text: /**
   *    Copyright (C) 2020-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 "mongo/db/update/document_diff_test_helpers.h"
  
  #include "mongo/bson/json.h"
  #include "mongo/db/update/document_diff_applier.h"
  #include "mongo/platform/random.h"
  
  namespace mongo::doc_diff {
  
  BSONObj createObjWithLargePrefix(const std::string& suffix) {
      const static auto largeObj = BSON("prefixLargeField" << std::string(200, 'a'));
      return largeObj.addFields(fromjson(suffix));
  }
  
  std::string getFieldName(int level, int fieldNum) {
      return str::stream() << "f" << level << fieldNum;
  }
  
  Value getScalarFieldValue(PseudoRandom* rng) {
      switch (rng->nextInt32(10)) {
          case 0:
              return Value("val"_sd);
          case 1:
              return Value(BSONNULL);
          case 2:
              return Value(-1LL);
          case 3:
              return Value(0);
          case 4:
              return Value(1.10);
          case 5:
              return Value(false);
          case 6:
              return Value(BSONRegEx("p"));
          case 7:
              return Value(Date_t());
          case 8:
              return Value(UUID::gen());
          case 9:
              return Value(BSONBinData("asdf", 4, BinDataGeneral));
          default:
              MONGO_UNREACHABLE;
      }
  }
  
  BSONObj generateDoc(PseudoRandom* rng, MutableDocument* doc, int depthLevel) {
      // Append a large field at each level so that the likelihood of generating a sub-diff is high.
      auto largeFieldObj = createObjWithLargePrefix("{}");
      doc->addField("prefixLargeField", Value(largeFieldObj.firstElement()));
  
      // Reduce the probabilty of generated nested objects as we go deeper. After depth level 6, we
      // should not be generating anymore nested objects.
      const double subObjProbability = 0.3 - (depthLevel * 0.05);
      const double subArrayProbability = 0.2 - (depthLevel * 0.05);
  
      const int numFields = (5 - depthLevel) + rng->nextInt32(4);
      for (int fieldNum = 0; fieldNum < numFields; ++fieldNum) {
          const auto fieldName = getFieldName(depthLevel, fieldNum);
          auto num = rng->nextCanonicalDouble();
          if (num <= subObjProbability) {
              MutableDocument subDoc;
              doc->addField(fieldName, Value(generateDoc(rng, &subDoc, depthLevel + 1)));
          } else if (num <= (subObjProbability + subArrayProbability)) {
              const auto arrayLength = rng->nextInt32(10);
              std::vector<Value> values;
              auto numSubObjs = 0;
              for (auto i = 0; i < arrayLength; i++) {
                  // The probablilty of generating a sub-object goes down as we generate more
                  // sub-objects and as the array position increases.
                  if (!rng->nextInt32(2 + numSubObjs + i)) {
                      MutableDocument subDoc;
  
                      // Ensure that the depth is higher as we generate more sub-objects, to avoid
                      // bloating up the document size exponentially.
                      values.push_back(
                          Value(generateDoc(rng, &subDoc, depthLevel + 1 + numSubObjs * 2)));
                      ++numSubObjs;
                  } else {
                      values.push_back(getScalarFieldValue(rng));
                  }
              }
  
              doc->addField(fieldName, Value(values));
          } else {
              doc->addField(fieldName, getScalarFieldValue(rng));
          }
      }
      return doc->freeze().toBson();
  }
  
  BSONObj applyDiffTestHelper(BSONObj preImage,
                              BSONObj diff,
                              bool mustCheckExistenceForInsertOperations) {
      UpdateIndexData indexData;
      return applyDiff(preImage, diff, &indexData, mustCheckExistenceForInsertOperations).postImage;
  }
  
  }  // namespace mongo::doc_diff
  