Solutions to reduce the perceived waiting time to save a contribution

[monsieurtanuki]

Problem

Each time we want to change a value, we see a dialog and we wait. We wait longer for picture updates: the files are bigger. That may break the momentum of the end-user.

Proposed solutions

1. We could run all the server changes as background tasks. It would be smooth and elegant, but perhaps frustrating because the computed fields like score would not be refreshed until all the changes are done, and that means (temporarily) incoherent data. But that mean we could fully operate offline and make changes regardless of the network.
2. We could gather the changes in one obvious operation. For instance, a dialog only once we exit the "edit product page", instead of when we exit "edit category" then "edit label" then "edit stores" then "edit nutrients".
3. Another solution mentioned in #2337 is to gather the UIs, e.g. on the same page "edit category", "edit label", "edit stores" and "edit nutrients"
4. Maybe a mix - background tasks for pictures and gathering changes for the texts

Additional context

It's not going to be trivial, but it should be exhilarating. (intellectually I mean)

Part of

• 503

[teolemon]

• 3. is purely a commodity for some power users, including me. Some will be distressed by the big view, some other by the view in sections.
• I think we should keep save on individual section, and add explicit Save and Cancel button in each section (exiting to save is confusing)
• We should have a superview that could either keep those buttons at the end of each section, or override it for a global save button (but honestly let's KISS)
• We should ensure that every change is done as background task, atomically and immediately (batching them is not desirable, since it increases the risk of failure, and we want to refresh the product as soon as this peculiar change is done, and please bear in mind that the user wants the score ASAP.)
• we can alter the view to mention the edit is being applied (or pending upload if we're offline) and that it will be refreshed just after that (and have a snackbar like we already have on product refresh)

[monsieurtanuki]

@teolemon Thank you for your comments.

Of course we'll need to batch the changes if there's no network. The alternate solution is to forbid the offline changes. Perhaps we could compute the score inside smoothie, as an "approximated score"?

Regarding UI, what about this?

[teolemon]

The issues mentioned above are mostly fixed and some were broken into individual issues. Closing