Application: gvSIG desktop

/* gvSIG. Geographic Information System of the Valencian Government

 *

 * Copyright (C) 2007-2008 Infrastructures and Transports Department

 * of the Valencian Gobernment (CIT)

 * 

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 * 

 * 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 General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, 

 * MA  02110-1301, USA.

 * 

 */

/*

 * AUTHORS (In addition to CIT):

 * 2008 {DiSiD Technologies}  {Create a JTable TableModel for a FeatureCollection}

 */

package org.gvsig.fmap.data.feature.paging;

import java.util.Iterator;

import org.gvsig.fmap.data.exceptions.ReadException;

import org.gvsig.fmap.data.feature.*;

/**

 * Helper class to access the values of a FeatureCollection by position. Handles

 * pagination automatically to avoid filling the memory in case of big

 * collections.

 * 

 * TODO: read values in the background when the returned value is near the end

 * of the page, instead of loading a page on demand.

 * 

 * @author <a href="mailto:cordin@disid.com">C?sar Ordi?ana</a>

 */

public class FeaturePagingHelperImpl implements

        FeaturePagingHelper {

    private FeatureQuery query;

    private FeatureCollection featureCollection;

    private FeatureStore featureStore;

    private int maxPageSize;

    private int numPages;

    private int currentPage = -1;

    private Feature[] values;

    /**

     * Constructs a FeatureCollectionPagingHelper from a FeatureCollection.

     * 

     * @param featureCollection

     *            to extract data from

     * @throws ReadException

     */

    public FeaturePagingHelperImpl(FeatureStore featureStore)

            throws ReadException {

        this(featureStore, DEFAULT_PAGE_SIZE);

    }

    /**

     * Constructs a FeatureCollectionPagingHelper from a FeatureCollection.

     * 

     * @param featureCollection

     *            to extract data from

     * @param pageSize

     *            the number of elements per page data

     * @throws ReadException

     */

    public FeaturePagingHelperImpl(FeatureStore featureStore,

            int pageSize) throws ReadException {

        this(featureStore, null, pageSize);

    }

    /**

     * Constructs a FeatureCollectionPagingHelper from a FeatureCollection.

     * 

     * @param featureCollection

     *            to extract data from

     * @throws ReadException

     */

    public FeaturePagingHelperImpl(FeatureStore featureStore,

            FeatureQuery featureQuery) throws ReadException {

        this(featureStore, featureQuery, DEFAULT_PAGE_SIZE);

    }

    /**

     * Constructs a FeatureCollectionPagingHelper from a FeatureCollection.

     * 

     * @param featureCollection

     *            to extract data from

     * @param pageSize

     *            the number of elements per page data

     * @throws ReadException

     */

    public FeaturePagingHelperImpl(FeatureStore featureStore,

            FeatureQuery featureQuery,

            int pageSize) throws ReadException {

        this.maxPageSize = pageSize;

        this.featureStore = featureStore;

        this.query = featureQuery;

        loadFeatureCollection();

        setNumPages(calculateNumPages());

    }

    public int getMaxPageSize() {

        return maxPageSize;

    }

    public void setMaxPageSize(int pageSize) {

        this.maxPageSize = pageSize;

        reloadCurrentPage();

    }

    public int getNumPages() {

        return numPages;

    }

    /**

     * Sets the number of pages.

     */

    private void setNumPages(int numPages) {

        this.numPages = numPages;

    }

    public int getCurrentPage() {

        return currentPage;

    }

    public void setCurrentPage(int page) {

        // TODO: change this message for a logging one through SLF4J

        System.out.println("Current page: " + page);

        if (page < 0) {

            throw new IndexOutOfBoundsException(

                    "Error, unable to set helper current page to a "

                            + "negative value: " + page);

        }

        if (page >= getNumPages()) {

            throw new IndexOutOfBoundsException(

                    "Error, unable to set helper current page to the page num. "

                            + page

                            + ", as the Collection only has " + getNumPages()

                            + " pages of Features");

        }

        currentPage = page;

        loadCurrentPageData();

    }

    public int getTotalSize() {

        return getFeatureCollection().size();

    }

    public Feature getFeatureAt(int index) {

        // Check if we have currently loaded the viewed page data,

        // or we need to load a new one

        int pageForIndex = (int) Math.floor(index / getMaxPageSize());

        if (pageForIndex != getCurrentPage()) {

            setCurrentPage(pageForIndex);

        }

        int positionForIndex = index - (getCurrentPage() * getMaxPageSize());

        return values[positionForIndex];

    }

    public Feature[] getCurrentPageFeatures() {

        return values;

    }

    public FeatureCollection getFeatureCollection() {

        return featureCollection;

    }

    public void reloadCurrentPage() {

        setNumPages(calculateNumPages());

        if (currentPage > -1) {

            loadCurrentPageData();

        }

    }

    public void reload() throws ReadException {

        loadFeatureCollection();

        reloadCurrentPage();

    }

    public FeatureStore getFeatureStore() {

        return featureStore;

    }

    public FeatureQuery getFeatureQuery() {

        return query;

    }

    /**

     * Calculates the number of pages.

     */

    private int calculateNumPages() {

        return ((int) Math.floor(getTotalSize() / getMaxPageSize())) + 1;

    }

    /**

     * Loads all the Features of the current page.

     */

    private void loadCurrentPageData() {

        int currentPage = getCurrentPage();

        int currentPageSize;

        if (currentPage < (numPages - 1)) {

            currentPageSize = getMaxPageSize();

        } else {

            currentPageSize = getTotalSize() - (currentPage * getMaxPageSize());

        }

        values = new Feature[currentPageSize];

        int firstPosition = currentPage * getMaxPageSize();

        Iterator iter = getFeatureCollection().iterator(firstPosition);

        int i = 0;

        while (iter.hasNext() && i < currentPageSize) {

            values[i] = (Feature) iter.next();

            i++;

        }

    }

    private void loadFeatureCollection() throws ReadException {

        if (featureCollection != null) {

            featureCollection.dispose();

        }

        if (query == null) {

            featureCollection = getFeatureStore().getFeatureCollection();

        } else {

            featureCollection = getFeatureStore().getFeatureCollection(query);

        }

    }

}