Difficulty when extending Tango

First things first, to understand Tango
1. There are too many components to remember.
2. After two days of not looking at the code space, you forget everything.
3. Flexibility -> Complexity. The class inheritance relationship is too complicated: diamond inheritance, many empty classes, and too many callbacks.
4. Unable to refactor due to the lack of tests.
5. Some functionalities are fancy, but nothing is related to the main logic.
6. Tango’s initial check of states is way too strict. A full snapshot is better?