[General behavior] Migrate Widget methods to classes

[g123k]

What

• By fixing issue Can't remove single products from carousel #2603, I have discovered the summary_card file, where a single Widget contains 700 lines of code! 😱
  This is generally a bad coding behavior for Flutter, knowing how the different trees work.
• I think we should take some time to go through the code and split this kind of Widgets.
• For the first step, I suggest listing all files and they start fixing them gradually.

Part of

• Refactoring (tracker) #2528

[monsieurtanuki]

• Maybe a duplicate with Refactoring: smaller dart files #1712.

[g123k]

Kind of a subtask ;) but thanks for the list of files @monsieurtanuki!

[monsieurtanuki]

Cool! I suggest that you (or whoever) do that explicitly, one by one, by creating a specific issue for each file like "summary_card.dart refactoring" issue:

• it can be very painful to review that kind of code if too many files are involved, and very frustrating for the developer to wait very long for a review
• I don't think it's a priority task - so let's not fall into the "purest code" rabbit hole while we have major issues pending (like offline or FDroid)
• it could be helpful for other developers to answer "hey, I'm actually working on this file, so let me do it / please do it fast / please do it later / I'll code another issue instead"

[g123k]

• I totally agree with you, the Fdroid thing is my priority right now.
• But as Can't remove single products from carousel #2603 highlights, this kind of reworking is sometimes required to fix side-effects errors

[monsieurtanuki]

Then I would encourage you to create a PR that just adds one TODO on top of each suspicious file (a dozen I guess), something like // TODO(g123k): if you're working on that file and if you have time, please split that file / that widget into smaller bits (e.g. less than 300 lines).
This way, next time any developer that edits one big file will be aware. And in the meanwhile everybody works on higher priorities.