/**
 *    Copyright (C) 2013 MongoDB 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 <string>

#include "mongo/db/query/explain_common.h"
#include "mongo/s/strategy.h"
#include "mongo/s/write_ops/batched_command_request.h"

namespace mongo {

    /**
     * Namespace for the collection of static methods used by commands in the implementation of
     * explain on mongos.
     */
    class ClusterExplain {
    public:
        /**
         * Given the BSON specification for a command, 'cmdObj', wraps the object in order to
         * produce the BSON for an explain of that command, at the given verbosity level
         * 'verbosity'.
         *
         * Adds the result to the BSONObj builder 'out'.
         */
        static void wrapAsExplain(const BSONObj& cmdObj,
                                  ExplainCommon::Verbosity verbosity,
                                  BSONObjBuilder* out);

        /**
         * Determines the kind of "execution stage" that mongos would use in order to collect
         * the results from the shards, assuming that the command being explained is a read
         * operation such as find or count.
         */
        static const char* getStageNameForReadOp(const std::vector<Strategy::CommandResult>& shardResults,
                                                 const BSONObj& explainObj);

        /**
         * Command implementations on mongos use this method to construct the sharded explain
         * output format based on the results from the shards in 'shardResults'.
         *
         * On success, the output is added to the BSONObj builder 'out'.
         */
        static Status buildExplainResult(const std::vector<Strategy::CommandResult>& shardResults,
                                         const char* mongosStageName,
                                         long long millisElapsed,
                                         BSONObjBuilder* out);

        //
        // Names of mock mongos execution stages.
        //

        static const char* kSingleShard;
        static const char* kMergeFromShards;
        static const char* kMergeSortFromShards;
        static const char* kWriteOnShards;

    private:
        /**
         * Returns an OK status if all shards support the explain command and returned sensible
         * results. Otherwise, returns a non-OK status and the entire explain should fail.
         */
        static Status validateShardResults(const std::vector<Strategy::CommandResult>& shardResults);

        /**
         * Populates the BSONObj builder 'out' with query planner explain information, based on
         * the results from the shards contained in 'shardResults'.
         *
         * The planner info will display 'mongosStageName' as the name of the execution stage
         * performed by mongos after gathering results from the shards.
         */
        static void buildPlannerInfo(const std::vector<Strategy::CommandResult>& shardResults,
                                     const char* mongosStageName,
                                     BSONObjBuilder* out);

        /**
         * Populates the BSONObj builder 'out' with execution stats explain information,
         * if the results from the shards in 'shardsResults' contain this info.
         *
         * Will display 'mongosStageName' as the name of the execution stage performed by mongos,
         * and 'millisElapsed' as the execution time of the mongos stage.
         */
        static void buildExecStats(const std::vector<Strategy::CommandResult>& shardResults,
                                   const char* mongosStageName,
                                   long long millisElapsed,
                                   BSONObjBuilder* out);
    };

} // namespace mongo