[Woo POS][Local Catalog] Add a periodic sync when the app is in the foreground

[staskus]

WOOMOB-1517
Related PR: #16244

Description

In #16244 I implemented a functionality to run hourly POS sync in the background.

In this PR, I'm implementing a similar functionality that should run when the app is in the foreground.

Outside the scope:

• Implementing specific criteria when sync happens or doesn't happen (cellular network, 30-day POS open window, etc.) we have a task for this

Solution

1. Created ForegroundPOSCatalogSyncDispatcher to be next to the background dispatcher for easier discoverability
2. ForegroundPOSCatalogSyncDispatcher uses DispatchSourceTimer, which is an efficient way to run a timer in the background. It has parameters such as leeway, which allows the system to prioritize other ongoing tasks and perform the work without precision, since precision is not that important for us.
3. ForegroundPOSCatalogSyncDispatcher observes the app going to and from the background to stop and restart the timer
4. When ForegroundPOSCatalogSyncDispatcher starts, the first sync is executed almost immediately, the next after 1 hour
5. POSCatalogSyncCoordinator decides whether to do incremental or full sync (if 24h have passed)
6. ForegroundPOSCatalogSyncDispatcher is started when the POS tab becomes visible and stopped if the POS tab becomes invisible, or if the app no longer has a coordinator or a siteID (logged out)

Steps to reproduce

It should be much easier to test compared to system background tasks! Important to verify that timer starts in expected times when logging in, launching app, going into foreground, switching sites...

Prerequisites:

• Set lower syncInterval in ForegroundPOSCatalogSyncDispatcher, for example 30 seconds

1. Launch the app
2. Observe the logs, you can filter ForegroundPOSCatalogSyncDispatcher for DDLog.. calls
3. When the POS tab becomes visible, the syncing should happen for the first time
4. After syncInterval it should repeat
5. Go to the background, timer should stop
6. Come back to the foreground, the timer should begin again, and sync should happen
7. Log out
8. The timer doesn't stop immediately; it should be stopped after the next syncInterval when the system notices that the app is no longer logged in
9. Log in
10. The timer should start again
11. Change to the site which is eligible for POS
12. The timer should restart
13. Change to the site which is ineligible for POS
14. The timer should be stopped

Testing information

Tested using iPad Air M2 26.0 simulator

---

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	pr16246-2dd0372
	Version	23.4
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	2dd0372
	Installation URL	3s465p9o2hmgg

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[iamgabrielma]

LGTM 🚢

[iamgabrielma]

Consider if passing the siteID in the DDLog here would be useful: When I switched from a POS-eligible store to a non-eligible one the only notice logged was that the timer stopped. Perhaps not necessary as we would see the siteID changing from context of other events.

[iamgabrielma]

Good use of detached and priority queue!

[iamgabrielma]

I'm guessing this needs to be lazy because the POS tab visibility and eligibility? Otherwise we would be paying for initializing the sync dispatcher despite the merchant not being able to use POS.

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 23.5. 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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