text: /**
   *    Copyright (C) 2013 10gen Inc.
   *
   *    This program is free software: you can redistribute it and/or  modify
   *    it under the terms of the GNU Affero General Public License, version 3,
   *    as published by the Free Software Foundation.
   *
   *    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
   *    GNU Affero General Public License for more details.
   *
   *    You should have received a copy of the GNU Affero General Public License
   *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   *    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 GNU Affero General 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 <vector>
  
  #include "mongo/bson/util/builder.h"
  #include "mongo/db/matcher/expression.h"
  
  namespace mongo {
  
      // output from enumerator to query planner
      class IndexTag : public MatchExpression::TagData {
      public:
          static const size_t kNoIndex;
  
          IndexTag() : index(kNoIndex), pos(0) {}
          IndexTag(size_t i) : index(i), pos(0) { }
          IndexTag(size_t i, size_t p) : index(i), pos(p) { }
  
          virtual ~IndexTag() { }
  
          virtual void debugString(StringBuilder* builder) const {
              *builder << " || Selected Index #" << index << " pos " << pos;
          }
  
          virtual MatchExpression::TagData* clone() const {
              return new IndexTag(index, pos);
          }
  
          // What index should we try to use for this leaf?
          size_t index;
  
          // What position are we in the index?  (Compound.)
          size_t pos;
      };
  
      // used internally
      class RelevantTag : public MatchExpression::TagData {
      public:
          RelevantTag() : elemMatchExpr(NULL), pathPrefix("") { }
  
          std::vector<size_t> first;
          std::vector<size_t> notFirst;
  
          // We don't know the full path from a node unless we keep notes as we traverse from the
          // root.  We do this once and store it.
          // TODO: Do a FieldRef / StringData pass.
          // TODO: We might want this inside of the MatchExpression.
          string path;
  
          // Points to the innermost containing $elemMatch. If this tag is
          // attached to an expression not contained in an $elemMatch, then
          // 'elemMatchExpr' is NULL. Not owned here.
          MatchExpression* elemMatchExpr;
  
          // If not contained inside an elemMatch, 'pathPrefix' contains the
          // part of 'path' prior to the first dot. For example, if 'path' is
          // "a.b.c", then 'pathPrefix' is "a". If 'path' is just "a", then
          // 'pathPrefix' is also "a".
          //
          // If tagging a predicate contained in an $elemMatch, 'pathPrefix'
          // holds the prefix of the path *inside* the $elemMatch. If this
          // tags predicate {a: {$elemMatch: {"b.c": {$gt: 1}}}}, then
          // 'pathPrefix' is "b".
          //
          // Used by the plan enumerator to make sure that we never
          // compound two predicates sharing a path prefix.
          std::string pathPrefix;
  
          virtual void debugString(StringBuilder* builder) const {
              *builder << " || First: ";
              for (size_t i = 0; i < first.size(); ++i) {
                  *builder << first[i] << " ";
              }
              *builder << "notFirst: ";
              for (size_t i = 0; i < notFirst.size(); ++i) {
                  *builder << notFirst[i] << " ";
              }
              *builder << "full path: " << path;
          }
  
          virtual MatchExpression::TagData* clone() const {
              RelevantTag* ret = new RelevantTag();
              ret->first = first;
              ret->notFirst = notFirst;
              return ret;
          }
      };
  
      /**
       * Tags each node of the tree with the lowest numbered index that the sub-tree rooted at that
       * node uses.
       *
       * Nodes that satisfy Indexability::nodeCanUseIndexOnOwnField are already tagged if there
       * exists an index that that node can use.
       */
      void tagForSort(MatchExpression* tree);
  
      /**
       * Sorts the tree using its IndexTag(s). Nodes that use the same index are adjacent to one
       * another.
       */
      void sortUsingTags(MatchExpression* tree);
  
  } // namespace mongo
  