/java/com/vaadin/ui/TabSheet.java

/*
 * Copyright 2000-2018 Vaadin Ltd.
 *
 * 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 com.vaadin.ui;

import java.io.Serializable;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Objects;

import org.jsoup.nodes.Attributes;
import org.jsoup.nodes.Element;

import com.vaadin.event.FieldEvents.BlurEvent;
import com.vaadin.event.FieldEvents.BlurListener;
import com.vaadin.event.FieldEvents.BlurNotifier;
import com.vaadin.event.FieldEvents.FocusAndBlurServerRpcDecorator;
import com.vaadin.event.FieldEvents.FocusEvent;
import com.vaadin.event.FieldEvents.FocusListener;
import com.vaadin.event.FieldEvents.FocusNotifier;
import com.vaadin.event.HasUserOriginated;
import com.vaadin.server.ErrorMessage;
import com.vaadin.server.KeyMapper;
import com.vaadin.server.Resource;
import com.vaadin.shared.ComponentConstants;
import com.vaadin.shared.Registration;
import com.vaadin.shared.ui.ContentMode;
import com.vaadin.shared.ui.tabsheet.TabState;
import com.vaadin.shared.ui.tabsheet.TabsheetClientRpc;
import com.vaadin.shared.ui.tabsheet.TabsheetServerRpc;
import com.vaadin.shared.ui.tabsheet.TabsheetState;
import com.vaadin.ui.Component.Focusable;
import com.vaadin.ui.declarative.DesignAttributeHandler;
import com.vaadin.ui.declarative.DesignContext;
import com.vaadin.ui.declarative.DesignException;

/**
 * TabSheet component.
 *
 * Tabs are typically identified by the component contained on the tab (see
 * {@link ComponentContainer}), and tab metadata (including caption, icon,
 * visibility, enabledness, closability etc.) is kept in separate {@link Tab}
 * instances.
 *
 * Tabs added with {@link #addComponent(Component)} get the caption and the icon
 * of the component at the time when the component is created, and these are not
 * automatically updated after tab creation.
 *
 * A tab sheet can have multiple tab selection listeners and one tab close
 * handler ({@link CloseHandler}), which by default removes the tab from the
 * TabSheet.
 *
 * The {@link TabSheet} can be styled with the .v-tabsheet, .v-tabsheet-tabs and
 * .v-tabsheet-content styles.
 *
 * The current implementation does not load the tabs to the UI before the first
 * time they are shown, but this may change in future releases.
 *
 * @author Vaadin Ltd.
 * @since 3.0
 */
public class TabSheet extends AbstractComponentContainer
        implements Focusable, FocusNotifier, BlurNotifier, SelectiveRenderer {

    /**
     * Client to server RPC implementation for TabSheet.
     *
     * @since 7.2
     */
    protected class TabsheetServerRpcImpl implements TabsheetServerRpc {

        @Override
        public void setSelected(String key) {
            setSelectedTab(keyMapper.get(key), true);
        }

        @Override
        public void closeTab(String key) {
            final Component tab = keyMapper.get(key);
            if (tab != null) {
                closeHandler.onTabClose(TabSheet.this, tab);
            }
        }
    }

    /**
     * List of component tabs (tab contents). In addition to being on this list,
     * there is a {@link Tab} object in tabs for each tab with meta-data about
     * the tab.
     */
    private final ArrayList<Component> components = new ArrayList<>();

    /**
     * Map containing information related to the tabs (caption, icon etc).
     */
    private final Map<Component, Tab> tabs = new HashMap<>();

    /**
     * Selected tab content component.
     */
    private Component selected = null;

    /**
     * Mapper between server-side component instances (tab contents) and keys
     * given to the client that identify tabs.
     */
    protected final KeyMapper<Component> keyMapper = new KeyMapper<>();

    /**
     * Handler to be called when a tab is closed.
     */
    private CloseHandler closeHandler;

    /**
     * Constructs a new TabSheet. A TabSheet is immediate by default, and the
     * default close handler removes the tab being closed.
     */
    public TabSheet() {
        super();

        registerRpc(rpc);
        registerRpc(new FocusAndBlurServerRpcDecorator(this, this::fireEvent));

        // expand horizontally by default
        setWidth(100, UNITS_PERCENTAGE);
        setCloseHandler(TabSheet::removeComponent);
    }

    /**
     * Constructs a new TabSheet containing the given components.
     *
     * @param components
     *            The components to add to the tab sheet. Each component will be
     *            added to a separate tab.
     */
    public TabSheet(Component... components) {
        this();
        addComponents(components);
    }

    /**
     * Gets the component container iterator for going through all the
     * components (tab contents).
     *
     * @return the unmodifiable Iterator of the tab content components
     */

    @Override
    public Iterator<Component> iterator() {
        return Collections.unmodifiableList(components).iterator();
    }

    /**
     * Gets the number of contained components (tabs). Consistent with the
     * iterator returned by {@link #getComponentIterator()}.
     *
     * @return the number of contained components
     */

    @Override
    public int getComponentCount() {
        return components.size();
    }

    /**
     * Removes a component and its corresponding tab.
     *
     * If the tab was selected, the first eligible (visible and enabled)
     * remaining tab is selected.
     *
     * @param component
     *            the component to be removed.
     */

    @Override
    public void removeComponent(Component component) {
        if (component != null && components.contains(component)) {

            int componentIndex = components.indexOf(component);
            super.removeComponent(component);
            keyMapper.remove(component);
            components.remove(component);

            Tab removedTab = tabs.remove(component);

            getState().tabs
                    .remove(((TabSheetTabImpl) removedTab).getTabState());

            if (component.equals(selected)) {
                if (components.isEmpty()) {
                    setSelected(null);
                } else {

                    int newSelectedIndex = selectedTabIndexAfterTabRemove(
                            componentIndex);

                    // Make sure the component actually exists, in case someone
                    // override it and provide a non existing component.
                    if (0 <= newSelectedIndex
                            && newSelectedIndex < components.size()) {

                        Component newSelectedComponent = components
                                .get(newSelectedIndex);

                        // Select only if the tab is enabled.
                        Tab newSelectedTab = tabs.get(newSelectedComponent);
                        if (newSelectedTab.isEnabled()) {
                            setSelected(newSelectedComponent);
                        }
                    }

                    // select the first enabled and visible tab, if any
                    updateSelection();
                    fireSelectedTabChange(false);
                }
            }
        }
    }

    /**
     * Called when a selected tab is removed to specify the new tab to select.
     * Can be overridden to provide another algorithm that calculates the new
     * selection.
     *
     * Current implementation will choose the first enabled tab to the right of
     * the removed tab if it's not the last one, otherwise will choose the
     * closer enabled tab to the left.
     *
     * @since 7.4
     * @param removedTabIndex
     *            the index of the selected tab which was just remove.
     * @return the index of the tab to be selected or -1 if there are no more
     *         enabled tabs to select.
     */
    protected int selectedTabIndexAfterTabRemove(int removedTabIndex) {

        for (int i = removedTabIndex; i < components.size(); i++) {
            Tab tab = getTab(i);
            if (tab.isEnabled()) {
                return i;
            }
        }

        for (int i = removedTabIndex - 1; i >= 0; i--) {
            Tab tab = getTab(i);
            if (tab.isEnabled()) {
                return i;
            }
        }

        return -1;
    }

    /**
     * Removes a {@link Tab} and the component associated with it, as previously
     * added with {@link #addTab(Component)},
     * {@link #addTab(Component, String, Resource)} or
     * {@link #addComponent(Component)}.
     * <p>
     * If the tab was selected, the first eligible (visible and enabled)
     * remaining tab is selected.
     * </p>
     *
     * @see #addTab(Component)
     * @see #addTab(Component, String, Resource)
     * @see #addComponent(Component)
     * @see #removeComponent(Component)
     * @param tab
     *            the Tab to remove
     */
    public void removeTab(Tab tab) {
        removeComponent(tab.getComponent());
    }

    /**
     * Adds a new tab into TabSheet. Component caption and icon are copied to
     * the tab metadata at creation time.
     *
     * @see #addTab(Component)
     *
     * @param c
     *            the component to be added.
     */

    @Override
    public void addComponent(Component c) {
        addTab(c);
    }

    /**
     * Adds a new tab into TabSheet.
     *
     * The first tab added to a tab sheet is automatically selected and a tab
     * selection event is fired.
     *
     * If the component is already present in the tab sheet, changes its caption
     * and returns the corresponding (old) tab, preserving other tab metadata.
     *
     * @param c
     *            the component to be added onto tab - should not be null.
     * @param caption
     *            the caption to be set for the component and used rendered in
     *            tab bar
     * @return the created {@link Tab}
     */
    public Tab addTab(Component c, String caption) {
        return addTab(c, caption, null);
    }

    /**
     * Adds a new tab into TabSheet.
     *
     * The first tab added to a tab sheet is automatically selected and a tab
     * selection event is fired.
     *
     * If the component is already present in the tab sheet, changes its caption
     * and icon and returns the corresponding (old) tab, preserving other tab
     * metadata.
     *
     * @param c
     *            the component to be added onto tab - should not be null.
     * @param caption
     *            the caption to be set for the component and used rendered in
     *            tab bar
     * @param icon
     *            the icon to be set for the component and used rendered in tab
     *            bar
     * @return the created {@link Tab}
     */
    public Tab addTab(Component c, String caption, Resource icon) {
        return addTab(c, caption, icon, components.size());
    }

    /**
     * Adds a new tab into TabSheet.
     *
     * The first tab added to a tab sheet is automatically selected and a tab
     * selection event is fired.
     *
     * If the component is already present in the tab sheet, changes its caption
     * and icon and returns the corresponding (old) tab, preserving other tab
     * metadata like the position.
     *
     * @param tabComponent
     *            the component to be added onto tab - should not be null.
     * @param caption
     *            the caption to be set for the component and used rendered in
     *            tab bar
     * @param icon
     *            the icon to be set for the component and used rendered in tab
     *            bar
     * @param position
     *            the position at where the the tab should be added.
     * @return the created {@link Tab}
     */
    public Tab addTab(Component tabComponent, String caption, Resource icon,
            int position) {
        if (tabComponent == null) {
            return null;
        } else if (tabs.containsKey(tabComponent)) {
            Tab tab = tabs.get(tabComponent);
            tab.setCaption(caption);
            tab.setIcon(icon);
            return tab;
        } else {
            components.add(position, tabComponent);

            TabSheetTabImpl tab = new TabSheetTabImpl(
                    keyMapper.key(tabComponent), caption, icon);

            getState().tabs.add(position, tab.getTabState());
            tabs.put(tabComponent, tab);

            if (selected == null) {
                setSelected(tabComponent);
                fireSelectedTabChange(false);
            }

            super.addComponent(tabComponent);

            return tab;
        }
    }

    /**
     * Adds a new tab into TabSheet. Component caption and icon are copied to
     * the tab metadata at creation time.
     *
     * If the tab sheet already contains the component, its tab is returned.
     *
     * @param c
     *            the component to be added onto tab - should not be null.
     * @return the created {@link Tab}
     */
    public Tab addTab(Component c) {
        return addTab(c, components.size());
    }

    /**
     * Adds a new tab into TabSheet. Component caption and icon are copied to
     * the tab metadata at creation time.
     *
     * If the tab sheet already contains the component, its tab is returned.
     *
     * @param component
     *            the component to be added onto tab - should not be null.
     * @param position
     *            The position where the tab should be added
     * @return the created {@link Tab}
     */
    public Tab addTab(Component component, int position) {
        Tab result = tabs.get(component);

        if (result == null) {
            result = addTab(component, component.getCaption(),
                    component.getIcon(), position);
        }

        return result;
    }

    /**
     * Moves all components from another container to this container. The
     * components are removed from the other container.
     *
     * If the source container is a {@link TabSheet}, component captions and
     * icons are copied from it.
     *
     * @param source
     *            the container components are removed from.
     */

    @Override
    public void moveComponentsFrom(ComponentContainer source) {
        for (final Iterator<Component> i = source.getComponentIterator(); i
                .hasNext();) {
            final Component c = i.next();
            String caption = null;
            Resource icon = null;
            String iconAltText = "";
            if (TabSheet.class.isAssignableFrom(source.getClass())) {
                Tab tab = ((TabSheet) source).getTab(c);
                caption = tab.getCaption();
                icon = tab.getIcon();
                iconAltText = tab.getIconAlternateText();
            }
            source.removeComponent(c);
            Tab tab = addTab(c, caption, icon);
            tab.setIconAlternateText(iconAltText);
        }
    }

    /**
     * Are the tab selection parts ("tabs") hidden.
     *
     * @return true if the tabs are hidden in the UI
     * @deprecated as of 7.5, use {@link #isTabsVisible()} instead
     */
    @Deprecated
    public boolean areTabsHidden() {
        return !isTabsVisible();
    }

    /**
     * Hides or shows the tab selection parts ("tabs").
     *
     * @param tabsHidden
     *            true if the tabs should be hidden
     * @deprecated as of 7.5, use {@link #setTabsVisible(boolean)} instead
     */
    @Deprecated
    public void hideTabs(boolean tabsHidden) {
        setTabsVisible(!tabsHidden);
    }

    /**
     * Sets whether the tab selection part should be shown in the UI.
     *
     * @since 7.5
     * @param tabsVisible
     *            true if the tabs should be shown in the UI, false otherwise
     */
    public void setTabsVisible(boolean tabsVisible) {
        getState().tabsVisible = tabsVisible;
    }

    /**
     * Checks if the tab selection part should be shown in the UI.
     *
     * @return true if the tabs are shown in the UI, false otherwise
     * @since 7.5
     */
    public boolean isTabsVisible() {
        return getState(false).tabsVisible;

    }

    /**
     * Returns the {@link Tab} (metadata) for a component. The {@link Tab}
     * object can be used for setting caption,icon, etc for the tab.
     *
     * @param c
     *            the component
     * @return The tab instance associated with the given component, or null if
     *         the tabsheet does not contain the component.
     */
    public Tab getTab(Component c) {
        return tabs.get(c);
    }

    /**
     * Returns the {@link Tab} (metadata) with the given index. The {@link Tab}
     * object can be used for setting caption,icon, etc for the tab.
     *
     * @param index
     *            the index of the tab
     * @return The tab with the given index, or null if the index is out of
     *         bounds.
     */
    public Tab getTab(int index) {
        if (index >= 0 && index < getComponentCount()) {
            return getTab(components.get(index));
        } else {
            return null;
        }
    }

    /**
     * Sets the selected tab. The tab is identified by the tab content
     * component. Does nothing if the tabsheet doesn't contain the component.
     *
     * @param component
     *            the component of the tab to select
     */
    public void setSelectedTab(Component component) {
        setSelectedTab(component, false);
    }

    /**
     * Sets the selected tab. The tab is identified by the tab content
     * component. Does nothing if the tabsheet doesn't contain the component.
     *
     * @param component
     *            the component of the tab to select
     * @param userOriginated
     *            <code>true</code> if the event originates from the client
     *            side, <code>false</code> otherwise
     * @since 8.1
     */
    public void setSelectedTab(Component component, boolean userOriginated) {
        if (component != null && components.contains(component)
                && !component.equals(selected)) {
            setSelected(component);
            updateSelection();
            fireSelectedTabChange(userOriginated);
            markAsDirty();
            getRpcProxy(TabsheetClientRpc.class).revertToSharedStateSelection();
        }
    }

    /**
     * Sets the selected tab in the TabSheet. Ensures that the selected tab is
     * repainted if needed.
     *
     * @param component
     *            The new selection or null for no selection
     */
    private void setSelected(Component component) {
        Tab tab = tabs.get(selected);

        selected = component;
        // Repaint of the selected component is needed as only the selected
        // component is communicated to the client. Otherwise this will be a
        // "cached" update even though the client knows nothing about the
        // connector
        if (selected != null) {
            tab = getTab(component);

            if (tab != null && tab.getDefaultFocusComponent() != null) {
                tab.getDefaultFocusComponent().focus();
            }

            getState().selected = keyMapper.key(selected);

            selected.markAsDirtyRecursive();
        } else {
            getState().selected = null;
        }
    }

    /**
     * Sets the selected tab. The tab is identified by the corresponding
     * {@link Tab Tab} instance. Does nothing if the tabsheet doesn't contain
     * the given tab.
     *
     * @param tab
     *            the tab to select
     */
    public void setSelectedTab(Tab tab) {
        if (tab != null) {
            setSelectedTab(tab.getComponent(), false);
        }
    }

    /**
     * Sets the selected tab, identified by its index. Does nothing if the
     * position is out of bounds.
     *
     * @param index
     *            the index of the tab to select
     */
    public void setSelectedTab(int index) {
        setSelectedTab(getTab(index));
    }

    /**
     * Checks if the current selection is valid, and updates the selection if
     * the previously selected component is not visible and enabled. The first
     * visible and enabled tab is selected if the current selection is empty or
     * invalid.
     *
     * This method does not fire tab change events, but the caller should do so
     * if appropriate.
     *
     * @return true if selection was changed, false otherwise
     */
    private boolean updateSelection() {
        Component originalSelection = selected;
        for (final Iterator<Component> i = getComponentIterator(); i
                .hasNext();) {
            final Component component = i.next();

            Tab tab = tabs.get(component);

            /*
             * If we have no selection, if the current selection is invisible or
             * if the current selection is disabled (but the whole component is
             * not) we select this tab instead
             */
            Tab selectedTabInfo = null;
            if (selected != null) {
                selectedTabInfo = tabs.get(selected);
            }
            if (selected == null || selectedTabInfo == null
                    || !selectedTabInfo.isVisible()
                    || !selectedTabInfo.isEnabled()) {

                // The current selection is not valid so we need to change
                // it
                if (tab.isEnabled() && tab.isVisible()) {
                    setSelected(component);
                    break;
                } else {
                    /*
                     * The current selection is not valid but this tab cannot be
                     * selected either.
                     */
                    setSelected(null);
                }
            }
        }
        return originalSelection != selected;
    }

    /**
     * Gets the selected tab content component.
     *
     * @return the selected tab contents
     */
    public Component getSelectedTab() {
        return selected;
    }

    private TabsheetServerRpcImpl rpc = new TabsheetServerRpcImpl();

    /**
     * Replaces a component (tab content) with another. This can be used to
     * change tab contents or to rearrange tabs. The tab position and some
     * metadata are preserved when moving components within the same
     * {@link TabSheet}.
     *
     * If the oldComponent is not present in the tab sheet, the new one is added
     * at the end.
     *
     * If the oldComponent is already in the tab sheet but the newComponent
     * isn't, the old tab is replaced with a new one, and the caption and icon
     * of the old one are copied to the new tab.
     *
     * If both old and new components are present, their positions are swapped.
     *
     * {@inheritDoc}
     */

    @Override
    public void replaceComponent(Component oldComponent,
            Component newComponent) {
        boolean selectAfterInserting = false;

        if (selected == oldComponent) {
            selectAfterInserting = true;
        }

        Tab newTab = tabs.get(newComponent);
        Tab oldTab = tabs.get(oldComponent);

        // Gets the locations
        int oldLocation = -1;
        int newLocation = -1;
        int location = 0;

        for (final Component component : components) {
            if (component == oldComponent) {
                oldLocation = location;
            }
            if (component == newComponent) {
                newLocation = location;
            }

            location++;
        }

        if (oldLocation == -1) {
            addComponent(newComponent);
        } else if (newLocation == -1) {
            if (selected == oldComponent) {
                setSelected(null);
            }
            removeComponent(oldComponent);
            newTab = addTab(newComponent, oldLocation);

            if (selectAfterInserting) {
                setSelected(newComponent);
            }

            // Copy all relevant metadata to the new tab (#8793)
            // TODO Should reuse the old tab instance instead?
            copyTabMetadata(oldTab, newTab);
        } else {
            components.set(oldLocation, newComponent);
            components.set(newLocation, oldComponent);

            if (selectAfterInserting) {
                setSelected(newComponent);
                // SelectedTabChangeEvent should be fired here as selected Tab
                // is changed.
                // Other cases are handled implicitly by removeComponent() and
                // addComponent()addTab()
                fireSelectedTabChange(false);
            }

            // Tab associations are not changed, but metadata is swapped between
            // the instances
            // TODO Should reassociate the instances instead?
            Tab tmp = new TabSheetTabImpl(null, null, null);
            copyTabMetadata(newTab, tmp);
            copyTabMetadata(oldTab, newTab);
            copyTabMetadata(tmp, oldTab);

            markAsDirty();
        }
    }

    /* Click event */

    private static final Method SELECTED_TAB_CHANGE_METHOD;
    static {
        try {
            SELECTED_TAB_CHANGE_METHOD = SelectedTabChangeListener.class
                    .getDeclaredMethod("selectedTabChange",
                            SelectedTabChangeEvent.class);
        } catch (final NoSuchMethodException e) {
            // This should never happen
            throw new RuntimeException(
                    "Internal error finding methods in TabSheet");
        }
    }

    /**
     * Selected tab change event. This event is sent when the selected (shown)
     * tab in the tab sheet is changed.
     *
     * @author Vaadin Ltd.
     * @since 3.0
     */
    public static class SelectedTabChangeEvent extends Component.Event
            implements HasUserOriginated {

        private final boolean userOriginated;

        /**
         * Creates a new instance of the event.
         *
         * @param source
         *            the source of the event
         * @param userOriginated
         *            <code>true</code> if the event originates from the client
         *            side, <code>false</code> otherwise
         * @since 8.1
         */
        public SelectedTabChangeEvent(Component source,
                boolean userOriginated) {
            super(source);
            this.userOriginated = userOriginated;
        }

        /**
         * The TabSheet where the event occurred.
         *
         * @return the TabSheet where the event occurred
         */
        public TabSheet getTabSheet() {
            return (TabSheet) getSource();
        }

        /**
         * {@inheritDoc}
         *
         * @since 8.1
         */
        @Override
        public boolean isUserOriginated() {
            return userOriginated;
        }
    }

    /**
     * Selected tab change event listener. The listener is called whenever
     * another tab is selected, including when adding the first tab to a
     * tabsheet.
     *
     * @author Vaadin Ltd.
     *
     * @since 3.0
     */
    @FunctionalInterface
    public interface SelectedTabChangeListener extends Serializable {

        /**
         * Selected (shown) tab in tab sheet has has been changed.
         *
         * @param event
         *            the selected tab change event.
         */
        public void selectedTabChange(SelectedTabChangeEvent event);
    }

    /**
     * Adds a tab selection listener.
     *
     * @see Registration
     *
     * @param listener
     *            the Listener to be added, not null
     * @return a registration object for removing the listener
     * @since 8.0
     */
    public Registration addSelectedTabChangeListener(
            SelectedTabChangeListener listener) {
        return addListener(SelectedTabChangeEvent.class, listener,
                SELECTED_TAB_CHANGE_METHOD);
    }

    /**
     * Removes a tab selection listener.
     *
     * @param listener
     *            the Listener to be removed.
     *
     * @deprecated As of 8.0, replaced by {@link Registration#remove()} in the
     *             registration object returned from
     *             {@link #removeSelectedTabChangeListener(SelectedTabChangeListener)}
     *             .
     */
    @Deprecated
    public void removeSelectedTabChangeListener(
            SelectedTabChangeListener listener) {
        removeListener(SelectedTabChangeEvent.class, listener,
                SELECTED_TAB_CHANGE_METHOD);
    }

    /**
     * Sends an event originating from the server, telling that the currently
     * selected tab has changed.
     *
     * @deprecated use {@link #fireSelectedTabChange(boolean)} to indicate the
     *             origin of the event
     */
    @Deprecated
    protected void fireSelectedTabChange() {
        fireSelectedTabChange(false);
    }

    /**
     * Sends an event that the currently selected tab has changed.
     *
     * @param userOriginated
     *            <code>true</code> if the event originates from the client
     *            side, <code>false</code> otherwise
     * @since 8.1
     */
    protected void fireSelectedTabChange(boolean userOriginated) {
        fireEvent(new SelectedTabChangeEvent(this, userOriginated));
    }

    /**
     * Tab meta-data for a component in a {@link TabSheet}.
     *
     * The meta-data includes the tab caption, icon, visibility and enabledness,
     * closability, description (tooltip) and an optional component error shown
     * in the tab.
     *
     * Tabs are identified by the component contained on them in most cases, and
     * the meta-data can be obtained with {@link TabSheet#getTab(Component)}.
     */
    public interface Tab extends Serializable {
        /**
         * Returns the visible status for the tab. An invisible tab is not shown
         * in the tab bar and cannot be selected.
         *
         * @return true for visible, false for hidden
         */
        public boolean isVisible();

        /**
         * Sets the visible status for the tab. An invisible tab is not shown in
         * the tab bar and cannot be selected, selection is changed
         * automatically when there is an attempt to select an invisible tab.
         *
         * @param visible
         *            true for visible, false for hidden
         */
        public void setVisible(boolean visible);

        /**
         * Returns the closability status for the tab.
         *
         * @return true if the tab is allowed to be closed by the end user,
         *         false for not allowing closing
         */
        public boolean isClosable();

        /**
         * Sets the closability status for the tab. A closable tab can be closed
         * by the user through the user interface. This also controls if a close
         * button is shown to the user or not.
         * <p>
         * Note! Currently only supported by TabSheet, not Accordion.
         * </p>
         *
         * @param closable
         *            true if the end user is allowed to close the tab, false
         *            for not allowing to close. Should default to false.
         */
        public void setClosable(boolean closable);

        /**
         * Set the component that should automatically focused when the tab is
         * selected.
         *
         * @param component
         *            the component to focus
         */
        public void setDefaultFocusComponent(Focusable component);

        /**
         * Get the component that should be automatically focused when the tab
         * is selected.
         *
         * @return the focusable component
         */
        public Focusable getDefaultFocusComponent();

        /**
         * Returns the enabled status for the tab. A disabled tab is shown as
         * such in the tab bar and cannot be selected.
         *
         * @return true for enabled, false for disabled
         */
        public boolean isEnabled();

        /**
         * Sets the enabled status for the tab. A disabled tab is shown as such
         * in the tab bar and cannot be selected.
         *
         * @param enabled
         *            true for enabled, false for disabled
         */
        public void setEnabled(boolean enabled);

        /**
         * Sets the caption for the tab.
         *
         * @param caption
         *            the caption to set
         */
        public void setCaption(String caption);

        /**
         * Gets the caption for the tab.
         */
        public String getCaption();

        /**
         * Gets the icon for the tab.
         */
        public Resource getIcon();

        /**
         * Sets the icon for the tab.
         *
         * @param icon
         *            the icon to set
         */
        public void setIcon(Resource icon);

        /**
         * Sets the icon and alt text for the tab.
         *
         * @param icon
         *            the icon to set
         */
        public void setIcon(Resource icon, String iconAltText);

        /**
         * Gets the icon alt text for the tab.
         *
         * @since 7.2
         */
        public String getIconAlternateText();

        /**
         * Sets the icon alt text for the tab.
         *
         * @since 7.2
         *
         * @param iconAltText
         *            the icon to set
         */
        public void setIconAlternateText(String iconAltText);

        /**
         * Gets the description for the tab. The description can be used to
         * briefly describe the state of the tab to the user, and is typically
         * shown as a tooltip when hovering over the tab.
         *
         * @return the description for the tab
         */
        public String getDescription();

        /**
         * Sets the description for the tab. The description can be used to
         * briefly describe the state of the tab to the user, and is typically
         * shown as a tooltip when hovering over the tab.
         * <p>
         * Setting a description through this method will additionally set the
         * content mode of the description to preformatted. For setting a
         * different content mode see the overload
         * {@link #setDescription(String, ContentMode)}.
         *
         * @param description
         *            the new description string for the tab.
         */
        public void setDescription(String description);

        /**
         * Sets the description for the tab. The description can be used to
         * briefly describe the state of the tab to the user, and is typically
         * shown as a tooltip when hovering over the tab.
         *
         * @see ContentMode
         *
         * @param description
         *            the new description string for the tab
         * @param mode
         *            content mode used to display the description
         *
         * @since 8.1
         */
        public void setDescription(String description, ContentMode mode);

        /**
         * Sets an error indicator to be shown in the tab. This can be used e.g.
         * to communicate to the user that there is a problem in the contents of
         * the tab.
         *
         * @see AbstractComponent#setComponentError(ErrorMessage)
         *
         * @param componentError
         *            error message or null for none
         */
        public void setComponentError(ErrorMessage componentError);

        /**
         * Gets the current error message shown for the tab.
         *
         * TODO currently not sent to the client
         *
         * @see AbstractComponent#setComponentError(ErrorMessage)
         */
        public ErrorMessage getComponentError();

        /**
         * Get the component related to the Tab.
         */
        public Component getComponent();

        /**
         * Sets a style name for the tab. The style name will be rendered as a
         * HTML class name, which can be used in a CSS definition.
         *
         * <pre>
         * Tab tab = tabsheet.addTab(tabContent, &quot;Tab text&quot;);
         * tab.setStyleName(&quot;mystyle&quot;);
         * </pre>
         * <p>
         * The used style name will be prefixed with "
         * {@code v-tabsheet-tabitemcell-}". For example, if you give a tab the
         * style "{@code mystyle}", the tab will get a "
         * {@code v-tabsheet-tabitemcell-mystyle}" style. You could then style
         * the component with:
         * </p>
         *
         * <pre>
         * .v-tabsheet-tabitemcell-mystyle {font-style: italic;}
         * </pre>
         *
         * @param styleName
         *            the new style to be set for tab
         * @see #getStyleName()
         */
        public void setStyleName(String styleName);

        /**
         * Gets the user-defined CSS style name of the tab. Built-in style names
         * defined in Vaadin or GWT are not returned.
         *
         * @return the style name or of the tab
         * @see #setStyleName(String)
         */
        public String getStyleName();

        /**
         * Adds an unique id for component that is used in the client-side for
         * testing purposes. Keeping identifiers unique is the responsibility of
         * the programmer.
         *
         * @param id
         *            An alphanumeric id
         */
        public void setId(String id);

        /**
         * Gets currently set debug identifier.
         *
         * @return current id, null if not set
         */
        public String getId();
    }

    /**
     * TabSheet's implementation of {@link Tab} - tab metadata.
     */
    public class TabSheetTabImpl implements Tab {

        private final TabState tabState;

        private Focusable defaultFocus;

        private ErrorMessage componentError;

        public TabSheetTabImpl(String key, String caption, Resource icon) {
            tabState = new TabState();

            if (caption == null) {
                caption = "";
            }

            tabState.key = key;
            tabState.caption = caption;

            setIcon(icon);
        }

        /**
         * Returns the tab caption. Can never be null.
         */

        @Override
        public String getCaption() {
            return tabState.caption;
        }

        @Override
        public void setCaption(String caption) {
            tabState.caption = caption;
            markAsDirty();
        }

        @Override
        public Resource getIcon() {
            return getResource(ComponentConstants.ICON_RESOURCE + tabState.key);
        }

        @Override
        public void setIcon(Resource icon) {
            // this might not be ideal (resetting icon altText), but matches
            // previous semantics
            setIcon(icon, "");
        }

        @Override
        public String getIconAlternateText() {
            return tabState.iconAltText;
        }

        @Override
        public void setIconAlternateText(String iconAltText) {
            tabState.iconAltText = iconAltText;
            markAsDirty();
        }

        @Override
        public void setDefaultFocusComponent(Focusable defaultFocus) {
            this.defaultFocus = defaultFocus;
        }

        @Override
        public Focusable getDefaultFocusComponent() {
            return defaultFocus;
        }

        @Override
        public boolean isEnabled() {
            return tabState.enabled;
        }

        @Override
        public void setEnabled(boolean enabled) {
            tabState.enabled = enabled;

            if (updateSelection()) {
                fireSelectedTabChange(false);
            }
            markAsDirty();
        }

        @Override
        public boolean isVisible() {
            return tabState.visible;
        }

        @Override
        public void setVisible(boolean visible) {
            tabState.visible = visible;

            if (updateSelection()) {
                fireSelectedTabChange(false);
            }
            markAsDirty();
        }

        @Override
        public boolean isClosable() {
            return tabState.closable;
        }

        @Override
        public void setClosable(boolean closable) {
            tabState.closable = closable;

            markAsDirty();
        }

        @Override
        public String getDescription() {
            return tabState.description;
        }

        @Override
        public void setDescription(String description) {
            setDescription(description, ContentMode.PREFORMATTED);
        }

        @Override
        public void setDescription(String description, ContentMode mode) {
            tabState.description = description;
            tabState.descriptionContentMode = mode;
            markAsDirty();
        }

        @Override
        public ErrorMessage getComponentError() {
            return componentError;
        }

        @Override
        public void setComponentError(ErrorMessage componentError) {
            this.componentError = componentError;

            if (componentError != null) {
                tabState.componentError = componentError
                        .getFormattedHtmlMessage();
                tabState.componentErrorLevel = componentError.getErrorLevel();
            } else {
                tabState.componentError = null;
                tabState.componentErrorLevel = null;
            }

            markAsDirty();
        }

        @Override
        public Component getComponent() {
            for (Map.Entry<Component, Tab> entry : tabs.entrySet()) {
                if (equals(entry.getValue())) {
                    return entry.getKey();
                }
            }
            return null;
        }

        @Override
        public void setStyleName(String styleName) {
            tabState.styleName = styleName;

            markAsDirty();
        }

        @Override
        public String getStyleName() {
            return tabState.styleName;
        }

        protected TabState getTabState() {
            return tabState;
        }

        @Override
        public void setId(String id) {
            tabState.id = id;
            markAsDirty();

        }

        @Override
        public String getId() {
            return tabState.id;
        }

        @Override
        public void setIcon(Resource icon, String iconAltText) {
            setResource(ComponentConstants.ICON_RESOURCE + tabState.key, icon);
            tabState.iconAltText = iconAltText;
        }
    }

    /**
     * CloseHandler is used to process tab closing events. Default behavior is
     * to remove the tab from the TabSheet.
     *
     * @author Jouni Koivuviita / Vaadin Ltd.
     * @since 6.2.0
     *
     */
    @FunctionalInterface
    public interface CloseHandler extends Serializable {

        /**
         * Called when a user has pressed the close icon of a tab in the client
         * side widget.
         *
         * @param tabsheet
         *            the TabSheet to which the tab belongs to
         * @param tabContent
         *            the component that corresponds to the tab whose close
         *            button was clicked
         */
        void onTabClose(final TabSheet tabsheet, final Component tabContent);
    }

    /**
     * Provide a custom {@link CloseHandler} for this TabSheet if you wish to
     * perform some additional tasks when a user clicks on a tabs close button,
     * e.g. show a confirmation dialogue before removing the tab.
     *
     * To remove the tab, if you provide your own close handler, you must call
     * {@link #removeComponent(Component)} yourself.
     *
     * The default CloseHandler for TabSheet will only remove the tab.
     *
     * @param handler
     */
    public void setCloseHandler(CloseHandler handler) {
        closeHandler = handler;
    }

    /**
     * Sets the position of the tab.
     *
     * @param tab
     *            The tab
     * @param position
     *            The new position of the tab
     */
    public void setTabPosition(Tab tab, int position) {
        int oldPosition = getTabPosition(tab);
        components.remove(oldPosition);
        components.add(position, tab.getComponent());

        getState().tabs.remove(oldPosition);
        getState().tabs.add(position, ((TabSheetTabImpl) tab).getTabState());
    }

    /**
     * Gets the position of the tab.
     *
     * @param tab
     *            The tab
     * @return
     */
    public int getTabPosition(Tab tab) {
        return components.indexOf(tab.getComponent());
    }

    @Override
    public void focus() {
        super.focus();
    }

    @Override
    public int getTabIndex() {
        return getState(false).tabIndex;
    }

    @Override
    public void setTabIndex(int tabIndex) {
        getState().tabIndex = tabIndex;
    }

    @Override
    public Registration addBlurListener(BlurListener listener) {
        return addListener(BlurEvent.EVENT_ID, BlurEvent.class, listener,
                BlurListener.blurMethod);
    }

    @Override
    public Registration addFocusListener(FocusListener listener) {
        return addListener(FocusEvent.EVENT_ID, FocusEvent.class, listener,
                FocusListener.focusMethod);
    }

    @Override
    public boolean isRendered(Component childComponent) {
        return childComponent == getSelectedTab();
    }

    /**
     * Copies properties from one Tab to another.
     *
     * @param from
     *            The tab whose data to copy.
     * @param to
     *            The tab to which copy the data.
     */
    private static void copyTabMetadata(Tab from, Tab to) {
        to.setCaption(from.getCaption());
        to.setIcon(from.getIcon(), from.getIconAlternateText());
        to.setDescription(from.getDescription());
        to.setVisible(from.isVisible());
        to.setEnabled(from.isEnabled());
        to.setClosable(from.isClosable());
        to.setStyleName(from.getStyleName());
        to.setComponentError(from.getComponentError());
    }

    @Override
    protected TabsheetState getState(boolean markAsDirty) {
        return (TabsheetState) super.getState(markAsDirty);
    }

    @Override
    protected TabsheetState getState() {
        return (TabsheetState) super.getState();
    }

    /*
     * (non-Javadoc)
     *
     * @see com.vaadin.ui.AbstractComponent#readDesign(org.jsoup.nodes .Element,
     * com.vaadin.ui.declarative.DesignContext)
     */
    @Override
    public void readDesign(Element design, DesignContext designContext) {
        super.readDesign(design, designContext);
        // create new tabs
        for (Element tab : design.children()) {
            if (!tab.tagName().equals("tab")) {
                throw new DesignException(
                        "Invalid tag name for tabsheet tab " + tab.tagName());
            }
            readTabFromDesign(tab, designContext);
        }
    }

    /**
     * Reads the given tab element from design
     *
     * @since 7.4
     *
     * @param tabElement
     *            the element to be read
     * @param designContext
     *            the design context
     */
    private void readTabFromDesign(Element tabElement,
            DesignContext designContext) {
        Attributes attr = tabElement.attributes();
        if (tabElement.children().size() != 1) {
            throw new DesignException(
                    "A tab must have exactly one child element");
        }
        // create the component that is in tab content
        Element content = tabElement.child(0);
        Component child = designContext.readDesign(content);
        Tab tab = this.addTab(child);
        if (attr.hasKey("visible")) {
            tab.setVisible(DesignAttributeHandler.readAttribute("visible", attr,
                    Boolean.class));
        }
        if (attr.hasKey("closable")) {
            tab.setClosable(DesignAttributeHandler.readAttribute("closable",
                    attr, Boolean.class));
        }
        if (attr.hasKey("caption")) {
            tab.setCaption(DesignAttributeHandler.readAttribute("caption", attr,
                    String.class));
        }
        if (attr.hasKey("enabled")) {
            tab.setEnabled(DesignAttributeHandler.readAttribute("enabled", attr,
                    Boolean.class));
        }
        if (attr.hasKey("icon")) {
            tab.setIcon(DesignAttributeHandler.readAttribute("icon", attr,
                    Resource.class));
        }
        if (attr.hasKey("icon-alt")) {
            tab.setIconAlternateText(DesignAttributeHandler
                    .readAttribute("icon-alt", attr, String.class));
        }
        if (attr.hasKey("description")) {
            tab.setDescription(DesignAttributeHandler
                    .readAttribute("description", attr, String.class));
        }
        if (attr.hasKey("style-name")) {
            tab.setStyleName(DesignAttributeHandler.readAttribute("style-name",
                    attr, String.class));
        }
        if (attr.hasKey("id")) {
            tab.setId(DesignAttributeHandler.readAttribute("id", attr,
                    String.class));
        }
        if (attr.hasKey("selected")) {
            boolean selected = DesignAttributeHandler.readAttribute("selected",
                    attr, Boolean.class);
            if (selected) {
                this.setSelectedTab(tab.getComponent(), false);
            }
        }
    }

    /**
     * Writes the given tab to design
     *
     * @since 7.4
     * @param design
     *            the design node for tabsheet
     * @param designContext
     *            the design context
     * @param tab
     *            the tab to be written
     */
    private void writeTabToDesign(Element design, DesignContext designContext,
            Tab tab) {
        // get default tab instance
        Tab def = new TabSheetTabImpl(null, null, null);
        // create element for tab
        Element tabElement = design.appendElement("tab");
        // add tab content
        tabElement.appendChild(designContext.createElement(tab.getComponent()));
        Attributes attr = tabElement.attributes();
        // write attributes
        DesignAttributeHandler.writeAttribute("visible", attr, tab.isVisible(),
                def.isVisible(), Boolean.class, designContext);
        DesignAttributeHandler.writeAttribute("closable", attr,
                tab.isClosable(), def.isClosable(), Boolean.class,
                designContext);
        DesignAttributeHandler.writeAttribute("caption", attr, tab.getCaption(),
                def.getCaption(), String.class, designContext);
        DesignAttributeHandler.writeAttribute("enabled", attr, tab.isEnabled(),
                def.isEnabled(), Boolean.class, designContext);
        DesignAttributeHandler.writeAttribute("icon", attr, tab.getIcon(),
                def.getIcon(), Resource.class, designContext);
        DesignAttributeHandler.writeAttribute("icon-alt", attr,
                tab.getIconAlternateText(), def.getIconAlternateText(),
                String.class, designContext);
        DesignAttributeHandler.writeAttribute("description", attr,
                tab.getDescription(), def.getDescription(), String.class,
                designContext);
        DesignAttributeHandler.writeAttribute("style-name", attr,
                tab.getStyleName(), def.getStyleName(), String.class,
                designContext);
        DesignAttributeHandler.writeAttribute("id", attr, tab.getId(),
                def.getId(), String.class, designContext);
        if (getSelectedTab() != null
                && getSelectedTab().equals(tab.getComponent())) {
            // use write attribute to get consistent handling for boolean
            DesignAttributeHandler.writeAttribute("selected", attr, true, false,
                    boolean.class, designContext);
        }
    }

    /*
     * (non-Javadoc)
     *
     * @see com.vaadin.ui.AbstractComponent#getCustomAttributes()
     */
    @Override
    protected Collection<String> getCustomAttributes() {
        Collection<String> attributes = super.getCustomAttributes();
        // no need to list tab attributes since they are considered internal
        return attributes;
    }

    /*
     * (non-Javadoc)
     *
     * @see com.vaadin.ui.AbstractComponent#writeDesign(org.jsoup.nodes.Element
     * , com.vaadin.ui.declarative.DesignContext)
     */
    @Override
    public void writeDesign(Element design, DesignContext designContext) {
        super.writeDesign(design, designContext);
        TabSheet def = designContext.getDefaultInstance(this);
        Attributes attr = design.attributes();

        // write tabs
        if (!designContext.shouldWriteChildren(this, def)) {
            return;
        }
        for (Component component : this) {
            Tab tab = this.getTab(component);
            writeTabToDesign(design, designContext, tab);
        }
    }

    /**
     * Sets whether HTML is allowed in the tab captions.
     * <p>
     * If set to true, the captions are rendered in the browser as HTML and the
     * developer is responsible for ensuring no harmful HTML is used. If set to
     * false, the content is rendered in the browser as plain text.
     * <p>
     * The default is false, i.e. render tab captions as plain text
     *
     * @param tabCaptionsAsHtml
     *            true if the tab captions are rendered as HTML, false if
     *            rendered as plain text
     * @since 7.4
     */
    public void setTabCaptionsAsHtml(boolean tabCaptionsAsHtml) {
        getState().tabCaptionsAsHtml = tabCaptionsAsHtml;
    }

    /**
     * Checks whether HTML is allowed in the tab captions.
     * <p>
     * The default is false, i.e. render tab captions as plain text
     *
     * @return true if the tab captions are rendered as HTML, false if rendered
     *         as plain text
     * @since 7.4
     */
    public boolean isTabCaptionsAsHtml() {
        return getState(false).tabCaptionsAsHtml;
    }
}