[Push] Allow UP distributor selection

[ArnyminerZ]

Purpose

Give the user the option to select their preferred push distributor when multiple are available.

Short description

When the unified push distributor setting is tapped, a new dialog is shown with the distributors available.

Choose endpoint	Dist. selected but no endpoint	Endpoint ready

It can happen that a distributor has been selected, but it has still not provided any endpoint. If that's the case, a new text is displayed: "Awaiting endpoint from ..."

There's a new preference now that stores the currently selected distributor, as well as the existing one that stores the push endpoint.

Note: Right now, if you have the app open, and install a new distributor, it won't show up immediately, you need to exit from settings, and enter again, no need to restart the app.

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[rfc2822]

Tested and looks very good!

As I understand it, we shouldn't "do" too much in the UI, so the actual UnifiedPush logic should be in the model.

Also let's call the variables etc. "pushDistributors" instead of "distributors" because distributors could also mean something else.

[rfc2822]

I have also cleaned up the tasks settings in AppSettings, please merge main-ose first

[rfc2822]

I wonder what should happen when there's only one distributor – should the selection popup even appear or should the only one be automatically registered, like it's done currently?

Also CC @devvv4ever

[devvv4ever]

I'm wondering if this should be an explicit user interaction. There could be the case that people don't want any Push at all and then they should have an option like: "Don't use any distributor" or just an option "None / Disabled".

I'd go for an auto-select if there is any distributor available, but also add an option to disable it at all on user wish. So the dialog would be nice to have in any case.

[ArnyminerZ]

I'd go for an auto-select if there is any distributor available, but also add an option to disable it at all on user wish. So the dialog would be nice to have in any case.

Done it 😄

[rfc2822]

I think we're already done.

There's however a crash:

1. I have only ntfy installed.
2. Start DAVx5, app settings, UnifiedPush, select None, OK.
3. Back, Back to close DAVx5.
4. Start DAVx5 again, choose app settings.
5. It crashes:

FATAL EXCEPTION: DefaultDispatcher-worker-1
Process: at.bitfire.davdroid, PID: 11179
java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object kotlinx.coroutines.flow.MutableStateFlow.emit(java.lang.Object, kotlin.coroutines.Continuation)' on a null object reference
	at at.bitfire.davdroid.ui.AppSettingsModel.loadPushDistributors(AppSettingsModel.kt:139)
	at at.bitfire.davdroid.ui.AppSettingsModel.access$loadPushDistributors(AppSettingsModel.kt:33)
	at at.bitfire.davdroid.ui.AppSettingsModel$1.invokeSuspend(AppSettingsModel.kt:43)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:101)
	at kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:113)
	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:89)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:589)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:823)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:720)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:707)
	Suppressed: kotlinx.coroutines.internal.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@39af90e, Dispatchers.IO]

[ArnyminerZ]

The UnifiedPush website is back online. This is the example they give:

import org.unifiedpush.android.connector.UnifiedPush.*
/* ... */

// Check if a distributor is already registered
getAckDistributor(context)?.let {
    // Re-register in case something broke
    // Options:
    // "instance" to handle multiple registrations
    // "features" empty array or [FEATURE_BYTES_MESSAGE]
    //    to be sure the distributor handles non-UTF-8 input
    // "messageForDistributor" that may be displayed by the distrib.
    registerApp(context)
    return
}
// Get a list of distributors that are available
val distributors = getDistributors(context)
// select one or show a dialog or whatever
val userDistrib = yourFunc(distributors)
// save the distributor
saveDistributor(context, userDistrib)
// register your app to the distributor
// Options:
// "instance" to handle multiple registrations
// "features" empty array or [FEATURE_BYTES_MESSAGE]
//    to be sure the distributor handles non-UTF-8 input
// "messageForDistributor" that may be displayed by the distrib.
registerApp(context)

I mean, regarding the getAckDistributor call

[rfc2822]

java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object kotlinx.coroutines.flow.MutableStateFlow.emit(java.lang.Object, kotlin.coroutines.Continuation)' on a null object reference

I think the correct way is to set value = (like in this example) instead of using emit. Can you try to reproduce the problem and does that make it go away?

[ArnyminerZ]

Can you try to reproduce the problem and does that make it go away?

I was able to reproduce, I think it was because we were calling init before declaring the variable, and even though it was in a coroutine, _pushDistributor wasn't initialized yet. I've moved it to the bottom and now it works correctly.

[rfc2822]

The init block position was a surprise… 👍🏻 Now looks good and works.

I have replaced the emit() by .value = although it does the same thing and shouldn't matter. However it seems more logical to set the value in the model (because we always use the value) and it's done like that in the example.