Bankomat: найти ошибки в коде и прокомментировать его строки

#include <iostream>
#include <map>
#include <stdexcept>
#include <cassert>
 
class ATMFactory;
 
class ATM
{
public:
   friend class ATMFactory;
   std::map<int, int> get_money(int64_t amount)
   {
      if (amount >= min_amount && amount <= max_amount)
      {
         return calculate(amount);
      }
      throw std::out_of_range("invalid_amount. Less than " + std::to_string(min_amount) + 
            " or more than " + std::to_string(max_amount));
   }
   int get_id() const
   {
      return id_;
   }
   enum monetary_unit { TEN = 10, FIFTY = 50, HUNDRED = 100, FIVE_HUNDRED = 500, THOUSAND = 1000 };
private:
   ATM(int id, int64_t min, int64_t max) :
      id_(id), min_amount(min), max_amount(max)
   {
   }
 
   void load_money(int ten, int fifty, int hundred, int five_hundred, int thousand)
   {
      money[TEN] = ten;
      money[FIFTY] = fifty;
      money[HUNDRED] = hundred;
      money[FIVE_HUNDRED] = five_hundred;
      money[THOUSAND] = thousand;
   }
 
   int64_t calculate_current(int64_t amount, std::map<int, int>& result, monetary_unit unit)
   {
      while (amount >= unit)
      {
         int cnt = amount / unit;
         if (money[unit] < cnt)
         {
            break;
         }
         result[unit] = cnt;
         money[unit] -= cnt;
         amount %= unit;
      }
      return amount;
   }
 
   std::map<int, int> calculate(int64_t amount)
   {
      if (amount % TEN)
      {
         throw std::invalid_argument("invalid_amount. Can't div to " + std::to_string(TEN));
      }
      std::map<int, int> result;
      amount = calculate_current(amount, result, THOUSAND);
      amount = calculate_current(amount, result, FIVE_HUNDRED);
      amount = calculate_current(amount, result, HUNDRED);
      amount = calculate_current(amount, result, FIFTY);
      amount = calculate_current(amount, result, TEN);
      return result;
   }
 
   const int id_;
   std::map<int, int> money;
   const int64_t min_amount;
   const int64_t max_amount;
};
 
class ATMFactory
{
public:
   static ATM create(int64_t min, int64_t max, int ten, int fifty, int hundred, int five_hundred, int thousand)
   {
      static int id = 0;
      ATM result(id++, min, max);
      result.load_money(ten, fifty, hundred, five_hundred, thousand);
      return result;
   }
};
 
int main()
{
   ATM test_atm = ATMFactory::create(0, 5000, 1, 1, 1, 1, 1);
   assert(test_atm.get_id() == 0);
   std::map<int, int> money = test_atm.get_money(1660);
   assert(money[ATM::TEN] == 1 && money[ATM::FIFTY] == 1 && money[ATM::HUNDRED] == 1 &&
          money[ATM::FIVE_HUNDRED] == 1 && money[ATM::THOUSAND] == 1);
   money = test_atm.get_money(10);
   assert(money.empty());
}