Move some content group and styles to FormattableContentKit

[mokagio]

These are needed by the WordPressData files, see #24242.

[dangermattic]

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[mokagio]

#24266

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[kean]

There are a few types like Notification that are dependent on on FormattableContentKit but mainly as a convenient way to cache some data:

/// Subject Blocks Transient Storage.
///
fileprivate var cachedSubjectContentGroup: FormattableContentGroup?

Would it be possible to extract these extensions and move them to the app target? They could use objc_assocciatedObject for caching.

Files like these do not belong to FormattableContentKit:

Modules/Sources/FormattableContentKit/Styles/WPStyleGuide+Notifications.swift

[mokagio]

Thanks @kean.

In my haste of getting WordPressData to build and run, I might be spending too little time evaluating what should be moved and what could be reworked.

I'll have a look here after closing #24267

[mokagio]

So I've been looking into this a bit and it's not straightforward. The main blocker is that Notification (an NSManagedObject which we need to move to WordPressData) uses the logic directly related to FormattableContentKit in its deinit.

I'm going to play around with this more on my Monday.

[kean]

the logic directly related to FormattableContentKit in its deinit.

I see. So it observes some of its own properties to reload the cached attributes. These properties can be observed from the outside – similarly to how we use ImageLoadingController with its lifetime tied to the associated image view.

// Name arbitrary 
final class NotificationFormattableContentController {
    weak var notification: Notification?

    private var cachedSubjectContentGroup: FormattableContentGroup?
    // ... 
 
    deinit {
        // Remove KVO observation
    }

    init(notification: Notification) {
        // 1. Set up obsever
        // 2. Set as associated object 
    }
}

ideally, I would just add NotificationViewModel, put the "formattable" code there, and use it in the UI. I'm not sure if it's going to be easy though. I'd just go with what's faster for now.

[mokagio]

I'd just go with what's faster for now.

Thanks @kean! I'll cash this is and log a tech debt issue, #24298, to address this later.