/**
    *
    * 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.IOException;
  import java.util.LinkedList;
  import java.util.List;
  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.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.MetaTableAccessor;
  import org.apache.hadoop.hbase.client.Connection;
  import org.apache.hadoop.hbase.errorhandling.ForeignException;
  import org.apache.hadoop.hbase.errorhandling.ForeignExceptionDispatcher;
  import org.apache.hadoop.hbase.executor.EventType;
  import org.apache.hadoop.hbase.master.AssignmentManager;
  import org.apache.hadoop.hbase.master.MasterFileSystem;
  import org.apache.hadoop.hbase.master.MasterServices;
  import org.apache.hadoop.hbase.master.MetricsSnapshot;
  import org.apache.hadoop.hbase.master.RegionStates;
  import org.apache.hadoop.hbase.master.SnapshotSentinel;
  import org.apache.hadoop.hbase.master.handler.TableEventHandler;
  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.RestoreSnapshotException;
  import org.apache.hadoop.hbase.snapshot.RestoreSnapshotHelper;
  import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;
  import org.apache.hadoop.hbase.snapshot.SnapshotManifest;
  
  /**
   * Handler to Restore a snapshot.
   *
   * <p>Uses {@link RestoreSnapshotHelper} to replace the table content with the
   * data available in the snapshot.
   */
  @InterfaceAudience.Private
  public class RestoreSnapshotHandler extends TableEventHandler implements SnapshotSentinel {
    private static final Log LOG = LogFactory.getLog(RestoreSnapshotHandler.class);
  
    private final HTableDescriptor hTableDescriptor;
    private final SnapshotDescription snapshot;
  
    private final ForeignExceptionDispatcher monitor;
    private final MetricsSnapshot metricsSnapshot = new MetricsSnapshot();
    private final MonitoredTask status;
  
    private volatile boolean stopped = false;
  
    public RestoreSnapshotHandler(final MasterServices masterServices,
        final SnapshotDescription snapshot, final HTableDescriptor htd) throws IOException {
      super(EventType.C_M_RESTORE_SNAPSHOT, htd.getTableName(), masterServices, masterServices);
  
      // Snapshot information
      this.snapshot = snapshot;
  
      // Monitor
      this.monitor = new ForeignExceptionDispatcher();
  
      // Check table exists.
      getTableDescriptor();
  
      // This is the new schema we are going to write out as this modification.
      this.hTableDescriptor = htd;
  
      this.status = TaskMonitor.get().createStatus(
        "Restoring  snapshot '" + snapshot.getName() + "' to table "
            + hTableDescriptor.getTableName());
    }
  
    @Override
    public RestoreSnapshotHandler prepare() throws IOException {
      return (RestoreSnapshotHandler) super.prepare();
    }
 
   /**
    * The restore table is executed in place.
    *  - The on-disk data will be restored - reference files are put in place without moving data
    *  -  [if something fail here: you need to delete the table and re-run the restore]
    *  - hbase:meta will be updated
    *  -  [if something fail here: you need to run hbck to fix hbase:meta entries]
    * The passed in list gets changed in this method
    */
   @Override
   protected void handleTableOperation(List<HRegionInfo> hris) throws IOException {
     MasterFileSystem fileSystemManager = masterServices.getMasterFileSystem();
     Connection conn = masterServices.getConnection();
     FileSystem fs = fileSystemManager.getFileSystem();
     Path rootDir = fileSystemManager.getRootDir();
     TableName tableName = hTableDescriptor.getTableName();
 
     try {
       // 1. Update descriptor
       this.masterServices.getTableDescriptors().add(hTableDescriptor);
 
       // 2. Execute the on-disk Restore
       LOG.debug("Starting restore snapshot=" + ClientSnapshotDescriptionUtils.toString(snapshot));
       Path snapshotDir = SnapshotDescriptionUtils.getCompletedSnapshotDir(snapshot, rootDir);
       SnapshotManifest manifest = SnapshotManifest.open(masterServices.getConfiguration(), fs,
                                                         snapshotDir, snapshot);
       RestoreSnapshotHelper restoreHelper = new RestoreSnapshotHelper(
           masterServices.getConfiguration(), fs, manifest,
           this.hTableDescriptor, rootDir, monitor, status);
       RestoreSnapshotHelper.RestoreMetaChanges metaChanges = restoreHelper.restoreHdfsRegions();
 
       // 3. Forces all the RegionStates to be offline
       //
       // The AssignmentManager keeps all the region states around
       // with no possibility to remove them, until the master is restarted.
       // This means that a region marked as SPLIT before the restore will never be assigned again.
       // To avoid having all states around all the regions are switched to the OFFLINE state,
       // which is the same state that the regions will be after a delete table.
       forceRegionsOffline(metaChanges);
 
       // 4. Applies changes to hbase:meta
       status.setStatus("Preparing to restore each region");
 
       // 4.1 Removes the current set of regions from META
       //
       // By removing also the regions to restore (the ones present both in the snapshot
       // and in the current state) we ensure that no extra fields are present in META
       // e.g. with a simple add addRegionToMeta() the splitA and splitB attributes
       // not overwritten/removed, so you end up with old informations
       // that are not correct after the restore.
       List<HRegionInfo> hrisToRemove = new LinkedList<HRegionInfo>();
       if (metaChanges.hasRegionsToRemove()) hrisToRemove.addAll(metaChanges.getRegionsToRemove());
       MetaTableAccessor.deleteRegions(conn, hrisToRemove);
 
       // 4.2 Add the new set of regions to META
       //
       // At this point the old regions are no longer present in META.
       // and the set of regions present in the snapshot will be written to META.
       // All the information in hbase:meta are coming from the .regioninfo of each region present
       // in the snapshot folder.
       hris.clear();
       if (metaChanges.hasRegionsToAdd()) hris.addAll(metaChanges.getRegionsToAdd());
       MetaTableAccessor.addRegionsToMeta(conn, hris, hTableDescriptor.getRegionReplication());
       if (metaChanges.hasRegionsToRestore()) {
         MetaTableAccessor.overwriteRegions(conn, metaChanges.getRegionsToRestore(),
           hTableDescriptor.getRegionReplication());
       }
       metaChanges.updateMetaParentRegions(this.server.getConnection(), hris);
 
       // At this point the restore is complete. Next step is enabling the table.
       LOG.info("Restore snapshot=" + ClientSnapshotDescriptionUtils.toString(snapshot) +
         " on table=" + tableName + " completed!");
     } catch (IOException e) {
       String msg = "restore snapshot=" + ClientSnapshotDescriptionUtils.toString(snapshot)
           + " failed. Try re-running the restore command.";
       LOG.error(msg, e);
       monitor.receive(new ForeignException(masterServices.getServerName().toString(), e));
       throw new RestoreSnapshotException(msg, e);
     }
   }
 
   private void forceRegionsOffline(final RestoreSnapshotHelper.RestoreMetaChanges metaChanges) {
     forceRegionsOffline(metaChanges.getRegionsToAdd());
     forceRegionsOffline(metaChanges.getRegionsToRestore());
     forceRegionsOffline(metaChanges.getRegionsToRemove());
   }
 
   private void forceRegionsOffline(final List<HRegionInfo> hris) {
     AssignmentManager am = this.masterServices.getAssignmentManager();
     RegionStates states = am.getRegionStates();
     if (hris != null) {
       for (HRegionInfo hri: hris) {
         states.regionOffline(hri);
       }
     }
   }
 
   @Override
   protected void completed(final Throwable exception) {
     this.stopped = true;
     if (exception != null) {
       status.abort("Restore snapshot '" + snapshot.getName() + "' failed because " +
           exception.getMessage());
     } else {
       status.markComplete("Restore snapshot '"+ snapshot.getName() +"'!");
     }
     metricsSnapshot.addSnapshotRestore(status.getCompletionTimestamp() - status.getStartTime());
     super.completed(exception);
   }
 
   @Override
   public boolean isFinished() {
     return this.stopped;
   }
 
   @Override
   public long getCompletionTimestamp() {
     return this.status.getCompletionTimestamp();
   }
 
   @Override
   public SnapshotDescription getSnapshot() {
     return snapshot;
   }
 
   @Override
   public void cancel(String why) {
     if (this.stopped) return;
     this.stopped = true;
     String msg = "Stopping restore snapshot=" + ClientSnapshotDescriptionUtils.toString(snapshot)
         + " because: " + why;
     LOG.info(msg);
     CancellationException ce = new CancellationException(why);
     this.monitor.receive(new ForeignException(masterServices.getServerName().toString(), ce));
   }
 
   @Override
   public ForeignException getExceptionIfFailed() {
     return this.monitor.getException();
   }
 
   @Override
   public void rethrowExceptionIfFailed() throws ForeignException {
     monitor.rethrowException();
   }
 }