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	/*
	* Copyright (c) 2012, 2016, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* Copyright (c) 2009-2012, Stephen Colebourne & Michael Nascimento Santos
	*
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions are met:
	*
	* * Redistributions of source code must retain the above copyright notice,
	* this list of conditions and the following disclaimer.
	*
	* * 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.
	*
	* * Neither the name of JSR-310 nor the names of its contributors
	* may be used to endorse or promote products derived from this software
	* without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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	* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
	* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/
	package java.time.zone;

	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.time.ZoneId;
	import java.time.ZonedDateTime;
	import java.util.ArrayList;
	import java.util.HashSet;
	import java.util.Iterator;
	import java.util.List;
	import java.util.NavigableMap;
	import java.util.Objects;
	import java.util.ServiceConfigurationError;
	import java.util.ServiceLoader;
	import java.util.Set;
	import java.util.concurrent.ConcurrentHashMap;
	import java.util.concurrent.ConcurrentMap;
	import java.util.concurrent.CopyOnWriteArrayList;
	import java.util.Collections;

	/**
	* Provider of time-zone rules to the system.
	* <p>
	* This class manages the configuration of time-zone rules.
	* The static methods provide the public API that can be used to manage the providers.
	* The abstract methods provide the SPI that allows rules to be provided.
	* <p>
	* ZoneRulesProvider may be installed in an instance of the Java Platform as
	* extension classes, that is, jar files placed into any of the usual extension
	* directories. Installed providers are loaded using the service-provider loading
	* facility defined by the {@link ServiceLoader} class. A ZoneRulesProvider
	* identifies itself with a provider configuration file named
	* {@code java.time.zone.ZoneRulesProvider} in the resource directory
	* {@code META-INF/services}. The file should contain a line that specifies the
	* fully qualified concrete zonerules-provider class name.
	* Providers may also be made available by adding them to the class path or by
	* registering themselves via {@link #registerProvider} method.
	* <p>
	* The Java virtual machine has a default provider that provides zone rules
	* for the time-zones defined by IANA Time Zone Database (TZDB). If the system
	* property {@code java.time.zone.DefaultZoneRulesProvider} is defined then
	* it is taken to be the fully-qualified name of a concrete ZoneRulesProvider
	* class to be loaded as the default provider, using the system class loader.
	* If this system property is not defined, a system-default provider will be
	* loaded to serve as the default provider.
	* <p>
	* Rules are looked up primarily by zone ID, as used by {@link ZoneId}.
	* Only zone region IDs may be used, zone offset IDs are not used here.
	* <p>
	* Time-zone rules are political, thus the data can change at any time.
	* Each provider will provide the latest rules for each zone ID, but they
	* may also provide the history of how the rules changed.
	*
	* @implSpec
	* This interface is a service provider that can be called by multiple threads.
	* Implementations must be immutable and thread-safe.
	* <p>
	* Providers must ensure that once a rule has been seen by the application, the
	* rule must continue to be available.
	* <p>
	* Providers are encouraged to implement a meaningful {@code toString} method.
	* <p>
	* Many systems would like to update time-zone rules dynamically without stopping the JVM.
	* When examined in detail, this is a complex problem.
	* Providers may choose to handle dynamic updates, however the default provider does not.
	*
	* @since 1.8
	*/
	public abstract class ZoneRulesProvider {

	/**
	* The set of loaded providers.
	*/
	private static final CopyOnWriteArrayList<ZoneRulesProvider> PROVIDERS = new CopyOnWriteArrayList<>();
	/**
	* The lookup from zone ID to provider.
	*/
	private static final ConcurrentMap<String, ZoneRulesProvider> ZONES = new ConcurrentHashMap<>(512, 0.75f, 2);

	/**
	* The zone ID data
	*/
	private static volatile Set<String> ZONE_IDS;

	static {
	// if the property java.time.zone.DefaultZoneRulesProvider is
	// set then its value is the class name of the default provider
	final List<ZoneRulesProvider> loaded = new ArrayList<>();
	AccessController.doPrivileged(new PrivilegedAction<>() {
	public Object run() {
	String prop = System.getProperty("java.time.zone.DefaultZoneRulesProvider");
	if (prop != null) {
	try {
	Class<?> c = Class.forName(prop, true, ClassLoader.getSystemClassLoader());
	@SuppressWarnings("deprecation")
	ZoneRulesProvider provider = ZoneRulesProvider.class.cast(c.newInstance());
	registerProvider(provider);
	loaded.add(provider);
	} catch (Exception x) {
	throw new Error(x);
	}
	} else {
	registerProvider(new TzdbZoneRulesProvider());
	}
	return null;
	}
	});

	ServiceLoader<ZoneRulesProvider> sl = ServiceLoader.load(ZoneRulesProvider.class, ClassLoader.getSystemClassLoader());
	Iterator<ZoneRulesProvider> it = sl.iterator();
	while (it.hasNext()) {
	ZoneRulesProvider provider;
	try {
	provider = it.next();
	} catch (ServiceConfigurationError ex) {
	if (ex.getCause() instanceof SecurityException) {
	continue; // ignore the security exception, try the next provider
	}
	throw ex;
	}
	boolean found = false;
	for (ZoneRulesProvider p : loaded) {
	if (p.getClass() == provider.getClass()) {
	found = true;
	}
	}
	if (!found) {
	registerProvider0(provider);
	loaded.add(provider);
	}
	}
	// CopyOnWriteList could be slow if lots of providers and each added individually
	PROVIDERS.addAll(loaded);
	}

	//-------------------------------------------------------------------------
	/**
	* Gets the set of available zone IDs.
	* <p>
	* These IDs are the string form of a {@link ZoneId}.
	*
	* @return the unmodifiable set of zone IDs, not null
	*/
	public static Set<String> getAvailableZoneIds() {
	return ZONE_IDS;
	}

	/**
	* Gets the rules for the zone ID.
	* <p>
	* This returns the latest available rules for the zone ID.
	* <p>
	* This method relies on time-zone data provider files that are configured.
	* These are loaded using a {@code ServiceLoader}.
	* <p>
	* The caching flag is designed to allow provider implementations to
	* prevent the rules being cached in {@code ZoneId}.
	* Under normal circumstances, the caching of zone rules is highly desirable
	* as it will provide greater performance. However, there is a use case where
	* the caching would not be desirable, see {@link #provideRules}.
	*
	* @param zoneId the zone ID as defined by {@code ZoneId}, not null
	* @param forCaching whether the rules are being queried for caching,
	* true if the returned rules will be cached by {@code ZoneId},
	* false if they will be returned to the user without being cached in {@code ZoneId}
	* @return the rules, null if {@code forCaching} is true and this
	* is a dynamic provider that wants to prevent caching in {@code ZoneId},
	* otherwise not null
	* @throws ZoneRulesException if rules cannot be obtained for the zone ID
	*/
	public static ZoneRules getRules(String zoneId, boolean forCaching) {
	Objects.requireNonNull(zoneId, "zoneId");
	return getProvider(zoneId).provideRules(zoneId, forCaching);
	}

	/**
	* Gets the history of rules for the zone ID.
	* <p>
	* Time-zones are defined by governments and change frequently.
	* This method allows applications to find the history of changes to the
	* rules for a single zone ID. The map is keyed by a string, which is the
	* version string associated with the rules.
	* <p>
	* The exact meaning and format of the version is provider specific.
	* The version must follow lexicographical order, thus the returned map will
	* be order from the oldest known rules to the newest available rules.
	* The default 'TZDB' group uses version numbering consisting of the year
	* followed by a letter, such as '2009e' or '2012f'.
	* <p>
	* Implementations must provide a result for each valid zone ID, however
	* they do not have to provide a history of rules.
	* Thus the map will always contain one element, and will only contain more
	* than one element if historical rule information is available.
	*
	* @param zoneId the zone ID as defined by {@code ZoneId}, not null
	* @return a modifiable copy of the history of the rules for the ID, sorted
	* from oldest to newest, not null
	* @throws ZoneRulesException if history cannot be obtained for the zone ID
	*/
	public static NavigableMap<String, ZoneRules> getVersions(String zoneId) {
	Objects.requireNonNull(zoneId, "zoneId");
	return getProvider(zoneId).provideVersions(zoneId);
	}

	/**
	* Gets the provider for the zone ID.
	*
	* @param zoneId the zone ID as defined by {@code ZoneId}, not null
	* @return the provider, not null
	* @throws ZoneRulesException if the zone ID is unknown
	*/
	private static ZoneRulesProvider getProvider(String zoneId) {
	ZoneRulesProvider provider = ZONES.get(zoneId);
	if (provider == null) {
	if (ZONES.isEmpty()) {
	throw new ZoneRulesException("No time-zone data files registered");
	}
	throw new ZoneRulesException("Unknown time-zone ID: " + zoneId);
	}
	return provider;
	}

	//-------------------------------------------------------------------------
	/**
	* Registers a zone rules provider.
	* <p>
	* This adds a new provider to those currently available.
	* A provider supplies rules for one or more zone IDs.
	* A provider cannot be registered if it supplies a zone ID that has already been
	* registered. See the notes on time-zone IDs in {@link ZoneId}, especially
	* the section on using the concept of a "group" to make IDs unique.
	* <p>
	* To ensure the integrity of time-zones already created, there is no way
	* to deregister providers.
	*
	* @param provider the provider to register, not null
	* @throws ZoneRulesException if a zone ID is already registered
	*/
	public static void registerProvider(ZoneRulesProvider provider) {
	Objects.requireNonNull(provider, "provider");
	registerProvider0(provider);
	PROVIDERS.add(provider);
	}

	/**
	* Registers the provider.
	*
	* @param provider the provider to register, not null
	* @throws ZoneRulesException if unable to complete the registration
	*/
	private static synchronized void registerProvider0(ZoneRulesProvider provider) {
	for (String zoneId : provider.provideZoneIds()) {
	Objects.requireNonNull(zoneId, "zoneId");
	ZoneRulesProvider old = ZONES.putIfAbsent(zoneId, provider);
	if (old != null) {
	throw new ZoneRulesException(
	"Unable to register zone as one already registered with that ID: " + zoneId +
	", currently loading from provider: " + provider);
	}
	}
	Set<String> combinedSet = new HashSet<String>(ZONES.keySet());
	ZONE_IDS = Collections.unmodifiableSet(combinedSet);
	}

	/**
	* Refreshes the rules from the underlying data provider.
	* <p>
	* This method allows an application to request that the providers check
	* for any updates to the provided rules.
	* After calling this method, the offset stored in any {@link ZonedDateTime}
	* may be invalid for the zone ID.
	* <p>
	* Dynamic update of rules is a complex problem and most applications
	* should not use this method or dynamic rules.
	* To achieve dynamic rules, a provider implementation will have to be written
	* as per the specification of this class.
	* In addition, instances of {@code ZoneRules} must not be cached in the
	* application as they will become stale. However, the boolean flag on
	* {@link #provideRules(String, boolean)} allows provider implementations
	* to control the caching of {@code ZoneId}, potentially ensuring that
	* all objects in the system see the new rules.
	* Note that there is likely to be a cost in performance of a dynamic rules
	* provider. Note also that no dynamic rules provider is in this specification.
	*
	* @return true if the rules were updated
	* @throws ZoneRulesException if an error occurs during the refresh
	*/
	public static boolean refresh() {
	boolean changed = false;
	for (ZoneRulesProvider provider : PROVIDERS) {
	changed \|= provider.provideRefresh();
	}
	return changed;
	}

	/**
	* Constructor.
	*/
	protected ZoneRulesProvider() {
	}

	//-----------------------------------------------------------------------
	/**
	* SPI method to get the available zone IDs.
	* <p>
	* This obtains the IDs that this {@code ZoneRulesProvider} provides.
	* A provider should provide data for at least one zone ID.
	* <p>
	* The returned zone IDs remain available and valid for the lifetime of the application.
	* A dynamic provider may increase the set of IDs as more data becomes available.
	*
	* @return the set of zone IDs being provided, not null
	* @throws ZoneRulesException if a problem occurs while providing the IDs
	*/
	protected abstract Set<String> provideZoneIds();

	/**
	* SPI method to get the rules for the zone ID.
	* <p>
	* This loads the rules for the specified zone ID.
	* The provider implementation must validate that the zone ID is valid and
	* available, throwing a {@code ZoneRulesException} if it is not.
	* The result of the method in the valid case depends on the caching flag.
	* <p>
	* If the provider implementation is not dynamic, then the result of the
	* method must be the non-null set of rules selected by the ID.
	* <p>
	* If the provider implementation is dynamic, then the flag gives the option
	* of preventing the returned rules from being cached in {@link ZoneId}.
	* When the flag is true, the provider is permitted to return null, where
	* null will prevent the rules from being cached in {@code ZoneId}.
	* When the flag is false, the provider must return non-null rules.
	*
	* @param zoneId the zone ID as defined by {@code ZoneId}, not null
	* @param forCaching whether the rules are being queried for caching,
	* true if the returned rules will be cached by {@code ZoneId},
	* false if they will be returned to the user without being cached in {@code ZoneId}
	* @return the rules, null if {@code forCaching} is true and this
	* is a dynamic provider that wants to prevent caching in {@code ZoneId},
	* otherwise not null
	* @throws ZoneRulesException if rules cannot be obtained for the zone ID
	*/
	protected abstract ZoneRules provideRules(String zoneId, boolean forCaching);

	/**
	* SPI method to get the history of rules for the zone ID.
	* <p>
	* This returns a map of historical rules keyed by a version string.
	* The exact meaning and format of the version is provider specific.
	* The version must follow lexicographical order, thus the returned map will
	* be order from the oldest known rules to the newest available rules.
	* The default 'TZDB' group uses version numbering consisting of the year
	* followed by a letter, such as '2009e' or '2012f'.
	* <p>
	* Implementations must provide a result for each valid zone ID, however
	* they do not have to provide a history of rules.
	* Thus the map will contain at least one element, and will only contain
	* more than one element if historical rule information is available.
	* <p>
	* The returned versions remain available and valid for the lifetime of the application.
	* A dynamic provider may increase the set of versions as more data becomes available.
	*
	* @param zoneId the zone ID as defined by {@code ZoneId}, not null
	* @return a modifiable copy of the history of the rules for the ID, sorted
	* from oldest to newest, not null
	* @throws ZoneRulesException if history cannot be obtained for the zone ID
	*/
	protected abstract NavigableMap<String, ZoneRules> provideVersions(String zoneId);

	/**
	* SPI method to refresh the rules from the underlying data provider.
	* <p>
	* This method provides the opportunity for a provider to dynamically
	* recheck the underlying data provider to find the latest rules.
	* This could be used to load new rules without stopping the JVM.
	* Dynamic behavior is entirely optional and most providers do not support it.
	* <p>
	* This implementation returns false.
	*
	* @return true if the rules were updated
	* @throws ZoneRulesException if an error occurs during the refresh
	*/
	protected boolean provideRefresh() {
	return false;
	}

	}

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