/**
   * Returns a new instance of this class based on the collection of ad group criteria provided.
   *
   * <p>NOTE: If retrieving existing criteria for use with this method, you must include all of the
   * fields in {@link #REQUIRED_SELECTOR_FIELDS} in your {@link Selector}.
   *
   * @param adGroupId the ID of the ad group
   * @param biddingStrategyConfig the {@link BiddingStrategyConfiguration} for the ad group
   * @param adGroupCriteria the non-null (but possibly empty) list of ad group criteria
   * @throws NullPointerException if any argument is null, any element in {@code adGroupCriteria} is
   *     null, or any required field from {@link #REQUIRED_SELECTOR_FIELDS} is missing from an
   *     element in {@code adGroupCriteria}
   * @throws IllegalArgumentException if {@code adGroupCriteria} does not include the root criterion
   *     of the product partition tree
   */
  public static ProductPartitionTree createAdGroupTree(
      Long adGroupId,
      BiddingStrategyConfiguration biddingStrategyConfig,
      List<AdGroupCriterion> adGroupCriteria) {
    Preconditions.checkNotNull(adGroupId, "Null ad group ID");
    Preconditions.checkNotNull(biddingStrategyConfig, "Null bidding strategy configuration");
    Preconditions.checkNotNull(adGroupCriteria, "Null criteria list");
    if (adGroupCriteria.isEmpty()) {
      return createEmptyAdGroupTree(adGroupId, biddingStrategyConfig);
    }

    ListMultimap<Long, AdGroupCriterion> parentIdMap = LinkedListMultimap.create();
    for (AdGroupCriterion adGroupCriterion : adGroupCriteria) {
      Preconditions.checkNotNull(
          adGroupCriterion.getCriterion(), "AdGroupCriterion has a null criterion");
      if (adGroupCriterion instanceof BiddableAdGroupCriterion) {
        BiddableAdGroupCriterion biddableCriterion = (BiddableAdGroupCriterion) adGroupCriterion;
        Preconditions.checkNotNull(
            biddableCriterion.getUserStatus(),
            "User status is null for criterion ID %s",
            biddableCriterion.getCriterion().getId());
        if (UserStatus.REMOVED.equals(biddableCriterion.getUserStatus())) {
          // Skip REMOVED criteria.
          continue;
        }
      }
      if (adGroupCriterion.getCriterion() instanceof ProductPartition) {
        ProductPartition partition = (ProductPartition) adGroupCriterion.getCriterion();
        parentIdMap.put(partition.getParentCriterionId(), adGroupCriterion);
      }
    }

    return createNonEmptyAdGroupTree(adGroupId, parentIdMap);
  }
  /**
   * Returns a new instance of this class by retrieving the product partitions of the specified ad
   * group. All parameters are required.
   */
  public static ProductPartitionTree createAdGroupTree(
      AdWordsServices services, AdWordsSession session, Long adGroupId)
      throws ApiException, RemoteException {
    // Get the AdGroupCriterionService.
    AdGroupCriterionServiceInterface criterionService =
        services.get(session, AdGroupCriterionServiceInterface.class);

    SelectorBuilder selectorBuilder =
        new SelectorBuilder()
            .fields(
                REQUIRED_SELECTOR_FIELD_ENUMS.toArray(
                    new AdGroupCriterionField[REQUIRED_SELECTOR_FIELD_ENUMS.size()]))
            .equals(AdGroupCriterionField.AdGroupId, adGroupId.toString())
            .equals(AdGroupCriterionField.CriteriaType, "PRODUCT_PARTITION")
            .in(
                AdGroupCriterionField.Status,
                UserStatus.ENABLED.getValue(),
                UserStatus.PAUSED.getValue())
            .limit(PAGE_SIZE);

    AdGroupCriterionPage adGroupCriterionPage;

    // A multimap from each product partition ID to its direct children.
    ListMultimap<Long, AdGroupCriterion> parentIdMap = LinkedListMultimap.create();
    int offset = 0;
    do {
      // Get the next page of results.
      adGroupCriterionPage = criterionService.get(selectorBuilder.build());

      if (adGroupCriterionPage != null && adGroupCriterionPage.getEntries() != null) {
        for (AdGroupCriterion adGroupCriterion : adGroupCriterionPage.getEntries()) {
          ProductPartition partition = (ProductPartition) adGroupCriterion.getCriterion();
          parentIdMap.put(partition.getParentCriterionId(), adGroupCriterion);
        }
        offset += adGroupCriterionPage.getEntries().length;
        selectorBuilder.increaseOffsetBy(PAGE_SIZE);
      }
    } while (offset < adGroupCriterionPage.getTotalNumEntries());

    // Construct the ProductPartitionTree from the parentIdMap.
    if (!parentIdMap.containsKey(null)) {
      Preconditions.checkState(
          parentIdMap.isEmpty(), "No root criterion found in the tree but the tree is not empty");
      return createEmptyAdGroupTree(
          adGroupId, getAdGroupBiddingStrategyConfiguration(services, session, adGroupId));
    }

    return createNonEmptyAdGroupTree(adGroupId, parentIdMap);
  }