Added mailboxes as local data sources (#1022)

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

@@ -0,0 +1,64 @@
+using MimeKit;
+
+namespace AIStudio.Tools.Mail;
+
+/// <summary>
+/// Reads how important the sender marked a mail.
+/// </summary>
+/// <remarks>
+/// Three headers say so, from three different eras, and mail programs send whichever they like,
+/// often more than one. They are read in this order, and the first one with a value AI Studio
+/// understands decides:
+/// <list type="number">
+///   <item>Importance (RFC 2156): low, normal or high. Outlook sends it.</item>
+///   <item>X-Priority: a number from 1 (highest) to 5 (lowest), often followed by a word such as "1 (Highest)".</item>
+///   <item>Priority (RFC 2156): non-urgent, normal or urgent.</item>
+/// </list>
+/// A header with a value nobody defined is skipped rather than read as normal, so that the next
+/// header still gets its say.
+/// </remarks>
+public static class MailImportanceDetection
+{
+    /// <summary>
+    /// Reads the importance from the header block of a mail.
+    /// </summary>
+    /// <param name="headers">The header block.</param>
+    /// <returns>The importance, NORMAL when no header says otherwise.</returns>
+    public static MailImportance Detect(HeaderList headers) =>
+        ReadImportance(headers[HeaderId.Importance]) ??
+        ReadXPriority(headers[HeaderId.XPriority]) ??
+        ReadPriority(headers[HeaderId.Priority]) ??
+        MailImportance.NORMAL;
+
+    private static MailImportance? ReadImportance(string? value) => value?.Trim().ToLowerInvariant() switch
+    {
+        "low" => MailImportance.LOW,
+        "normal" => MailImportance.NORMAL,
+        "high" => MailImportance.HIGH,
+        _ => null,
+    };
+
+    private static MailImportance? ReadXPriority(string? value)
+    {
+        // Only the leading digit counts, as in "2 (High)", and it has to stand alone:
+        var trimmed = value?.TrimStart();
+        if (string.IsNullOrEmpty(trimmed) || (trimmed.Length > 1 && char.IsDigit(trimmed[1])))
+            return null;
+
+        return trimmed[0] switch
+        {
+            '1' or '2' => MailImportance.HIGH,
+            '3' => MailImportance.NORMAL,
+            '4' or '5' => MailImportance.LOW,
+            _ => null,
+        };
+    }
+
+    private static MailImportance? ReadPriority(string? value) => value?.Trim().ToLowerInvariant() switch
+    {
+        "non-urgent" => MailImportance.LOW,
+        "normal" => MailImportance.NORMAL,
+        "urgent" => MailImportance.HIGH,
+        _ => null,
+    };
+}