/**
    *
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.hadoop.hbase.zookeeper;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.classification.InterfaceAudience;
  import org.apache.hadoop.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.Abortable;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.exceptions.ZooKeeperConnectionException;
  import org.apache.hadoop.hbase.util.Threads;
  import org.apache.zookeeper.KeeperException;
  import org.apache.zookeeper.WatchedEvent;
  import org.apache.zookeeper.Watcher;
  import org.apache.zookeeper.ZooDefs;
  import org.apache.zookeeper.data.ACL;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.concurrent.CountDownLatch;
  
  /**
   * Acts as the single ZooKeeper Watcher.  One instance of this is instantiated
   * for each Master, RegionServer, and client process.
   *
   * <p>This is the only class that implements {@link Watcher}.  Other internal
   * classes which need to be notified of ZooKeeper events must register with
   * the local instance of this watcher via {@link #registerListener}.
   *
   * <p>This class also holds and manages the connection to ZooKeeper.  Code to
   * deal with connection related events and exceptions are handled here.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Evolving
  public class ZooKeeperWatcher implements Watcher, Abortable, Closeable {
    private static final Log LOG = LogFactory.getLog(ZooKeeperWatcher.class);
  
    // Identifier for this watcher (for logging only).  It is made of the prefix
    // passed on construction and the zookeeper sessionid.
    private String identifier;
  
    // zookeeper quorum
    private String quorum;
  
    // zookeeper connection
    private RecoverableZooKeeper recoverableZooKeeper;
  
    // abortable in case of zk failure
    protected Abortable abortable;
    // Used if abortable is null
    private boolean aborted = false;
  
    // listeners to be notified
    private final List<ZooKeeperListener> listeners =
      new CopyOnWriteArrayList<ZooKeeperListener>();
  
    // Used by ZKUtil:waitForZKConnectionIfAuthenticating to wait for SASL
    // negotiation to complete
    public CountDownLatch saslLatch = new CountDownLatch(1);
  
    // node names
  
    // base znode for this cluster
    public String baseZNode;
    // znode containing location of server hosting meta region
    public String metaServerZNode;
    // znode containing ephemeral nodes of the regionservers
    public String rsZNode;
    // znode containing ephemeral nodes of the draining regionservers
    public String drainingZNode;
    // znode of currently active master
    private String masterAddressZNode;
    // znode of this master in backup master directory, if not the active master
    public String backupMasterAddressesZNode;
    // znode containing the current cluster state
    public String clusterStateZNode;
    // znode used for region transitioning and assignment
    public String assignmentZNode;
   // znode used for table disabling/enabling
   public String tableZNode;
   // znode containing the unique cluster ID
   public String clusterIdZNode;
   // znode used for log splitting work assignment
   public String splitLogZNode;
   // znode containing the state of the load balancer
   public String balancerZNode;
   // znode containing the lock for the tables
   public String tableLockZNode;
   // znode containing the state of recovering regions
   public String recoveringRegionsZNode;
 
   // Certain ZooKeeper nodes need to be world-readable
   public static final ArrayList<ACL> CREATOR_ALL_AND_WORLD_READABLE =
     new ArrayList<ACL>() { {
       add(new ACL(ZooDefs.Perms.READ,ZooDefs.Ids.ANYONE_ID_UNSAFE));
       add(new ACL(ZooDefs.Perms.ALL,ZooDefs.Ids.AUTH_IDS));
     }};
 
   private final Configuration conf;
 
   private final Exception constructorCaller;
 
   /**
    * Instantiate a ZooKeeper connection and watcher.
    * @param identifier string that is passed to RecoverableZookeeper to be used as
    * identifier for this instance. Use null for default.
    * @throws IOException
    * @throws ZooKeeperConnectionException
    */
   public ZooKeeperWatcher(Configuration conf, String identifier,
       Abortable abortable) throws ZooKeeperConnectionException, IOException {
     this(conf, identifier, abortable, false);
   }
 
   /**
    * Instantiate a ZooKeeper connection and watcher.
    * @param conf
    * @param identifier string that is passed to RecoverableZookeeper to be used as identifier for
    *          this instance. Use null for default.
    * @param abortable Can be null if there is on error there is no host to abort: e.g. client
    *          context.
    * @param canCreateBaseZNode
    * @throws IOException
    * @throws ZooKeeperConnectionException
    */
   public ZooKeeperWatcher(Configuration conf, String identifier,
       Abortable abortable, boolean canCreateBaseZNode)
   throws IOException, ZooKeeperConnectionException {
     this.conf = conf;
     // Capture a stack trace now.  Will print it out later if problem so we can
     // distingush amongst the myriad ZKWs.
     try {
       throw new Exception("ZKW CONSTRUCTOR STACK TRACE FOR DEBUGGING");
     } catch (Exception e) {
       this.constructorCaller = e;
     }
     this.quorum = ZKConfig.getZKQuorumServersString(conf);
     // Identifier will get the sessionid appended later below down when we
     // handle the syncconnect event.
     this.identifier = identifier;
     this.abortable = abortable;
     setNodeNames(conf);
     this.recoverableZooKeeper = ZKUtil.connect(conf, quorum, this, identifier);
     if (canCreateBaseZNode) {
       createBaseZNodes();
     }
   }
 
   private void createBaseZNodes() throws ZooKeeperConnectionException {
     try {
       // Create all the necessary "directories" of znodes
       ZKUtil.createWithParents(this, baseZNode);
       ZKUtil.createAndFailSilent(this, assignmentZNode);
       ZKUtil.createAndFailSilent(this, rsZNode);
       ZKUtil.createAndFailSilent(this, drainingZNode);
       ZKUtil.createAndFailSilent(this, tableZNode);
       ZKUtil.createAndFailSilent(this, splitLogZNode);
       ZKUtil.createAndFailSilent(this, backupMasterAddressesZNode);
       ZKUtil.createAndFailSilent(this, tableLockZNode);
       ZKUtil.createAndFailSilent(this, recoveringRegionsZNode);
     } catch (KeeperException e) {
       throw new ZooKeeperConnectionException(
           prefix("Unexpected KeeperException creating base node"), e);
     }
   }
 
   @Override
   public String toString() {
     return this.identifier;
   }
 
   /**
    * Adds this instance's identifier as a prefix to the passed <code>str</code>
    * @param str String to amend.
    * @return A new string with this instance's identifier as prefix: e.g.
    * if passed 'hello world', the returned string could be
    */
   public String prefix(final String str) {
     return this.toString() + " " + str;
   }
 
   /**
    * Set the local variable node names using the specified configuration.
    */
   private void setNodeNames(Configuration conf) {
     baseZNode = conf.get(HConstants.ZOOKEEPER_ZNODE_PARENT,
         HConstants.DEFAULT_ZOOKEEPER_ZNODE_PARENT);
     metaServerZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.metaserver", "meta-region-server"));
     rsZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.rs", "rs"));
     drainingZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.draining.rs", "draining"));
     masterAddressZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.master", "master"));
     backupMasterAddressesZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.backup.masters", "backup-masters"));
     clusterStateZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.state", "running"));
     assignmentZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.unassigned", "region-in-transition"));
     tableZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.tableEnableDisable", "table"));
     clusterIdZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.clusterId", "hbaseid"));
     splitLogZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.splitlog", HConstants.SPLIT_LOGDIR_NAME));
     balancerZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.balancer", "balancer"));
     tableLockZNode = ZKUtil.joinZNode(baseZNode,
         conf.get("zookeeper.znode.tableLock", "table-lock"));
     recoveringRegionsZNode = ZKUtil.joinZNode(baseZNode,
       conf.get("zookeeper.znode.recovering.regions", "recovering-regions"));
   }
 
   /**
    * Register the specified listener to receive ZooKeeper events.
    * @param listener
    */
   public void registerListener(ZooKeeperListener listener) {
     listeners.add(listener);
   }
 
   /**
    * Register the specified listener to receive ZooKeeper events and add it as
    * the first in the list of current listeners.
    * @param listener
    */
   public void registerListenerFirst(ZooKeeperListener listener) {
     listeners.add(0, listener);
   }
 
   public void unregisterListener(ZooKeeperListener listener) {
     listeners.remove(listener);
   }
 
   /**
    * Clean all existing listeners
    */
   public void unregisterAllListeners() {
     listeners.clear();
   }
 
   /**
    * @return The number of currently registered listeners
    */
   public int getNumberOfListeners() {
     return listeners.size();
   }
 
   /**
    * Get the connection to ZooKeeper.
    * @return connection reference to zookeeper
    */
   public RecoverableZooKeeper getRecoverableZooKeeper() {
     return recoverableZooKeeper;
   }
 
   public void reconnectAfterExpiration() throws IOException, InterruptedException {
     recoverableZooKeeper.reconnectAfterExpiration();
   }
 
   /**
    * Get the quorum address of this instance.
    * @return quorum string of this zookeeper connection instance
    */
   public String getQuorum() {
     return quorum;
   }
 
   /**
    * Method called from ZooKeeper for events and connection status.
    * <p>
    * Valid events are passed along to listeners.  Connection status changes
    * are dealt with locally.
    */
   @Override
   public void process(WatchedEvent event) {
     LOG.debug(prefix("Received ZooKeeper Event, " +
         "type=" + event.getType() + ", " +
         "state=" + event.getState() + ", " +
         "path=" + event.getPath()));
 
     switch(event.getType()) {
 
       // If event type is NONE, this is a connection status change
       case None: {
         connectionEvent(event);
         break;
       }
 
       // Otherwise pass along to the listeners
 
       case NodeCreated: {
         for(ZooKeeperListener listener : listeners) {
           listener.nodeCreated(event.getPath());
         }
         break;
       }
 
       case NodeDeleted: {
         for(ZooKeeperListener listener : listeners) {
           listener.nodeDeleted(event.getPath());
         }
         break;
       }
 
       case NodeDataChanged: {
         for(ZooKeeperListener listener : listeners) {
           listener.nodeDataChanged(event.getPath());
         }
         break;
       }
 
       case NodeChildrenChanged: {
         for(ZooKeeperListener listener : listeners) {
           listener.nodeChildrenChanged(event.getPath());
         }
         break;
       }
     }
   }
 
   // Connection management
 
   /**
    * Called when there is a connection-related event via the Watcher callback.
    * <p>
    * If Disconnected or Expired, this should shutdown the cluster. But, since
    * we send a KeeperException.SessionExpiredException along with the abort
    * call, it's possible for the Abortable to catch it and try to create a new
    * session with ZooKeeper. This is what the client does in HCM.
    * <p>
    * @param event
    */
   private void connectionEvent(WatchedEvent event) {
     switch(event.getState()) {
       case SyncConnected:
         // Now, this callback can be invoked before the this.zookeeper is set.
         // Wait a little while.
         long finished = System.currentTimeMillis() +
           this.conf.getLong("hbase.zookeeper.watcher.sync.connected.wait", 2000);
         while (System.currentTimeMillis() < finished) {
           Threads.sleep(1);
           if (this.recoverableZooKeeper != null) break;
         }
         if (this.recoverableZooKeeper == null) {
           LOG.error("ZK is null on connection event -- see stack trace " +
             "for the stack trace when constructor was called on this zkw",
             this.constructorCaller);
           throw new NullPointerException("ZK is null");
         }
         this.identifier = this.identifier + "-0x" +
           Long.toHexString(this.recoverableZooKeeper.getSessionId());
         // Update our identifier.  Otherwise ignore.
         LOG.debug(this.identifier + " connected");
         break;
 
       // Abort the server if Disconnected or Expired
       case Disconnected:
         LOG.debug(prefix("Received Disconnected from ZooKeeper, ignoring"));
         break;
 
       case Expired:
         String msg = prefix(this.identifier + " received expired from " +
           "ZooKeeper, aborting");
         // TODO: One thought is to add call to ZooKeeperListener so say,
         // ZooKeeperNodeTracker can zero out its data values.
         if (this.abortable != null) {
           this.abortable.abort(msg, new KeeperException.SessionExpiredException());
         }
         break;
 
       case ConnectedReadOnly:
         break;
 
       default:
         throw new IllegalStateException("Received event is not valid.");
     }
   }
 
   /**
    * Forces a synchronization of this ZooKeeper client connection.
    * <p>
    * Executing this method before running other methods will ensure that the
    * subsequent operations are up-to-date and consistent as of the time that
    * the sync is complete.
    * <p>
    * This is used for compareAndSwap type operations where we need to read the
    * data of an existing node and delete or transition that node, utilizing the
    * previously read version and data.  We want to ensure that the version read
    * is up-to-date from when we begin the operation.
    */
   public void sync(String path) {
     this.recoverableZooKeeper.sync(path, null, null);
   }
 
   /**
    * Handles KeeperExceptions in client calls.
    * <p>
    * This may be temporary but for now this gives one place to deal with these.
    * <p>
    * TODO: Currently this method rethrows the exception to let the caller handle
    * <p>
    * @param ke
    * @throws KeeperException
    */
   public void keeperException(KeeperException ke)
   throws KeeperException {
     LOG.error(prefix("Received unexpected KeeperException, re-throwing exception"), ke);
     throw ke;
   }
 
   /**
    * Handles InterruptedExceptions in client calls.
    * <p>
    * This may be temporary but for now this gives one place to deal with these.
    * <p>
    * TODO: Currently, this method does nothing.
    *       Is this ever expected to happen?  Do we abort or can we let it run?
    *       Maybe this should be logged as WARN?  It shouldn't happen?
    * <p>
    * @param ie
    */
   public void interruptedException(InterruptedException ie) {
     LOG.debug(prefix("Received InterruptedException, doing nothing here"), ie);
     // At least preserver interrupt.
     Thread.currentThread().interrupt();
     // no-op
   }
 
   /**
    * Close the connection to ZooKeeper.
    *
    * @throws InterruptedException
    */
   public void close() {
     try {
       if (recoverableZooKeeper != null) {
         recoverableZooKeeper.close();
       }
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
     }
   }
 
   public Configuration getConfiguration() {
     return conf;
   }
 
   @Override
   public void abort(String why, Throwable e) {
     if (this.abortable != null) this.abortable.abort(why, e);
     else this.aborted = true;
   }
 
   @Override
   public boolean isAborted() {
     return this.abortable == null? this.aborted: this.abortable.isAborted();
   }
 
   /**
    * @return Path to the currently active master.
    */
   public String getMasterAddressZNode() {
     return this.masterAddressZNode;
   }
 
 }