Function.cpp

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

struct Image
{
    double quality;
    double freshness;
    double rating;
};

struct Params
{
    double a;
    double b;
    double c;
};

class FunctionPart
{
public:
    FunctionPart(char new_operation, double new_value)
    {
        operation = new_operation;
        value = new_value;
    }
    double Apply(double source_value) const
    {
        if (operation == '+')
        {
            return source_value + value;
        }
        else if (operation == '-')
        {
            return source_value - value;
        }
    }
    void Invert()
    {
        if (operation == '+')
        {
            operation = '-';
        }
        else if (operation == '-')
        {
            operation = '+';
        }
    }
private:
    char operation;
    double value;
};

class Function
{
public:
    void AddPart(char operation, double value)
    {
        parts.push_back({operation, value});
    }
    double Apply(double value) const
    {
        for (const auto& part : parts)
        {
            value = part.Apply(value);
        }
        return value;
    }
    void Invert()
    {
        for (auto& part : parts)
        {
            part.Invert();
        }
        reverse(begin(parts), end(parts));
    }
private:
    vector<FunctionPart> parts;
};

Function MakeWeightFunction(const Params& params, const Image& image)
{
    Function function;
    function.AddPart('-', image.freshness * params.a + params.b);
    function.AddPart('+', image.rating * params.c);
    return function;
}

double ComputeImageWeight(const Params& params, const Image& image)
{
    Function function = MakeWeightFunction(params, image);
    return function.Apply(image.quality);
}

double ComputeQualityByWeight(const Params& params, const Image& image,
    double weight)
{
    Function function = MakeWeightFunction(params, image);
    function.Invert();
    return function.Apply(weight);
}

int main(void)
{
	Image image = {10, 2, 6};
	Params params = {4, 2, 6};
	cout << ComputeImageWeight(params, image) << endl;
	cout << ComputeQualityByWeight(params, image, 46) << endl;
	return 0;
}