content: /*
   * 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.kafka.streams.processor.internals.assignment;
  
  import org.apache.kafka.streams.processor.TaskId;
  import org.apache.kafka.streams.processor.assignment.ProcessId;
  
  import org.slf4j.Logger;
  
  import java.util.Map;
  import java.util.Set;
  import java.util.function.Function;
  
  import static java.util.stream.Collectors.toMap;
  
  final class StandbyTaskAssignmentUtils {
      private StandbyTaskAssignmentUtils() {}
  
      static ConstrainedPrioritySet createLeastLoadedPrioritySetConstrainedByAssignedTask(final Map<ProcessId, ClientState> clients) {
          return new ConstrainedPrioritySet((client, t) -> !clients.get(client).hasAssignedTask(t),
                                            client -> clients.get(client).assignedTaskLoad());
      }
  
      static void pollClientAndMaybeAssignAndUpdateRemainingStandbyTasks(final int numStandbyReplicas,
                                                                         final Map<ProcessId, ClientState> clients,
                                                                         final Map<TaskId, Integer> tasksToRemainingStandbys,
                                                                         final ConstrainedPrioritySet standbyTaskClientsByTaskLoad,
                                                                         final TaskId activeTaskId,
                                                                         final Logger log) {
          int numRemainingStandbys = tasksToRemainingStandbys.get(activeTaskId);
          while (numRemainingStandbys > 0) {
              final ProcessId client = standbyTaskClientsByTaskLoad.poll(activeTaskId);
              if (client == null) {
                  break;
              }
              clients.get(client).assignStandby(activeTaskId);
              numRemainingStandbys--;
              standbyTaskClientsByTaskLoad.offer(client);
              tasksToRemainingStandbys.put(activeTaskId, numRemainingStandbys);
          }
  
          if (numRemainingStandbys > 0) {
              log.warn("Unable to assign {} of {} standby tasks for task [{}]. " +
                       "There is not enough available capacity. You should " +
                       "increase the number of application instances " +
                       "to maintain the requested number of standby replicas.",
                       numRemainingStandbys, numStandbyReplicas, activeTaskId);
          }
      }
  
      static Map<TaskId, Integer> computeTasksToRemainingStandbys(final int numStandbyReplicas,
                                                                  final Set<TaskId> statefulTaskIds) {
          return statefulTaskIds.stream().collect(toMap(Function.identity(), t -> numStandbyReplicas));
      }
  }
  