code: /*
   * 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.skywalking.generator;
  
  import java.util.HashSet;
  import java.util.Set;
  import java.util.concurrent.ThreadLocalRandom;
  import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
  import com.google.common.base.Preconditions;
  import lombok.Data;
  
  @JsonDeserialize(builder = IntGenerator.Builder.class)
  public final class IntGenerator implements Generator<Long> {
      private final boolean limitedDomain;
      private final Long min;
      private final Long max;
      private final Integer domainSize;
      private final ThreadLocalRandom random = ThreadLocalRandom.current();
      private final Set<Long> domain = new HashSet<>();
  
      public IntGenerator(Builder builder) {
          min = builder.min;
          max = builder.max;
          domainSize = builder.domainSize;
          limitedDomain = builder.domainSize != null && builder.domainSize > 0;
  
          reset();
      }
  
      @Override
      public Long next() {
          if (!limitedDomain) {
              return next0();
          }
          return domain
              .stream()
              .skip(random.nextInt(domain.size()))
              .findFirst()
              .orElseThrow(() -> new RuntimeException("Should never happen"));
      }
  
      @Override
      public void reset() {
          if (limitedDomain) {
              domain.clear();
  
              while (domain.size() < domainSize) {
                  domain.add(next0());
              }
          }
      }
  
      private long next0() {
          if (min != null && max != null) {
              return random.nextLong(max - min + 1) + min; // Might overflow, but it's not worthy to check
          }
          if (min != null) {
              return Math.abs(random.nextLong()) + min;
          }
          return random.nextLong(max);
      }
  
      @Override
      public String toString() {
          return String.valueOf(next());
      }
  
      @Data
      public static class Builder {
          private Long min;
          private Long max;
          private Integer domainSize;
  
          public IntGenerator build() {
              if (min != null && max != null) {
                  Preconditions.checkArgument(min <= max, "min must be <= max");
                  if (domainSize != null) {
                      Preconditions.checkArgument(domainSize <= max - min,
                          "domain size must be <= max - min");
                  }
              }
              return new IntGenerator(this);
          }
      }
  }
  