/**
    * 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.master.snapshot;
  
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.concurrent.CancellationException;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.MetaTableAccessor;
  import org.apache.hadoop.hbase.errorhandling.ForeignException;
  import org.apache.hadoop.hbase.errorhandling.ForeignExceptionDispatcher;
  import org.apache.hadoop.hbase.errorhandling.ForeignExceptionSnare;
  import org.apache.hadoop.hbase.executor.EventHandler;
  import org.apache.hadoop.hbase.executor.EventType;
  import org.apache.hadoop.hbase.master.MasterServices;
  import org.apache.hadoop.hbase.master.MetricsSnapshot;
  import org.apache.hadoop.hbase.master.SnapshotSentinel;
  import org.apache.hadoop.hbase.master.TableLockManager;
  import org.apache.hadoop.hbase.master.TableLockManager.TableLock;
  import org.apache.hadoop.hbase.monitoring.MonitoredTask;
  import org.apache.hadoop.hbase.monitoring.TaskMonitor;
  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.SnapshotDescription;
  import org.apache.hadoop.hbase.snapshot.ClientSnapshotDescriptionUtils;
  import org.apache.hadoop.hbase.snapshot.SnapshotCreationException;
  import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;
  import org.apache.hadoop.hbase.snapshot.SnapshotManifest;
  import org.apache.hadoop.hbase.util.FSUtils;
  import org.apache.hadoop.hbase.util.Pair;
  import org.apache.hadoop.hbase.zookeeper.MetaTableLocator;
  import org.apache.zookeeper.KeeperException;
  
  /**
   * A handler for taking snapshots from the master.
   *
   * This is not a subclass of TableEventHandler because using that would incur an extra hbase:meta scan.
   *
   * The {@link #snapshotRegions(List)} call should get implemented for each snapshot flavor.
   */
  @InterfaceAudience.Private
  public abstract class TakeSnapshotHandler extends EventHandler implements SnapshotSentinel,
      ForeignExceptionSnare {
    private static final Log LOG = LogFactory.getLog(TakeSnapshotHandler.class);
  
    private volatile boolean finished;
  
    // none of these should ever be null
    protected final MasterServices master;
    protected final MetricsSnapshot metricsSnapshot = new MetricsSnapshot();
    protected final SnapshotDescription snapshot;
    protected final Configuration conf;
    protected final FileSystem fs;
    protected final Path rootDir;
    private final Path snapshotDir;
    protected final Path workingDir;
    private final MasterSnapshotVerifier verifier;
    protected final ForeignExceptionDispatcher monitor;
    protected final TableLockManager tableLockManager;
    protected final TableLock tableLock;
    protected final MonitoredTask status;
    protected final TableName snapshotTable;
    protected final SnapshotManifest snapshotManifest;
  
    protected HTableDescriptor htd;
  
    /**
     * @param snapshot descriptor of the snapshot to take
     * @param masterServices master services provider
     */
    public TakeSnapshotHandler(SnapshotDescription snapshot, final MasterServices masterServices) {
      super(masterServices, EventType.C_M_SNAPSHOT_TABLE);
      assert snapshot != null : "SnapshotDescription must not be nul1";
     assert masterServices != null : "MasterServices must not be nul1";
 
     this.master = masterServices;
     this.snapshot = snapshot;
     this.snapshotTable = TableName.valueOf(snapshot.getTable());
     this.conf = this.master.getConfiguration();
     this.fs = this.master.getMasterFileSystem().getFileSystem();
     this.rootDir = this.master.getMasterFileSystem().getRootDir();
     this.snapshotDir = SnapshotDescriptionUtils.getCompletedSnapshotDir(snapshot, rootDir);
     this.workingDir = SnapshotDescriptionUtils.getWorkingSnapshotDir(snapshot, rootDir);
     this.monitor = new ForeignExceptionDispatcher(snapshot.getName());
     this.snapshotManifest = SnapshotManifest.create(conf, fs, workingDir, snapshot, monitor);
 
     this.tableLockManager = master.getTableLockManager();
     this.tableLock = this.tableLockManager.writeLock(
         snapshotTable,
         EventType.C_M_SNAPSHOT_TABLE.toString());
 
     // prepare the verify
     this.verifier = new MasterSnapshotVerifier(masterServices, snapshot, rootDir);
     // update the running tasks
     this.status = TaskMonitor.get().createStatus(
       "Taking " + snapshot.getType() + " snapshot on table: " + snapshotTable);
   }
 
   private HTableDescriptor loadTableDescriptor()
       throws FileNotFoundException, IOException {
     HTableDescriptor htd =
       this.master.getTableDescriptors().get(snapshotTable);
     if (htd == null) {
       throw new IOException("HTableDescriptor missing for " + snapshotTable);
     }
     return htd;
   }
 
   public TakeSnapshotHandler prepare() throws Exception {
     super.prepare();
     this.tableLock.acquire(); // after this, you should ensure to release this lock in
                               // case of exceptions
     boolean success = false;
     try {
       this.htd = loadTableDescriptor(); // check that .tableinfo is present
       success = true;
     } finally {
       if (!success) {
         releaseTableLock();
       }
     }
 
     return this;
   }
 
   /**
    * Execute the core common portions of taking a snapshot. The {@link #snapshotRegions(List)}
    * call should get implemented for each snapshot flavor.
    */
   @Override
   public void process() {
     String msg = "Running " + snapshot.getType() + " table snapshot " + snapshot.getName() + " "
         + eventType + " on table " + snapshotTable;
     LOG.info(msg);
     status.setStatus(msg);
     try {
       // If regions move after this meta scan, the region specific snapshot should fail, triggering
       // an external exception that gets captured here.
       SnapshotDescriptionUtils.createInProgressTag(workingDir, fs);
       // write down the snapshot info in the working directory
       SnapshotDescriptionUtils.writeSnapshotInfo(snapshot, workingDir, fs);
       snapshotManifest.addTableDescriptor(this.htd);
       monitor.rethrowException();
 
       List<Pair<HRegionInfo, ServerName>> regionsAndLocations;
       if (TableName.META_TABLE_NAME.equals(snapshotTable)) {
         regionsAndLocations = new MetaTableLocator().getMetaRegionsAndLocations(
           server.getZooKeeper());
       } else {
         regionsAndLocations = MetaTableAccessor.getTableRegionsAndLocations(
           server.getZooKeeper(), server.getConnection(), snapshotTable, false);
       }
 
       // run the snapshot
       snapshotRegions(regionsAndLocations);
       monitor.rethrowException();
 
       // extract each pair to separate lists
       Set<String> serverNames = new HashSet<String>();
       for (Pair<HRegionInfo, ServerName> p : regionsAndLocations) {
         if (p != null && p.getFirst() != null && p.getSecond() != null) {
           HRegionInfo hri = p.getFirst();
           if (hri.isOffline() && (hri.isSplit() || hri.isSplitParent())) continue;
           serverNames.add(p.getSecond().toString());
         }
       }
 
       // flush the in-memory state, and write the single manifest
       status.setStatus("Consolidate snapshot: " + snapshot.getName());
       snapshotManifest.consolidate();
 
       // verify the snapshot is valid
       status.setStatus("Verifying snapshot: " + snapshot.getName());
       verifier.verifySnapshot(this.workingDir, serverNames);
 
       // complete the snapshot, atomically moving from tmp to .snapshot dir.
       completeSnapshot(this.snapshotDir, this.workingDir, this.fs);
       msg = "Snapshot " + snapshot.getName() + " of table " + snapshotTable + " completed";
       status.markComplete(msg);
       LOG.info(msg);
       metricsSnapshot.addSnapshot(status.getCompletionTimestamp() - status.getStartTime());
     } catch (Exception e) {
       status.abort("Failed to complete snapshot " + snapshot.getName() + " on table " +
           snapshotTable + " because " + e.getMessage());
       String reason = "Failed taking snapshot " + ClientSnapshotDescriptionUtils.toString(snapshot)
           + " due to exception:" + e.getMessage();
       LOG.error(reason, e);
       ForeignException ee = new ForeignException(reason, e);
       monitor.receive(ee);
       // need to mark this completed to close off and allow cleanup to happen.
       cancel(reason);
     } finally {
       LOG.debug("Launching cleanup of working dir:" + workingDir);
       try {
         // if the working dir is still present, the snapshot has failed.  it is present we delete
         // it.
         if (fs.exists(workingDir) && !this.fs.delete(workingDir, true)) {
           LOG.error("Couldn't delete snapshot working directory:" + workingDir);
         }
       } catch (IOException e) {
         LOG.error("Couldn't delete snapshot working directory:" + workingDir);
       }
       releaseTableLock();
     }
   }
 
   protected void releaseTableLock() {
     if (this.tableLock != null) {
       try {
         this.tableLock.release();
       } catch (IOException ex) {
         LOG.warn("Could not release the table lock", ex);
       }
     }
   }
 
   /**
    * Reset the manager to allow another snapshot to proceed
    *
    * @param snapshotDir final path of the snapshot
    * @param workingDir directory where the in progress snapshot was built
    * @param fs {@link FileSystem} where the snapshot was built
    * @throws SnapshotCreationException if the snapshot could not be moved
    * @throws IOException the filesystem could not be reached
    */
   public void completeSnapshot(Path snapshotDir, Path workingDir, FileSystem fs)
       throws SnapshotCreationException, IOException {
     LOG.debug("Sentinel is done, just moving the snapshot from " + workingDir + " to "
         + snapshotDir);
     if (!fs.rename(workingDir, snapshotDir)) {
       throw new SnapshotCreationException("Failed to move working directory(" + workingDir
           + ") to completed directory(" + snapshotDir + ").");
     }
     finished = true;
   }
 
   /**
    * Snapshot the specified regions
    */
   protected abstract void snapshotRegions(List<Pair<HRegionInfo, ServerName>> regions)
       throws IOException, KeeperException;
 
   /**
    * Take a snapshot of the specified disabled region
    */
   protected void snapshotDisabledRegion(final HRegionInfo regionInfo)
       throws IOException {
     snapshotManifest.addRegion(FSUtils.getTableDir(rootDir, snapshotTable), regionInfo);
     monitor.rethrowException();
     status.setStatus("Completed referencing HFiles for offline region " + regionInfo.toString() +
         " of table: " + snapshotTable);
   }
 
   @Override
   public void cancel(String why) {
     if (finished) return;
 
     this.finished = true;
     LOG.info("Stop taking snapshot=" + ClientSnapshotDescriptionUtils.toString(snapshot) +
         " because: " + why);
     CancellationException ce = new CancellationException(why);
     monitor.receive(new ForeignException(master.getServerName().toString(), ce));
   }
 
   @Override
   public boolean isFinished() {
     return finished;
   }
 
   @Override
   public long getCompletionTimestamp() {
     return this.status.getCompletionTimestamp();
   }
 
   @Override
   public SnapshotDescription getSnapshot() {
     return snapshot;
   }
 
   @Override
   public ForeignException getExceptionIfFailed() {
     return monitor.getException();
   }
 
   @Override
   public void rethrowExceptionIfFailed() throws ForeignException {
     monitor.rethrowException();
   }
 
   @Override
   public void rethrowException() throws ForeignException {
     monitor.rethrowException();
   }
 
   @Override
   public boolean hasException() {
     return monitor.hasException();
   }
 
   @Override
   public ForeignException getException() {
     return monitor.getException();
   }
 
 }