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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.
   */
  
  package org.apache.cassandra.simulator.systems;
  
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.function.LongSupplier;
  import java.util.function.Supplier;
  
  import org.apache.cassandra.service.paxos.Ballot;
  import org.apache.cassandra.service.paxos.BallotGenerator;
  import org.apache.cassandra.simulator.RandomSource;
  import org.apache.cassandra.simulator.RandomSource.Choices;
  
  import static org.apache.cassandra.service.paxos.Ballot.atUnixMicrosWithLsb;
  
  // TODO (feature): link with SimulateTime, and otherwise improve
  public class SimulatedBallots
  {
      enum Next { ONE, JUMP, TO_LATEST }
  
      final LongSupplier uniqueSupplier; // must be unique for all ballots
      final RandomSource random;
      final Choices<Next> nextChoice;
      final LongSupplier nextJump;
      final AtomicLong latest = new AtomicLong(1L);
  
      public SimulatedBallots(RandomSource random, Supplier<LongSupplier> jumpsSupplier)
      {
          this.uniqueSupplier = random.uniqueUniformSupplier(Long.MIN_VALUE, Long.MAX_VALUE);
          this.random = random;
          this.nextChoice = Choices.random(random, Next.values());
          this.nextJump = jumpsSupplier.get();
      }
  
      class Generator extends AtomicLong implements BallotGenerator
      {
          public Generator()
          {
              super(1L);
          }
  
          public Ballot atUnixMicros(long unixMicros, Ballot.Flag flag)
          {
              return atUnixMicrosWithLsb(unixMicros, uniqueSupplier.getAsLong(), flag);
          }
  
          public Ballot next(long minUnixMicros, Ballot.Flag flag)
          {
              return Ballot.atUnixMicrosWithLsb(nextBallotTimestampMicros(minUnixMicros), uniqueSupplier.getAsLong(), flag);
          }
  
          public Ballot stale(long from, long to, Ballot.Flag flag)
          {
              return Ballot.atUnixMicrosWithLsb(random.uniform(from, to), uniqueSupplier.getAsLong(), flag);
          }
  
          private long nextBallotTimestampMicros(long minUnixMicros)
          {
              long next;
              switch (nextChoice.choose(random))
              {
                  default: throw new IllegalStateException();
                  case TO_LATEST:
                      minUnixMicros = Math.max(latest.get(), minUnixMicros);
                  case ONE:
                      next = accumulateAndGet(minUnixMicros, (a, b) -> Math.max(a, b) + 1);
                      break;
                  case JUMP:
                      long jump = Math.max(1, nextJump.getAsLong());
                      next = addAndGet(jump);
                      if (next < minUnixMicros)
                          next = accumulateAndGet(minUnixMicros, (a, b) -> Math.max(a, b) + 1);
              }
              latest.accumulateAndGet(next, Math::max);
              return next;
          }
  
          public long prevUnixMicros()
          {
              return get();
          }
      }
  
      public BallotGenerator get()
      {
          return new Generator();
      }
  }
  