Calendar - mail mapping.

2026-02-10 21:35:55 +01:00
parent 10dd42b63f
commit 870a5e2bf6
10 changed files with 818 additions and 21 deletions
@@ -0,0 +1,121 @@
+using System;
+using System.IO;
+using System.Linq;
+using System.Text;
+using MimeKit;
+
+namespace Wino.Core.Extensions;
+
+public static class CalendarInvitationExtensions
+{
+    public static string ExtractInvitationUid(this MimeMessage message)
+    {
+        if (message == null)
+        {
+            return null;
+        }
+
+        var icsContent = GetCalendarContent(message);
+        if (string.IsNullOrWhiteSpace(icsContent))
+        {
+            return null;
+        }
+
+        var unfolded = UnfoldIcs(icsContent);
+        var veventSection = ExtractFirstVEventSection(unfolded);
+        if (string.IsNullOrWhiteSpace(veventSection))
+        {
+            return null;
+        }
+
+        return TryReadIcsProperty(veventSection, "UID", out var uid)
+            ? uid
+            : null;
+    }
+
+    private static string GetCalendarContent(MimeMessage message)
+    {
+        var textPart = message.BodyParts
+            .OfType<TextPart>()
+            .FirstOrDefault(p => p.ContentType?.MimeType?.Equals("text/calendar", StringComparison.OrdinalIgnoreCase) == true);
+
+        if (textPart != null)
+        {
+            return textPart.Text;
+        }
+
+        var mimePart = message.BodyParts
+            .OfType<MimePart>()
+            .FirstOrDefault(p => p.ContentType?.MimeType?.Equals("text/calendar", StringComparison.OrdinalIgnoreCase) == true);
+
+        if (mimePart == null)
+        {
+            return null;
+        }
+
+        using var stream = new MemoryStream();
+        mimePart.Content.DecodeTo(stream);
+        var bytes = stream.ToArray();
+        if (bytes.Length == 0)
+        {
+            return null;
+        }
+
+        var charset = mimePart.ContentType?.Charset;
+        var encoding = string.IsNullOrWhiteSpace(charset) ? Encoding.UTF8 : Encoding.GetEncoding(charset);
+        return encoding.GetString(bytes);
+    }
+
+    private static string UnfoldIcs(string content)
+        => content
+            .Replace("\r\n ", string.Empty, StringComparison.Ordinal)
+            .Replace("\r\n\t", string.Empty, StringComparison.Ordinal)
+            .Replace("\n ", string.Empty, StringComparison.Ordinal)
+            .Replace("\n\t", string.Empty, StringComparison.Ordinal);
+
+    private static string ExtractFirstVEventSection(string ics)
+    {
+        const string beginVevent = "BEGIN:VEVENT";
+        const string endVevent = "END:VEVENT";
+
+        var beginIndex = ics.IndexOf(beginVevent, StringComparison.OrdinalIgnoreCase);
+        if (beginIndex < 0)
+        {
+            return string.Empty;
+        }
+
+        var endIndex = ics.IndexOf(endVevent, beginIndex, StringComparison.OrdinalIgnoreCase);
+        if (endIndex < 0)
+        {
+            return ics[beginIndex..];
+        }
+
+        return ics.Substring(beginIndex, endIndex - beginIndex + endVevent.Length);
+    }
+
+    private static bool TryReadIcsProperty(string icsSection, string propertyName, out string value)
+    {
+        value = string.Empty;
+        var lines = icsSection.Split(["\r\n", "\n"], StringSplitOptions.RemoveEmptyEntries);
+
+        foreach (var rawLine in lines)
+        {
+            var line = rawLine.Trim();
+            if (!line.StartsWith(propertyName, StringComparison.OrdinalIgnoreCase))
+            {
+                continue;
+            }
+
+            var colonIndex = line.IndexOf(':');
+            if (colonIndex <= 0 || colonIndex >= line.Length - 1)
+            {
+                continue;
+            }
+
+            value = line[(colonIndex + 1)..].Trim();
+            return !string.IsNullOrWhiteSpace(value);
+        }
+
+        return false;
+    }
+}