database: Add new, public notmuch_database_remove_message

This will allow applications to support the removal of messages, (such
as when a file is deleted from the mail store). No removal support is
provided yet in commands such as "notmuch new".

lib/database.cc

@@ -1278,6 +1278,59 @@ notmuch_database_add_message (notmuch_database_t *notmuch,
     return ret;
 }
 
+notmuch_status_t
+notmuch_database_remove_message (notmuch_database_t *notmuch,
+				 const char *filename)
+{
+    Xapian::WritableDatabase *db;
+    void *local = talloc_new (notmuch);
+    const char *direntry_prefix = _find_prefix ("direntry");
+    char *direntry, *term;
+    Xapian::PostingIterator i, end;
+    Xapian::Document document;
+    notmuch_status_t status;
+
+    if (notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY) {
+	fprintf (stderr, "Attempted to update a read-only database.\n");
+	return NOTMUCH_STATUS_READONLY_DATABASE;
+    }
+
+    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+
+    status = _notmuch_database_filename_to_direntry (local, notmuch,
+						     filename, &direntry);
+    if (status)
+	return status;
+
+    term = talloc_asprintf (notmuch, "%s%s", direntry_prefix, direntry);
+
+    find_doc_ids_for_term (notmuch, term, &i, &end);
+
+    for ( ; i != end; i++) {
+	Xapian::TermIterator j;
+
+	document = find_document_for_doc_id (notmuch, *i);
+
+	document.remove_term (term);
+
+	j = document.termlist_begin ();
+	j.skip_to (direntry_prefix);
+
+	/* Was this the last direntry in the message? */
+	if (j == document.termlist_end () ||
+	    strncmp ((*j).c_str (), direntry_prefix, strlen (direntry_prefix)))
+	{
+	    db->delete_document (document.get_docid ());
+	} else {
+	    db->replace_document (document.get_docid (), document);
+	}
+    }
+
+    talloc_free (local);
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
 notmuch_tags_t *
 _notmuch_convert_tags (void *ctx, Xapian::TermIterator &i,
 		       Xapian::TermIterator &end)

lib/notmuch.h

@@ -267,6 +267,19 @@ notmuch_database_add_message (notmuch_database_t *database,
 			      const char *filename,
 			      notmuch_message_t **message);
 
+/* Remove a message from the given notmuch database.
+ *
+ * Note that the only this particular filename association is removed
+ * from the database. If the same message (as determined by the
+ * message ID) is still available via other filenames, then the
+ * message will persist in the database for those filenames. When the
+ * last filename is removed for a particular message, the database
+ * content for that message will be entirely removed.
+ */
+notmuch_status_t
+notmuch_database_remove_message (notmuch_database_t *database,
+				 const char *filename);
+
 /* Find a message with the given message_id.
  *
  * If the database contains a message with the given message_id, then