/**
 *    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

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

namespace mongo {

class Collection;
class CollectionPtr;

class QueryPlannerAnalysis {
public:
    /**
     * Checks solution nodes for geo match expressions to apply an optimization.
     *
     * If a geo match expression is on a field with a corresponding 2dsphere index we can
     * skip expensive validation of geometries in the matcher, since those geometries were
     * validated when they were indexed.
     */
    static void analyzeGeo(const QueryPlannerParams& params, QuerySolutionNode* solnRoot);

    /**
     * Takes an index key pattern and returns an object describing the "maximal sort" that this
     * index can provide.  Returned object is in normalized sort form (all elements have value 1
     * or -1).
     *
     * Examples:
     * - {a: 1, b: -1} => {a: 1, b: -1}
     * - {a: true} => {a: 1}
     * - {a: "hashed"} => {}
     * - {a: 1, b: "text", c: 1} => {a: 1}
     */
    static BSONObj getSortPattern(const BSONObj& indexKeyPattern);

    /**
     * In brief: performs sort and covering analysis.
     *
     * The solution rooted at 'solnRoot' provides data for the query, whether through some
     * configuration of indices or through a collection scan.  Additional stages may be required to
     * perform sorting, projection, or other operations that are independent of the source of the
     * data.  These stages are added atop 'solnRoot'.
     *
     * Returns a null pointer if a solution cannot be constructed given the requirements in
     * 'params'.
     */
    static std::unique_ptr<QuerySolution> analyzeDataAccess(
        const CanonicalQuery& query,
        const QueryPlannerParams& params,
        std::unique_ptr<QuerySolutionNode> solnRoot);

    /**
     * Sort the results, if there is a sort required.
     *
     * The mandatory output parameters 'blockingSortOut' and 'explodeForSortOut' indicate if the
     * generated sub-plan contains a blocking QSN, such as 'SortNode', and if the sub-plan was
     * "exploded" to obtain an indexed sort (see QueryPlannerAnalysis::explodeForSort()).
     */
    static std::unique_ptr<QuerySolutionNode> analyzeSort(
        const CanonicalQuery& query,
        const QueryPlannerParams& params,
        std::unique_ptr<QuerySolutionNode> solnRoot,
        bool* blockingSortOut,
        bool* explodeForSortOut);

    /**
     * Internal helper function used by analyzeSort.
     *
     * Rewrites an index scan over many point intervals as an OR of many index scans in order to
     * obtain an indexed sort.  For full details, see SERVER-1205.
     *
     * Here is an example:
     *
     * Consider the query find({a: {$in: [1,2]}}).sort({b: 1}) with using the index {a:1, b:1}.
     *
     * Our default solution will be to construct one index scan with the bounds a:[[1,1],[2,2]]
     * and b: [MinKey, MaxKey].
     *
     * However, this is logically equivalent to the union of the following scans:
     * a:[1,1], b:[MinKey, MaxKey]
     * a:[2,2], b:[MinKey, MaxKey]
     *
     * Since the bounds on 'a' are a point, each scan provides the sort order {b:1} in addition
     * to {a:1, b:1}.
     *
     * If we union these scans with a merge sort instead of a normal hashing OR, we can preserve
     * the sort order that each scan provides.
     */
    static bool explodeForSort(const CanonicalQuery& query,
                               const QueryPlannerParams& params,
                               std::unique_ptr<QuerySolutionNode>* solnRoot);

    /**
     * Walks the QuerySolutionNode tree rooted in 'soln', and looks for a ProjectionNodeSimple that
     * is a child of GroupNode, and has a dependency set that's a super set of the the dependency
     * set of the GroupNode. If that condition is met the ProjectionNodeSimple is redundant and can
     * thus be elimiated to improve performance of the plan. Otherwise, this is a noop.
     */
    static std::unique_ptr<QuerySolution> removeInclusionProjectionBelowGroup(
        std::unique_ptr<QuerySolution> soln);

    /**
     * For the provided 'foreignCollName' and 'foreignFieldName' corresponding to an EqLookupNode,
     * returns what join algorithm should be used to execute it. In particular:
     * - An empty array is produced for each document if the foreign collection does not exist.
     * - An indexed nested loop join is chosen if an index on the foreign collection can be used to
     * answer the join predicate. Also returns which index on the foreign collection should be
     * used to answer the predicate.
     * - A hash join is chosen if disk use is allowed and if the foreign collection is sufficiently
     * small.
     * - A nested loop join is chosen in all other cases.
     */
    static std::pair<EqLookupNode::LookupStrategy, boost::optional<IndexEntry>>
    determineLookupStrategy(
        const std::string& foreignCollName,
        const std::string& foreignField,
        const std::map<NamespaceString, SecondaryCollectionInfo>& collectionsInfo,
        bool allowDiskUse,
        const CollatorInterface* collator);

    /**
     * Checks if the foreign collection is eligible for the hash join algorithm. We conservatively
     * choose the hash join algorithm for cases when the hash table is unlikely to spill to disk.
     */
    static bool isEligibleForHashJoin(const SecondaryCollectionInfo& foreignCollInfo);
};

}  // namespace mongo