/**
    * 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.List;
  import java.util.Map;
  import java.util.Set;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  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.client.RegionReplicaUtil;
  import org.apache.hadoop.hbase.MetaTableAccessor;
  import org.apache.hadoop.hbase.master.MasterServices;
  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.SnapshotDescription;
  import org.apache.hadoop.hbase.protobuf.generated.SnapshotProtos.SnapshotRegionManifest;
  import org.apache.hadoop.hbase.snapshot.ClientSnapshotDescriptionUtils;
  import org.apache.hadoop.hbase.snapshot.CorruptedSnapshotException;
  import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;
  import org.apache.hadoop.hbase.snapshot.SnapshotManifest;
  import org.apache.hadoop.hbase.snapshot.SnapshotReferenceUtil;
  import org.apache.hadoop.hbase.util.FSUtils;
  import org.apache.hadoop.hbase.zookeeper.MetaTableLocator;
  
  /**
   * General snapshot verification on the master.
   * <p>
   * This is a light-weight verification mechanism for all the files in a snapshot. It doesn't
   * attempt to verify that the files are exact copies (that would be paramount to taking the
   * snapshot again!), but instead just attempts to ensure that the files match the expected
   * files and are the same length.
   * <p>
   * Taking an online snapshots can race against other operations and this is an last line of
   * defense.  For example, if meta changes between when snapshots are taken not all regions of a
   * table may be present.  This can be caused by a region split (daughters present on this scan,
   * but snapshot took parent), or move (snapshots only checks lists of region servers, a move could
   * have caused a region to be skipped or done twice).
   * <p>
   * Current snapshot files checked:
   * <ol>
   * <li>SnapshotDescription is readable</li>
   * <li>Table info is readable</li>
   * <li>Regions</li>
   * </ol>
   * <ul>
   * <li>Matching regions in the snapshot as currently in the table</li>
   * <li>{@link HRegionInfo} matches the current and stored regions</li>
   * <li>All referenced hfiles have valid names</li>
   * <li>All the hfiles are present (either in .archive directory in the region)</li>
   * <li>All recovered.edits files are present (by name) and have the correct file size</li>
   * </ul>
   */
  @InterfaceAudience.Private
  @InterfaceStability.Unstable
  public final class MasterSnapshotVerifier {
    private static final Log LOG = LogFactory.getLog(MasterSnapshotVerifier.class);
  
    private SnapshotDescription snapshot;
    private FileSystem workingDirFs;
    private TableName tableName;
    private MasterServices services;
  
    /**
     * @param services services for the master
     * @param snapshot snapshot to check
     * @param workingDirFs the file system containing the temporary snapshot information
     */
    public MasterSnapshotVerifier(MasterServices services,
        SnapshotDescription snapshot, FileSystem workingDirFs) {
      this.workingDirFs = workingDirFs;
      this.services = services;
      this.snapshot = snapshot;
      this.tableName = TableName.valueOf(snapshot.getTable());
    }
  
    /**
     * Verify that the snapshot in the directory is a valid snapshot
    * @param snapshotDir snapshot directory to check
    * @param snapshotServers {@link org.apache.hadoop.hbase.ServerName} 
    * of the servers that are involved in the snapshot
    * @throws CorruptedSnapshotException if the snapshot is invalid
    * @throws IOException if there is an unexpected connection issue to the filesystem
    */
   public void verifySnapshot(Path snapshotDir, Set<String> snapshotServers)
       throws CorruptedSnapshotException, IOException {
     SnapshotManifest manifest = SnapshotManifest.open(services.getConfiguration(), workingDirFs,
                                                       snapshotDir, snapshot);
     // verify snapshot info matches
     verifySnapshotDescription(snapshotDir);
 
     // check that tableinfo is a valid table description
     verifyTableInfo(manifest);
 
     // check that each region is valid
     verifyRegions(manifest);
   }
 
   /**
    * Check that the snapshot description written in the filesystem matches the current snapshot
    * @param snapshotDir snapshot directory to check
    */
   private void verifySnapshotDescription(Path snapshotDir) throws CorruptedSnapshotException {
     SnapshotDescription found = SnapshotDescriptionUtils.readSnapshotInfo(workingDirFs,
         snapshotDir);
     if (!this.snapshot.equals(found)) {
       throw new CorruptedSnapshotException("Snapshot read (" + found
           + ") doesn't equal snapshot we ran (" + snapshot + ").", snapshot);
     }
   }
 
   /**
    * Check that the table descriptor for the snapshot is a valid table descriptor
    * @param manifest snapshot manifest to inspect
    */
   private void verifyTableInfo(final SnapshotManifest manifest) throws IOException {
     HTableDescriptor htd = manifest.getTableDescriptor();
     if (htd == null) {
       throw new CorruptedSnapshotException("Missing Table Descriptor", snapshot);
     }
 
     if (!htd.getNameAsString().equals(snapshot.getTable())) {
       throw new CorruptedSnapshotException("Invalid Table Descriptor. Expected "
         + snapshot.getTable() + " name, got " + htd.getNameAsString(), snapshot);
     }
   }
 
   /**
    * Check that all the regions in the snapshot are valid, and accounted for.
    * @param manifest snapshot manifest to inspect
    * @throws IOException if we can't reach hbase:meta or read the files from the FS
    */
   private void verifyRegions(final SnapshotManifest manifest) throws IOException {
     List<HRegionInfo> regions;
     if (TableName.META_TABLE_NAME.equals(tableName)) {
       regions = new MetaTableLocator().getMetaRegions(services.getZooKeeper());
     } else {
       regions = MetaTableAccessor.getTableRegions(services.getZooKeeper(),
         services.getConnection(), tableName);
     }
     // Remove the non-default regions
     RegionReplicaUtil.removeNonDefaultRegions(regions);
 
     Map<String, SnapshotRegionManifest> regionManifests = manifest.getRegionManifestsMap();
     if (regionManifests == null) {
       String msg = "Snapshot " + ClientSnapshotDescriptionUtils.toString(snapshot) + " looks empty";
       LOG.error(msg);
       throw new CorruptedSnapshotException(msg);
     }
 
     String errorMsg = "";
     if (regionManifests.size() != regions.size()) {
       errorMsg = "Regions moved during the snapshot '" +
                    ClientSnapshotDescriptionUtils.toString(snapshot) + "'. expected=" +
                    regions.size() + " snapshotted=" + regionManifests.size() + ".";
       LOG.error(errorMsg);
     }
 
     // Verify HRegionInfo
     for (HRegionInfo region : regions) {
       SnapshotRegionManifest regionManifest = regionManifests.get(region.getEncodedName());
       if (regionManifest == null) {
         // could happen due to a move or split race.
         String mesg = " No snapshot region directory found for region:" + region;
         if (errorMsg.isEmpty()) errorMsg = mesg;
         LOG.error(mesg);
         continue;
       }
 
       verifyRegionInfo(region, regionManifest);
     }
 
     if (!errorMsg.isEmpty()) {
       throw new CorruptedSnapshotException(errorMsg);
     }
 
     // Verify Snapshot HFiles
     // Requires the root directory file system as HFiles are stored in the root directory
     SnapshotReferenceUtil.verifySnapshot(services.getConfiguration(),
         FSUtils.getRootDirFileSystem(services.getConfiguration()), manifest);
   }
 
   /**
    * Verify that the regionInfo is valid
    * @param region the region to check
    * @param manifest snapshot manifest to inspect
    */
   private void verifyRegionInfo(final HRegionInfo region,
       final SnapshotRegionManifest manifest) throws IOException {
     HRegionInfo manifestRegionInfo = HRegionInfo.convert(manifest.getRegionInfo());
     if (!region.equals(manifestRegionInfo)) {
       String msg = "Manifest region info " + manifestRegionInfo +
                    "doesn't match expected region:" + region;
       throw new CorruptedSnapshotException(msg, snapshot);
     }
   }
 }