Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Tools/Databases/IndexStore/MailMessageEntity.cs

@@ -0,0 +1,87 @@
+namespace AIStudio.Tools.Databases.IndexStore;
+
+/// <summary>
+/// What the index knows about one mail beyond its text, one row per mail and mailbox.
+/// </summary>
+/// <remarks>
+/// The mail itself is a row in embedded_files, whose primary key this row shares. Indexing a mail
+/// again deletes that row first, and the cascade takes this one with it. So this row is written
+/// after the last chunk of a mail, never before.
+/// </remarks>
+internal sealed class MailMessageEntity
+{
+    public string ParentFileId { get; set; } = string.Empty;
+
+    public string DataSourceId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The Message-ID header, empty when the mail has none.
+    /// </summary>
+    public string MessageId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The Message-ID the In-Reply-To header names, empty when there is none.
+    /// </summary>
+    public string InReplyTo { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The Message-IDs of the References header, oldest first and separated by spaces, the way the
+    /// header itself lists them. A Message-ID cannot contain a space, so nothing gets lost.
+    /// </summary>
+    public string ReferenceMessageIds { get; set; } = string.Empty;
+
+    /// <summary>
+    /// When the sender says the mail was written (Date header), or null when it does not say so readably.
+    /// </summary>
+    public DateTimeOffset? SentAtUtc { get; set; }
+
+    /// <summary>
+    /// When the mail arrived at the server (INTERNALDATE).
+    /// </summary>
+    /// <remarks>
+    /// Unlike the Date header, the sender has no say in this one. It is also the date IMAP compares
+    /// against when the time range of a mailbox gets searched.
+    /// </remarks>
+    public DateTimeOffset ReceivedAtUtc { get; set; }
+
+    /// <summary>
+    /// LOW, NORMAL or HIGH, stored by name.
+    /// </summary>
+    public string Importance { get; set; } = string.Empty;
+
+    /// <summary>
+    /// How the content of the mail is encrypted, NONE when it is not, stored by name.
+    /// </summary>
+    /// <remarks>
+    /// There is no separate flag for whether a mail is encrypted: it would only be a second copy of
+    /// this column, free to disagree with it. A kind written by a newer version still is not NONE,
+    /// so such a mail still counts as encrypted.
+    /// </remarks>
+    public string EncryptionKind { get; set; } = string.Empty;
+
+    /// <summary>
+    /// A hash over the mail as the server delivered it, independent of how AI Studio turns it into text.
+    /// </summary>
+    public string MailHash { get; set; } = string.Empty;
+
+    /// <summary>
+    /// When AI Studio found this mail for the first time.
+    /// </summary>
+    public DateTimeOffset FirstSeenUtc { get; set; }
+
+    /// <summary>
+    /// When the mail lost its last location, or null while it has one.
+    /// </summary>
+    /// <remarks>
+    /// A mail which is moved disappears from one folder before it shows up in the other one, maybe
+    /// only in the next run. Removing it at once would embed it again when it reappears, so it stays
+    /// for one more run.
+    /// </remarks>
+    public DateTimeOffset? OrphanedAtUtc { get; set; }
+
+    public List<MailAddressEntity> Addresses { get; set; } = [];
+
+    public List<MailPartEntity> Parts { get; set; } = [];
+
+    public List<MailLocationEntity> Locations { get; set; } = [];
+}