Memento - An example

gistfile1.txt

public class CAMemberServiceCredit
{
    public string MemberSeparator { get; private set; }

    // ReoccurCharge 1 in the format stored in database
    public string ReoccurChrg1 { get; private set; }

    // ReoccurCharge 2 in the format stored in database
    public string ReoccurChrg2 { get; private set; }

    // ReoccurCharge 3 in the format stored in database
    public string ReoccurChrg3 { get; private set; }

    private static readonly BcdConverter _bcdConverter = new BcdConverter(precision: 5);

    #region parsed fields

    public string Code1
    {
        get
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg1) || ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccuChrg1 is not in correct format: '" + ReoccurChrg1 + "'");
            return ReoccurChrg1.Substring(0, 2);
        }
        set
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg1) || ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccurChrg1 is not in correct format: '" + ReoccurChrg1 + "'");
            if (string.IsNullOrWhiteSpace(value) || value.Length != 2)
                throw new InvalidOperationException("Invalid value: '" + value + "'");
            ReoccurChrg1 = value + ReoccurChrg1.Substring(2, 4);
        }
    }

    public string Code2
    {
        get
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg2) || ReoccurChrg2.Length != 6)
                throw new InvalidOperationException("ReoccuChrg1 is not in correct format: '" + ReoccurChrg2 + "'");
            return ReoccurChrg2.Substring(0, 2);
        }
        set
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg2) || ReoccurChrg2.Length != 6)
                throw new InvalidOperationException("ReoccurChrg2 is not in correct format: '" + ReoccurChrg2 + "'");
            if (string.IsNullOrWhiteSpace(value) || value.Length != 2)
                throw new InvalidOperationException("Invalid value: '" + value + "'");
            ReoccurChrg2 = value + ReoccurChrg2.Substring(2, 4);
        }
    }

    public string Code3
    {
        get
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg3) || ReoccurChrg3.Length != 6)
                throw new InvalidOperationException("ReoccuChrg1 is not in correct format: '" + ReoccurChrg3 + "'");
            return ReoccurChrg3.Substring(0, 2);
        }
        set
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg3) || ReoccurChrg3.Length != 6)
                throw new InvalidOperationException("ReoccurChrg3 is not in correct format: '" + ReoccurChrg3 + "'");
            if (string.IsNullOrWhiteSpace(value) || value.Length != 2)
                throw new InvalidOperationException("Invalid value: '" + value + "'");
            ReoccurChrg3 = value + ReoccurChrg3.Substring(2, 4);
        }
    }

    public decimal ReoccurAmt1
    {
        get
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg1) || ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccuChrg1 is not in correct format: '" + ReoccurChrg1 + "'");
            return _bcdConverter.UnpackAmount(ReoccurChrg1.Substring(2, 4));
        }
        set
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg1) || ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccurChrg1 is not in correct format: '" + ReoccurChrg1 + "'");
            ReoccurChrg1 = Code1 + _bcdConverter.PackAmount(value);
            if (ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccurChrg1 length has to be 6. It is: " + ReoccurChrg1.Length);
        }
    }

    public decimal ReoccurAmt2
    {
        get
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg1) || ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccurChrg1 is not in correct format: '" + ReoccurChrg1 + "'");
            return _bcdConverter.UnpackAmount(ReoccurChrg2.Substring(2, 4));
        }
        set
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg1) || ReoccurChrg1.Length != 6)
                throw new InvalidOperationException("ReoccurChrg1 is not in correct format: '" + ReoccurChrg1 + "'");
            ReoccurChrg2 = Code2 + _bcdConverter.PackAmount(value);
        }
    }

    public decimal ReoccurAmt3
    {
        get
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg3) || ReoccurChrg3.Length != 6)
                throw new InvalidOperationException("ReoccurChrg3 is not in correct format: '" + ReoccurChrg3 + "'");
            return _bcdConverter.UnpackAmount(ReoccurChrg3.Substring(2, 4));
        }
        set
        {
            if (string.IsNullOrWhiteSpace(ReoccurChrg3) || ReoccurChrg3.Length != 6)
                throw new InvalidOperationException("ReoccurChrg3 is not in correct format: '" + ReoccurChrg3 + "'");
            ReoccurChrg3 = Code3 + _bcdConverter.PackAmount(value);
        }
    }

    #endregion

    public CAAuditEntry RecordPaymentForPastDues(decimal amount, string chargeCode)
    {
        Debug.Assert(string.IsNullOrWhiteSpace(chargeCode) == false);
        CAMemberServicePaymentMemento memento = new CAMemberServicePaymentMemento(this);

        if (amount == 0)
            return null;

        if (amount < 0)
            throw new ArgumentOutOfRangeException("Negative credits cannot be posted to MemberDetl: " + amount);

        // Note: Amount should be deducted
        if (chargeCode == Code1)
        {
            ReoccurAmt1 -= amount;
        }
        else if (chargeCode == Code2)
        {
            ReoccurAmt2 -= amount;
        }
        else if (chargeCode == Code3)
        {
            ReoccurAmt3 -= amount;
        }
        else if (Code1 == "00" && ReoccurAmt1 == 0)
        {
            ReoccurAmt1 = amount;
            Code1 = chargeCode;
        }
        else if (Code2 == "00" && ReoccurAmt2 == 0)
        {
            ReoccurAmt2 = amount;
            Code2 = chargeCode;
        }
        else if (Code3 == "00" && ReoccurAmt3 == 0)
        {
            ReoccurAmt3 = amount;
            Code3 = chargeCode;
        }
        else
        {
            throw new InvalidOperationException(string.Format(
                "Cannot credit ${0} to MemberSeparator {1} " +
                " because all three ReoccurChrg fields are populated with other charges. Namely, {0}, {1}, {2}",
                Code1,
                Code2,
                Code3));
        }
        return memento.GetAuditEntryForChanges(this);
    }

    private class CAMemberServicePaymentMemento
    {
        private CAMemberServiceCredit _original;

        public CAMemberServicePaymentMemento(CAMemberServiceCredit original)
        {
            _original = original.MemberwiseClone() as CAMemberServiceCredit;
        }

        public CAAuditEntry GetAuditEntryForChanges(CAMemberServiceCredit modified)
        {
            if (_original.MemberSeparator != modified.MemberSeparator)
                throw new InvalidOperationException(
                    string.Format("Cannot audit entries related to different member seps. Original:{0} modified:{1}",
                    _original.MemberSeparator,
                    modified.MemberSeparator));

            var entry = CAAuditEntry.CreateNewAuditEntryForPastDuesRecovery(_original.MemberSeparator);

            if (_original.ReoccurChrg1 != modified.ReoccurChrg1)
            {
                entry.CAField = ReOccurCharge.REOCCURCHG_001.Description();
                entry.OldValue = _original.ReoccurChrg1;
                entry.NewValue = modified.ReoccurChrg1;
            }
            else if (_original.ReoccurChrg2 != modified.ReoccurChrg2)
            {
                entry.CAField = ReOccurCharge.REOCCURCHG_002.Description();
                entry.OldValue = _original.ReoccurChrg2;
                entry.NewValue = modified.ReoccurChrg2;
            }
            else if (_original.ReoccurChrg3 != modified.ReoccurChrg3)
            {
                entry.CAField = ReOccurCharge.REOCCURCHG_003.Description();
                entry.OldValue = _original.ReoccurChrg3;
                entry.NewValue = modified.ReoccurChrg3;
            }
            return entry.CAField == null ? null : entry;
        }
    }

    public override string ToString()
    {
        return string.Format("MemberSeparator: {0} ReoccurChrg1: {1} ReoccurChrg2:{2} ReoccurChrg3:{3} ", MemberSeparator, ReoccurChrg1, ReoccurChrg2, ReoccurChrg3);
    }
}