Add last_remark() method

lib/PostText/Model/Remark.pm

@@ -72,4 +72,19 @@ sub get_last_page_by_thread_id($self, $thread_id) {
     $last_page;
 }
 
+sub last_remark($self, $thread_id) {
+    my $date_format = $self->{'date_format'};
+
+    $self->pg->db->query(<<~'END_SQL', $date_format, $thread_id)->hash();
+        SELECT remark_id               AS id,
+               TO_CHAR(remark_date, ?) AS date,
+               remark_author           AS author,
+               remark_body             AS body
+          FROM remarks
+         WHERE thread_id = ?
+         ORDER BY remark_date
+          DESC LIMIT 1;
+       END_SQL
+}
+
 1;