/**
 *    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/query/canonical_query.h"
#include "mongo/db/query/query_planner_params.h"
#include "mongo/db/query/query_solution.h"

namespace mongo {

    class CachedSolution;
    class Collection;

    /**
     * QueryPlanner's job is to provide an entry point to the query planning and optimization
     * process.
     */
    class QueryPlanner {
    public:
        /**
         * Outputs a series of possible solutions for the provided 'query' into 'out'.  Uses the
         * indices and other data in 'params' to plan with.
         *
         * Caller owns pointers in *out.
         */
        static Status plan(const CanonicalQuery& query,
                           const QueryPlannerParams& params,
                           std::vector<QuerySolution*>* out);

        /**
         * Helper that does most of the heavy lifting for the planFromCache
         * method which this overloads. Whereas the overloaded version plans
         * from cache twice (once for the winning solution and once from the
         * backup solution), this version plans from cache once.
         *
         * It requires a single SolutionCacheData, rather than a CachedSolution, which
         * owns a vector of SolutionCacheData instances.
         */
        static Status planFromCache(const CanonicalQuery& query,
                                    const QueryPlannerParams& params,
                                    const SolutionCacheData& cacheData,
                                    QuerySolution** out);

        /**
         * Attempt to generate a query solution, given data retrieved
         * from the plan cache.
         *
         * @param query -- query for which we are generating a plan
         * @param params -- planning parameters
         * @param cachedSoln -- the CachedSolution retrieved from the plan cache.
         * @param out -- an out-parameter which will be filled in with the solution
         *   generated from the cache data
         * @param backupOut -- if 'out' contains a blocking sort, then backoutOut may
         *  contain an alternative solution with no blocking sort; otherwise it will
         *  contain NULL on return.
         */
        static Status planFromCache(const CanonicalQuery& query,
                                    const QueryPlannerParams& params,
                                    const CachedSolution& cachedSoln,
                                    QuerySolution** out,
                                    QuerySolution** backupOut);

        /**
         * Used to generated the index tag tree that will be inserted
         * into the plan cache. This data gets stashed inside a QuerySolution
         * until it can be inserted into the cache proper.
         *
         * @param taggedTree -- a MatchExpression with index tags that has been
         *   produced by the enumerator.
         * @param relevantIndices -- a list of the index entries used to tag
         *   the tree (i.e. index numbers in the tags refer to entries in this vector)
         *
         * On success, a new tagged tree is returned through the out-parameter 'out'.
         * The caller has ownership of both taggedTree and *out.
         *
         * On failure, 'out' is set to NULL.
         */
        static Status cacheDataFromTaggedTree(const MatchExpression* const taggedTree,
                                              const std::vector<IndexEntry>& relevantIndices,
                                              PlanCacheIndexTree** out);

        /**
         * @param filter -- an untagged MatchExpression
         * @param indexTree -- a tree structure retrieved from the
         *   cache with index tags that indicates how 'filter' should
         *   be tagged.
         * @param indexMap -- needed in order to put the proper index
         *   numbers inside the index tags
         *
         * On success, 'filter' is mutated so that it has all the
         * index tags needed in order for the access planner to recreate
         * the cached plan.
         *
         * On failure, the tag state attached to the nodes of 'filter'
         * is invalid. Planning from the cache should be aborted.
         *
         * Does not take ownership of either filter or indexTree.
         */
        static Status tagAccordingToCache(MatchExpression* filter,
                                          const PlanCacheIndexTree* const indexTree,
                                          const std::map<BSONObj, size_t>& indexMap);
    };

}  // namespace mongo
