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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by both ImageJ and SCIFIO.
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 * %%
 * Copyright (C) 2009 - 2016 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
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package org.scijava.prefs;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.scijava.log.LogService;
import org.scijava.plugin.Parameter;
import org.scijava.plugin.Plugin;
import org.scijava.service.Service;

/**
 * Default {@link PrefService} implementation, which persists preferences to
 * disk using the {@link java.util.prefs.Preferences} API.
 *
 * @author Mark Hiner
 * @author Curtis Rueden
 * @author Grant Harris
 */
@Plugin(type = Service.class)
public class DefaultPrefService extends AbstractPrefService {

	@Parameter(required = false)
	private LogService log;

	// -- Global preferences --

	@Override
	public String get(final String name) {
		return get((Class) null, name);
	}

	@Override
	public String get(final String name, final String defaultValue) {
		return get(null, name, defaultValue);
	}

	@Override
	public boolean getBoolean(final String name, final boolean defaultValue) {
		return getBoolean(null, name, defaultValue);
	}

	@Override
	public double getDouble(final String name, final double defaultValue) {
		return getDouble(null, name, defaultValue);
	}

	@Override
	public float getFloat(final String name, final float defaultValue) {
		return getFloat(null, name, defaultValue);
	}

	@Override
	public int getInt(final String name, final int defaultValue) {
		return getInt(null, name, defaultValue);
	}

	@Override
	public long getLong(final String name, final long defaultValue) {
		return getLong(null, name, defaultValue);
	}

	@Override
	public void put(final String name, final String value) {
		put(null, name, value);
	}

	@Override
	public void put(final String name, final boolean value) {
		put(null, name, value);
	}

	@Override
	public void put(final String name, final double value) {
		put(null, name, value);
	}

	@Override
	public void put(final String name, final float value) {
		put(null, name, value);
	}

	@Override
	public void put(final String name, final int value) {
		put(null, name, value);
	}

	@Override
	public void put(final String name, final long value) {
		put(null, name, value);
	}

	// -- Class-specific preferences --

	@Override
	public String get(final Class c, final String name) {
		return get(c, name, null);
	}

	@Override
	public String get(final Class c, final String name,
		final String defaultValue)
	{
		return prefs(c).get(key(c, name), defaultValue);
	}

	@Override
	public boolean getBoolean(final Class c, final String name,
		final boolean defaultValue)
	{
		return prefs(c).getBoolean(key(c, name), defaultValue);
	}

	@Override
	public double getDouble(final Class c, final String name,
		final double defaultValue)
	{
		return prefs(c).getDouble(key(c, name), defaultValue);
	}

	@Override
	public float getFloat(final Class c, final String name,
		final float defaultValue)
	{
		return prefs(c).getFloat(key(c, name), defaultValue);
	}

	@Override
	public int
		getInt(final Class c, final String name, final int defaultValue)
	{
		return prefs(c).getInt(key(c, name), defaultValue);
	}

	@Override
	public long getLong(final Class c, final String name,
		final long defaultValue)
	{
		return prefs(c).getLong(key(c, name), defaultValue);
	}

	@Override
	public void put(final Class c, final String name, final String value) {
		prefs(c).put(key(c, name), value);
	}

	@Override
	public void put(final Class c, final String name, final boolean value) {
		prefs(c).putBoolean(key(c, name), value);
	}

	@Override
	public void put(final Class c, final String name, final double value) {
		prefs(c).putDouble(key(c, name), value);
	}

	@Override
	public void put(final Class c, final String name, final float value) {
		prefs(c).putFloat(key(c, name), value);
	}

	@Override
	public void put(final Class c, final String name, final int value) {
		prefs(c).putInt(key(c, name), value);
	}

	@Override
	public void put(final Class c, final String name, final long value) {
		prefs(c).putLong(key(c, name), value);
	}

	@Override
	public void clear(final Class c) {
		prefs(c).clear();
	}

	// -- Other/unsorted --

	// TODO - Evaluate which of these methods are really needed, and which are
	// duplicate of similar functionality above.

	@Override
	public void clearAll() {
		for (final String name : allPrefs())
			prefs(name).removeNode();
	}

	@Override
	public void clear(final String key) {
		clear((Class) null, key);
	}

	@Override
	public void clear(final Class prefClass, final String key) {
		prefs(prefClass).clear(key);
	}

	@Override
	public void clear(final String absolutePath, final String key) {
		prefs(absolutePath).clear(key);
	}

	@Override
	public void remove(final Class prefClass, final String key) {
		prefs(prefClass).remove(key);
	}

	@Override
	public void remove(final String absolutePath, final String key) {
		prefs(absolutePath).remove(key);
	}

	@Override
	public void putMap(final Map map, final String key) {
		putMap((Class) null, map, key);
	}

	@Override
	public void putMap(final Class prefClass, final Map map,
		final String key)
	{
		prefs(prefClass).node(key).putMap(map);
	}

	@Override
	public void putMap(final String absolutePath, final Map map,
		final String key)
	{
		prefs(absolutePath).node(key).putMap(map);
	}

	@Override
	public void putMap(final Class prefClass, final Map map) {
		prefs(prefClass).putMap(map);
	}

	@Override
	public void putMap(final String absolutePath, final Map map) {
		prefs(absolutePath).putMap(map);
	}

	@Override
	public Map getMap(final String key) {
		return getMap((Class) null, key);
	}

	@Override
	public Map getMap(final Class prefClass, final String key)
	{
		return prefs(prefClass).node(key).getMap();
	}

	@Override
	public Map
		getMap(final String absolutePath, final String key)
	{
		return prefs(absolutePath).node(key).getMap();
	}

	@Override
	public Map getMap(final Class prefClass) {
		return prefs(prefClass).getMap();
	}

	@Override
	public void putList(final List list, final String key) {
		putList((Class) null, list, key);
	}

	@Override
	public void putList(final Class prefClass, final List list,
		final String key)
	{
		prefs(prefClass).node(key).putList(list);
	}

	@Override
	public void putList(final String absolutePath, final List list,
		final String key)
	{
		prefs(absolutePath).node(key).putList(list);
	}

	@Override
	public void putList(final Class prefClass, final List list) {
		prefs(prefClass).putList(list);
	}

	@Override
	public void putList(final String absolutePath, final List list) {
		prefs(absolutePath).putList(list);
	}

	@Override
	public List getList(final String key) {
		return getList((Class) null, key);
	}

	@Override
	public List getList(final Class prefClass, final String key) {
		return prefs(prefClass).node(key).getList();
	}

	@Override
	public List getList(final String absolutePath, final String key) {
		return prefs(absolutePath).node(key).getList();
	}

	@Override
	public List getList(final Class prefClass) {
		return prefs(prefClass).getList();
	}

	@Override
	public Iterable getIterable(final String key) {
		return getIterable((Class) null, key);
	}

	@Override
	public Iterable getIterable(final Class prefClass, final String key) {
		return prefs(prefClass).node(key).getIterable();
	}

	@Override
	public void putIterable(final Iterable iterable, final String key) {
		putIterable((Class) null, iterable, key);
	}

	@Override
	public void putIterable(final Class prefClass, final Iterable iterable, final String key) {
		prefs(prefClass).node(key).node(key).putIterable(iterable);
	}

	// -- Helper methods --

	private static String key(final Class c, final String name) {
		return c == null ? name : c.getSimpleName() + "." + name;
	}

	private SmartPrefs prefs(final Class c) {
		return new SmartPrefs(java.util.prefs.Preferences.userNodeForPackage(
			c == null ? PrefService.class : c), log);
	}

	private SmartPrefs prefs(final String absolutePath) {
		return new SmartPrefs(java.util.prefs.Preferences.userRoot().node(
			absolutePath), log);
	}

	private String[] allPrefs() {
		try {
			return java.util.prefs.Preferences.userRoot().childrenNames();
		}
		catch (java.util.prefs.BackingStoreException exc) {
			if (log != null) log.error(exc);
			return new String[0];
		}
	}

	// -- Helper classes --

	/**
	 * Smart wrapper around {@link java.util.prefs.Preferences} which
	 * encapsulates, improves and enhances its behavior.
	 */
	private static class SmartPrefs {

		private final java.util.prefs.Preferences p;
		private final LogService log;

		public SmartPrefs(final java.util.prefs.Preferences p,
			final LogService log)
		{
			this.p = p;
			this.log = log;
		}

		// -- SmartPrefs methods --

		public void clear(final String key) {
			if (nodeExists(key)) node(key).clear();
		}

		public void remove(final String key) {
			if (nodeExists(key)) node(key).removeNode();
		}

		public void putMap(final Map map) {
			final Iterator> iter = map.entrySet().iterator();
			while (iter.hasNext()) {
				final Entry entry = iter.next();
				final String key = entry.getKey().toString();
				final Object value = entry.getValue();
				put(key, value);
			}

		}

		public Map getMap() {
			final Map map = new HashMap();
			final String[] keys = keys();
			for (int index = 0; index < keys.length; index++) {
				map.put(keys[index], get(keys[index]));
			}
			return map;
		}

		public void putList(final List list) {
			for (int index = 0; list != null && index < list.size(); index++) {
				final Object value = list.get(index);
				put("" + index, value);
			}
		}

		public List getList() {
			final List list = new ArrayList();
			for (int index = 0; index < 1000; index++) {
				final String value = get("" + index);
				if (value == null) {
					break;
				}
				list.add(value);
			}
			return list;
		}

		public void putIterable(final Iterable iterable) {
			int index = 0;
			for (final String value : iterable) {
				put("" + index++, value);
			}
		}

		public Iterable getIterable() {
			return new Iterable() {
				@Override
				public Iterator iterator() {
					return new Iterator() {
						private String value;
						private int index;
						{
							findNext();
						}

						@Override
						public String next() {
							final String result = value;
							findNext();
							return result;
						}

						@Override
						public boolean hasNext() {
							return value != null;
						}

						@Override
						public void remove() {
							throw new UnsupportedOperationException();
						}

						private void findNext() {
							if (index < 0) return;
							value = get("" + index);
							index = value == null ? -1 : index + 1;
						}
					};
				}
			};
		}

		// -- Adapted Preferences methods --

		/** @see java.util.prefs.Preferences#put */
		public void put(final String key, final Object value) {
			p.put(safeKey(key), safeValue(value));
		}

		/** @see java.util.prefs.Preferences#get(String, String) */
		public String get(final String key) {
			return get(key, null);
		}

		/** @see java.util.prefs.Preferences#get(String, String) */
		public String get(final String key, final String def) {
			return p.get(safeKey(key), def);
		}

		/** @see java.util.prefs.Preferences#clear() */
		public void clear() {
			try {
				p.clear();
			}
			catch (java.util.prefs.BackingStoreException exc) {
				if (log != null) log.error(exc);
			}
		}

		/** @see java.util.prefs.Preferences#putInt(String, int) */
		public void putInt(final String key, final int value) {
			p.putInt(safeKey(key), value);
		}

		/** @see java.util.prefs.Preferences#getInt(String, int) */
		public int getInt(final String key, final int def) {
			return p.getInt(safeKey(key), def);
		}

		/** @see java.util.prefs.Preferences#putLong(String, long) */
		public void putLong(final String key, final long value) {
			p.putLong(safeKey(key), value);
		}

		/** @see java.util.prefs.Preferences#getLong(String, long) */
		public long getLong(final String key, final long def) {
			return p.getLong(safeKey(key), def);
		}

		/** @see java.util.prefs.Preferences#putBoolean(String, boolean) */
		public void putBoolean(final String key, final boolean value) {
			p.putBoolean(safeKey(key), value);
		}

		/** @see java.util.prefs.Preferences#getFloat(String, float) */
		public boolean getBoolean(final String key, final boolean def) {
			return p.getBoolean(safeKey(key), def);
		}

		/** @see java.util.prefs.Preferences#putFloat(String, float) */
		public void putFloat(final String key, final float value) {
			p.putFloat(safeKey(key), value);
		}

		/** @see java.util.prefs.Preferences#getFloat(String, float) */
		public float getFloat(final String key, final float def) {
			return p.getFloat(safeKey(key), def);
		}

		/** @see java.util.prefs.Preferences#putDouble(String, double) */
		public void putDouble(final String key, final double value) {
			p.putDouble(safeKey(key), value);
		}

		/** @see java.util.prefs.Preferences#getDouble(String, double) */
		public double getDouble(final String key, final double def) {
			return p.getDouble(safeKey(key), def);
		}

		/** @see java.util.prefs.Preferences#keys() */
		public String[] keys() {
			try {
				final String[] keys = p.keys();
				for (int i = 0; i < keys.length; i++) {
					keys[i] = safeKey(keys[i]);
				}
				return keys;
			}
			catch (final java.util.prefs.BackingStoreException exc) {
				if (log != null) log.error(exc);
				return new String[0];
			}
		}

		/** @see java.util.prefs.Preferences#node(String) */
		public SmartPrefs node(final String pathName) {
			return new SmartPrefs(p.node(safeName(pathName)), log);
		}

		/** @see java.util.prefs.Preferences#nodeExists(String) */
		public boolean nodeExists(final String pathName) {
			try {
				return p.nodeExists(safeName(pathName));
			}
			catch (final java.util.prefs.BackingStoreException exc) {
				if (log != null) log.error(exc);
				return false;
			}
		}

		/** @see java.util.prefs.Preferences#removeNode() */
		public void removeNode() {
			try {
				p.removeNode();
			}
			catch (final java.util.prefs.BackingStoreException exc) {
				if (log != null) log.error(exc);
			}
		}

		// -- Helper methods --

		private String safeKey(final String key) {
			return makeSafe(key, java.util.prefs.Preferences.MAX_KEY_LENGTH);
		}

		private String safeValue(final Object value) {
			if (value == null) return null;
			return makeSafe(value.toString(),
				java.util.prefs.Preferences.MAX_VALUE_LENGTH);
		}

		private String safeName(final String name) {
			return makeSafe(name, java.util.prefs.Preferences.MAX_NAME_LENGTH);
		}

		/**
		 * This method limits the given string to the specified maximum length using
		 * its latter characters prepended with "..." as needed.
		 * 
		 * This is necessary because the Java Preferences API does not allow:
		 * 
		 * 
		 * Keys longer than {@link java.util.prefs.Preferences#MAX_KEY_LENGTH}
		 * 
		 * Values longer than
		 * {@link java.util.prefs.Preferences#MAX_VALUE_LENGTH}
		 * Node names longer than
		 * {@link java.util.prefs.Preferences#MAX_NAME_LENGTH}
		 * 
		 */
		private String makeSafe(final String s, final int max) {
			final int len = s.length();
			if (len < max) return s;
			return "..." + s.substring(len - max + 3, len);
		}

	}

}