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#ifndef OSDEV_COMPONENTS_MQTT_COMPILETIMEDIGITS_H
#define OSDEV_COMPONENTS_MQTT_COMPILETIMEDIGITS_H

// std
#include <string>

#include "compiletimestring.h"

namespace osdev {
namespace components {
namespace mqtt {

/**
 * @brief Calculate the number of digits needed to represent a given value in a given base.
 * @tparam B The base to use.
 * @param value The value to represent.
 * @return The number of digits.
 */
template <unsigned B>
constexpr std::size_t numberOfDigits(unsigned value) noexcept
{
    static_assert(B > 0, "base must be larger than zero");
    return (value / B) == 0 ? 1 : (1 + numberOfDigits<B>(value / B));
}

/**
 * @return stringified digit that represents the given single digit value.
 * @note Values can range from 0 to 37 inclusive which maps on 0-9A-Z.
 */
template <unsigned value>
constexpr char digit() noexcept
{
    static_assert(value <= 37, "Value must lie between 0 and 37 both inclusive");
    return (value < 10 ? '0' + static_cast<char>(value) : 'A' + static_cast<char>(value) - 10);
}

/**
 * @brief Recursive template definition that is used to determine the value of a given number N in a given base B.
 * @tparam N The number to obtain the representation for.
 * @tparam B The base to use.
 * @tparam Len The length of the representation including the 0 terminator.
 *         If not provided the length is calculated on first instantiation of this template.
 * @tparam remains Empty parameter pack on first instantiation. Will be filled further by every following instantiation.
 */
template <unsigned N, unsigned B, std::size_t Len = numberOfDigits<B>(N) + 1, unsigned... remains>
struct Digits
{

    static constexpr auto create() noexcept -> std::array<char, Len>
    {
        static_assert(B > 0, "base must be larger than zero");
        return Digits<N / B, B, Len, digit<N % B>(), remains...>::create();
    }
};

/**
 * @brief Termination template that will return the actual hex digit array that represents the given value.
 * @tparam B The base to use.
 * @tparam Len The length of the hexadecimal representation including 0 terminator.
 * @tparam remains Parameter pack that contains the hexadecimal character representations.
 */
template <unsigned B, std::size_t Len, unsigned... remains>
struct Digits<0, B, Len, remains...>
{

    static constexpr auto create() noexcept -> std::array<char, Len>
    {
        static_assert(sizeof...(remains) + 1 == Len, "Parameter 'Len' must be equal to the length of the parameter pack 'remains' including the termination zero");
        return std::array<char, Len>{ { remains..., 0 } };
    }
};

/**
 * @brief Digits builder can be used in combination with the compiletime_string.
 * @tparam N The number to obtain the compile time string representation for.
 * @tparam B The base to use (up to 37).
 * This template struct defines a produce() method and the return type of that method.
 */
template <unsigned N, unsigned B>
struct ProduceDigits
{
    /**
     * @brief Return type definition of the produce method.
     */
    using return_t = std::array<char, numberOfDigits<B>(N) + 1>;

    /**
     * @brief Produce the actual representation.
     */
    static constexpr return_t produce() noexcept
    {
        return Digits<N, B>::create();
    }
};

}       // End namespace mqtt
}       // End namespace components
}       // End namespace osdev

#endif  // OSDEV_COMPONENTS_MQTT_COMPILETIMEDIGITS_H