Fixing issues with replies.

Wino.Core.Domain/Extensions/MailHeaderExtensions.cs

@@ -1,10 +1,26 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 
 namespace Wino.Core.Domain.Extensions;
 
 public static class MailHeaderExtensions
 {
+    public static string NormalizeMessageId(string value)
+    {
+        if (value == null)
+            return null;
+
+        var normalized = StripAngleBrackets(value)?.Trim();
+        return string.IsNullOrWhiteSpace(normalized) ? string.Empty : normalized;
+    }
+
+    public static string ToHeaderMessageId(string value)
+    {
+        var normalized = NormalizeMessageId(value);
+        return string.IsNullOrEmpty(normalized) ? string.Empty : $"<{normalized}>";
+    }
+
     /// <summary>
     /// Strips angle brackets from a Message-ID or In-Reply-To value.
     /// RFC 5322 Message-IDs are formatted as &lt;id@domain&gt;, but MimeKit
@@ -29,14 +45,53 @@ public static class MailHeaderExtensions
     /// like "&lt;id1@domain&gt; &lt;id2@domain&gt;". This converts them to "id1@domain;id2@domain".
     /// </summary>
     public static string NormalizeReferences(string rawReferences)
+        => JoinStoredReferences(SplitMessageIds(rawReferences));
+
+    public static IEnumerable<string> SplitMessageIds(string values)
     {
-        if (string.IsNullOrEmpty(rawReferences)) return rawReferences;
+        if (string.IsNullOrWhiteSpace(values))
+            return [];
 
-        var ids = rawReferences
+        return values
             .Split(new[] { ' ', '\t', '\r', '\n', ';', ',' }, StringSplitOptions.RemoveEmptyEntries)
-            .Select(StripAngleBrackets)
+            .Select(NormalizeMessageId)
             .Where(id => !string.IsNullOrEmpty(id));
+    }
 
-        return string.Join(";", ids);
+    public static string JoinStoredReferences(IEnumerable<string> values)
+        => string.Join(";", NormalizeDistinctMessageIds(values));
+
+    public static string BuildReferencesHeaderValue(IEnumerable<string> values)
+        => string.Join(" ", NormalizeDistinctMessageIds(values).Select(ToHeaderMessageId));
+
+    public static List<string> BuildReferencesChain(IEnumerable<string> existingReferences, string parentMessageId)
+    {
+        var results = NormalizeDistinctMessageIds(existingReferences).ToList();
+        var normalizedParentMessageId = NormalizeMessageId(parentMessageId);
+
+        if (!string.IsNullOrEmpty(normalizedParentMessageId) &&
+            !results.Contains(normalizedParentMessageId, StringComparer.OrdinalIgnoreCase))
+        {
+            results.Add(normalizedParentMessageId);
+        }
+
+        return results;
+    }
+
+    private static IEnumerable<string> NormalizeDistinctMessageIds(IEnumerable<string> values)
+    {
+        if (values == null)
+            yield break;
+
+        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+        foreach (var value in values)
+        {
+            var normalized = NormalizeMessageId(value);
+            if (string.IsNullOrEmpty(normalized) || !seen.Add(normalized))
+                continue;
+
+            yield return normalized;
+        }
     }
 }