/*

 * Copyright (c) 2007-2008 Nokia Corporation and/or its subsidiary(-ies).

 * All rights reserved.

 * This component and the accompanying materials are made available

 * under the terms of the License "Eclipse Public License v1.0"

 * which accompanies this distribution, and is available

 * at the URL "http://www.eclipse.org/legal/epl-v10.html".

 *

 * Initial Contributors:

 * Nokia Corporation - initial contribution.

 *

 * Contributors:

 *

 * Description:  

 *

 */

package com.nokia.helium.metadata.fmpp;

import java.util.List;

import javax.persistence.EntityManager;

import javax.persistence.Query;

import org.apache.log4j.Logger;

import freemarker.template.SimpleNumber;

import freemarker.template.SimpleScalar;

import freemarker.template.TemplateModel;

import freemarker.template.TemplateSequenceModel;

class ORMSequenceModel implements TemplateSequenceModel {

    public static final int PAGE_SIZE = 750;

    private static Logger log = Logger.getLogger(ORMSequenceModel.class);

    private Query query;

    private int currentPage;

    private List<Object> data;

    private int size;

    private EntityManager entityManager;

    private String queryString;    

    @SuppressWarnings("unchecked")

    public ORMSequenceModel(EntityManager entityManager, String queryString) {

        log.debug("ORMSequenceModel: " + queryString);

        this.queryString = queryString;

        this.entityManager = entityManager;

        // Caching the full size

        int page = 0;

        do {

            query = entityManager.createQuery(queryString);

            query.setFirstResult(PAGE_SIZE * page);

            query.setMaxResults(PAGE_SIZE);

            data = query.getResultList();

            // incrementing the size and page.

            size += data.size();

            page++;

        } while (data.size() == PAGE_SIZE);

        // First query

        currentPage = 0;

        query = entityManager.createQuery(queryString);

        query.setFirstResult(currentPage);

        query.setMaxResults(PAGE_SIZE);

        data = query.getResultList();

    }

    /**

     * {@inheritDoc}

     */

    public int size() {

        return size;

    }

    /**

     * {@inheritDoc}

     */

    @SuppressWarnings("unchecked")

    public synchronized TemplateModel get(int index) {

        // Calculating the requested page

        int page = index / PAGE_SIZE;

        // Shall we load a new page

        if (page != currentPage) {

            query = entityManager.createQuery(queryString);

            query.setFirstResult(page * PAGE_SIZE);

            query.setMaxResults(PAGE_SIZE);

            data = query.getResultList();

            currentPage = page;

            if (data.size() == 0) {

                return null;

            }

        }

        // Are we out of bound.

        if (data.size() <= index % PAGE_SIZE) {

            return null;

        }

        // Let's get the object.

        Object obj = data.get(index % PAGE_SIZE);

        if (obj instanceof String) {

            return new SimpleScalar((String)obj);

        } else if (obj instanceof Number) {

            return new SimpleNumber((Number)obj);

        } else if (obj == null) {

            return null;

        } else {

            return new ORMObjectModel(obj);

        }

    }

}