[#15] MailWindow: Add email sending feature

Elwig/Documents/Document.cs

@@ -5,6 +5,7 @@ using Elwig.Helpers;
 using System.Collections.Generic;
 using System.Linq;
 using Elwig.Helpers.Printing;
+using MimeKit;
 
 namespace Elwig.Documents {
     public abstract partial class Document : IDisposable {
@@ -150,6 +151,16 @@ namespace Elwig.Documents {
             Pdf.Show(_pdfFile.NewReference(), Title + (this is BusinessDocument b ? $" - {b.Member.Name}" : ""));
         }
 
+        public MimePart AsEmailAttachment(string filename) {
+            if (PdfPath == null) throw new InvalidOperationException("Pdf file has not been generated yet");
+            return new("application", "pdf") {
+                Content = new MimeContent(File.OpenRead(PdfPath)),
+                ContentDisposition = new ContentDisposition(ContentDisposition.Attachment),
+                ContentTransferEncoding = ContentEncoding.Base64,
+                FileName = filename
+            };
+        }
+
         private class MergedDocument(IEnumerable<Document> docs) : Document("Mehrere Dokumente") {
             public IEnumerable<Document> Documents = docs;
         }