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 * 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.
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package java.time.zone;

import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.util.Collections;
import java.util.HashSet;
import java.util.NavigableMap;
import java.util.Objects;
import java.util.ServiceLoader;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * 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 {
      // BEGIN Android-changed: use a single hard-coded provider.
      /*
      // 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);
      */
      ZoneRulesProvider provider = new IcuZoneRulesProvider();
      registerProvider(provider);
      // END Android-changed: use a single hard-coded provider.
    }

    // -------------------------------------------------------------------------
    /**
     * 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;
    }
}
