// ordering.h

/*    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 "mongo/bson/bsonobj.h"
#include "mongo/bson/bsonobjiterator.h"

namespace mongo {

// todo: ideally move to db/ instead of bson/, but elim any dependencies first

/** A precomputation of a BSON index or sort key pattern.  That is something like:
       { a : 1, b : -1 }
    The constructor is private to make conversion more explicit so we notice where we call make().
    Over time we should push this up higher and higher.
*/
class Ordering {
    unsigned bits;
    Ordering(unsigned b) : bits(b) {}

public:
    Ordering(const Ordering& r) : bits(r.bits) {}
    void operator=(const Ordering& r) {
        bits = r.bits;
    }

    /** so, for key pattern { a : 1, b : -1 }
        get(0) == 1
        get(1) == -1
    */
    int get(int i) const {
        return ((1 << i) & bits) ? -1 : 1;
    }

    // for woCompare...
    unsigned descending(unsigned mask) const {
        return bits & mask;
    }

    /*operator std::string() const {
        StringBuilder buf;
        for ( unsigned i=0; i<nkeys; i++)
            buf.append( get(i) > 0 ? "+" : "-" );
        return buf.str();
    }*/

    static Ordering make(const BSONObj& obj) {
        unsigned b = 0;
        BSONObjIterator k(obj);
        unsigned n = 0;
        while (1) {
            BSONElement e = k.next();
            if (e.eoo())
                break;
            uassert(13103, "too many compound keys", n <= 31);
            if (e.number() < 0)
                b |= (1 << n);
            n++;
        }
        return Ordering(b);
    }
};
}
