Quarantine sample that reports recurring failures to email (sample for Lokad.CQRS v2.0)

SampleQuarantine.cs

// This quarantine sample uses in-memory quarantine to detect repetitive processing failures
// It records each failure into the streaming container (which could be file/Azure)
// When failure threshold is breached, we send an email to the hardcoded address.
// failure message contains all information about failures and message contents
public sealed class MailQuarantine : IEnvelopeQuarantine
{
    readonly SmtpHandlerCore _core;
    readonly IStreamingContainer _container;
    readonly MemoryQuarantine _quarantine = new MemoryQuarantine();

    public MailQuarantine(SmtpHandlerCore core, IStreamingRoot root)
    {
        _core = core;
        _container = root.GetContainer("sample-errors").Create();
    }

    public bool TryToQuarantine(EnvelopeTransportContext context, Exception ex)
    {
        var quarantined = _quarantine.TryToQuarantine(context, ex);

        try
        {
            var item = GetStreamingItem(context);
            var data = "";
            try
            {
                data = item.ReadText();
            }
            catch (StreamingItemNotFoundException)
            {
            }

            var builder = new StringBuilder(data);
            if (builder.Length == 0)
            {
                DescribeMessage(builder, context);
            }

            builder.AppendLine("[Exception]");
            builder.AppendLine(DateTime.UtcNow.ToString());
            builder.AppendLine(ex.ToString());
            builder.AppendLine();

            var text = builder.ToString();
            item.WriteText(text);

            if (quarantined)
                ReportFailure(text, context.Unpacked);
        }
        catch (Exception x)
        {
            Trace.WriteLine(x.ToString());
        }

        return quarantined;
    }

    IStreamingItem GetStreamingItem(EnvelopeTransportContext context)
    {
        var createdOnUtc = context.Unpacked.CreatedOnUtc;

        var file = string.Format("{0:yyyy-MM-dd-HH-mm}-{1}-engine.txt",
            createdOnUtc,
            context.Unpacked.EnvelopeId.ToLowerInvariant());

        return _container.GetItem(file);
    }

    public void TryRelease(EnvelopeTransportContext context)
    {
        _quarantine.TryRelease(context);
    }

    static void DescribeMessage(StringBuilder builder, EnvelopeTransportContext context)
    {
        builder.AppendLine(string.Format("{0,12}: {1}", "Queue", context.QueueName));
        builder.AppendLine(context.Unpacked.PrintToString(o => JsonConvert.SerializeObject(o, Formatting.Indented)));
    }

    void ReportFailure(string text, ImmutableEnvelope envelope)
    {
        var name = envelope.Items
            .Select(e => e.MappedType.Name)
            .Select(e => StringUtil.MemberNameToCaption(e.Replace("Command", "")))
            .FirstOrDefault() ?? "N/A";

        var subject = string.Format("[Error]: Sample fails to '{0}'", name);

        var builder = new StringBuilder();
        builder.AppendFormat(
            @"<p>Dear Lokad.CQRS Developer,</p><p>Something just went horribly wrong - there is a problem that I can't resolve. Please check the error log <strong>ASAP</strong>.</p>
                    <p>Here are a few details to help you out:</p><pre>");

        builder.AppendLine(EncoderUtil.EncodeForPre(text));

        builder.AppendFormat(
            "</pre><p>Sincerely,<br /> Lokad.CQRS AI</p>");

        var mail = new MailMessage()
            {
                Body = builder.ToString(),
                Subject = subject,
                IsBodyHtml = true,
            };
        mail.To.Add(new MailAddress("contact@company.com", "Sample Support"));
        _core.Send(mail);
    }
}