/*!
 * This program is free software; you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License, version 2.1 as published by the Free Software
 * Foundation.
 *
 * You should have received a copy of the GNU Lesser General Public License along with this
 * program; if not, you can obtain a copy at http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
 * or from the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * This program 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.
 *
 * Copyright (c) 2002-2013 Pentaho Corporation..  All rights reserved.
 */

package org.pentaho.reporting.engine.classic.core.function;

import org.pentaho.reporting.engine.classic.core.event.PageEventListener;
import org.pentaho.reporting.engine.classic.core.event.ReportEvent;
import org.pentaho.reporting.engine.classic.core.states.LayoutProcess;

import java.io.IOException;
import java.io.ObjectInputStream;

/**
 * Calculates the sum of a field for an entire page. The function will also reset by group if the optional
 * <code>group</code> parameter is specified. If the specified group spans a page break, the sum will be reset with the
 * new page and sum only the items for the group from the subsequent page.
 *
 * @author Thomas Morgner
 */
public class TotalPageSumFunction extends TotalGroupSumFunction implements PageEventListener {
  /**
   * holds the collection of values associated with pages and groups
   */
  private transient PageGroupValues values;

  private int pageIndex = 0;

  /**
   * Default Constructor.
   */
  public TotalPageSumFunction() {
    values = new PageGroupValues();
  }

  protected boolean isPrepareRunLevel( final ReportEvent event ) {
    if ( event.getState().isPrepareRun() && event.getState().getLevel() == LayoutProcess.LEVEL_PAGINATE ) {
      return true;
    }
    return false;
  }

  /**
   * If this is the group associated with the function, store away the final value
   *
   * @param event
   *          the event.
   */
  public void groupFinished( final ReportEvent event ) {
    if ( FunctionUtilities.isDefinedGroup( getGroup(), event ) ) {
      storeValue( event );
    }
  }

  /**
   * Handles the pageStartedEvent.
   *
   * @param event
   *          the report event.
   */
  public void pageStarted( final ReportEvent event ) {
    pageIndex++;
    clear();
  }

  /**
   * Handles the pageFinishedEvent. Stores the current page value and clears the counter. pageFinished can be hit
   * multiple times for a single page, but the stored value should be consistent.
   *
   * @param event
   *          the report event.
   */
  public void pageFinished( final ReportEvent event ) {
    storeValue( event );
  }

  public Object getValue() {
    return values.get( pageIndex, currentGroupKey );
  }

  private void storeValue( final ReportEvent event ) {
    if ( isPrepareRunLevel( event ) ) {
      values.put( pageIndex, currentGroupKey, super.getValue() );
    }
  }

  /**
   * Return a completly separated copy of this function. The copy no longer shares any changeable objects with the
   * original function.
   *
   * @return a copy of this function.
   */
  public Expression getInstance() {
    final TotalPageSumFunction function = (TotalPageSumFunction) super.getInstance();
    function.values = new PageGroupValues();
    return function;
  }

  /**
   * Helper function for the serialization.
   *
   * @param in
   *          the input stream.
   * @throws java.io.IOException
   *           if an IO error occured.
   * @throws ClassNotFoundException
   *           if a required class could not be found.
   */
  private void readObject( final ObjectInputStream in ) throws IOException, ClassNotFoundException {
    in.defaultReadObject();
    values = new PageGroupValues();
  }
}