/// <summary>
        /// Makes a withdrawal of <paramref name="amount"/> from an account with specified <paramref name="iban"/>
        /// </summary>
        /// <param name="iban">IBAN of an account to make withdrawal</param>
        /// <param name="amount">withdrawal amount</param>
        /// <returns>new account balance</returns>
        /// <exception cref="ArgumentException">withdrawal amount is lesser than minimal</exception>
        public decimal MakeWithdrawal(string iban, decimal amount)
        {
            if (string.IsNullOrWhiteSpace(iban))
            {
                throw new ArgumentException("No IBAN is given.", "IBAN");
            }

            if (amount < MINWITHDRAWAL)
            {
                throw new ArgumentException("Minimum withdrawal amount is " + MINWITHDRAWAL.ToString("C"));
            }



            var account = BankAccountMapper.FromDTO(Storage.GetAccount(iban));

            if (amount > account.Balance)
            {
                throw new InvalidOperationException("account balance is less than withdrawal amount");
            }

            account.Balance     -= amount;
            account.BonusPoints -= BonusCalculator.CalculateWithdrawalBonus(account, amount);
            Storage.UpdateAccount(BankAccountMapper.ToDTO(account));

            return(account.Balance);
        }
        /// <summary>
        /// Opens a new account for <paramref name="holder"/> with <paramref name="startBalance"/>.
        /// </summary>
        /// <param name="holder">person's full name</param>
        /// <param name="startBalance">first deposit amount</param>
        /// <returns>IBAN of a new account</returns>
        /// <exception cref="ArgumentException">Start balance is lesser than minimal.</exception>
        public string OpenAccount(string holder, decimal startBalance)
        {
            if (string.IsNullOrWhiteSpace(holder))
            {
                throw new ArgumentException("No significant characters are given.", "holder");
            }

            if (startBalance < MINDEPOSIT)
            {
                throw new ArgumentException($"Cannot create a bank account with balance lesser than {MINDEPOSIT}");
            }

            BankAccount account;

            if (startBalance <= 1000)
            {
                account = new StandardAccount(IBANGenerator.GenerateIBAN(), holder, startBalance, bonusPoints: 0);
            }
            else if (startBalance <= 10000)
            {
                account = new GoldAccount(IBANGenerator.GenerateIBAN(), holder, startBalance, bonusPoints: 5);
            }
            else
            {
                account = new PlatinumAccount(IBANGenerator.GenerateIBAN(), holder, startBalance, bonusPoints: 10);
            }

            Storage.AddAccount(BankAccountMapper.ToDTO(account));

            return(account.IBAN);
        }
        /// <summary>
        /// Makes a deposit of <paramref name="amount"/> to an account with specified <paramref name="iban"/>.
        /// </summary>
        /// <param name="iban">IBAN of an account to make deposit</param>
        /// <param name="amount">deposit amount</param>
        /// <returns>new account balance</returns>
        /// <exception cref="ArgumentException">deposit amount is lesser than minimal</exception>
        public decimal MakeDeposit(string iban, decimal amount)
        {
            if (string.IsNullOrWhiteSpace(iban))
            {
                throw new ArgumentException("No IBAN is given.", "IBAN");
            }

            if (amount < MINDEPOSIT)
            {
                throw new ArgumentException("Minimum deposit amount is " + MINDEPOSIT.ToString("C"));
            }

            var account = BankAccountMapper.FromDTO(Storage.GetAccount(iban));

            account.Balance     += amount;
            account.BonusPoints += BonusCalculator.CalculateDepositBonus(account, amount);
            Storage.UpdateAccount(BankAccountMapper.ToDTO(account));

            return(account.Balance);
        }