#include <iomanip>
#include <iostream>
#include <map>
#include <string>
#include <variant>
#include <vector>

class JSON_Field;
using JSON_List = std::vector<JSON_Field>;

class JSON
{
public:

    JSON_Field& operator[](std::string const& key)
    {
        return fields[key];
    }

    JSON_Field const& operator[](std::string const& key) const
    {
        return fields.at(key);
    }

    void print(std::ostream& os, int indent = 0) const;

private:

    std::map<std::string, JSON_Field> fields { };

};

class JSON_Field
{
public:

    JSON_Field() = default;

    template <typename T>
    JSON_Field(T&& field)
        : data { std::forward<T>(field) }
    {
    }

    JSON_Field(JSON_Field const&) = default;
    JSON_Field(JSON_Field&&) = default;
    ~JSON_Field() = default;
    JSON_Field& operator=(JSON_Field const&) = default;
    JSON_Field& operator=(JSON_Field&&) = default;

    template <typename T>
    JSON_Field& operator=(T&& parameter)
    {
        data = std::forward<T>(parameter);
        return *this;
    }

    void print(std::ostream& os, int indent = 0) const
    {
        switch (data.index())
        {
        case 0: print_number(os); break;
        case 1: print_list(os, indent); break;
        case 2: std::get<2>(data).print(os, indent); break;
        default: break;
        }
    }

private:

    void print_number(std::ostream& os) const
    {
        os << std::get<0>(data);
    }

    void print_list(std::ostream& os, int indent) const
    {
        os << "[";
        bool first { true };
        for (JSON_Field const& field : std::get<1>(data))
        {
            if (first)
                first = false;
            else
                os << ", ";
            field.print(os, indent);
        }
        os << "]";
    }

    std::variant<double, JSON_List, JSON> data;

};

void JSON::print(std::ostream& os, int indent) const
{
    os << "{" << std::endl;

    bool first { true };
    for (auto&& [key, value] : fields)
    {
        if (first)
        {
            first = false;
        }
        else
        {
            os << "," << std::endl;
        }

        os << std::setw(indent + 2) << "";
        os << '"' << key << "\" : ";
        value.print(os, indent + 2);
    }
    os << std::endl << std::setw(indent) << "" << "}";
}

int main()
{
    JSON json1;
    json1["d"] = 0.0;
    json1["e"] = 6.0;

    JSON json2;
    json2["a"] = 5.0;
    json2["b"] = JSON_List{ 1.0, JSON_List{ 2.0, 3.0 }, 4.0 };
    json2["c"] = std::move(json1);

    json2.print(std::cout);
    std::cout << std::endl;

    std::cout << "====" << std::endl;
    JSON json3;
    json3["list"] = JSON_List{ 0.5, std::move(json2), 1.5 };
    json3["number"] = -1.5;

    json3.print(std::cout);
    std::cout << std::endl;
}