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 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
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package org.apache.cayenne.project.upgrade;

import org.apache.cayenne.ConfigurationException;
import org.apache.cayenne.resource.Resource;

/**
 * A stateful helper object for analyzing the projects and performing upgrades.
 * 
 * @since 3.1
 */
public interface UpgradeHandler {

    /**
     * Returns the original configuration source for the project before the upgrade.
     */
    Resource getProjectSource();

    /**
     * Returns a metadata object containing information about the upgrade to be performed.
     * Users should call this method before invoking {@link #performUpgrade()}, to make
     * sure upgrade is needed and possible. Tools (like CayenneModeler) may use this
     * object to build user-friendly messages asking for user input on the upgrade.
     */
    UpgradeMetaData getUpgradeMetaData();

    /**
     * Performs an in-place project configuration upgrade, throwing a
     * {@link ConfigurationException} if the upgrade fails. Before doing the upgrade,
     * check the handler {@link UpgradeMetaData}. Upgrades will succeed only for projects
     * that have {@link UpgradeType#UPGRADE_NEEDED} or
     * {@link UpgradeType#UPGRADE_NOT_NEEDED} statuses. In the later case of course,
     * upgrade will simply be skipped.
     * 
     * @return a configuration Resource for the upgraded project. Depending on the upgrade
     *         type, it may be the same resource as the original configuration, or a
     *         totally different resource.
     */
    Resource performUpgrade() throws ConfigurationException;
}