content: /*
   * This library is part of OpenCms -
   * the Open Source Content Management System
   *
   * Copyright (C) Alkacon Software (https://www.alkacon.com)
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   * Lesser General Public License for more details.
   *
   * For further information about Alkacon Software, please see the
   * company website: https://www.alkacon.com
   *
   * For further information about OpenCms, please see the
   * project website: https://www.opencms.org
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  
  package org.opencms.ade.galleries.client.ui;
  
  import org.opencms.ade.galleries.shared.CmsGallerySearchBean;
  import org.opencms.ade.galleries.shared.CmsResultItemBean;
  import org.opencms.ade.galleries.shared.I_CmsGalleryProviderConstants.SortParams;
  
  import java.util.List;
  
  import com.google.gwt.core.client.Scheduler;
  import com.google.gwt.core.client.Scheduler.ScheduledCommand;
  import com.google.gwt.event.dom.client.ScrollEvent;
  import com.google.gwt.event.dom.client.ScrollHandler;
  import com.google.gwt.user.client.ui.ScrollPanel;
  
  /**
   * Scroll handler class which loads more items in the front of the search result list when the user scrolls to the
   * top.<p>
   */
  public class CmsResultsBackwardsScrollHandler implements ScrollHandler {
  
      /** The scroll threshold in pixels. */
      public static final int SCROLL_THRESHOLD = 50;
  
      /** Flag used to temporarily disable the scroll handler. */
      protected boolean m_enabled = true;
  
      /** The index of the first shown page. */
      protected int m_firstShownPage;
  
      /** The number of results per page. */
      protected int m_pageSize;
  
      /** The list of search result beans. */
      protected List<CmsResultItemBean> m_resultBeans;
  
      /** The search results tab. */
      protected CmsResultsTab m_resultsTab;
  
      /** The search bean. */
      protected CmsGallerySearchBean m_searchBean;
  
      /**
       * Creates a new handler instance for a given results tab.<p>
       *
       * @param resultsTab the results tab for which to create the handler
       */
      public CmsResultsBackwardsScrollHandler(CmsResultsTab resultsTab) {
  
          m_resultsTab = resultsTab;
      }
  
      /**
       * Checks whether more items can be loaded at the front of the list.<p>
       *
       * @return true if more items can be loaded at the front of the list
       */
      public boolean hasMore() {
  
          return m_firstShownPage > 1;
      }
  
      /**
       * @see com.google.gwt.event.dom.client.ScrollHandler#onScroll(com.google.gwt.event.dom.client.ScrollEvent)
       */
      public void onScroll(ScrollEvent event) {
  
          if (m_searchBean == null) {
              return;
          }
          if (m_resultBeans == null) {
              return;
          }
          if (!m_enabled) {
              return;
          }
          final ScrollPanel scrollPanel = (ScrollPanel)event.getSource();
          final int scrollPos = scrollPanel.getVerticalScrollPosition();
          if ((scrollPos <= SCROLL_THRESHOLD) && hasMore()) {
              m_enabled = false;
              Scheduler.get().scheduleDeferred(new ScheduledCommand() {
  
                  /**
                   * @see com.google.gwt.core.client.Scheduler.ScheduledCommand#execute()
                   */
                  public void execute() {
  
                      m_enabled = true;
                      m_resultsTab.getList().setVerticalScrollPosition(50);
                  }
              });
              loadPreviousPage();
          }
  
      }
  
      /**
       * Updates the handler with a new search bean.<p>
       *
       * @param searchBean the search bean
       */
      public void updateSearchBean(CmsGallerySearchBean searchBean) {
  
          m_searchBean = searchBean;
          if (searchBean != null) {
              m_pageSize = searchBean.getMatchesPerPage();
              int lastPage = searchBean.getLastPage();
              // we don't just store the search bean because it gets reused for multiple searches
              // and so the result list may change.
              m_resultBeans = searchBean.getResults();
              if (lastPage != -1) {
                  loadPage(lastPage);
                  m_firstShownPage = lastPage;
                  if (lastPage > 1) {
                      loadPage(lastPage - 1);
                      m_firstShownPage = lastPage - 1;
                  }
              }
          } else {
              m_resultBeans = null;
          }
      }
  
      /**
       * Loads a page with a given index.<p>
       *
       * @param pageNum the index of the page to load
       */
      protected void loadPage(int pageNum) {
  
          int start = (pageNum - 1) * m_pageSize;
          List<CmsResultItemBean> results = m_resultBeans;
          int end = start + m_pageSize;
          if (end > results.size()) {
              end = results.size();
          }
          List<CmsResultItemBean> page = results.subList(start, end);
          boolean showPath = SortParams.path_asc.name().equals(m_searchBean.getSortOrder())
              || SortParams.path_desc.name().equals(m_searchBean.getSortOrder());
          m_resultsTab.addContentItems(page, true, showPath);
      }
  
      /**
       * Loads the page before the first shown page.<p>
       */
      protected void loadPreviousPage() {
  
          loadPage(m_firstShownPage - 1);
          m_firstShownPage -= 1;
      }
  
  }
  