/**
 *    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.
 */

#pragma once

#include <memory>

#include "mongo/base/disallow_copying.h"
#include "mongo/base/status.h"


namespace mongo {

    class CanonicalQuery;
    class Database;
    class DeleteRequest;
    class OperationContext;

    /**
     * Implementation of the processing of a delete operation in a mongod.
     *
     * The executor has two important methods, prepare() and execute().  The prepare() method can
     * run without locks, and does whatever parsing and precomputation can be done without access to
     * database data.  The execute method performs the delete, but the caller must already hold the
     * appropriate database lock.
     *
     * Expected usage is approximately:
     *   DeleteRequest request(...);
     *   // configure request
     *   DeleteExecutor executor(&request);
     *   uassertStatusOK(executor.prepare());
     *   // Get locks, get ready to execute.
     *   try {
     *       long long nDeleted = executor.execute();
     *   }
     *   catch (const DBException& ex) {
     *       // Error handling.
     *   }
     */
    class DeleteExecutor {
        MONGO_DISALLOW_COPYING(DeleteExecutor);
    public:
        /**
         * Constructs a delete executor.
         *
         * The object pointed to by "request" must stay in scope for the life of the constructed
         * executor.
         */
        explicit DeleteExecutor(const DeleteRequest* request);

        ~DeleteExecutor();

        /**
         * Performs preparatory work that does not require database locks.
         *
         * Returns Status::OK() on success.  Other results indicate that the executor will not run
         * correctly, and should be abandoned.
         *
         * Calling prepare() is optional.  It is available for situations in which the user
         * wishes to do as much work as possible before acquiring database locks.
         */
        Status prepare();

        /**
         * Execute a delete.  Requires the caller to hold the database lock on the
         * appropriate resources for the request.
         *
         * Returns the number of documents deleted.
         */
        long long execute(OperationContext* txn, Database* db);

    private:
        /// Unowned pointer to the request object that this executor will process.
        const DeleteRequest* const _request;

        /// Parsed query object, or NULL if the query proves to be an id hack query.
        std::auto_ptr<CanonicalQuery> _canonicalQuery;

        /// Flag indicating if the query has been successfully parsed.
        bool _isQueryParsed;

    };

}  // namespace mongo
