Generate series pages

lib/DB/Series.rakumod

@@ -22,3 +22,14 @@ method contains-post(Int:D $post-id --> Bool:D) {
         False
     }
 }
+
+#| Returns the date of the lastest post
+method latest-post($db) {
+    my @posts = @!post-ids.map(-> $i {$db.posts{$i}});
+    if @posts {
+        my $most-recent-post = @posts.max(*.posted-at);
+        $most-recent-post.posted-at
+    } else {
+        Nil
+    }
+}