/**
 *    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/db/diskloc.h"
#include "mongo/db/exec/plan_stage.h"
#include "mongo/db/exec/projection_exec.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/matcher/expression.h"

namespace mongo {

    struct ProjectionStageParams {
        enum ProjectionImplementation {
            // The default case.  Will handle every projection.
            NO_FAST_PATH,

            // The projection is simple inclusion and is totally covered by one index.
            COVERED_ONE_INDEX,

            // The projection is simple inclusion and we expect an object.
            SIMPLE_DOC
        };

        ProjectionStageParams() : projImpl(NO_FAST_PATH), fullExpression(NULL) { }

        ProjectionImplementation projImpl;

        // The projection object.  We lack a ProjectionExpression or similar so we use a BSONObj.
        BSONObj projObj;

        // If we have a positional or elemMatch projection we need a MatchExpression to pull out the
        // right data.
        // Not owned here, we do not take ownership.
        const MatchExpression* fullExpression;

        // If (COVERED_ONE_INDEX == projObj) this is the key pattern we're extracting covered data
        // from.  Otherwise, this field is ignored.
        BSONObj coveredKeyObj;
    };

    /**
     * This stage computes a projection.
     */
    class ProjectionStage : public PlanStage {
    public:
        ProjectionStage(const ProjectionStageParams& params,
                        WorkingSet* ws,
                        PlanStage* child);

        virtual ~ProjectionStage();

        virtual bool isEOF();
        virtual StageState work(WorkingSetID* out);

        virtual void prepareToYield();
        virtual void recoverFromYield();
        virtual void invalidate(const DiskLoc& dl, InvalidationType type);

        PlanStageStats* getStats();

        typedef unordered_set<StringData, StringData::Hasher> FieldSet;

        /**
         * Given the projection spec for a simple inclusion projection,
         * 'projObj', populates 'includedFields' with the set of field
         * names to be included.
         */
        static void getSimpleInclusionFields(const BSONObj& projObj,
                                             FieldSet* includedFields);

        /**
         * Applies a simple inclusion projection to 'in', including
         * only the fields specified by 'includedFields'.
         *
         * The resulting document is constructed using 'bob'.
         */
        static void transformSimpleInclusion(const BSONObj& in,
                                             const FieldSet& includedFields,
                                             BSONObjBuilder& bob);

    private:
        Status transform(WorkingSetMember* member);

        scoped_ptr<ProjectionExec> _exec;

        // _ws is not owned by us.
        WorkingSet* _ws;
        scoped_ptr<PlanStage> _child;

        // Stats
        CommonStats _commonStats;

        // Fast paths:
        ProjectionStageParams::ProjectionImplementation _projImpl;

        // Used by all projection implementations.
        BSONObj _projObj;

        // Data used for both SIMPLE_DOC and COVERED_ONE_INDEX paths.
        // Has the field names present in the simple projection.
        unordered_set<StringData, StringData::Hasher> _includedFields;

        //
        // Used for the COVERED_ONE_INDEX path.
        //
        BSONObj _coveredKeyObj;

        // Field names can be empty in 2.4 and before so we can't use them as a sentinel value.
        // If the i-th entry is true we include the i-th field in the key.
        vector<bool> _includeKey;

        // If the i-th entry of _includeKey is true this is the field name for the i-th key field.
        vector<StringData> _keyFieldNames;
    };

}  // namespace mongo
