/**
 *    Copyright (C) 2014 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.
 */

#include "mongo/platform/basic.h"

#include "mongo/db/commands/explain_cmd.h"

#include <boost/optional.hpp>

#include "mongo/client/dbclientinterface.h"
#include "mongo/db/catalog/database.h"
#include "mongo/db/client.h"
#include "mongo/db/commands.h"
#include "mongo/db/query/explain.h"
#include "mongo/db/repl/replication_coordinator_global.h"
#include "mongo/rpc/metadata/server_selection_metadata.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {

using std::string;

static CmdExplain cmdExplain;

Status CmdExplain::checkAuthForCommand(ClientBasic* client,
                                       const std::string& dbname,
                                       const BSONObj& cmdObj) {
    if (Object != cmdObj.firstElement().type()) {
        return Status(ErrorCodes::BadValue, "explain command requires a nested object");
    }

    BSONObj explainObj = cmdObj.firstElement().Obj();

    Command* commToExplain = Command::findCommand(explainObj.firstElementFieldName());
    if (NULL == commToExplain) {
        mongoutils::str::stream ss;
        ss << "unknown command: " << explainObj.firstElementFieldName();
        return Status(ErrorCodes::CommandNotFound, ss);
    }

    return commToExplain->checkAuthForCommand(client, dbname, explainObj);
}

bool CmdExplain::run(OperationContext* txn,
                     const string& dbname,
                     BSONObj& cmdObj,
                     int options,
                     string& errmsg,
                     BSONObjBuilder& result) {
    ExplainCommon::Verbosity verbosity;
    Status parseStatus = ExplainCommon::parseCmdBSON(cmdObj, &verbosity);
    if (!parseStatus.isOK()) {
        return appendCommandStatus(result, parseStatus);
    }

    // This is the nested command which we are explaining.
    BSONObj explainObj = cmdObj.firstElement().Obj();

    Command* commToExplain = Command::findCommand(explainObj.firstElementFieldName());
    if (NULL == commToExplain) {
        mongoutils::str::stream ss;
        ss << "Explain failed due to unknown command: " << explainObj.firstElementFieldName();
        Status explainStatus(ErrorCodes::CommandNotFound, ss);
        return appendCommandStatus(result, explainStatus);
    }

    // Check whether the child command is allowed to run here. TODO: this logic is
    // copied from Command::execCommand and should be abstracted. Until then, make
    // sure to keep it up to date.
    repl::ReplicationCoordinator* replCoord = repl::getGlobalReplicationCoordinator();
    bool iAmPrimary = replCoord->canAcceptWritesForDatabase(dbname);
    bool commandCanRunOnSecondary = commToExplain->slaveOk();

    bool commandIsOverriddenToRunOnSecondary = commToExplain->slaveOverrideOk() &&
        (rpc::ServerSelectionMetadata::get(txn).isSecondaryOk() ||
         rpc::ServerSelectionMetadata::get(txn).getReadPreference() != boost::none);
    bool iAmStandalone = !txn->writesAreReplicated();

    const bool canRunHere = iAmPrimary || commandCanRunOnSecondary ||
        commandIsOverriddenToRunOnSecondary || iAmStandalone;

    if (!canRunHere) {
        mongoutils::str::stream ss;
        ss << "Explain's child command cannot run on this node. "
           << "Are you explaining a write command on a secondary?";
        appendCommandStatus(result, false, ss);
        return false;
    }

    // Actually call the nested command's explain(...) method.
    Status explainStatus = commToExplain->explain(txn, dbname, explainObj, verbosity, &result);
    if (!explainStatus.isOK()) {
        return appendCommandStatus(result, explainStatus);
    }

    return true;
}

}  // namespace mongo