Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Tools/Mail/MailTextSource.cs

@@ -0,0 +1,35 @@
+using MimeKit;
+
+namespace AIStudio.Tools.Mail;
+
+/// <summary>
+/// What MailTextBuilder reads one mail from.
+/// </summary>
+/// <remarks>
+/// Not a whole mail on purpose: the sync fetches the header block and the structure first, and
+/// the text parts only of a mail which turns out readable. The attachments themselves are never
+/// part of this, only their names.
+/// </remarks>
+/// <param name="Headers">The complete header block of the mail.</param>
+/// <param name="HtmlBody">The HTML part a reader sees, decoded from its transfer encoding and charset, or null when there is none.</param>
+/// <param name="TextBody">The plain text part, decoded likewise, or null when there is none.</param>
+/// <param name="AttachmentNames">The file names of the attachments, in their order, without the signature of a signed mail.</param>
+/// <param name="StructureEncryption">How the structure of the mail says its content is encrypted, see MailEncryptionDetection.</param>
+public sealed record MailTextSource(HeaderList Headers, string? HtmlBody, string? TextBody, IReadOnlyList<string> AttachmentNames, MailEncryptionKind StructureEncryption)
+{
+    /// <summary>
+    /// Takes everything from a mail which was fetched or loaded as a whole.
+    /// </summary>
+    /// <param name="message">The parsed mail.</param>
+    /// <returns>The source for MailTextBuilder.</returns>
+    public static MailTextSource FromMessage(MimeMessage message)
+    {
+        var attachmentNames = message.Attachments
+            .Where(attachment => !MailAttachmentRules.IsSignature(attachment.ContentType))
+            .Select(attachment => attachment.ContentDisposition?.FileName ?? attachment.ContentType.Name ?? string.Empty)
+            .Where(name => !string.IsNullOrWhiteSpace(name))
+            .ToList();
+
+        return new(message.Headers, message.HtmlBody, message.TextBody, attachmentNames, MailEncryptionDetection.Detect(message.Body));
+    }
+}