text: /**
   *    Copyright (C) 2018-present MongoDB, Inc.
   *
   *    This program is free software: you can redistribute it and/or modify
   *    it under the terms of the Server Side Public License, version 1,
   *    as published by MongoDB, Inc.
   *
   *    This program is distributed in the hope that it will be useful,
   *    but WITHOUT ANY WARRANTY; without even the implied warranty of
   *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *    Server Side Public License for more details.
   *
   *    You should have received a copy of the Server Side Public License
   *    along with this program. If not, see
   *    <http://www.mongodb.com/licensing/server-side-public-license>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the Server Side Public License in all respects for
   *    all of the code used other than as permitted herein. If you modify file(s)
   *    with this exception, you may extend this exception to your version of the
   *    file(s), but you are not obligated to do so. If you do not wish to do so,
   *    delete this exception statement from your version. If you delete this
   *    exception statement from all source files in the program, then also delete
   *    it in the license file.
   */
  
  #include "mongo/platform/basic.h"
  
  #include <boost/intrusive_ptr.hpp>
  #include <vector>
  
  #include "mongo/bson/bsonmisc.h"
  #include "mongo/bson/bsonobj.h"
  #include "mongo/bson/bsonobjbuilder.h"
  #include "mongo/db/exec/document_value/document.h"
  #include "mongo/db/exec/document_value/document_value_test_util.h"
  #include "mongo/db/exec/document_value/value.h"
  #include "mongo/db/pipeline/aggregation_context_fixture.h"
  #include "mongo/db/pipeline/document_source_group.h"
  #include "mongo/db/pipeline/document_source_mock.h"
  #include "mongo/db/pipeline/document_source_sort.h"
  #include "mongo/db/pipeline/document_source_sort_by_count.h"
  #include "mongo/unittest/unittest.h"
  
  namespace mongo {
  namespace {
  using boost::intrusive_ptr;
  using std::list;
  using std::vector;
  
  /**
   * Fixture to test that $sortByCount returns a DocumentSourceGroup and DocumentSourceSort.
   */
  class SortByCountReturnsGroupAndSort : public AggregationContextFixture {
  public:
      void testCreateFromBsonResult(BSONObj sortByCountSpec, Value expectedGroupExplain) {
          list<intrusive_ptr<DocumentSource>> result =
              DocumentSourceSortByCount::createFromBson(sortByCountSpec.firstElement(), getExpCtx());
  
          ASSERT_EQUALS(result.size(), 2UL);
  
          const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result.front().get());
          ASSERT(groupStage);
  
          const auto* sortStage = dynamic_cast<DocumentSourceSort*>(result.back().get());
          ASSERT(sortStage);
  
          // Serialize the DocumentSourceGroup and DocumentSourceSort from $sortByCount so that we can
          // check the explain output to make sure $group and $sort have the correct fields.
          const auto explain = ExplainOptions::Verbosity::kQueryPlanner;
          vector<Value> explainedStages;
          groupStage->serializeToArray(explainedStages, explain);
          sortStage->serializeToArray(explainedStages, explain);
          ASSERT_EQUALS(explainedStages.size(), 2UL);
  
          auto groupExplain = explainedStages[0];
          ASSERT_VALUE_EQ(groupExplain["$group"], expectedGroupExplain);
  
          auto sortExplain = explainedStages[1];
          auto expectedSortExplain = Value{Document{{"sortKey", Document{{"count", -1}}}}};
          ASSERT_VALUE_EQ(sortExplain["$sort"], expectedSortExplain);
      }
  };
  
  TEST_F(SortByCountReturnsGroupAndSort, ExpressionFieldPathSpec) {
      BSONObj spec = BSON("$sortByCount"
                          << "$x");
      Value expectedGroupExplain =
          Value{Document{{"_id", "$x"_sd}, {"count", Document{{"$sum", Document{{"$const", 1}}}}}}};
      testCreateFromBsonResult(spec, expectedGroupExplain);
  }
  
  TEST_F(SortByCountReturnsGroupAndSort, ExpressionInObjectSpec) {
      BSONObj spec = BSON("$sortByCount" << BSON("$floor"
                                                 << "$x"));
      Value expectedGroupExplain =
          Value{Document{{"_id", Document{{"$floor", Value{BSON_ARRAY("$x")}}}},
                         {"count", Document{{"$sum", Document{{"$const", 1}}}}}}};
      testCreateFromBsonResult(spec, expectedGroupExplain);
  
      spec = BSON("$sortByCount" << BSON("$eq" << BSON_ARRAY("$x" << 15)));
      expectedGroupExplain =
          Value{Document{{"_id", Document{{"$eq", Value{BSON_ARRAY("$x" << BSON("$const" << 15))}}}},
                         {"count", Document{{"$sum", Document{{"$const", 1}}}}}}};
      testCreateFromBsonResult(spec, expectedGroupExplain);
  }
  
  /**
   * Fixture to test error cases of the $sortByCount stage.
   */
  class InvalidSortByCountSpec : public AggregationContextFixture {
  public:
      list<intrusive_ptr<DocumentSource>> createSortByCount(BSONObj sortByCountSpec) {
          auto specElem = sortByCountSpec.firstElement();
          return DocumentSourceSortByCount::createFromBson(specElem, getExpCtx());
      }
  };
  
  TEST_F(InvalidSortByCountSpec, NonObjectNonStringSpec) {
      BSONObj spec = BSON("$sortByCount" << 1);
      ASSERT_THROWS_CODE(createSortByCount(spec), AssertionException, 40149);
  
      spec = BSON("$sortByCount" << BSONNULL);
      ASSERT_THROWS_CODE(createSortByCount(spec), AssertionException, 40149);
  }
  
  TEST_F(InvalidSortByCountSpec, NonExpressionInObjectSpec) {
      BSONObj spec = BSON("$sortByCount" << BSON("field1"
                                                 << "$x"));
      ASSERT_THROWS_CODE(createSortByCount(spec), AssertionException, 40147);
  }
  
  TEST_F(InvalidSortByCountSpec, NonFieldPathStringSpec) {
      BSONObj spec = BSON("$sortByCount"
                          << "test");
      ASSERT_THROWS_CODE(createSortByCount(spec), AssertionException, 40148);
  }
  
  }  // namespace
  }  // namespace mongo
  