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   * 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.
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  package org.apache.cassandra.repair;
  
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  
  import com.google.common.base.Preconditions;
  
  import org.apache.cassandra.concurrent.ExecutorPlus;
  import org.apache.cassandra.config.DatabaseDescriptor;
  import org.apache.cassandra.db.ColumnFamilyStore;
  import org.apache.cassandra.db.Keyspace;
  import org.apache.cassandra.dht.Range;
  import org.apache.cassandra.dht.Token;
  import org.apache.cassandra.locator.InetAddressAndPort;
  import org.apache.cassandra.metrics.RepairMetrics;
  import org.apache.cassandra.repair.consistent.SyncStatSummary;
  import org.apache.cassandra.service.snapshot.SnapshotManager;
  import org.apache.cassandra.streaming.PreviewKind;
  import org.apache.cassandra.utils.DiagnosticSnapshotService;
  import org.apache.cassandra.utils.TimeUUID;
  import org.apache.cassandra.utils.concurrent.Future;
  
  public class PreviewRepairTask extends AbstractRepairTask
  {
      private final TimeUUID parentSession;
      private final List<CommonRange> commonRanges;
      private final boolean excludedDeadNodes;
      private final String[] cfnames;
      private volatile String successMessage = name() + " completed successfully";
  
      protected PreviewRepairTask(RepairCoordinator coordinator, TimeUUID parentSession, List<CommonRange> commonRanges, boolean excludedDeadNodes, String[] cfnames)
      {
          super(coordinator);
          this.parentSession = parentSession;
          this.commonRanges = commonRanges;
          this.excludedDeadNodes = excludedDeadNodes;
          this.cfnames = cfnames;
      }
  
      @Override
      public String name()
      {
          return "Repair preview";
      }
  
      @Override
      public String successMessage()
      {
          return successMessage;
      }
  
      @Override
      public Future<CoordinatedRepairResult> performUnsafe(ExecutorPlus executor, Scheduler validationScheduler)
      {
          Future<CoordinatedRepairResult> f = runRepair(parentSession, false, executor, validationScheduler, commonRanges, excludedDeadNodes, cfnames);
          return f.map(result -> {
              if (result.hasFailed())
                  return result;
  
              PreviewKind previewKind = options.getPreviewKind();
              Preconditions.checkState(previewKind != PreviewKind.NONE, "Preview is NONE");
              SyncStatSummary summary = new SyncStatSummary(true);
              summary.consumeSessionResults(result.results);
  
              final String message;
              if (summary.isEmpty())
              {
                  message = previewKind == PreviewKind.REPAIRED ? "Repaired data is in sync" : "Previewed data was in sync";
              }
              else
              {
                  message = (previewKind == PreviewKind.REPAIRED ? "Repaired data is inconsistent\n" : "Preview complete\n") + summary;
                  if (previewKind == PreviewKind.REPAIRED)
                      maybeSnapshotReplicas(parentSession, keyspace, result.results.get()); // we know its present as summary used it
              }
              emitMetrics(summary);
              successMessage += "; " + message;
              coordinator.notification(message);
  
              return result;
          });
      }
  
      private void emitMetrics(SyncStatSummary summary)
      {
          if (!summary.isEmpty())
              RepairMetrics.previewFailures.inc();
  
          summary.getTotals().forEach((key, table) -> {
              if (table.isCounter())
                  return;
  
              ColumnFamilyStore cfs = Keyspace.open(key.left).getColumnFamilyStore(key.right);
              cfs.metric.tokenRangesPreviewedDesynchronized.mark(table.getRanges());
              cfs.metric.bytesPreviewedDesynchronized.mark(table.getBytes());
          });
      }
  
      private void maybeSnapshotReplicas(TimeUUID parentSession, String keyspace, List<RepairSessionResult> results)
      {
          if (!DatabaseDescriptor.snapshotOnRepairedDataMismatch())
              return;
  
          try
          {
              Set<String> mismatchingTables = new HashSet<>();
              Set<InetAddressAndPort> nodes = new HashSet<>();
              Set<Range<Token>> ranges = new HashSet<>();
              for (RepairSessionResult sessionResult : results)
              {
                  for (RepairResult repairResult : emptyIfNull(sessionResult.repairJobResults))
                  {
                      for (SyncStat stat : emptyIfNull(repairResult.stats))
                      {
                          if (!stat.differences.isEmpty())
                          {
                              mismatchingTables.add(repairResult.desc.columnFamily);
                              ranges.addAll(stat.differences);
                          }
                          // snapshot all replicas, even if they don't have any differences
                          nodes.add(stat.nodes.coordinator);
                          nodes.add(stat.nodes.peer);
                      }
                  }
              }
  
              String snapshotName = DiagnosticSnapshotService.getSnapshotName(DiagnosticSnapshotService.REPAIRED_DATA_MISMATCH_SNAPSHOT_PREFIX);
              for (String table : mismatchingTables)
              {
                  // we can just check snapshot existence locally since the repair coordinator is always a replica (unlike in the read case)
                  if (!SnapshotManager.instance.exists(keyspace, table, snapshotName))
                  {
                      List<Range<Token>> normalizedRanges = Range.normalize(ranges);
                      logger.info("{} Snapshotting {}.{} for preview repair mismatch for ranges {} with tag {} on instances {}",
                                  options.getPreviewKind().logPrefix(parentSession),
                                  keyspace, table, normalizedRanges, snapshotName, nodes);
                      DiagnosticSnapshotService.repairedDataMismatch(Keyspace.open(keyspace).getColumnFamilyStore(table).metadata(),
                                                                     nodes,
                                                                     normalizedRanges);
                  }
                  else
                  {
                      logger.info("{} Not snapshotting {}.{} - snapshot {} exists",
                                  options.getPreviewKind().logPrefix(parentSession),
                                  keyspace, table, snapshotName);
                  }
              }
          }
          catch (Exception e)
          {
              logger.error("{} Failed snapshotting replicas", options.getPreviewKind().logPrefix(parentSession), e);
          }
      }
  
      private static <T> Iterable<T> emptyIfNull(Iterable<T> iter)
      {
          if (iter == null)
              return Collections.emptyList();
          return iter;
      }
  }
  