Structure refactor to handle state transitions

[BreezeWhite]

From the backend insights, this project has drawn some attention and used by some people. Though it functions to help people who want to buy THSR tickets, there are still lots of inconvenience using this program.

There was no detail design due to the lack of related knowledge about how to deal with state transition, meaning after each step you input the required information, there is no way back to modify what've been done, or return to the beginning. All there is an intuitive end-to-end flow of buying the ticket, a none-or-all process, making no mistakes while input.

An enhancement is thus here issued.

To better handle state transition problems, a huge refactor of code base, which takes time to develop and validate. Inspired by topics explaining about this issue, the motivation to upgrade the program has been triggered. More than just for fun, but actually to practice to realize what I've learned about all kinds of design patterns.

Well, saying all that much, this is just a note for myself lol. If anyone seeing this issue and also interested by the idea, feel free to join and contribute. All kinds of advises, code suggestions, or anything are welcome, and I would very appreciate. ^^