From d21b7a5a48f381f999fbffd2c3a09037d93764fa Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Mon, 10 Aug 2026 06:07:14 -0400
Subject: [PATCH] feat(notifications): EmailTransport enum + parser for the EWS
 transport discriminator

---
 .../EmailTransport.cs                         | 50 +++++++++++++++++++
 .../EmailTransportParserTests.cs              | 40 +++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 src/ZB.MOM.WW.ScadaBridge.NotificationService/EmailTransport.cs
 create mode 100644 tests/ZB.MOM.WW.ScadaBridge.NotificationService.Tests/EmailTransportParserTests.cs

diff --git a/src/ZB.MOM.WW.ScadaBridge.NotificationService/EmailTransport.cs b/src/ZB.MOM.WW.ScadaBridge.NotificationService/EmailTransport.cs
new file mode 100644
index 00000000..6b78a15f
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.NotificationService/EmailTransport.cs
@@ -0,0 +1,50 @@
+namespace ZB.MOM.WW.ScadaBridge.NotificationService;
+
+/// <summary>
+/// The email delivery transports the service supports. The configured
+/// <c>SmtpConfiguration.Transport</c> string is parsed into this enum to choose
+/// which client actually submits the message.
+/// </summary>
+public enum EmailTransport
+{
+    /// <summary>Direct SMTP submission via MailKit (the original path).</summary>
+    Smtp,
+
+    /// <summary>On-prem Exchange Web Services — one CreateItem SOAP call over HTTPS.</summary>
+    Ews,
+}
+
+/// <summary>
+/// Parses the free-text <c>SmtpConfiguration.Transport</c> value into an
+/// <see cref="EmailTransport"/>, rejecting unknown values rather than silently
+/// falling back to SMTP.
+/// </summary>
+public static class EmailTransportParser
+{
+    /// <summary>
+    /// Parses a configured transport string. A null or empty value defaults to
+    /// <see cref="EmailTransport.Smtp"/> — every pre-EWS configuration row stores no
+    /// transport and is an SMTP row. An unknown value is a configuration error that
+    /// retrying cannot fix, so it throws and the delivery adapter surfaces it as a
+    /// permanent failure (mirrors <see cref="SmtpTlsModeParser"/>).
+    /// </summary>
+    /// <param name="transport">The transport string to parse (Smtp or Ews); null/empty defaults to Smtp.</param>
+    /// <exception cref="ArgumentException">The value is not one of Smtp/Ews.</exception>
+    /// <returns>The corresponding <see cref="EmailTransport"/> enum value.</returns>
+    public static EmailTransport Parse(string? transport)
+    {
+        if (string.IsNullOrWhiteSpace(transport))
+        {
+            return EmailTransport.Smtp;
+        }
+
+        return transport.Trim().ToLowerInvariant() switch
+        {
+            "smtp" => EmailTransport.Smtp,
+            "ews" => EmailTransport.Ews,
+            _ => throw new ArgumentException(
+                $"Unknown email transport '{transport}'. Expected one of: Smtp, Ews.",
+                nameof(transport)),
+        };
+    }
+}
diff --git a/tests/ZB.MOM.WW.ScadaBridge.NotificationService.Tests/EmailTransportParserTests.cs b/tests/ZB.MOM.WW.ScadaBridge.NotificationService.Tests/EmailTransportParserTests.cs
new file mode 100644
index 00000000..e19cc33f
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.NotificationService.Tests/EmailTransportParserTests.cs
@@ -0,0 +1,40 @@
+namespace ZB.MOM.WW.ScadaBridge.NotificationService.Tests;
+
+/// <summary>
+/// Tests for parsing the configured email transport discriminator into the two-state enum.
+/// </summary>
+public class EmailTransportParserTests
+{
+    [Theory]
+    [InlineData("Smtp", EmailTransport.Smtp)]
+    [InlineData("smtp", EmailTransport.Smtp)]
+    [InlineData("SMTP", EmailTransport.Smtp)]
+    [InlineData("Ews", EmailTransport.Ews)]
+    [InlineData("ews", EmailTransport.Ews)]
+    [InlineData("EWS", EmailTransport.Ews)]
+    [InlineData("  ews  ", EmailTransport.Ews)]
+    public void Parse_KnownTransports_ReturnsExpected(string input, EmailTransport expected)
+    {
+        Assert.Equal(expected, EmailTransportParser.Parse(input));
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void Parse_NullOrEmpty_DefaultsToSmtp(string? input)
+    {
+        // Every pre-EWS SmtpConfiguration row stores no transport; those rows are SMTP rows.
+        Assert.Equal(EmailTransport.Smtp, EmailTransportParser.Parse(input));
+    }
+
+    [Theory]
+    [InlineData("Graph")]
+    [InlineData("smtps")]
+    public void Parse_UnknownTransport_Throws(string input)
+    {
+        // An unknown transport must be rejected, not silently treated as SMTP.
+        var ex = Assert.Throws<ArgumentException>(() => EmailTransportParser.Parse(input));
+        Assert.Contains(input, ex.Message);
+    }
+}