Copyright (c) 2004, 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
    Semion Chichelnitsky (semion@il.ibm.com) - bug 208564
    Jan-Ove Weichel (janove.weichel@vogella.com) - bug 474359
/*******************************************************************************
 * Copyright (c) 2004, 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
 *     Semion Chichelnitsky (semion@il.ibm.com) - bug 208564
 *     Jan-Ove Weichel (janove.weichel@vogella.com) - bug 474359
 *******************************************************************************/
package org.eclipse.core.internal.preferences;

import java.io.*;
import java.lang.ref.WeakReference;
import java.util.*;
import java.util.Map.Entry;
import java.util.concurrent.atomic.AtomicReference;
import org.eclipse.core.internal.runtime.RuntimeLog;
import org.eclipse.core.runtime.*;
import org.eclipse.core.runtime.preferences.*;
import org.eclipse.osgi.util.NLS;
import org.osgi.framework.Bundle;
import org.osgi.framework.Constants;
import org.osgi.service.prefs.BackingStoreException;
import org.osgi.service.prefs.Preferences;

Since:
3.0/**
 * @since 3.0
 */
public class PreferencesService implements IPreferencesService {
	
The interval between passes over the preference tree to canonicalize
strings.
/**
	 * The interval between passes over the preference tree to canonicalize
	 * strings.
	 */
	private static final long STRING_SHARING_INTERVAL = 300000;
	private static final String MATCH_TYPE_PREFIX = "prefix"; //$NON-NLS-1$

	// the order of search scopes when people don't have a specific order set
	private static String[] DEFAULT_DEFAULT_LOOKUP_ORDER = new String[] { //
	InstanceScope.SCOPE, //
			ConfigurationScope.SCOPE, //
			DefaultScope.SCOPE};
	private static final char EXPORT_ROOT_PREFIX = '!';
	private static final char BUNDLE_VERSION_PREFIX = '@';
	private static final float EXPORT_VERSION = 3;
	private static final String VERSION_KEY = "file_export_version"; //$NON-NLS-1$
	private static final String EMPTY_STRING = ""; //$NON-NLS-1$

	private static PreferencesService instance;
	static final RootPreferences root = new RootPreferences();
	private static final Map<String, LookupOrder> defaultsRegistry = Collections.synchronizedMap(new HashMap<String, LookupOrder>());
	private Object registryHelper = null;
	private final Map<String, EclipsePreferences> defaultScopes = new HashMap<>();

	
The last time analysis was done to remove duplicate strings
/**
	 * The last time analysis was done to remove duplicate strings
	 */
	private long lastStringSharing = 0;

	/*
	 * Create and return an IStatus object with ERROR severity and the
	 * given message and exception.
	 */
	private static IStatus createStatusError(String message, Exception e) {
		return new Status(IStatus.ERROR, PrefsMessages.OWNER_NAME, IStatus.ERROR, message, e);
	}

	/*
	 * Return the instance.
	 */
	public static PreferencesService getDefault() {
		if (instance == null)
			instance = new PreferencesService();
		return instance;
	}

	static void log(IStatus status) {
		RuntimeLog.log(status);
	}

	PreferencesService() {
		super();
		initializeDefaultScopes();
	}


	@Override
	public void applyPreferences(IEclipsePreferences tree, IPreferenceFilter[] filters) throws CoreException {
		if (filters == null || filters.length == 0)
			return;
		try {
			internalApply(tree, filters);
			// save the preferences
			try {
				getRootNode().node(tree.absolutePath()).flush();
			} catch (BackingStoreException e) {
				throw new CoreException(createStatusError(PrefsMessages.preferences_saveProblems, e));
			}

			//this typically causes a major change to the preference tree, so force string sharing
			lastStringSharing = 0;
			shareStrings();
		} catch (BackingStoreException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_applyProblems, e));
		}
	}


	@Override
	public IStatus applyPreferences(IExportedPreferences preferences) throws CoreException {
		// TODO investigate refactoring to merge with new #apply(IEclipsePreferences, IPreferenceFilter[]) APIs
		if (preferences == null)
			throw new IllegalArgumentException();

		if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
			PrefsMessages.message("Applying exported preferences: " + ((ExportedPreferences) preferences).toDeepDebugString()); //$NON-NLS-1$

		final MultiStatus result = new MultiStatus(PrefsMessages.OWNER_NAME, IStatus.OK, PrefsMessages.preferences_applyProblems, null);

		IEclipsePreferences modifiedNode = firePreApplyEvent(preferences);

		// create a visitor to apply the given set of preferences
		IPreferenceNodeVisitor visitor = new IPreferenceNodeVisitor() {
			@Override
			public boolean visit(IEclipsePreferences node) throws BackingStoreException {
				IEclipsePreferences globalNode;
				if (node.parent() == null)
					globalNode = root;
				else
					globalNode = (IEclipsePreferences) root.node(node.absolutePath());
				ExportedPreferences epNode = (ExportedPreferences) node;

				// if this node is an export root then we need to remove
				// it from the global preferences before continuing.
				boolean removed = false;
				if (epNode.isExportRoot()) {
					if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
						PrefsMessages.message("Found export root: " + epNode.absolutePath()); //$NON-NLS-1$
					// TODO should only have to do this if any of my children have properties to set
					globalNode.removeNode();
					removed = true;
				}

				// iterate over the preferences in this node and set them
				// in the global space.
				String[] keys = epNode.properties.keys();

				// if this node was removed then we need to create a new one
				if (removed)
					globalNode = (IEclipsePreferences) root.node(node.absolutePath());

				// the list for properties to remove
				List<String> propsToRemove = new ArrayList<>();
				for (String key : globalNode.keys()) {
					propsToRemove.add(key);
				}

				if (keys.length > 0) {
					String key = null;
					for (String k : keys) {
						key = k;
						// preferences that are not in the applied node
						// will be removed
						propsToRemove.remove(key);
						// intern strings we import because some people
						// in their property change listeners use identity
						// instead of equals. See bug 20193 and 20534.
						key = key.intern();
						String value = node.get(key, null);
						if (value != null) {
							if (EclipsePreferences.DEBUG_PREFERENCE_SET)
								PrefsMessages.message("Setting: " + globalNode.absolutePath() + '/' + key + '=' + value); //$NON-NLS-1$
							globalNode.put(key, value);
						}
					}
				}

				String keyToRemove = null;
				for (Iterator<String> it = propsToRemove.iterator(); it.hasNext();) {
					keyToRemove = it.next();
					keyToRemove = keyToRemove.intern();
					if (EclipsePreferences.DEBUG_PREFERENCE_SET)
						PrefsMessages.message("Removing: " + globalNode.absolutePath() + '/' + keyToRemove); //$NON-NLS-1$
					globalNode.remove(keyToRemove);
				}

				// keep visiting children
				return true;
			}
		};

		try {
			// start by visiting the root
			modifiedNode.accept(visitor);
		} catch (BackingStoreException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_applyProblems, e));
		}

		// save the preferences
		try {
			getRootNode().node(modifiedNode.absolutePath()).flush();
		} catch (BackingStoreException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_saveProblems, e));
		}

		if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
			PrefsMessages.message("Current list of all settings: " + ((EclipsePreferences) getRootNode()).toDeepDebugString()); //$NON-NLS-1$
		//this typically causes a major change to the preference tree, so force string sharing
		lastStringSharing = 0;
		shareStrings();
		return result;
	}

	private boolean containsKeys(IEclipsePreferences aRoot) throws BackingStoreException {
		final boolean result[] = new boolean[] {false};
		IPreferenceNodeVisitor visitor = new IPreferenceNodeVisitor() {
			@Override
			public boolean visit(IEclipsePreferences node) throws BackingStoreException {
				if (node.keys().length != 0)
					result[0] = true;
				return !result[0];
			}
		};
		aRoot.accept(visitor);
		return result[0];
	}

	/*
	 * Convert the given properties file from legacy format to
	 * one which is Eclipse 3.0 compliant.
	 *
	 * Convert the plug-in version indicator entries to export roots.
	 */
	private Properties convertFromLegacy(Properties properties) {
		Properties result = new Properties();
		String prefix = IPath.SEPARATOR + InstanceScope.SCOPE + IPath.SEPARATOR;
		for (Entry<?, ?> entry : properties.entrySet()) {
			String key = (String) entry.getKey();
			String value = (String) entry.getValue();
			if (value != null) {
				int index = key.indexOf(IPath.SEPARATOR);
				if (index == -1) {
					result.put(BUNDLE_VERSION_PREFIX + key, value);
					result.put(EXPORT_ROOT_PREFIX + prefix + key, EMPTY_STRING);
				} else {
					String path = key.substring(0, index);
					key = key.substring(index + 1);
					result.put(EclipsePreferences.encodePath(prefix + path, key), value);
				}
			}
		}
		return result;
	}

	/*
	 * Convert the given properties file into a node hierarchy suitable for
	 * importing.
	 */
	private IExportedPreferences convertFromProperties(Properties properties) {
		IExportedPreferences result = ExportedPreferences.newRoot();
		for (Entry<?, ?> entry : properties.entrySet()) {
			String path = (String) entry.getKey();
			String value = (String) entry.getValue();
			if (path.charAt(0) == EXPORT_ROOT_PREFIX) {
				ExportedPreferences current = (ExportedPreferences) result.node(path.substring(1));
				current.setExportRoot();
			} else if (path.charAt(0) == BUNDLE_VERSION_PREFIX) {
				ExportedPreferences current = (ExportedPreferences) result.node(InstanceScope.SCOPE).node(path.substring(1));
				current.setVersion(value);
			} else {
				String[] decoded = EclipsePreferences.decodePath(path);
				path = decoded[0] == null ? EMPTY_STRING : decoded[0];
				ExportedPreferences current = (ExportedPreferences) result.node(path);
				String key = decoded[1];
				current.put(key, value);
			}
		}
		if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
			PrefsMessages.message("Converted preferences file to IExportedPreferences tree: " + ((ExportedPreferences) result).toDeepDebugString()); //$NON-NLS-1$
		return result;
	}

	/*
	 * excludesList is guaranteed not to be null
	 */
	private SortedProperties convertToProperties(IEclipsePreferences preferences, final String[] excludesList) throws BackingStoreException {
		final SortedProperties result = new SortedProperties();
		final int baseLength = preferences.absolutePath().length();

		// create a visitor to do the export
		IPreferenceNodeVisitor visitor = new IPreferenceNodeVisitor() {
			@Override
			public boolean visit(IEclipsePreferences node) throws BackingStoreException {
				// don't store defaults
				String absolutePath = node.absolutePath();
				String scope = getScope(absolutePath);
				if (DefaultScope.SCOPE.equals(scope))
					return false;
				String path = absolutePath.length() <= baseLength ? EMPTY_STRING : EclipsePreferences.makeRelative(absolutePath.substring(baseLength));
				// check the excludes list to see if this node should be considered
				for (String exclude : excludesList) {
					String exclusion = EclipsePreferences.makeRelative(exclude);
					if (path.startsWith(exclusion))
						return false;
				}
				boolean needToAddVersion = InstanceScope.SCOPE.equals(scope);
				// check the excludes list for each preference
				String[] keys = node.keys();
				for (String key : keys) {
					boolean ignore = false;
					for (int j = 0; !ignore && j < excludesList.length; j++)
						if (EclipsePreferences.encodePath(path, key).startsWith(EclipsePreferences.makeRelative(excludesList[j])))
							ignore = true;
					if (!ignore) {
						String value = node.get(key, null);
						if (value != null) {
							if (needToAddVersion) {
								String bundle = getBundleName(absolutePath);
								if (bundle != null) {
									String version = getBundleVersion(bundle);
									if (version != null)
										result.put(BUNDLE_VERSION_PREFIX + bundle, version);
								}
								needToAddVersion = false;
							}
							result.put(EclipsePreferences.encodePath(absolutePath, key), value);
						}
					}
				}
				return true;
			}
		};

		// start by visiting the root that we were passed in
		preferences.accept(visitor);

		// return the properties object
		return result;
	}

	
Copy key/value pairs from the source to the destination. If the key list is null
then copy all associations.
If the depth is 0, then this operation is performed only on the source node. Otherwise
it is performed on the source node's subtree.
Params:
depth – one of 0 or -1/**
	 * Copy key/value pairs from the source to the destination. If the key list is null
	 * then copy all associations.
	 *
	 * If the depth is 0, then this operation is performed only on the source node. Otherwise
	 * it is performed on the source node's subtree.
	 *
	 * @param depth one of 0 or -1
	 */
	void copyFromTo(Preferences source, Preferences destination, String[] keys, int depth) throws BackingStoreException {
		String[] keysToCopy = keys == null ? source.keys() : keys;
		for (String key : keysToCopy) {
			String value = source.get(key, null);
			if (value != null) {
				destination.put(key, value);
			}
		}
		if (depth == 0)
			return;
		String[] children = source.childrenNames();
		for (String child : children) {
			copyFromTo(source.node(child), destination.node(child), keys, depth);
		}
	}

	public WeakReference<Object> applyRuntimeDefaults(String name, WeakReference<Object> pluginReference) {
		if (registryHelper == null)
			return null;
		return ((PreferenceServiceRegistryHelper) registryHelper).applyRuntimeDefaults(name, pluginReference);
	}

	private void initializeDefaultScopes() {
		defaultScopes.put(BundleDefaultsScope.SCOPE, new BundleDefaultPreferences());
		root.addChild(BundleDefaultsScope.SCOPE, null);
		defaultScopes.put(DefaultScope.SCOPE, new DefaultPreferences());
		root.addChild(DefaultScope.SCOPE, null);
		defaultScopes.put(InstanceScope.SCOPE, new InstancePreferences());
		root.addChild(InstanceScope.SCOPE, null);
		defaultScopes.put(ConfigurationScope.SCOPE, new ConfigurationPreferences());
		root.addChild(ConfigurationScope.SCOPE, null);
	}

	public IEclipsePreferences createNode(String key) {
		IScope scope = defaultScopes.get(key);
		if (scope == null) {
			if (registryHelper == null)
				return new EclipsePreferences(root, key);
			return ((PreferenceServiceRegistryHelper) registryHelper).createNode(root, key);
		}
		return scope.create(root, key);
	}


	@Override
	public void exportPreferences(IEclipsePreferences node, IPreferenceFilter[] filters, OutputStream stream) throws CoreException {
		if (filters == null || filters.length == 0)
			return;
		try {
			internalExport(node, filters, stream);
		} catch (BackingStoreException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_exportProblems, e));
		}
	}


	@Override
	public IStatus exportPreferences(IEclipsePreferences node, OutputStream output, String[] excludesList) throws CoreException {
		// TODO investigate refactoring to merge with new #export(IEclipsePreferences, IPreferenceFilter[]) APIs
		if (node == null || output == null)
			throw new IllegalArgumentException();
		SortedProperties properties = null;
		if (excludesList == null)
			excludesList = new String[0];
		try {
			properties = convertToProperties(node, excludesList);
			if (properties.isEmpty())
				return Status.OK_STATUS;
			properties.put(VERSION_KEY, Float.toString(EXPORT_VERSION));
			properties.put(EXPORT_ROOT_PREFIX + node.absolutePath(), EMPTY_STRING);
		} catch (BackingStoreException e) {
			throw new CoreException(createStatusError(e.getMessage(), e));
		}
		try {
			properties.store(output, null);
		} catch (IOException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_exportProblems, e));
		}
		return Status.OK_STATUS;
	}

	/*
	 * Give clients a chance to modify the tree before it is applied globally
	 */
	private IEclipsePreferences firePreApplyEvent(IEclipsePreferences tree) {
		if (registryHelper == null)
			return tree;
		final IEclipsePreferences[] result = new IEclipsePreferences[] {tree};
		ListenerList<PreferenceModifyListener> listeners = ((PreferenceServiceRegistryHelper) registryHelper).getModifyListeners();
		for (final PreferenceModifyListener listener : listeners) {
			ISafeRunnable job = new ISafeRunnable() {
				@Override
				public void handleException(Throwable exception) {
					// already logged in Platform#run()
				}

				@Override
				public void run() throws Exception {
					result[0] = listener.preApply(result[0]);
				}
			};
			SafeRunner.run(job);
		}
		return result[0];
	}


	@Override
	public String get(String key, String defaultValue, Preferences[] nodes) {
		if (nodes == null)
			return defaultValue;
		for (Preferences node : nodes) {
			if (node != null) {
				String result = node.get(key, null);
				if (result != null)
					return result;
			}
		}
		return defaultValue;
	}


	@Override
	public boolean getBoolean(String qualifier, String key, boolean defaultValue, IScopeContext[] scopes) {
		String result = get(EclipsePreferences.decodePath(key)[1], null, getNodes(qualifier, key, scopes));
		return result == null ? defaultValue : Boolean.valueOf(result).booleanValue();
	}

	/*
	 * Return the name of the bundle from the given path.
	 * It is assumed that that path is:
	 * - absolute
	 * - in the instance scope
	 */
	String getBundleName(String path) {
		if (path.length() == 0 || path.charAt(0) != IPath.SEPARATOR)
			return null;
		int first = path.indexOf(IPath.SEPARATOR, 1);
		if (first == -1)
			return null;
		int second = path.indexOf(IPath.SEPARATOR, first + 1);
		return second == -1 ? path.substring(first + 1) : path.substring(first + 1, second);
	}

	/*
	 * Return the version for the bundle with the given name. Return null if it
	 * is not known or there is a problem.
	 */
	String getBundleVersion(String bundleName) {
		Bundle bundle = PreferencesOSGiUtils.getDefault().getBundle(bundleName);
		if (bundle != null) {
			Object version = bundle.getHeaders(EMPTY_STRING).get(Constants.BUNDLE_VERSION);
			if (version != null && version instanceof String)
				return (String) version;
		}
		return null;
	}


	@Override
	public byte[] getByteArray(String qualifier, String key, byte[] defaultValue, IScopeContext[] scopes) {
		String result = get(EclipsePreferences.decodePath(key)[1], null, getNodes(qualifier, key, scopes));
		return result == null ? defaultValue : Base64.decode(result.getBytes());
	}


	@Override
	public String[] getDefaultLookupOrder(String qualifier, String key) {
		LookupOrder order = defaultsRegistry.get(getRegistryKey(qualifier, key));
		return order == null ? null : order.getOrder();
	}


	@Override
	public double getDouble(String qualifier, String key, double defaultValue, IScopeContext[] scopes) {
		String value = get(EclipsePreferences.decodePath(key)[1], null, getNodes(qualifier, key, scopes));
		if (value == null)
			return defaultValue;
		try {
			return Double.parseDouble(value);
		} catch (NumberFormatException e) {
			return defaultValue;
		}
	}


	@Override
	public float getFloat(String qualifier, String key, float defaultValue, IScopeContext[] scopes) {
		String value = get(EclipsePreferences.decodePath(key)[1], null, getNodes(qualifier, key, scopes));
		if (value == null)
			return defaultValue;
		try {
			return Float.parseFloat(value);
		} catch (NumberFormatException e) {
			return defaultValue;
		}
	}


	@Override
	public int getInt(String qualifier, String key, int defaultValue, IScopeContext[] scopes) {
		String value = get(EclipsePreferences.decodePath(key)[1], null, getNodes(qualifier, key, scopes));
		if (value == null)
			return defaultValue;
		try {
			return Integer.parseInt(value);
		} catch (NumberFormatException e) {
			return defaultValue;
		}
	}




	@Override
	public long getLong(String qualifier, String key, long defaultValue, IScopeContext[] scopes) {
		String value = get(EclipsePreferences.decodePath(key)[1], null, getNodes(qualifier, key, scopes));
		if (value == null)
			return defaultValue;
		try {
			return Long.parseLong(value);
		} catch (NumberFormatException e) {
			return defaultValue;
		}
	}


	@Override
	public String[] getLookupOrder(String qualifier, String key) {
		String[] order = getDefaultLookupOrder(qualifier, key);
		// if there wasn't an exact match based on both qualifier and simple name
		// then do a lookup based only on the qualifier
		if (order == null && key != null)
			order = getDefaultLookupOrder(qualifier, null);
		if (order == null)
			order = DEFAULT_DEFAULT_LOOKUP_ORDER;
		return order;
	}

	private Preferences[] getNodes(final String qualifier, String key, final IScopeContext[] contexts) {
		String[] order = getLookupOrder(qualifier, key);
		final String childPath = EclipsePreferences.makeRelative(EclipsePreferences.decodePath(key)[0]);
		final ArrayList<Preferences> result = new ArrayList<>();
		for (String scopeString : order) {
			AtomicReference<IllegalStateException> error = new AtomicReference<>();
			SafeRunner.run(new ISafeRunnable() {

				private IScopeContext context;

				@Override
				public void run() throws Exception {
					boolean found = false;
					for (int j = 0; contexts != null && j < contexts.length; j++) {
						context = contexts[j];
						if (context != null && context.getName().equals(scopeString)) {
							Preferences node = context.getNode(qualifier);
							if (node != null) {
								found = true;
								if (childPath != null)
									node = node.node(childPath);
								result.add(node);
							}
						}
					}
					if (!found) {
						Preferences node = getRootNode().node(scopeString).node(qualifier);
						if (childPath != null)
							node = node.node(childPath);
						result.add(node);
					}
					found = false;
				}

				@Override
				public void handleException(Throwable exception) {
					// See bug 514333 and org.eclipse.core.internal.runtime.DataArea.assertLocationInitialized()
					// If we see an IllegalStateException flying and the explicit init is required, we should not continue
					if (context instanceof InstanceScope && exception instanceof IllegalStateException && Boolean.getBoolean("osgi.dataAreaRequiresExplicitInit")) { //$NON-NLS-1$
						error.set((IllegalStateException) exception);
					} else {
						log(new Status(IStatus.ERROR, Activator.PI_PREFERENCES, PrefsMessages.preferences_contextError, exception));
					}
				}
			});

			IllegalStateException illegalState = error.get();
			if (illegalState != null) {
				// See bug 514333: don't allow clients to read (empty) instance prefs if the instance area is not initialized yet
				throw illegalState;
			}
		}
		return result.toArray(new Preferences[result.size()]);
	}

	/*
	 * Convert the given qualifier and key into a key to use in the look-up registry.
	 */
	private String getRegistryKey(String qualifier, String key) {
		if (qualifier == null)
			throw new IllegalArgumentException();
		if (key == null)
			return qualifier;
		return qualifier + '/' + key;
	}

	@Override
	public IEclipsePreferences getRootNode() {
		return root;
	}

	/*
	 * Return the string which is the scope for the given path.
	 * Return the empty string if it cannot be determined.
	 */
	String getScope(String path) {
		if (path == null || path.length() == 0)
			return EMPTY_STRING;
		int startIndex = path.indexOf(IPath.SEPARATOR);
		if (startIndex == -1)
			return path;
		if (path.length() == 1)
			return EMPTY_STRING;
		int endIndex = path.indexOf(IPath.SEPARATOR, startIndex + 1);
		if (endIndex == -1)
			endIndex = path.length();
		return path.substring(startIndex + 1, endIndex);
	}


	@Override
	public String getString(String qualifier, String key, String defaultValue, IScopeContext[] scopes) {
		return get(EclipsePreferences.decodePath(key)[1], defaultValue, getNodes(qualifier, key, scopes));
	}


	@Override
	public IStatus importPreferences(InputStream input) throws CoreException {
		if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
			PrefsMessages.message("Importing preferences..."); //$NON-NLS-1$
		return applyPreferences(readPreferences(input));
	}

	
Filter the given tree so it only contains values which apply to the specified filters
then apply the resulting tree to the main preference tree.
/**
	 * Filter the given tree so it only contains values which apply to the specified filters
	 * then apply the resulting tree to the main preference tree.
	 */
	private void internalApply(IEclipsePreferences tree, IPreferenceFilter[] filters) throws BackingStoreException {
		ArrayList<IEclipsePreferences> trees = new ArrayList<>();
		for (IPreferenceFilter filter : filters) {
			trees.add(trimTree(tree, filter));
		}
		// merge the union of the matching filters
		IEclipsePreferences toApply = mergeTrees(trees.toArray(new IEclipsePreferences[trees.size()]));

		// fire an event to give people a chance to modify the tree
		toApply = firePreApplyEvent(toApply);

		// actually apply the settings
		IPreferenceNodeVisitor visitor = new IPreferenceNodeVisitor() {
			@Override
			public boolean visit(IEclipsePreferences node) throws BackingStoreException {
				String[] keys = node.keys();
				if (keys.length == 0)
					return true;
				copyFromTo(node, getRootNode().node(node.absolutePath()), keys, 0);
				return true;
			}
		};
		toApply.accept(visitor);
	}

	
Take the preference tree and trim it so it only holds values applying to the given filters.
Then export the resulting tree to the given output stream.
/**
	 * Take the preference tree and trim it so it only holds values applying to the given filters.
	 * Then export the resulting tree to the given output stream.
	 */
	private void internalExport(IEclipsePreferences node, IPreferenceFilter filters[], OutputStream output) throws BackingStoreException, CoreException {
		ArrayList<IEclipsePreferences> trees = new ArrayList<>();
		for (IPreferenceFilter filter : filters) {
			trees.add(trimTree(node, filter));
		}
		IEclipsePreferences toExport = mergeTrees(trees.toArray(new IEclipsePreferences[trees.size()]));
		exportPreferences(toExport, output, (String[]) null);
	}

	/*
	 * Return true if the given tree contains information that the specified filter is interested
	 * in, and false otherwise.
	 */
	private boolean internalMatches(IEclipsePreferences tree, IPreferenceFilter filter) throws BackingStoreException {
		String[] scopes = filter.getScopes();
		if (scopes == null)
			throw new IllegalArgumentException();
		String treePath = tree.absolutePath();
		// see if this node is applicable by going over all our scopes
		for (String scope : scopes) {
			Map<String, PreferenceFilterEntry[]> mapping = filter.getMapping(scope);
			// if the mapping is null then we match everything
			if (mapping == null) {
				// if we are the root check to see if the scope exists
				if (tree.parent() == null && tree.nodeExists(scope)) {
					if (containsKeys((IEclipsePreferences) tree.node(scope)))
						return true;
				}
				// otherwise check to see if we are in the right scope
				if (scopeMatches(scope, tree) && containsKeys(tree))
					return true;
				continue;
			}
			// iterate over the list of declared nodes
			for (String nodePath : mapping.keySet()) {
				String nodeFullPath = '/' + scope + '/' + nodePath;
				// if this subtree isn't in a hierarchy we are interested in, then go to the next one
				if (!nodeFullPath.startsWith(treePath))
					continue;
				// get the child node
				String childPath = nodeFullPath.substring(treePath.length());
				childPath = EclipsePreferences.makeRelative(childPath);
				if (tree.nodeExists(childPath)) {
					PreferenceFilterEntry[] entries;
					// protect against wrong classes since this is user-code
					try {
						entries = mapping.get(nodePath);
					} catch (ClassCastException e) {
						log(createStatusError(PrefsMessages.preferences_classCastFilterEntry, e));
						continue;
					}
					// if there are no entries defined then we return false even if we
					// are supposed to match on the existence of the node as a whole (bug 88820)
					Preferences child = tree.node(childPath);
					if (entries == null) {
						if (child.keys().length != 0 || child.childrenNames().length != 0)
							return true;
					} else {
						// otherwise check to see if we have any applicable keys
						for (PreferenceFilterEntry entry : entries) {
							if (entry == null) {
								continue;
							}
							if (entry.getMatchType() == null) {
								if (child.get(entry.getKey(), null) != null) {
									return true;
								}
							} else if (internalMatchesWithMatchType(entry, child.keys())) {
								return true;
							}
						}
					}
				}
			}
		}
		return false;
	}

	/*
	 * Internal method that collects the matching filters for the given tree and returns them.
	 */
	private IPreferenceFilter[] internalMatches(IEclipsePreferences tree, IPreferenceFilter[] filters) throws BackingStoreException {
		ArrayList<IPreferenceFilter> result = new ArrayList<>();
		for (IPreferenceFilter filter : filters) {
			if (internalMatches(tree, filter)) {
				result.add(filter);
			}
		}
		return result.toArray(new IPreferenceFilter[result.size()]);
	}

	/*
	 * Internal method that check the matching preferences for entry with specific match type.
	 */
	private boolean internalMatchesWithMatchType(PreferenceFilterEntry entry, String[] keys) {
		if (keys == null || keys.length == 0)
			return false;
		String key = entry.getKey();
		String matchType = entry.getMatchType();
		if (!matchType.equalsIgnoreCase(MATCH_TYPE_PREFIX))
			return false;
		for (String k : keys) {
			if (k.startsWith(key)) {
				return true;
			}
		}
		return false;
	}

	/*
	 * Returns a boolean value indicating whether or not the given Properties
	 * object is the result of a preference export previous to Eclipse 3.0.
	 *
	 * Check the contents of the file. In Eclipse 3.0 we printed out a file
	 * version key.
	 */
	private boolean isLegacy(Properties properties) {
		return properties.getProperty(VERSION_KEY) == null;
	}


	@Override
	public IPreferenceFilter[] matches(IEclipsePreferences tree, IPreferenceFilter[] filters) throws CoreException {
		if (filters == null || filters.length == 0)
			return new IPreferenceFilter[0];
		try {
			return internalMatches(tree, filters);
		} catch (BackingStoreException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_matching, e));
		}
	}

	private IEclipsePreferences mergeTrees(IEclipsePreferences[] trees) throws BackingStoreException {
		if (trees.length == 1)
			return trees[0];
		final IEclipsePreferences result = ExportedPreferences.newRoot();
		if (trees.length == 0)
			return result;
		IPreferenceNodeVisitor visitor = new IPreferenceNodeVisitor() {
			@Override
			public boolean visit(IEclipsePreferences node) throws BackingStoreException {
				Preferences destination = result.node(node.absolutePath());
				copyFromTo(node, destination, null, 0);
				return true;
			}
		};
		for (IEclipsePreferences tree : trees) {
			tree.accept(visitor);
		}
		return result;
	}


	@Override
	public IExportedPreferences readPreferences(InputStream input) throws CoreException {
		if (input == null)
			throw new IllegalArgumentException();

		if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
			PrefsMessages.message("Reading preferences from stream..."); //$NON-NLS-1$

		// read the file into a properties object
		Properties properties = new Properties();
		try {
			properties.load(input);
		} catch (IOException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_importProblems, e));
		} catch (IllegalArgumentException e) {
			throw new CoreException(createStatusError(PrefsMessages.preferences_importProblems, e));
		} finally {
			try {
				input.close();
			} catch (IOException e) {
				// ignore
			}
		}

		// an empty file is an invalid file format
		if (properties.isEmpty())
			throw new CoreException(createStatusError(PrefsMessages.preferences_invalidFileFormat, null));

		// manipulate the file if it from a legacy preference export
		if (isLegacy(properties)) {
			if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
				PrefsMessages.message("Read legacy preferences file, converting to 3.0 format..."); //$NON-NLS-1$
			properties = convertFromLegacy(properties);
		} else {
			if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
				PrefsMessages.message("Read preferences file."); //$NON-NLS-1$
			properties.remove(VERSION_KEY);
		}

		// convert the Properties object into an object to return
		return convertFromProperties(properties);
	}

	
Return true if the given node is in the specified scope and false otherwise.
/**
	 * Return true if the given node is in the specified scope and false otherwise.
	 */
	private boolean scopeMatches(String scope, IEclipsePreferences tree) {
		// the root isn't in any scope
		if (tree.parent() == null)
			return false;
		// fancy math to get the first segment of the path
		String path = tree.absolutePath();
		int index = path.indexOf('/', 1);
		String sub = path.substring(1, index == -1 ? path.length() : index);
		return scope.equals(sub);
	}


	@Override
	public void setDefaultLookupOrder(String qualifier, String key, String[] order) {
		String registryKey = getRegistryKey(qualifier, key);
		if (order == null)
			defaultsRegistry.remove(registryKey);
		else {
			LookupOrder obj = new LookupOrder(order);
			defaultsRegistry.put(registryKey, obj);
		}
	}

	public void setRegistryHelper(Object registryHelper) {
		if (this.registryHelper != null && this.registryHelper != registryHelper)
			((PreferenceServiceRegistryHelper) this.registryHelper).stop();
		this.registryHelper = registryHelper;
	}

	
Shares all duplicate equal strings referenced by the preference service.
/**
	 * Shares all duplicate equal strings referenced by the preference service.
	 */
	void shareStrings() {
		long now = System.currentTimeMillis();
		if (now - lastStringSharing < STRING_SHARING_INTERVAL)
			return;
		StringPool pool = new StringPool();
		root.shareStrings(pool);
		if (EclipsePreferences.DEBUG_PREFERENCE_GENERAL)
			System.out.println("Preference string sharing saved: " + pool.getSavedStringCount()); //$NON-NLS-1$
		lastStringSharing = now;
	}

	/*
	 * Return a tree which contains only nodes and keys which are applicable to the given filter.
	 */
	private IEclipsePreferences trimTree(IEclipsePreferences tree, IPreferenceFilter filter) throws BackingStoreException {
		IEclipsePreferences result = (IEclipsePreferences) ExportedPreferences.newRoot().node(tree.absolutePath());
		String[] scopes = filter.getScopes();
		if (scopes == null)
			throw new IllegalArgumentException();
		String treePath = tree.absolutePath();
	    // see if this node is applicable by going over all our scopes
		for (String scope : scopes) {
			Map<String, PreferenceFilterEntry[]> mapping = filter.getMapping(scope);
			// if the mapping is null then copy everything if the scope matches
			if (mapping == null) {
				// if we are the root node then check our children
				if (tree.parent() == null && tree.nodeExists(scope))
					copyFromTo(tree.node(scope), result.node(scope), null, -1);
				// ensure we are in the correct scope
				else if (scopeMatches(scope, tree))
					copyFromTo(tree, result, null, -1);
				continue;
			}
			// iterate over the list of declared nodes
			for (String nodePath : mapping.keySet()) {
				String nodeFullPath = '/' + scope + '/' + nodePath;
				// if this subtree isn't in a hierarchy we are interested in, then go to the next one
				if (!nodeFullPath.startsWith(treePath))
					continue;
				// get the child node
				String childPath = nodeFullPath.substring(treePath.length());
				childPath = EclipsePreferences.makeRelative(childPath);
				if (tree.nodeExists(childPath)) {
					Preferences child = tree.node(childPath);
					PreferenceFilterEntry[] entries;
					// protect against wrong classes since this is passed in by the user
					try {
						entries = mapping.get(nodePath);
					} catch (ClassCastException e) {
						log(createStatusError(PrefsMessages.preferences_classCastFilterEntry, e));
						continue;
					}
					String[] keys = null;
					if (entries != null) {
						ArrayList<String> list = new ArrayList<>();
						for (PreferenceFilterEntry entry : entries) {
							if (entry != null) {
								addMatchedKeys(list, entry, child.keys());
							}
						}
						keys = list.toArray(new String[list.size()]);
					}
					// do infinite depth if there are no keys specified since the parent matched.
					copyFromTo(tree.node(childPath), result.node(childPath), keys, keys == null ? -1 : 0);
				}
			}
		}
		return result;
	}

	/*
	 * Internal method that adds to the given list the matching preferences for entry with or without specific match type.
	 */
	private void addMatchedKeys(ArrayList<String> list, PreferenceFilterEntry entry, String[] keys) {
		String matchType = entry.getMatchType();
		if (matchType == null) {
			list.add(entry.getKey());
			return;
		}
		if (keys == null)
			return;
		String key = entry.getKey();
		for (String k : keys) {
			if (matchType.equals(MATCH_TYPE_PREFIX) && k.startsWith(key)) {
				list.add(k);
			}
		}
	}

	
Compares two plugin version identifiers to see if their preferences
are compatible.  If they are not compatible, a warning message is
added to the given multi-status, according to the following rules:
- plugins that differ in service number: no status
- plugins that differ in minor version: WARNING status
- plugins that differ in major version:
	- where installed plugin is newer: WARNING status
	- where installed plugin is older: ERROR status
Params:
bundle – the name of the bundle
pref – The version identifier of the preferences to be loaded
installed – The version identifier of the installed plugin/**
	 * Compares two plugin version identifiers to see if their preferences
	 * are compatible.  If they are not compatible, a warning message is
	 * added to the given multi-status, according to the following rules:
	 *
	 * - plugins that differ in service number: no status
	 * - plugins that differ in minor version: WARNING status
	 * - plugins that differ in major version:
	 * 	- where installed plugin is newer: WARNING status
	 * 	- where installed plugin is older: ERROR status
	 * @param bundle the name of the bundle
	 * @param pref The version identifier of the preferences to be loaded
	 * @param installed The version identifier of the installed plugin
	 */
	IStatus validatePluginVersions(String bundle, PluginVersionIdentifier pref, PluginVersionIdentifier installed) {
		if (installed.getMajorComponent() == pref.getMajorComponent() && installed.getMinorComponent() == pref.getMinorComponent())
			return null;
		int severity;
		if (installed.getMajorComponent() < pref.getMajorComponent())
			severity = IStatus.ERROR;
		else
			severity = IStatus.WARNING;
		String msg = NLS.bind(PrefsMessages.preferences_incompatible, (new Object[] {pref, bundle, installed}));
		return new Status(severity, PrefsMessages.OWNER_NAME, 1, msg, null);
	}

	public IStatus validateVersions(IPath path) {
		final MultiStatus result = new MultiStatus(PrefsMessages.OWNER_NAME, IStatus.INFO, PrefsMessages.preferences_validate, null);
		IPreferenceNodeVisitor visitor = new IPreferenceNodeVisitor() {
			@Override
			public boolean visit(IEclipsePreferences node) {
				if (!(node instanceof ExportedPreferences))
					return false;

				// calculate the version in the file
				ExportedPreferences realNode = (ExportedPreferences) node;
				String version = realNode.getVersion();
				if (version == null || !PluginVersionIdentifier.validateVersion(version).isOK())
					return true;
				PluginVersionIdentifier versionInFile = new PluginVersionIdentifier(version);

				// calculate the version of the installed bundle
				String bundleName = getBundleName(node.absolutePath());
				if (bundleName == null)
					return true;
				String stringVersion = getBundleVersion(bundleName);
				if (stringVersion == null || !PluginVersionIdentifier.validateVersion(stringVersion).isOK())
					return true;
				PluginVersionIdentifier versionInMemory = new PluginVersionIdentifier(stringVersion);

				// verify the versions based on the matching rules
				IStatus verification = validatePluginVersions(bundleName, versionInFile, versionInMemory);
				if (verification != null)
					result.add(verification);

				return true;
			}
		};

		InputStream input = null;
		try {
			input = new BufferedInputStream(new FileInputStream(path.toFile()));
			IExportedPreferences prefs = readPreferences(input);
			prefs.accept(visitor);
		} catch (FileNotFoundException e) {
			// ignore...if the file does not exist then all is OK
		} catch (CoreException e) {
			result.add(createStatusError(PrefsMessages.preferences_validationException, e));
		} catch (BackingStoreException e) {
			result.add(createStatusError(PrefsMessages.preferences_validationException, e));
		}
		return result;
	}

	/*
	 * Return the default search lookup order for when nothing is set.
	*/
	public String[] getDefaultDefaultLookupOrder() {
		return DEFAULT_DEFAULT_LOOKUP_ORDER;
	}

	/*
	 * Set the default search order to use when there is nothing else set. Clients should not
	 * call this method because it is in an internal class and has been created solely for use by
	 * the org.eclipse.core.resources bundle in response to this bug:
	 *     https://bugs.eclipse.org/330320
	 */
	public void setDefaultDefaultLookupOrder(String[] order) {
		// shouldn't happen but let's protect against an NPE.
		if (order == null)
			order = new String[0];
		DEFAULT_DEFAULT_LOOKUP_ORDER = order;
	}
}