#include <iostream>
#include <vector>
#include <list>
#include <set>

template <typename T>
class Ping_Pong
{
public:

    template <typename Container>
    Ping_Pong(Container const& data)
        : data { data.begin(), data.end() }
    {
    }

    T const& operator[](int index) const
    {
        int size { static_cast<int>(data.size()) };

        index = index % (2 * size);
        if (index < 0)
        {
            index += 2 * size;
            index = index % (2 * size);
        }

        if (index < size)
            return data[index];
        index = size - (index - size) - 1;
        return data[index];
    }

    void append(T const& element)
    {
        data.push_back(element);
    }

private:

    std::vector<T> data { };

};

int main()
{
    {
        std::vector<int> v { 0, 1, 2, 3 } ;
        Ping_Pong<int> p { v };

        for (int i { -10 }; i <= 10; ++i)
            std::cout << p[i] << " ";
        std::cout << std::endl;

        p.append(4);
        for (int i { -10 }; i <= 10; ++i)
            std::cout << p[i] << " ";

        std::cout << std::endl;
    }

    {
        std::list<std::string> v { "PONTUS", "ERIC", "MALTE", "NILS", "EDVIN" };
        Ping_Pong<std::string> p { v };

        for (int i { -4 }; i <= 5; ++i)
            std::cout << p[i] << " ";
        std::cout << std::endl;

        p.append("CHRISTOFFER");
        for (int i { -4 }; i <= 5; ++i)
            std::cout << p[i] << " ";

        std::cout << std::endl;
    }

    {
        std::vector<int> v { 0, 1 };
        std::set<int> s { 0, 1 };
        Ping_Pong<int> p { v };

        // se till att behållaren inte är en mallparameter till Ping_Pong.
        p = Ping_Pong<int>{ s };

        for (int i { -9 }; i <= 10; ++i)
            std::cout << p[i] << " ";
        std::cout << std::endl;
    }
}