/* ================================================================

 * Cewolf : Chart enabling Web Objects Framework

 * ================================================================

 *

 * Project Info:  http://cewolf.sourceforge.net

 * Project Lead:  Guido Laures (guido@laures.de);

 *

 * (C) Copyright 2002, by Guido Laures

 *

 * 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.

 *

 * 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 de.laures.cewolf;

import java.io.Serializable;

import java.util.Date;

import java.util.Map;

/**

 * Produces a {@link org.jfree.data.Dataset} which will be rendered 

 * as a chart 	afterwards.

 * @see org.jfree.data.Dataset

 * @author  Guido Laures

 * @since 0.1

 */

public interface DatasetProducer extends Serializable {

    /**

     * By default the the name of the JSP attribute 

     * holding the producer instance is passed to the 

     * produceDataset method as a prameter.

     */

    public static final String PRODUCER_ATTRIBUTE_NAME = "de.laures.cewolf.DatasetProducer.id";

    /**

     * Produces a {@link org.jfree.data.Dataset} object.

     * @param params additional params for the dataset production. All elements

     * of this HashMap are of type <code>java.io.Serializable</code>. This is

     * necessary to ensure the the serialization of the dataset producer into

     * the http session. To provide a producer with additional production

     * parameters the <param> tag is used (see tag library documentation).

     * It is recommended to synchronize implementations of this method to avoid

     * concurrency problems.

     * @return an object of type <code>org.jfree.data.Dataset</code>.

     * @throws DatasetProduceException if an error occured during production

     * @since 0.2

     */

    Object produceDataset(Map params) throws DatasetProduceException;

	/**

	 * This method is called by the Cewolf framework to check if a formerly

	 * produced data can be reused. If the data which had already been used

	 * for chart rendering is still valid this method should return <code>true</code>.

	 * If possible the Cewolf framework will try to reuse the rendered chart

	 * image. If this is not possible because of some circumstances (e.g. the chart

	 * had been removed from the image cache) the produceDataset method is called afterwards.

	 * Therefore there is no guarantee that the dataset production is always 

	 * avoided if this method returns <code>true</true>.

	 * @param params the production parameters of the already produced data

	 * @param since the point in time when the already produced data had been produced

	 * @return <code>true</code> if the data which had been produced with the 

	 * passed in parameters has expired since its creation, <code>false</code> 

	 * otherwise

	 * @since 0.9

	 */

	boolean hasExpired(Map params, Date since);

	/**

	 * Tis method returns a unique ID for a DatasetProducer from this class.

	 * Producers with the same ID are supposed to produce the same data when

	 * called with the same paramters.

	 * @return the unique ID for instances of this poducer class

	 * @since 0.9

	 */

	String getProducerId();

}