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Cayenne Object Persistence Framework
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package org.apache.cayenne.project;

import java.util.Collection;

import org.apache.cayenne.conf.Configuration;

/**
 * @since 1.1
 * @author Andrus Adamchik
 */
// TODO: andrus, 7/16/2006 - upgrade handler is rather primitive and relies on individual
// loaders to be able to read older versions and convert them to the latest one in memory.
// So this handler simply checks the version to trigger the update in the calling UI, and
// saves what's been already loaded.
abstract class ApplicationUpgradeHandler {

    private static final ApplicationUpgradeHandler sharedInstance = new UpgradeHandler_2_0();

    static ApplicationUpgradeHandler sharedHandler() {
        return sharedInstance;
    }

    abstract String supportedVersion();

    abstract int checkForUpgrades(Configuration project, Collection appendMessages);

    abstract void performUpgrade(ApplicationProject project) throws ProjectException;

    int compareVersion(String version) {
        double supported = decodeVersion(supportedVersion());
        double newVersion = decodeVersion(version);
        return supported < newVersion ? -1 : (supported == newVersion) ? 0 : 1;
    }

    static double decodeVersion(String version) {
        if (version == null || version.trim().length() == 0) {
            return 0;
        }

        // leave the first dot, and treat remaining as a fraction
        // remove all non digit chars
        StringBuffer buffer = new StringBuffer(version.length());
        boolean dotProcessed = false;
        for (int i = 0; i < version.length(); i++) {
            char nextChar = version.charAt(i);
            if (nextChar == '.' && !dotProcessed) {
                dotProcessed = true;
                buffer.append('.');
            }
            else if (Character.isDigit(nextChar)) {
                buffer.append(nextChar);
            }
        }

        return Double.parseDouble(buffer.toString());
    }

    static class UpgradeHandler_2_0 extends UpgradeHandler_1_1 {

        final static String _1_2_PACKAGE_PREFIX = "org.objectstyle.cayenne.";
        final static String _2_0_PACKAGE_PREFIX = "org.apache.cayenne.";

        String supportedVersion() {
            return "2.0";
        }
    }

    static class UpgradeHandler_1_1 extends ApplicationUpgradeHandler {

        String supportedVersion() {
            return "1.1";
        }

        void performUpgrade(ApplicationProject project) throws ProjectException {
            project.setModified(true);
            project.getConfiguration().setProjectVersion(supportedVersion());
            project.save();
        }

        int checkForUpgrades(Configuration project, Collection appendMessages) {
            String loadedVersion = project.getProjectVersion();
            int versionState = compareVersion(loadedVersion);
            if (versionState < 0) {
                String versionLabel = (loadedVersion != null) ? loadedVersion : "?";
                appendMessages.add("Newer Project Version Detected: \""
                        + versionLabel
                        + "\"");
                return Project.UPGRADE_STATUS_NEW;
            }
            else if (versionState > 0) {
                String versionLabel = (loadedVersion != null) ? loadedVersion : "?";
                appendMessages.add("Older Project Version Detected: \""
                        + versionLabel
                        + "\"");
                return Project.UPGRADE_STATUS_OLD;
            }
            else {
                return Project.UPGRADE_STATUS_CURRENT;
            }
        }
    }
}