#include "robot_name.h"

#include <algorithm>
#include <stdexcept>
#include <set>
#include <random>


namespace robot_name {

using namespace std;


namespace {

typedef uniform_int_distribution<char> distribution_t;

const size_t alpha_part_size = 2;
const size_t digit_part_size = 3;


string random_string(size_t size, distribution_t &distribution)
{
    static default_random_engine engine;

    auto random_char = [&distribution]() -> char {
        return distribution(engine);
    };

    string result(size, 0);
    generate_n(result.begin(), size, random_char);

    return result;
};

}


robot::robot()
{
    reset();
}

void robot::reset()
{
    static set<name_t>  used_names;
    static const size_t name_capacity = pow('Z' - 'A' + 1, alpha_part_size)
                                      * pow('9' - '0' + 1, digit_part_size);

    static distribution_t alpha_distribution('A', 'Z');
    static distribution_t digit_distribution('0', '9');

    if (used_names.size() >= name_capacity)
        throw length_error("no more names available");

    string new_name;

    do {

        new_name = random_string(alpha_part_size, alpha_distribution)
                 + random_string(digit_part_size, digit_distribution);

    } while (used_names.count(new_name));

    used_names.erase(name_);
    name_ = new_name;
    used_names.insert(name_);
}

const name_t &robot::name() const
{
    return name_;
}

}