Improved mailboxes to include sent mails and drafts (#1038)

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

@@ -3,7 +3,7 @@ namespace AIStudio.Tools.Mail;
 /// <summary>
 /// The folders of a mailbox the sync works through.
 /// </summary>
-/// <param name="Folders">The folders, the inbox first and the others by their full names.</param>
+/// <param name="Folders">The folders: the inbox first, then those for sent mails and for drafts, then the others by their full names.</param>
 /// <param name="RootFolderFound">False when the mailbox is limited to a root folder the server no longer lists, e.g. because somebody renamed it.</param>
 public sealed record MailFolderSelection(IReadOnlyList<MailServerFolder> Folders, bool RootFolderFound)
 {
@@ -15,15 +15,24 @@ public sealed record MailFolderSelection(IReadOnlyList<MailServerFolder> Folders
     /// trash and the junk folder never count: what lies there was thrown away or never wanted, and
     /// the root folder cannot be one of them either.
     ///
+    /// The folders for sent mails and for drafts may come along from outside the root folder. Only
+    /// the folders themselves, as the server marks them, without their subfolders. Their names
+    /// differ by server and language, so a server which does not mark them leaves nothing to tell
+    /// them by, and guessing by name could pull in any folder.
+    ///
     /// The virtual folders for flagged and for important mails count only when they are the root
     /// folder. Each of them shows mails which lie in another folder as well, so the sync would only
     /// fetch the same mails twice. The folder holding all mails is different: at Gmail, an archived
     /// mail lies there and nowhere else.
+    ///
+    /// The sent mails and the drafts follow right after the inbox, so that the first sync of a
+    /// mailbox reaches them early, before the folders the user sorted mails into.
     /// </remarks>
     /// <param name="serverFolders">The folders as the server lists them.</param>
     /// <param name="rootFolder">The full name of the root folder, or empty for the whole mailbox.</param>
+    /// <param name="includeSentAndDrafts">Whether the folders for sent mails and for drafts count outside the root folder as well.</param>
     /// <returns>The selection.</returns>
-    public static MailFolderSelection Select(IReadOnlyList<MailServerFolder> serverFolders, string rootFolder)
+    public static MailFolderSelection Select(IReadOnlyList<MailServerFolder> serverFolders, string rootFolder, bool includeSentAndDrafts)
     {
         //
         // Empty, not blank, stands for the whole mailbox: the empty name is what the folder picker
@@ -35,9 +44,9 @@ public sealed record MailFolderSelection(IReadOnlyList<MailServerFolder> Folders
         var hasRootFolder = !string.IsNullOrEmpty(rootFolder);
         var folders = serverFolders
             .Where(folder => folder is { CanSelect: true, SpecialUse: not (MailFolderSpecialUse.TRASH or MailFolderSpecialUse.JUNK) })
-            .Where(folder => !hasRootFolder || IsAtOrBelow(folder, rootFolder))
+            .Where(folder => !hasRootFolder || IsAtOrBelow(folder, rootFolder) || (includeSentAndDrafts && folder.SpecialUse is (MailFolderSpecialUse.SENT or MailFolderSpecialUse.DRAFTS)))
             .Where(folder => folder.SpecialUse is not (MailFolderSpecialUse.FLAGGED or MailFolderSpecialUse.IMPORTANT) || (hasRootFolder && IsRootFolder(folder, rootFolder)))
-            .OrderByDescending(folder => folder.IsInbox)
+            .OrderBy(GetSyncRank)
             .ThenBy(folder => folder.FullName, StringComparer.Ordinal)
             .ToList();
 
@@ -45,6 +54,29 @@ public sealed record MailFolderSelection(IReadOnlyList<MailServerFolder> Folders
         return new(folders, rootFolderFound);
     }
 
+    /// <summary>
+    /// From which day on the mails of a folder belong into the index.
+    /// </summary>
+    /// <remarks>
+    /// Drafts count however old they are, as flagged mails do: a draft was never received, and an
+    /// old one may be just the one the user wants to finish now.
+    /// </remarks>
+    /// <param name="folder">The folder.</param>
+    /// <param name="receivedSince">The first day of the period of the mailbox, or null for all mails.</param>
+    /// <returns>The first day for this folder, or null for all of its mails.</returns>
+    public static DateTimeOffset? GetReceivedSince(MailServerFolder folder, DateTimeOffset? receivedSince) => folder.SpecialUse is MailFolderSpecialUse.DRAFTS ? null : receivedSince;
+
+    /// <summary>
+    /// Where a folder comes in the order the sync works through them.
+    /// </summary>
+    private static int GetSyncRank(MailServerFolder folder) => folder switch
+    {
+        { IsInbox: true } => 0,
+        { SpecialUse: MailFolderSpecialUse.SENT } => 1,
+        { SpecialUse: MailFolderSpecialUse.DRAFTS } => 2,
+        _ => 3,
+    };
+
     /// <summary>
     /// Whether a folder is the root folder, which IMAP names case-insensitively only for the inbox.
     /// </summary>