// matchable.h

/**
 *    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 "mongo/bson/bsonobj.h"
#include "mongo/db/field_ref.h"
#include "mongo/db/matcher/path.h"

namespace mongo {

    class MatchableDocument {
    public:
        // Inlining to allow subclasses to see that this is a no-op and avoid a function call.
        // Speeds up query execution measurably.
        virtual ~MatchableDocument() {}

        virtual BSONObj toBSON() const = 0;

        /**
         * The neewly returned ElementIterator is allowed to keep a pointer to path.
         * So the caller of this function should make sure path is in scope until 
         * the ElementIterator is deallocated
        */
        virtual ElementIterator* allocateIterator( const ElementPath* path ) const = 0;

        virtual void releaseIterator( ElementIterator* iterator ) const = 0;

        class IteratorHolder {
        public:
            IteratorHolder( const MatchableDocument* doc, const ElementPath* path ) {
                _doc = doc;
                _iterator = _doc->allocateIterator( path );
            }

            ~IteratorHolder() {
                _doc->releaseIterator( _iterator );
            }

            ElementIterator* operator->() const {
                return _iterator;
            }
        private:
            const MatchableDocument* _doc;
            ElementIterator* _iterator;
        };
    };

    class BSONMatchableDocument : public MatchableDocument {
    public:
        BSONMatchableDocument( const BSONObj& obj );
        virtual ~BSONMatchableDocument();

        virtual BSONObj toBSON() const { return _obj; }

        virtual ElementIterator* allocateIterator( const ElementPath* path ) const {
            if ( _iteratorUsed )
                return new BSONElementIterator( path, _obj );
            _iteratorUsed = true;
            _iterator.reset( path, _obj );
            return &_iterator;
        }

        virtual void releaseIterator( ElementIterator* iterator ) const {
            if ( iterator == &_iterator ) {
                _iteratorUsed = false;
            }
            else {
                delete iterator;
            }
        }

    private:
        BSONObj _obj;
        mutable BSONElementIterator _iterator;
        mutable bool _iteratorUsed;
    };
}
