Target: our design only allows one global list. Each user should have a separate list.
TDD technique to learn: adapt existing code using an incremental, step-by-step process which takes you from working state to working state (avoid crashing).
## 7.1 Small Design When Necessary
### Not Big Design Up Front
* Traditional software dev: *Big Design Up Front*
* New software dev cycle: Agile, put MVP (Minimum Viable Product) out early, and let design evolve gradually
Planning for MVP:
* Each user can store their own list
* A list is made up of several items, with a description as attribute
* Saved List should be permanent
### YAGNI!
Agile gospel: YAGNI (You Aren't Gonna Need It). Don't overthink about design (e.g. username? list title?) No matter how cool the idea was, you won't end up using it.
### REST(ish)
* QUES: Our data structure sit in model of Model-View-Controller (MVC). How should View & Controller work?
* ANS: **REST (Representational State Transfer)** is the usual approach to design web-based APIs. But currently we don't stick strickly to it. (Visit Appendix F for full REST API implementation)
Design of our to-do list app:
* REST suggest that URL structure should match our data structure. So each list have its own URL `/list/<list identifier>`
* View a list: use GET request. (It's a normal browser visit to the page)
* Create a brand new list: a special URL will accept POST requests `lists/new`
* Add new item to list: have a separate URL to send POST requests `/lists/<list identifier>/add_item`
