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.
   */
  
  #pragma once
  
  #include "mongo/db/index/index_access_method.h"
  #include "mongo/db/index/wildcard_key_generator.h"
  #include "mongo/db/jsobj.h"
  #include "mongo/db/query/index_bounds.h"
  
  namespace mongo {
  
  /**
   * Class which is responsible for generating and providing access to Wildcard index keys. Any index
   * created with { "$**": ±1 } or { "path.$**": ±1 } uses this class.
   *
   * $** indexes store a special metadata key for each path in the index that is multikey. This class
   * provides an interface to access the multikey metadata: see getMultikeyPaths().
   */
  class WildcardAccessMethod final : public SortedDataIndexAccessMethod {
  public:
      WildcardAccessMethod(IndexCatalogEntry* wildcardState,
                           std::unique_ptr<SortedDataInterface> btree);
  
      /**
       * Returns 'true' if the index should become multikey on the basis of the passed arguments.
       * Because it is possible for a $** index to generate multiple keys per document without any of
       * them lying along a multikey (i.e. array) path, this method will only return 'true' if one or
       * more multikey metadata keys have been generated; that is, if the 'multikeyMetadataKeys'
       * vector is non-empty.
       */
      bool shouldMarkIndexAsMultikey(size_t numberOfKeys,
                                     const KeyStringSet& multikeyMetadataKeys,
                                     const MultikeyPaths& multikeyPaths) const final;
  
      /**
       * Returns a pointer to the WildcardProjection owned by the underlying WildcardKeyGenerator.
       */
      const WildcardProjection* getWildcardProjection() const {
          return _keyGen.getWildcardProjection();
      }
  
  private:
      void doGetKeys(OperationContext* opCtx,
                     const CollectionPtr& collection,
                     SharedBufferFragmentBuilder& pooledBufferBuilder,
                     const BSONObj& obj,
                     GetKeysContext context,
                     KeyStringSet* keys,
                     KeyStringSet* multikeyMetadataKeys,
                     MultikeyPaths* multikeyPaths,
                     boost::optional<RecordId> id) const final;
  
      const WildcardKeyGenerator _keyGen;
  };
  }  // namespace mongo
  