ClickHouse/src/AggregateFunctions/AggregateFunctionMaxIntersections.h

#pragma once

#include <base/sort.h>

#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnsNumber.h>

#include <IO/ReadHelpers.h>
#include <IO/WriteHelpers.h>

#include <Common/ArenaAllocator.h>
#include <Common/NaNUtils.h>
#include <Common/assert_cast.h>

#include <AggregateFunctions/IAggregateFunction.h>

#define AGGREGATE_FUNCTION_MAX_INTERSECTIONS_MAX_ARRAY_SIZE 0xFFFFFF


namespace DB
{
struct Settings;

namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
    extern const int TOO_LARGE_ARRAY_SIZE;
}


/** maxIntersections: returns maximum count of the intersected intervals defined by start_column and end_column values,
  * maxIntersectionsPosition: returns leftmost position of maximum intersection of intervals.
  */

/// Similar to GroupArrayNumericData.
template <typename T>
struct MaxIntersectionsData
{
    /// Left or right end of the interval and signed weight; with positive sign for begin of interval and negative sign for end of interval.
    using Value = std::pair<T, Int64>;

    // Switch to ordinary Allocator after 4096 bytes to avoid fragmentation and trash in Arena
    using Allocator = MixedAlignedArenaAllocator<alignof(Value), 4096>;
    using Array = PODArray<Value, 32, Allocator>;

    Array value;
};

enum class AggregateFunctionIntersectionsKind
{
    Count,
    Position
};

template <typename PointType>
class AggregateFunctionIntersectionsMax final
    : public IAggregateFunctionDataHelper<MaxIntersectionsData<PointType>, AggregateFunctionIntersectionsMax<PointType>>
{
private:
    AggregateFunctionIntersectionsKind kind;

public:
    AggregateFunctionIntersectionsMax(AggregateFunctionIntersectionsKind kind_, const DataTypes & arguments)
        : IAggregateFunctionDataHelper<MaxIntersectionsData<PointType>, AggregateFunctionIntersectionsMax<PointType>>(arguments, {}, createResultType(kind_))
        , kind(kind_)
    {
        if (!isNativeNumber(arguments[0]))
            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "{}: first argument must be represented by integer", getName());

        if (!isNativeNumber(arguments[1]))
            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "{}: second argument must be represented by integer", getName());

        if (!arguments[0]->equals(*arguments[1]))
            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "{}: arguments must have the same type", getName());
    }

    String getName() const override
    {
        return kind == AggregateFunctionIntersectionsKind::Count
            ? "maxIntersections"
            : "maxIntersectionsPosition";
    }

    static DataTypePtr createResultType(AggregateFunctionIntersectionsKind kind_)
    {
        if (kind_ == AggregateFunctionIntersectionsKind::Count)
            return std::make_shared<DataTypeUInt64>();
        else
            return std::make_shared<DataTypeNumber<PointType>>();
    }

    bool allocatesMemoryInArena() const override { return false; }

    void add(AggregateDataPtr __restrict place, const IColumn ** columns, size_t row_num, Arena * arena) const override
    {
        PointType left = assert_cast<const ColumnVector<PointType> &>(*columns[0]).getData()[row_num];
        PointType right = assert_cast<const ColumnVector<PointType> &>(*columns[1]).getData()[row_num];

        if (!isNaN(left))
            this->data(place).value.push_back(std::make_pair(left, Int64(1)), arena);

        if (!isNaN(right))
            this->data(place).value.push_back(std::make_pair(right, Int64(-1)), arena);
    }

    void merge(AggregateDataPtr __restrict place, ConstAggregateDataPtr rhs, Arena * arena) const override
    {
        auto & cur_elems = this->data(place);
        auto & rhs_elems = this->data(rhs);

        cur_elems.value.insert(rhs_elems.value.begin(), rhs_elems.value.end(), arena);
    }

    void serialize(ConstAggregateDataPtr __restrict place, WriteBuffer & buf, std::optional<size_t> /* version */) const override
    {
        const auto & value = this->data(place).value;
        size_t size = value.size();
        writeVarUInt(size, buf);

        /// In this version, pairs were serialized with padding.
        /// We must ensure that padding bytes are zero-filled.

        static_assert(offsetof(typename MaxIntersectionsData<PointType>::Value, first) == 0);
        static_assert(offsetof(typename MaxIntersectionsData<PointType>::Value, second) > 0);

        char zero_padding[offsetof(typename MaxIntersectionsData<PointType>::Value, second) - sizeof(value[0].first)]{};

        for (size_t i = 0; i < size; ++i)
        {
            writePODBinary(value[i].first, buf);
            writePODBinary(zero_padding, buf);
            writePODBinary(value[i].second, buf);
        }
    }

    void deserialize(AggregateDataPtr __restrict place, ReadBuffer & buf, std::optional<size_t> /* version */, Arena * arena) const override
    {
        size_t size = 0;
        readVarUInt(size, buf);

        if (unlikely(size > AGGREGATE_FUNCTION_MAX_INTERSECTIONS_MAX_ARRAY_SIZE))
            throw Exception(ErrorCodes::TOO_LARGE_ARRAY_SIZE,
                            "Too large array size (maximum: {})", AGGREGATE_FUNCTION_MAX_INTERSECTIONS_MAX_ARRAY_SIZE);

        auto & value = this->data(place).value;

        value.resize(size, arena);
        buf.readStrict(reinterpret_cast<char *>(value.data()), size * sizeof(value[0]));
    }

    void insertResultInto(AggregateDataPtr __restrict place, IColumn & to, Arena *) const override
    {
        Int64 current_intersections = 0;
        Int64 max_intersections = 0;
        PointType position_of_max_intersections = 0;

        /// const_cast because we will sort the array
        auto & array = this->data(place).value;

        /// Sort by position; for equal position, sort by weight to get deterministic result.
        ::sort(array.begin(), array.end());

        for (const auto & point_weight : array)
        {
            current_intersections += point_weight.second;
            if (current_intersections > max_intersections)
            {
                max_intersections = current_intersections;
                position_of_max_intersections = point_weight.first;
            }
        }

        if (kind == AggregateFunctionIntersectionsKind::Count)
        {
            auto & result_column = assert_cast<ColumnUInt64 &>(to).getData();
            result_column.push_back(max_intersections);
        }
        else
        {
            auto & result_column = assert_cast<ColumnVector<PointType> &>(to).getData();
            result_column.push_back(position_of_max_intersections);
        }
    }
};

}