/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    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
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    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 Server Side 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


namespace mongo {

class OperationContext;
class ServiceContext;

/**
 * Used to detect when a shard's shardIdentity document has been rolled back.  Since rolling back
 * the shardIdentity document is illegal (as we can't clear the in-memory state associated with it),
 * we force the mongod to shut down if it happens.  We detect shardIdentity rollback by checking in
 * the OpObserver for that document to be deleted.  We can't shut down right at that moment,
 * however, as doing so would interrupt the rollback process and leave the document in place for
 * when the server is restarted.  Instead, when we detect the shardIdentity document being deleted,
 * we call recordThatRollbackHappened() on this class, which records the fact that the shardIdentity
 * document was deleted as part of the rollback, and then when we exit rollback we check
 * didRollbackHappen() and shut down if so.
 *
 * No concurrency control is needed in this class as recordThatRollbackHappened can only happen in
 * an OpObserver detecting that the document was deleted, and didRollbackHappen is only called on
 * exiting rollback, and there can only be one of those things happening at any given time.
 */
class ShardIdentityRollbackNotifier {
    ShardIdentityRollbackNotifier(const ShardIdentityRollbackNotifier&) = delete;
    ShardIdentityRollbackNotifier& operator=(const ShardIdentityRollbackNotifier&) = delete;

public:
    ShardIdentityRollbackNotifier();

    /**
     * Retrieves the ShardIdentityRollbackNotifier associated with the specified service context.
     */
    static ShardIdentityRollbackNotifier* get(OperationContext* opCtx);
    static ShardIdentityRollbackNotifier* get(ServiceContext* opCtx);

    /**
     * Records the fact that the shardIdentity document was rolled back.
     */
    void recordThatRollbackHappened() {
        _rollbackHappened = true;
    }

    /**
     * Checks whether the shardIdentity document was rolled back.
     */
    bool didRollbackHappen() {
        return _rollbackHappened;
    }

private:
    // Whether or not a rollback of the shardIdentity document has been detected.
    // No concurrency control necessary since this is only consulted during
    bool _rollbackHappened = false;
};

}  // namespace mongo