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/* Copyright 2009 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#pragma once

#include "jsobj.h"
#include "mongo/db/index/btree_key_generator.h"

namespace mongo {

    //maximum number of intervals produced by $in queries.
    static const unsigned MAX_IN_COMBINATIONS = 4000000;

    /**
* One side of an interval of BSONElements, defined by a value and a boolean indicating if the
* interval includes the value.
*/
    struct FieldBound {
        BSONElement _bound;
        bool _inclusive;
        bool operator==( const FieldBound &other ) const {
            return _bound.woCompare( other._bound ) == 0 &&
                   _inclusive == other._inclusive;
        }
        void flipInclusive() { _inclusive = !_inclusive; }
    };

    // Keep track of what special indices we're using. This can be nontrivial
    // because an index could be required by one operator but not by another.
    struct SpecialIndices {
        // Unlike true/false, this is readable. :)
        enum IndexRequired {
            INDEX_REQUIRED,
            NO_INDEX_REQUIRED,
        };
        map<string, bool> _indexRequired;

        bool has(const string& name) const {
            return _indexRequired.end() != _indexRequired.find(name);
        }

        SpecialIndices combineWith(const SpecialIndices& other) {
            SpecialIndices ret = *this;
            for (map<string, bool>::const_iterator it = other._indexRequired.begin();
                 it != other._indexRequired.end(); ++it) {
                ret._indexRequired[it->first] = ret._indexRequired[it->first] || it->second;
            }
            return ret;
        }


        void add(const string& name, IndexRequired req) {
            _indexRequired[name] = _indexRequired[name] || (req == INDEX_REQUIRED);
        }

        bool allRequireIndex() const {
            for (map<string, bool>::const_iterator it = _indexRequired.begin();
                 it != _indexRequired.end(); ++it) {
                if (!it->second) { return false; }
            }
            return true;
        }

        bool empty() const { return _indexRequired.empty(); }
        string toString() const {
            stringstream ss;
            for (map<string, bool>::const_iterator it = _indexRequired.begin();
                 it != _indexRequired.end(); ++it) {
                ss << it->first;
                ss << (it->second ? " (needs index)" : " (no index needed)");
                ss << ", ";
            }
            return ss.str();
        }
    };

    /** An interval defined between a lower and an upper FieldBound. */
    struct FieldInterval {
        FieldInterval() : _cachedEquality( -1 ) {}
        FieldInterval( const BSONElement& e ) : _cachedEquality( -1 ) {
            _lower._bound = _upper._bound = e;
            _lower._inclusive = _upper._inclusive = true;
        }
        FieldBound _lower;
        FieldBound _upper;
        /**
* @return true when the interval can contain one or more values.
* NOTE May also return true in certain 'empty' discrete cases like x > false && x < true.
*/
        bool isStrictValid() const {
            int cmp = _lower._bound.woCompare( _upper._bound, false );
            return ( cmp < 0 || ( cmp == 0 && _lower._inclusive && _upper._inclusive ) );
        }
        /** @return true if the interval is an equality constraint. */
        bool equality() const;
        mutable int _cachedEquality;

        string toString() const;
    };

    /**
* An ordered list of FieldIntervals expressing constraints on valid
* BSONElement values for a field.
*/
    class FieldRange {
    public:
        /**
* Creates a FieldRange representing a superset of the BSONElement values matching a query
* expression element.
* @param e - The query expression element.
* @param isNot - Indicates that 'e' appears within a query $not clause and its matching
* semantics are inverted.
* @param optimize - If true, the range may be bracketed by 'e''s data type.
* TODO It is unclear why 'optimize' is optional, see SERVER-5165.
*/
        FieldRange( const BSONElement &e , bool isNot, bool optimize );

        void setElemMatchContext( const BSONElement& elemMatchContext ) {
            _elemMatchContext = elemMatchContext;
        }

        /**
* @return Range intersection with 'other'.
* @param singleKey - Indicate whether intersection will be performed in a single value or
* multi value context.
*/
        const FieldRange &intersect( const FieldRange &other, bool singleKey );
        /** @return Range union with 'other'. */
        const FieldRange &operator|=( const FieldRange &other );
        /** @return Range of elements elements included in 'this' but not 'other'. */
        const FieldRange &operator-=( const FieldRange &other );
        /** @return true iff this range is a subset of 'other'. */
        bool operator<=( const FieldRange &other ) const;

        /**
* If there are any valid values for this range, the extreme values can
* be extracted.
*/
        
        BSONElement min() const { verify( !empty() ); return _intervals[ 0 ]._lower._bound; }
        BSONElement max() const { verify( !empty() ); return _intervals[ _intervals.size() - 1 ]._upper._bound; }
        bool minInclusive() const { verify( !empty() ); return _intervals[ 0 ]._lower._inclusive; }
        bool maxInclusive() const { verify( !empty() ); return _intervals[ _intervals.size() - 1 ]._upper._inclusive; }

        /** @return true iff this range expresses a single equality interval. */
        bool equality() const;
        /**
* @return true iff this range includes all BSONElements
* (the range is the universal set of BSONElements).
*/
        bool universal() const;
        /** @return true iff this range includes no BSONElements. */
        bool empty() const { return _intervals.empty(); }
        /**
* @return true in many cases when this FieldRange represents the exact set of BSONElement
* values matching the query expression element used to construct the FieldRange. This
* attribute is used to implement higher level optimizations and is computed with a simple
* implementation that identifies common (but not all) cases of this property and may return
* false negatives.
*/
        bool mustBeExactMatchRepresentation() const { return _exactMatchRepresentation; }
        /* Checks whether this FieldRange is a non-empty union of point-intervals.
* Examples:
* FieldRange( { a:3 } ), isPointIntervalSet() -> true
* FieldRange( { a:{ $in:[ 1, 2 ] } } ), isPointIntervalSet() -> true
* FieldRange( { a:{ $gt:5 } } ), isPointIntervalSet() -> false
* FieldRange( {} ), isPointIntervalSet() -> false
*/
        bool isPointIntervalSet() const;
        const BSONElement& elemMatchContext() const { return _elemMatchContext; }
        
        /** Empty the range so it includes no BSONElements. */
        void makeEmpty() { _intervals.clear(); }
        const vector<FieldInterval> &intervals() const { return _intervals; }
        const SpecialIndices& getSpecial() const { return _special; }
        /** Make component intervals noninclusive. */
        void setExclusiveBounds();
        /**
* Constructs a range where all FieldIntervals and FieldBounds are in
* the opposite order of the current range.
* NOTE the resulting intervals might not be strictValid().
*/
        void reverse( FieldRange &ret ) const;

        string toString() const;
    private:
        BSONObj addObj( const BSONObj &o );
        void finishOperation( const vector<FieldInterval> &newIntervals, const FieldRange &other,
                              bool exactMatchRepresentation );
        vector<FieldInterval> _intervals;
        // Owns memory for our BSONElements.
        vector<BSONObj> _objData;
        SpecialIndices _special; // Index type name of a non standard (eg '2d') index required by a
                              // parsed query operator (eg '$near'). Could be >1.
        bool _exactMatchRepresentation;
        BSONElement _elemMatchContext; // Parent $elemMatch object of the field constraint that
                                       // generated this FieldRange. For example if the query is
                                       // { a:{ $elemMatch:{ b:1, c:1 } } }, then the
                                       // _elemMatchContext for the FieldRange on 'a.b' is the query
                                       // element having field name '$elemMatch'.
    };

    /**
* A set of FieldRanges determined from constraints on the fields of a query,
* that may be used to determine index bounds.
*/
    class FieldRangeSet {
    public:
        friend class OrRangeGenerator;
        friend class FieldRangeVector;
        /**
* Creates a FieldRangeSet representing a superset of the documents matching a query.
* @param ns - The query's namespace.
* @param query - The query.
* @param singleKey - Indicates that document fields contain single values (there are no
* multiply valued fields).
* @param optimize - If true, each field's value range may be bracketed by data type.
* TODO It is unclear why 'optimize' is optional, see SERVER-5165.
*/
        FieldRangeSet( const char *ns, const BSONObj &query , bool singleKey , bool optimize );

        /** @return range for the given field. */
        const FieldRange &range( const char *fieldName ) const;
        /** @return range for the given field. Public for testing. */
        FieldRange &range( const char *fieldName );
        /** @return the number of non universal ranges. */
        int numNonUniversalRanges() const;
        /** @return the field ranges comprising this set. */
        const map<string,FieldRange> &ranges() const { return _ranges; }
        /**
* @return true if a match could be possible on every field. Generally this
* is not useful information for a single key FieldRangeSet and
* matchPossibleForIndex() should be used instead.
*/
        bool matchPossible() const;
        /**
* @return true if a match could be possible given the value of _singleKey
* and index key 'keyPattern'.
* @param keyPattern May be {} or {$natural:1} for a non index scan.
*/
        bool matchPossibleForIndex( const BSONObj &keyPattern ) const;
        /**
* @return true in many cases when this FieldRangeSet represents the exact set of BSONObjs
* matching the query expression used to construct the FieldRangeSet. This attribute is
* used to implement higher level optimizations and is computed with a simple implementation
* that identifies common (but not all) cases of this property and may return false
* negatives.
*/
        bool mustBeExactMatchRepresentation() const { return _exactMatchRepresentation; }
        
        /* Checks whether this FieldRangeSet is a non-empty union of point-intervals
* on a given field.
* Examples:
* FieldRangeSet({a : 3}), isPointIntervalSet("a") -> true
* FieldRangeSet({a : {$in : [1 , 2]}}), isPointIntervalSet("a") -> true
* FieldRangeSet({}), isPointIntervalSet("a") -> false
* FieldRangeSet({b : 1}), isPointIntervalSet("a") -> false
*
* Used in determining "suitability" for hashedindexes, and also in
* sharding for determining the relevant shards for a query.
*
* TODO: move this into FieldRange instead of FieldRangeSet
*/
        bool isPointIntervalSet( const string& fieldname ) const;

        const char *ns() const { return _ns.c_str(); }
        
        // QueryPattern pattern( const BSONObj &sort = BSONObj() ) const;
        SpecialIndices getSpecial() const;

        /**
* @return a FieldRangeSet approximation of the documents in 'this' but
* not in 'other'. The approximation will be a superset of the documents
* in 'this' but not 'other'.
*/
        const FieldRangeSet &operator-=( const FieldRangeSet &other );
        /** @return intersection of 'this' with 'other'. */
        const FieldRangeSet &operator&=( const FieldRangeSet &other );

        /**
* @return - A new FieldRangeSet based on this FieldRangeSet, but with only
* a subset of the fields.
* @param fields - Only fields which are represented as field names in this object
* will be included in the returned FieldRangeSet.
*/
        FieldRangeSet *subset( const BSONObj &fields ) const;
        
        /**
* @return A new FieldRangeSet based on this FieldRangeSet, but with all field names
* prefixed by the specified @param prefix field name.
*/
        FieldRangeSet* prefixed( const string& prefix ) const;
        
        bool singleKey() const { return _singleKey; }
        
        BSONObj originalQuery() const { return _queries[ 0 ]; }
        
        string toString() const;

    private:
        /**
* Private constructor for implementation specific delegate objects.
* @param boundElemMatch - If false, FieldRanges will not be computed for $elemMatch
* expressions.
*/
        FieldRangeSet( const char* ns, const BSONObj& query, bool singleKey, bool optimize,
                       bool boundElemMatch );
        /** Initializer shared by the constructors. */
        void init( bool optimize );

        void appendQueries( const FieldRangeSet &other );
        void makeEmpty();

        /**
* Query parsing routines.
* TODO integrate these with an external query parser shared by the matcher. SERVER-1009
*/
        void handleMatchField( const BSONElement& matchElement, bool optimize );
        void handleConjunctionClauses( const BSONObj& clauses, bool optimize );
        void handleOp( const char* matchFieldName, const BSONElement& op, bool isNot,
                       bool optimize );
        void handleNotOp( const char* matchFieldName, const BSONElement& notOp, bool optimize );
        void handleElemMatch( const char* matchFieldName, const BSONElement& elemMatch, bool isNot,
                              bool optimize );

        /** Must be called when a match element is skipped or modified to generate a FieldRange. */
        void adjustMatchField();
        void intersectMatchField( const char *fieldName, const BSONElement &matchElement,
                                 bool isNot, bool optimize );
        static FieldRange *__universalRange;
        const FieldRange &universalRange() const;
        map<string,FieldRange> _ranges;
        string _ns;
        // Owns memory for FieldRange BSONElements.
        vector<BSONObj> _queries;
        bool _singleKey;
        bool _exactMatchRepresentation;
        bool _boundElemMatch;
    };

    class NamespaceDetails;
    
    /**
* A pair of FieldRangeSets, one representing constraints for single key
* indexes and the other representing constraints for multi key indexes and
* unindexed scans. In several member functions the caller is asked to
* supply an index so that the implementation may utilize the proper
* FieldRangeSet and return results that are appropriate with respect to that
* supplied index.
*/
    class FieldRangeSetPair {
    public:
        FieldRangeSetPair( const char *ns, const BSONObj &query, bool optimize=true )
        :_singleKey( ns, query, true, optimize ), _multiKey( ns, query, false, optimize ) {}

        /**
* @return the appropriate single or multi key FieldRangeSet for the specified index.
* @param idxNo -1 for non index scan.
*/
        const FieldRangeSet &frsForIndex( const NamespaceDetails* nsd, int idxNo ) const;

        /** @return a field range in the single key FieldRangeSet. */
        const FieldRange &shardKeyRange( const char *fieldName ) const {
            return _singleKey.range( fieldName );
        }
        /** @return true if the range limits are equivalent to an empty query. */
        bool noNonUniversalRanges() const;
        /** @return false if a match is impossible regardless of index. */
        bool matchPossible() const { return _multiKey.matchPossible(); }
        /**
* @return false if a match is impossible on the specified index.
* @param idxNo -1 for non index scan.
*/
        bool matchPossibleForIndex( NamespaceDetails *d, int idxNo, const BSONObj &keyPattern ) const;
        
        const char *ns() const { return _singleKey.ns(); }

        SpecialIndices getSpecial() const { return _singleKey.getSpecial(); }

        /** Intersect with another FieldRangeSetPair. */
        FieldRangeSetPair &operator&=( const FieldRangeSetPair &other );
        /**
* Subtract a FieldRangeSet, generally one expressing a range that has
* already been scanned.
*/
        FieldRangeSetPair &operator-=( const FieldRangeSet &scanned );
        
        bool matchPossibleForSingleKeyFRS( const BSONObj &keyPattern ) const {
            return _singleKey.matchPossibleForIndex( keyPattern );
        }
        
        BSONObj originalQuery() const { return _singleKey.originalQuery(); }

        const FieldRangeSet getSingleKeyFRS() const { return _singleKey; }
        const FieldRangeSet getMultiKeyFRS() const { return _singleKey; }

        string toString() const;
    private:
        FieldRangeSetPair( const FieldRangeSet &singleKey, const FieldRangeSet &multiKey )
        :_singleKey( singleKey ), _multiKey( multiKey ) {}
        void assertValidIndex( const NamespaceDetails *d, int idxNo ) const;
        void assertValidIndexOrNoIndex( const NamespaceDetails *d, int idxNo ) const;
        /** matchPossibleForIndex() must be true. */
        FieldRangeSet _singleKey;
        FieldRangeSet _multiKey;
        friend class OrRangeGenerator;
        friend struct QueryUtilIndexed;
    };
    
    /**
* An ordered list of fields and their FieldRanges, corresponding to valid
* index keys for a given index spec.
*/
    class FieldRangeVector {
    public:
        /**
* @param frs The valid ranges for all fields, as defined by the query spec. None of the
* fields in indexSpec may be empty() ranges of frs.
* @param indexSpec The index spec (key pattern and info)
* @param direction The direction of index traversal
*/
        FieldRangeVector( const FieldRangeSet &frs, BSONObj keyPattern, int direction );

        /**
* Methods for identifying compound start and end btree bounds describing this field range
* vector.
*
* A FieldRangeVector contains the FieldRange bounds for every field of an index. A
* FieldRangeVectorIterator may be used to efficiently search for btree keys within these
* bounds. Alternatively, a single compound field interval of the btree may be scanned,
* between a compound field start point and end point. If isSingleInterval() is true then
* the interval between the start and end points will be an exact description of this
* FieldRangeVector, otherwise the start/end interval will be a superset of this
* FieldRangeVector. For example:
*
* index { a:1 }, query { a:{ $gt:2, $lte:4 } }
* -> frv ( 2, 4 ]
* -> start/end bounds ( { '':2 }, { '':4 } ]
*
* index { a:1, b:1 }, query { a:2, b:{ $gte:7, $lt:9 } }
* -> frv [ 2, 2 ], [ 7, 9 )
* -> start/end bounds [ { '':2, '':7 }, { '':2, '':9 } )
*
* index { a:1, b:-1 }, query { a:2, b:{ $gte:7, $lt:9 } }
* -> frv [ 2, 2 ], ( 9, 7 ]
* -> start/end bounds ( { '':2, '':9 }, { '':2, '':7 } ]
*
* index { a:1, b:1 }, query { a:{ $gte:7, $lt:9 } }
* -> frv [ 7, 9 )
* -> start/end bounds [ { '':7, '':MinKey }, { '':9, '':MinKey } )
*
* index { a:1, b:1 }, query { a:{ $gte:2, $lte:5 }, b:{ $gte:7, $lte:9 } }
* -> frv [ 2, 5 ], [ 7, 9 ]
* -> start/end bounds [ { '':2, '':7 }, { '':5, '':9 } ]
* (isSingleInterval() == false)
*/

        /**
* @return true if this FieldRangeVector represents a single interval within a btree,
* comprised of all keys between a single start point and a single end point.
*/
        bool isSingleInterval() const;

        /**
* @return a starting point for an index traversal, a lower bound on the ranges represented
* by this FieldRangeVector according to the btree's native ordering.
*/
        BSONObj startKey() const;

        /** @return true if the startKey() bound is inclusive. */
        bool startKeyInclusive() const;

        /**
* @return an end point for an index traversal, an upper bound on the ranges represented
* by this FieldRangeVector according to the btree's native ordering.
*/
        BSONObj endKey() const;

        /** @return true if the endKey() bound is inclusive. */
        bool endKeyInclusive() const;

        /** @return the number of index ranges represented by 'this' */
        unsigned size() const;

        /** @return a client readable representation of 'this' */
        BSONObj obj() const;
        
        /**
* @return true iff the provided document matches valid ranges on all
* of this FieldRangeVector's fields, which is the case iff this document
* would be returned while scanning the index corresponding to this
* FieldRangeVector. This function is used for $or clause deduping.
*/
        bool matches( const BSONObj &obj ) const;

        /**
* @return true if all values in the provided index key are contained within the field
* ranges of their respective fields in this FieldRangeVector.
*
* For example, given a query { a:3, b:4 } and index { a:1, b:1 }, the FieldRangeVector is
* [ [[ 3, 3 ]], [[ 4, 4 ]] ], consisting of field range [[ 3, 3 ]] on field 'a' and
* [[ 4, 4 ]] on field 'b'. The index key { '':3, '':4 } matches, but the index key
* { '':3, '':5 } does not match because the value 5 in the second field is not contained in
* the field range [[ 4, 4 ]] for field 'b'.
*/
        bool matchesKey( const BSONObj& key ) const;

        /**
* @return first key of 'obj' that would be encountered by a forward
* index scan using this FieldRangeVector, BSONObj() if no such key.
*/
        BSONObj firstMatch( const BSONObj &obj ) const;

        /**
* @return true if all ranges within the field range set on fields of this index are
* represented in this field range vector. May be false in certain multikey index cases
* when intervals on two fields cannot both be used, see comments related to SERVER-958 in
* FieldRangeVector().
*/
        bool hasAllIndexedRanges() const { return _hasAllIndexedRanges; }

        string toString() const;
        
    private:
        int matchingLowElement( const BSONElement &e, int i, bool direction, bool &lowEquality ) const;
        bool matchesElement( const BSONElement &e, int i, bool direction ) const;
        vector<FieldRange> _ranges;
        BSONObj _keyPattern;
        int _direction;
        vector<BSONObj> _queries; // make sure mem owned
        bool _hasAllIndexedRanges;
        friend class FieldRangeVectorIterator;

        vector<const char*> _fieldNames;
        vector<BSONElement> _fixed;
        // See FieldRangeVector::matches for comment on key generation.
        scoped_ptr<BtreeKeyGenerator> _keyGenerator;
    };
    
    /**
* Helper class for iterating through an ordered representation of keys
* to find those keys that match a specified FieldRangeVector.
*/
    class FieldRangeVectorIterator {
    public:
        /**
* @param v - a FieldRangeVector representing matching keys.
* @param singleIntervalLimit - The maximum number of keys to match a single (compound)
* interval before advancing to the next interval. Limit checking is disabled if 0.
*/
        FieldRangeVectorIterator( const FieldRangeVector &v, int singleIntervalLimit );

        /**
* @return Suggested advance method through an ordered list of keys with lookup support
* (generally a btree).
* -2 Iteration is complete, no need to advance further.
* -1 Advance to the next ordered key, without skipping.
* >=0 Skip parameter, let's call it 'r'. If after() is true, skip past the key prefix
* comprised of the first r elements of curr. For example, if curr is {a:1,b:1}, the
* index is {a:1,b:1}, the direction is 1, and r == 1, skip past {a:1,b:MaxKey}. If
* after() is false, skip to the key comprised of the first r elements of curr followed
* by the (r+1)th and greater elements of cmp() (with inclusivity specified by the
* (r+1)th and greater elements of inc()). For example, if curr is {a:1,b:1}, the
* index is {a:1,b:1}, the direction is 1, r == 1, cmp()[1] == b:4, and inc()[1] ==
* true, then skip to {a:1,b:4}. Note that the element field names in curr and cmp()
* should generally be ignored when performing index key comparisons.
* @param curr The key at the current position in the list of keys. Values of curr must be
* supplied in order.
*/
        int advance( const BSONObj &curr );
        const vector<const BSONElement *> &cmp() const { return _cmp; }
        const vector<bool> &inc() const { return _inc; }
        bool after() const { return _after; }
        void prepDive();

        /**
* Helper class representing a position within a vector of ranges. Public for testing.
*/
        class CompoundRangeCounter {
        public:
            CompoundRangeCounter( int size, int singleIntervalLimit );
            int size() const { return (int)_i.size(); }
            int get( int i ) const { return _i[ i ]; }
            void set( int i, int newVal );
            void inc( int i );
            void setZeroes( int i );
            void setUnknowns( int i );
            void incSingleIntervalCount() {
                if ( isTrackingIntervalCounts() ) ++_singleIntervalCount;
            }
            bool hasSingleIntervalCountReachedLimit() const {
                return isTrackingIntervalCounts() && _singleIntervalCount >= _singleIntervalLimit;
            }
            void resetIntervalCount() { _singleIntervalCount = 0; }
            string toString() const;
        private:
            bool isTrackingIntervalCounts() const { return _singleIntervalLimit > 0; }
            vector<int> _i;
            int _singleIntervalCount;
            int _singleIntervalLimit;
        };

        /**
* Helper class for matching a BSONElement with the bounds of a FieldInterval. Some
* internal comparison results are cached. Public for testing.
*/
        class FieldIntervalMatcher {
        public:
            FieldIntervalMatcher( const FieldInterval &interval, const BSONElement &element,
                                 bool reverse );
            bool isEqInclusiveUpperBound() const {
                return upperCmp() == 0 && _interval._upper._inclusive;
            }
            bool isGteUpperBound() const { return upperCmp() >= 0; }
            bool isEqExclusiveLowerBound() const {
                return lowerCmp() == 0 && !_interval._lower._inclusive;
            }
            bool isLtLowerBound() const { return lowerCmp() < 0; }
        private:
            struct BoundCmp {
                BoundCmp() : _cmp(), _valid() {}
                void set( int cmp ) { _cmp = cmp; _valid = true; }
                int _cmp;
                bool _valid;
            };
            int mayReverse( int val ) const { return _reverse ? -val : val; }
            int cmp( const BSONElement &bound ) const {
                return mayReverse( _element.woCompare( bound, false ) );
            }
            void setCmp( BoundCmp &boundCmp, const BSONElement &bound ) const {
                boundCmp.set( cmp( bound ) );
            }
            int lowerCmp() const;
            int upperCmp() const;
            const FieldInterval &_interval;
            const BSONElement &_element;
            bool _reverse;
            mutable BoundCmp _lowerCmp;
            mutable BoundCmp _upperCmp;
        };

    private:
        /**
* @return values similar to advance()
* -2 Iteration is complete for the current interval.
* -1 Iteration is not complete for the current interval.
* >=0 Return value to be forwarded by advance().
*/
        int validateCurrentInterval( int intervalIdx, const BSONElement &currElt,
                                    bool reverse, bool first, bool &eqInclusiveUpperBound );
        
        /** Skip to curr / i / nextbounds. */
        int advanceToLowerBound( int i );
        /** Skip to curr / i / superlative. */
        int advancePast( int i );
        /** Skip to curr / i / superlative and reset following interval positions. */
        int advancePastZeroed( int i );

        bool hasReachedLimitForLastInterval( int intervalIdx ) const {
            return
                _i.hasSingleIntervalCountReachedLimit() &&
                ( intervalIdx + 1 == _endNonUniversalRanges );
        }

        /** @return the index of the last non universal range + 1. */
        int endNonUniversalRanges() const;

        const FieldRangeVector &_v;
        CompoundRangeCounter _i;
        vector<const BSONElement*> _cmp;
        vector<bool> _inc;
        bool _after;
        int _endNonUniversalRanges;
    };
    
    /**
* As we iterate through $or clauses this class generates a FieldRangeSetPair
* for the current $or clause, in some cases by excluding ranges that were
* included in a previous clause.
*/
    class OrRangeGenerator {
    public:
        OrRangeGenerator( const char *ns, const BSONObj &query , bool optimize=true );

        /** @return true iff we are done scanning $or clauses, or if there are no $or clauses. */
        bool orRangesExhausted() const { return _orSets.empty(); }
        /** Iterates to the next $or clause by removing the current $or clause. */
        void popOrClause( NamespaceDetails *nsd, int idxNo, const BSONObj &keyPattern );
        void popOrClauseSingleKey();
        /** @return FieldRangeSetPair for the current $or clause. */
        FieldRangeSetPair *topFrsp() const;
        /**
* @return original FieldRangeSetPair for the current $or clause. While the
* original bounds are looser, they are composed of fewer ranges and it
* is faster to do operations with them; when they can be used instead of
* more precise bounds, they should.
*/
        FieldRangeSetPair *topFrspOriginal() const;
        
        SpecialIndices getSpecial() const { return _baseSet.getSpecial(); }
    private:
        void assertMayPopOrClause();
        void _popOrClause( const FieldRangeSet *toDiff, NamespaceDetails *d, int idxNo, const BSONObj &keyPattern );
        FieldRangeSetPair _baseSet;
        list<FieldRangeSetPair> _orSets;
        list<FieldRangeSetPair> _originalOrSets;
        // ensure memory is owned
        list<FieldRangeSetPair> _oldOrSets;
        bool _orFound;
        friend struct QueryUtilIndexed;
    };

    /** returns a string that when used as a matcher, would match a super set of regex()
returns "" for complex regular expressions
used to optimize queries in some simple regex cases that start with '^'

if purePrefix != NULL, sets it to whether the regex can be converted to a range query
*/
    string simpleRegex(const char* regex, const char* flags, bool* purePrefix=NULL);

    /** returns the upper bound of a query that matches prefix */
    string simpleRegexEnd( string prefix );

    long long applySkipLimit( long long num , const BSONObj& cmd );
    
    bool isSimpleIdQuery( const BSONObj& query );

} // namespace mongo

#include "queryutil-inl.h"
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