/**
 *    Copyright (C) 2022-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 <map>

#include "mongo/db/exec/sbe/values/value.h"
#include "mongo/db/query/stats/scalar_histogram.h"
#include "mongo/db/query/stats/stats_gen.h"

namespace mongo::stats {
using TypeCounts = std::map<sbe::value::TypeTags, double>;

/**
 * By default, aggregates the total number of tag counts in the histogram together.
 * If 'isHistogrammable' is set to true, then only counts histogrammable types.
 * Otherwise, if 'isHistogrammable' is set to false, then only counts non-histogrammable types.
 **/
double getTotalCount(const TypeCounts& tc, boost::optional<bool> isHistogrammable = boost::none);

class ArrayHistogram {
public:
    /**
     * Factory method for constructing an empty scalar histogram.
     */
    static std::shared_ptr<const ArrayHistogram> make();

    /**
     * Factory method for constructing an ArrayHistogram using StatsPath IDL as input.
     */
    static std::shared_ptr<const ArrayHistogram> make(Statistics stats);

    /**
     * Factory method for constructing a scalar histogram (no array fields).
     */
    static std::shared_ptr<const ArrayHistogram> make(ScalarHistogram scalar,
                                                      TypeCounts typeCounts,
                                                      double sampleSize,
                                                      double trueCount = 0.0,
                                                      double falseCount = 0.0,
                                                      double nanCount = 0.0,
                                                      bool validate = true);

    /**
     * Factory method for constructing an array field histogram. All array fields must be
     * initialized.
     */
    static std::shared_ptr<const ArrayHistogram> make(ScalarHistogram scalar,
                                                      TypeCounts typeCounts,
                                                      ScalarHistogram arrayUnique,
                                                      ScalarHistogram arrayMin,
                                                      ScalarHistogram arrayMax,
                                                      TypeCounts arrayTypeCounts,
                                                      double sampleSize,
                                                      double emptyArrayCount = 0.0,
                                                      double trueCount = 0.0,
                                                      double falseCount = 0.0,
                                                      double nanCount = 0.0,
                                                      bool validate = true);

    // ArrayHistogram is neither copy-constructible nor copy-assignable.
    ArrayHistogram(const ArrayHistogram&) = delete;
    ArrayHistogram& operator=(const ArrayHistogram&) = delete;

    // However, it is move-constructible and move-assignable.
    ArrayHistogram(ArrayHistogram&&) = default;
    ArrayHistogram& operator=(ArrayHistogram&&) = default;
    ~ArrayHistogram() = default;

    std::string toString() const;

    // Serialize to BSON for storage in stats collection.
    BSONObj serialize() const;

    const ScalarHistogram& getScalar() const;
    const ScalarHistogram& getArrayUnique() const;
    const ScalarHistogram& getArrayMin() const;
    const ScalarHistogram& getArrayMax() const;
    const TypeCounts& getTypeCounts() const;
    const TypeCounts& getArrayTypeCounts() const;

    // Returns whether or not this histogram includes array data points.
    bool isArray() const;

    // Get the total number of arrays in the histogram's path including empty arrays.
    double getArrayCount() const;

    // Get the total number of empty arrays ( [] ) in the histogram's path.
    double getEmptyArrayCount() const {
        return _emptyArrayCount;
    }

    // Get the count of true booleans.
    double getTrueCount() const {
        return _trueCount;
    }

    // Get the count of false booleans.
    double getFalseCount() const {
        return _falseCount;
    }

    // Get the count of NaNs.
    double getNanCount() const {
        return _nanCount;
    }

    // Returns the count of a type as known by the respective type counter. If the type is not
    // present in the TypeCounts map, returns 0.
    double getTypeCount(sbe::value::TypeTags tag) const;
    double getArrayTypeCount(sbe::value::TypeTags tag) const;

    // Returns the sum of counts of all types known by the respective type counter.
    double getTotalTypeCount() const;
    double getTotalArrayTypeCount() const;

    // Returns the proportion of the overall collection that was comprised by the sample used to
    // gnerate this histogram.
    double getSampleSize() const {
        return _sampleSize;
    }

private:
    // Constructs an empty scalar histogram.
    ArrayHistogram();

    // Constructor for scalar field histograms.
    ArrayHistogram(ScalarHistogram scalar,
                   TypeCounts typeCounts,
                   double sampleSize,
                   double trueCount = 0.0,
                   double falseCount = 0.0,
                   double nanCount = 0.0);

    // Constructor for array field histograms. We have to initialize all array fields in this case.
    ArrayHistogram(ScalarHistogram scalar,
                   TypeCounts typeCounts,
                   ScalarHistogram arrayUnique,
                   ScalarHistogram arrayMin,
                   ScalarHistogram arrayMax,
                   TypeCounts arrayTypeCounts,
                   double sampleSize,
                   double emptyArrayCount = 0.0,
                   double trueCount = 0.0,
                   double falseCount = 0.0,
                   double nanCount = 0.0);

    /* Fields for all paths. */

    // Contains values which appeared originally as scalars on the path.
    ScalarHistogram _scalar;
    // The number of values of each type.
    TypeCounts _typeCounts;
    // The number of empty arrays - they are not accounted for in the histograms.
    double _emptyArrayCount;
    // The counts of true & false booleans.
    double _trueCount;
    double _falseCount;
    // The count of NaNs.
    double _nanCount;
    // The exact number of documents in the sample used to build the histogram.
    double _sampleSize;

    /* Fields for array paths (only initialized if arrays are present). */

    // Contains unique scalar values originating from arrays.
    boost::optional<ScalarHistogram> _arrayUnique;
    // Contains minimum values originating from arrays **per class**.
    boost::optional<ScalarHistogram> _arrayMin;
    // Contains maximum values originating from arrays **per class**.
    boost::optional<ScalarHistogram> _arrayMax;
    // The number of values of each type inside all arrays.
    boost::optional<TypeCounts> _arrayTypeCounts;
};

/**
 * Returns an owned BSON Object representing data matching mongo::Statistics IDL.
 */
BSONObj makeStatistics(double documents,
                       double sampleRate,
                       std::shared_ptr<const ArrayHistogram> arrayHistogram);

/**
 * Returns an owned BSON Object representing data matching mongo::StatsPath IDL.
 */
BSONObj makeStatsPath(StringData path,
                      double documents,
                      double sampleRate,
                      std::shared_ptr<const ArrayHistogram> arrayHistogram);
}  // namespace mongo::stats