[Woo POS] Coupons: Fetch from remote

[iamgabrielma]

Closes: #15324

Description

This PR adds the ability to fetch coupons from remote to the coupons service. First, we attempt to fetch from the remote. If this fails, we'll attempt to fetch from storage. If fails, we just return an empty list of coupons (for the moment)

We might change the fetching strategy, for now it seemed adequate to attempt remote first and local storage later.

Screen.Recording.2025-03-26.at.13.58.58.mov

Testing information

• On POS, tap the coupons button
• Observe the loading screen and coupons being loaded from remote
• Stop the app and throw an error from CouponsRemote.loadAllCoupons():

    public func loadAllCoupons(for siteID: Int64,
                               pageNumber: Int = CouponsRemote.Default.pageNumber,
                               pageSize: Int = CouponsRemote.Default.pageSize) async throws -> [Coupon] {
        throw NSError(domain: "oops", code: -1)
        try await withCheckedThrowingContinuation { continuation in
   ...
    }

• Observe that we'll still load coupons, but this time they come from the storage fallback:

"Failed to load coupons from remote:" Error Domain=oops Code=-1 "(null)"

---

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

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[iamgabrielma]

We might change the fetching strategy, for now it seemed adequate to attempt remote first and local storage later.

I'm not sure but I think we might have discussed to do the opposite? Storage first and remote later?

[wpmobilebot]

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

	App Name	WooCommerce iOS
	Build Number	pr15423-d47f648
	Version	22.0
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	d47f648
	App Center Build	WooCommerce - Prototype Builds #13419

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[staskus]

I'm not sure but I think we might have discussed to do the opposite? Storage first and remote later?

@iamgabrielma Yes, I imagined we could do local first so the results would appear immediately, but update them with remote ones. How does the current IPP implementation work? As I understand, it's storage-first. My idea was to keep the same strategy as IPP to save time on coming up with alternatives.

Observe the loading screen and coupons being loaded from remote

A full-screen loading doesn't work here. A good point is that we need to ask a designer to consider how we display a loading state. Asked here p1742974197820449-slack-C070SJRA8DP

[staskus]

This is how IPP works.

I added a new coupon and returned to the screen. After a moment, a new coupon appeared. We could sync with the design on this as well. Maybe we could show a small loading indicator somewhere as well while the network request is ongoing. Wdyt?

ScreenRecording_03-26-2025.09-36-12_1.mov

[iamgabrielma]

we could do local first so the results would appear immediately, but update them with remote ones. How does the current IPP implementation work? As I understand, it's storage-first. My idea was to keep the same strategy as IPP to save time on coming up with alternatives.

That sounds good, I'll take a deeper look of how we do it in coupons in the app and make the changes to do local first -> then update with remote results. I'll see if I can change the loading indicator on this PR as well or add the "ghost rows" separately 👍