Refactor app state

[vgeorge]

While working on implementing mosaics I realized that the state of the application was really difficult to change. In the first version of Pearl we used React Context to manage the different interface flows, relying on the useEffect/useReducer to handle side effects. It turns out that this approach places the application state and side effect logic in different places, leading to a very fragmented codebase. Adding features or fixing bugs is very slow.

I started to evaluate the possibility of refactoring the code and I ended up finding XState, which seems to me to be the best approach for interfaces with a high level of complexity. Another possible refactoring approach would be to rewrite the contexts and reducers and try to organize them better, but still the logic and state would be separated. This video explains very well the difference from XState and useReducer implementations. The chart from video provides a summary of the approaches:

So far I managed to update the app state logic to make the prediction panel selectors work and I'm getting close rewiring a prediction run. Unfortunately this refactor will affect most functionality on the project page, but progress has been steady and the development experience with XState is great.

My goal in this PR is to get all the functionality of the prediction tab working, specifically creating a new project, opening an existing project, creating multiple AOIs and timeframes. Retrain and refinement tabs will be added later.

This is a work in progress, please let me know if you have questions/comments.

cc @geohacker @srmsoumya @LanesGood

[vgeorge]

@geohacker This is ready for a first review.

As I commented before, there are features that had to be disabled momentarily because of the refactor. In this PR I want implement all the features in the prediction tab, excluding AOI editing. The list of features to cover is:

• Run live prediction on new project
• Run live prediction on existing project
• Switch between AOIs
• Create new AOIs on existing projects
• Run batch prediction on new project
• Run batch prediction on existing project
• Load mosaic of existing AOIs

The first four should be working already. I'll tick the list once items are reviewed and covered by tests. Please let me know your comments.

[geohacker]

Thanks so much for your work on this @vgeorge. I wasn't able to go through the entire PR — it's quite massive ⛰️. I was able to test and confirm expected workflow. Couple of regressions that are already noted that we'll address in a different PR. 🙇