Copyright (c) 2005, 2015 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2005, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.internal.preferences;

import java.util.Hashtable;
import org.eclipse.core.internal.runtime.RuntimeLog;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.core.runtime.preferences.IPreferencesService;
import org.eclipse.osgi.service.environment.EnvironmentInfo;
import org.osgi.framework.*;
import org.osgi.util.tracker.ServiceTracker;
import org.osgi.util.tracker.ServiceTrackerCustomizer;

The Preferences bundle activator.
/**
 * The Preferences bundle activator.
 */
public class Activator implements BundleActivator, ServiceTrackerCustomizer<Object, Object> {

	public static final String PI_PREFERENCES = "org.eclipse.equinox.preferences"; //$NON-NLS-1$

	
Eclipse property. Set to false to avoid registering JobManager
as an OSGi service.
/**
	 * Eclipse property. Set to <code>false</code> to avoid registering JobManager
	 * as an OSGi service.
	 */
	private static final String PROP_REGISTER_PERF_SERVICE = "eclipse.service.pref"; //$NON-NLS-1$
	// the system property
	private static final String PROP_CUSTOMIZATION = "eclipse.pluginCustomization"; //$NON-NLS-1$

	
Track the registry service - only register preference service if the registry is
available
/**
	 * Track the registry service - only register preference service if the registry is
	 * available
	 */
	private ServiceTracker<?, ?> registryServiceTracker;

	
The bundle associated this plug-in
/**
	 * The bundle associated this plug-in
	 */
	private static BundleContext bundleContext;

	
This plugin provides a Preferences service.
/**
	 * This plugin provides a Preferences service.
	 */
	private ServiceRegistration<IPreferencesService> preferencesService;

	
This plugin provides the OSGi Preferences service.
/**
	 * This plugin provides the OSGi Preferences service.
	 */
	private ServiceRegistration<org.osgi.service.prefs.PreferencesService> osgiPreferencesService;


	@Override
	public void start(BundleContext context) throws Exception {
		bundleContext = context;
		// Open the services first before processing the command-line args, order is important! (Bug 150288)
		PreferencesOSGiUtils.getDefault().openServices();
		processCommandLine();

		boolean shouldRegister = !"false".equalsIgnoreCase(context.getProperty(PROP_REGISTER_PERF_SERVICE)); //$NON-NLS-1$
		if (shouldRegister) {
			preferencesService = bundleContext.registerService(IPreferencesService.class, PreferencesService.getDefault(), new Hashtable<String, Object>());
			osgiPreferencesService = bundleContext.registerService(org.osgi.service.prefs.PreferencesService.class, new OSGiPreferencesServiceManager(bundleContext), null);
		}
		// use the string for the class name here in case the registry isn't around
		registryServiceTracker = new ServiceTracker<>(bundleContext, "org.eclipse.core.runtime.IExtensionRegistry", this); //$NON-NLS-1$
		registryServiceTracker.open();
	}


	@Override
	public void stop(BundleContext context) throws Exception {
		PreferencesOSGiUtils.getDefault().closeServices();
		if (registryServiceTracker != null) {
			registryServiceTracker.close();
			registryServiceTracker = null;
		}
		if (preferencesService != null) {
			preferencesService.unregister();
			preferencesService = null;
		}
		if (osgiPreferencesService != null) {
			osgiPreferencesService.unregister();
			osgiPreferencesService = null;
		}
		bundleContext = null;
	}

	static BundleContext getContext() {
		return bundleContext;
	}


	@Override
	public synchronized Object addingService(ServiceReference<Object> reference) {
		Object service = bundleContext.getService(reference);
		// this check is important as it avoids early loading of PreferenceServiceRegistryHelper and allows
		// this bundle to operate with out necessarily resolving against the registry
		if (service != null) {
			try {
				Object helper = new PreferenceServiceRegistryHelper(PreferencesService.getDefault(), service);
				PreferencesService.getDefault().setRegistryHelper(helper);
			} catch (Exception e) {
				RuntimeLog.log(new Status(IStatus.ERROR, PI_PREFERENCES, 0, PrefsMessages.noRegistry, e));
			} catch (NoClassDefFoundError error) {
				// Normally this catch would not be needed since we should never see the
				// IExtensionRegistry service without resolving against registry.
				// However, the check is very lenient with split packages and this can happen when
				// the preferences bundle is already resolved at the time the registry bundle is installed.
				// For this case we ignore the error. When refreshed the bundle will be rewired correctly.
				// null is returned because we don't want to track this particular service reference.
				return null;
			}
		}
		//return the registry service so we track it
		return service;
	}


	@Override
	public void modifiedService(ServiceReference<Object> reference, Object service) {
		// nothing to do
	}


	@Override
	public synchronized void removedService(ServiceReference<Object> reference, Object service) {
		PreferencesService.getDefault().setRegistryHelper(null);
		bundleContext.ungetService(reference);
	}

	
Look for the plug-in customization file in the system properties and command-line args.
/**
	 * Look for the plug-in customization file in the system properties and command-line args.
	 */
	private void processCommandLine() {
		// check the value of the system property first because its quicker.
		// if it exists, then set it otherwise look at the command-line arguments.
		String value = bundleContext.getProperty(PROP_CUSTOMIZATION);
		if (value != null) {
			DefaultPreferences.pluginCustomizationFile = value;
			return;
		}

		ServiceTracker<?, EnvironmentInfo> environmentTracker = new ServiceTracker<>(bundleContext, EnvironmentInfo.class, null);
		environmentTracker.open();
		EnvironmentInfo environmentInfo = environmentTracker.getService();
		environmentTracker.close();
		if (environmentInfo == null)
			return;
		String[] args = environmentInfo.getNonFrameworkArgs();
		if (args == null || args.length == 0)
			return;

		for (int i = 0; i < args.length; i++) {
			if (args[i].equalsIgnoreCase(IPreferencesConstants.PLUGIN_CUSTOMIZATION)) {
				if (args.length > i + 1) // make sure the file name is actually there
					DefaultPreferences.pluginCustomizationFile = args[i + 1];
				break; // only interested in this one
			}
		}
	}
}