Signing back in: fixes issues with outdated podcast information

[leandroalonso]

Fixes #791 (comment)

We recently had an issue where a user had all their podcasts removed from folders when signing back in on another device.

This happened because they had outdated information and the app marked it as unsynced.

To test

With onlyMarkPodcastsUnsyncedForNewUsers enabled

1. Go to Profile > Settings > Beta Features > enable onlyMarkPodcastsUnsyncedForNewUsers
2. Sign in to a Plus account
3. Create a folder with some podcasts in it and refresh
4. Log out
5. Go to Settings > Developer > Clear all folder information
6. Subscribe to a few new podcasts
7. Log back into the same account
8. ✅ Under "Podcasts" the folder should be visible and with the same podcasts from before
9. Go to Profile > Refresh Now
10. ✅ Login into the web player, and ensure the newly subscribed podcasts were correctly synced

With onlyMarkPodcastsUnsyncedForNewUsers disabled

1. Go to Profile > Settings > Beta Features > disable onlyMarkPodcastsUnsyncedForNewUsers
2. Add a breakpoint in SyncSigninViewController.swift:337
3. Sign in to a Plus account
4. Create a folder with some podcasts in it and refresh
5. Log out
6. Go to Settings > Developer > Clear all folder information
7. Log back into the same account
8. ✅ Breakpoint should hit
9. ✅ Under "Podcasts" the podcasts will be out of their folders

Checklist

• I have considered if this change warrants user-facing release notes and have added them to CHANGELOG.md if necessary.
• I have considered adding unit tests for my changes.
• I have updated (or requested that someone edit) the spreadsheet to reflect any new or changed analytics.

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 7.65. This milestone is due in less than 2 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

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[leandroalonso]

@geekygecko Before merging this I'd like to double-check with you as I might be missing any user case.

The app will only mark all podcasts as unsynced if the user has never logged in to any account in this device.

[geekygecko]

If they have just signed in, the last sync should be nil already. 🤔
If they signed out for six months and subscribed to many podcasts, then signed in again, won't that mean those new podcasts won't appear on their other devices?

[leandroalonso]

won't that mean those new podcasts won't appear on their other devices?

Based on my tests it syncs just fine (as per the PR description)

[SergioEstevao]

Code looks good and tested the scenario described and all worked correctly.

I do wonder why do we need to do step 4, Clear all folder information, the end user will not be able to do that, shouldn't this work correctly even without doing that?

[leandroalonso]

I do wonder why do we need to do step 4, Clear all folder information, the end user will not be able to do that, shouldn't this work correctly even without doing that?

Very good question, @SergioEstevao. I should have been more explicit in the PR description.

if you test these same steps in trunk (including using the "Clear all folder information"), your podcasts will be out of their folders when you sign back.

This is to simulate the issue that happened that is reported in #791 (comment)

A user won't be able to do that, but in the past, we had a bug that caused this scenario. A user with an old device with this "wrong data" can end up with their podcasts out of their folders, which is exactly what happened for this user.

[leandroalonso]

@SergioEstevao could you please review again? I added a feature flag so we can toggle this behavior in case it's needed.

[SergioEstevao]

All working great, and FF doing it's job!