Move the no-post guard up to PrepublishingViewModel

The guard added in the previous commit only covered the HOME screen, but a
restored sheet navigates to whatever screen was saved in KEY_SCREEN_STATE. On a
restore into TAGS, CATEGORIES or PUBLISH the sheet stayed open over an empty
EditPostRepository and still crashed on the first interaction, via
requireNotNull(post) in updateAsync.

Guarding in PrepublishingViewModel.start() instead covers every screen the sheet
can restore into, and reuses the existing dismissBottomSheet channel, so the
dismissSheet LiveData and the parentFragment cast are no longer needed. The
PrepublishingHomeViewModel early return stays as a last line of defense, since
the dismissal is asynchronous and the FragmentManager can restore that fragment
before it commits.

Also reverts the EditPostRepository.status leniency: with the guard in place its
only reader is unreachable with a null post, so returning UNKNOWN just hid the
missing post from the other callers.

Author: nbradbury

WordPress/src/main/java/org/wordpress/android/ui/posts/EditPostRepository.kt

@@ -73,7 +73,7 @@ class EditPostRepository
     val password: String
         get() = post!!.password
     val status: PostStatus
-        get() = post?.let { fromPost(it) } ?: PostStatus.UNKNOWN
+        get() = fromPost(post!!)
     val isPage: Boolean
         get() = post!!.isPage
     val isLocalDraft: Boolean

WordPress/src/main/java/org/wordpress/android/ui/posts/prepublishing/PrepublishingBottomSheetFragment.kt

@@ -191,7 +191,7 @@ class PrepublishingBottomSheetFragment : WPBottomSheetDialogFragment(),
             KEY_SCREEN_STATE
         )
         val site = requireNotNull(arguments?.getSerializableCompat<SiteModel>(SITE))
-        viewModel.start(site, prepublishingScreenState)
+        viewModel.start(site, prepublishingScreenState, getEditorHook().editPostRepository.hasPost())
     }
 
     private fun navigateToScreen(navigationTarget: PrepublishingNavigationTarget) {

WordPress/src/main/java/org/wordpress/android/ui/posts/prepublishing/PrepublishingViewModel.kt

@@ -62,10 +62,21 @@ class PrepublishingViewModel @Inject constructor(private val dispatcher: Dispatc
 
     fun start(
         site: SiteModel,
-        currentScreenFromSavedState: PrepublishingScreen?
+        currentScreenFromSavedState: PrepublishingScreen?,
+        hasPost: Boolean = true
     ) {
         this.site = site
 
+        // The sheet is a DialogFragment, so the FragmentManager restores it after a config change or
+        // process death even when the host hasn't loaded a post. Guarding here rather than in an
+        // individual screen's ViewModel covers every screen the sheet can restore into, since the
+        // saved screen below may be TAGS, CATEGORIES or PUBLISH rather than HOME.
+        if (!hasPost) {
+            AppLog.e(T.POSTS, "Prepublishing sheet started without a post; dismissing.")
+            _dismissBottomSheet.postValue(Event(Unit))
+            return
+        }
+
         // Set screen: use saved state if available (config change), otherwise reset to HOME (dismissal + reopen)
         val targetScreen = currentScreenFromSavedState ?: HOME
         this.currentScreen = targetScreen

WordPress/src/main/java/org/wordpress/android/ui/posts/prepublishing/home/PrepublishingHomeFragment.kt

@@ -3,7 +3,6 @@ package org.wordpress.android.ui.posts.prepublishing.home
 import android.content.Context
 import android.os.Bundle
 import android.view.View
-import androidx.fragment.app.DialogFragment
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.ViewModelProvider
 import androidx.recyclerview.widget.LinearLayoutManager
@@ -103,11 +102,6 @@ class PrepublishingHomeFragment : Fragment(R.layout.post_prepublishing_home_frag
             actionClickedListener?.onSubmitButtonClicked(publishPost)
         }
 
-        viewModel.dismissSheet.observeEvent(viewLifecycleOwner) {
-            // allowing state loss because this can run while the host activity is already finishing
-            (parentFragment as? DialogFragment)?.dismissAllowingStateLoss()
-        }
-
         viewModel.start(getEditPostRepository(), getSite())
     }
 

WordPress/src/main/java/org/wordpress/android/ui/posts/prepublishing/home/PrepublishingHomeViewModel.kt

@@ -50,9 +50,6 @@ class PrepublishingHomeViewModel @Inject constructor(
     private val _onSubmitButtonClicked = MutableLiveData<Event<PublishPost>>()
     val onSubmitButtonClicked: LiveData<Event<PublishPost>> = _onSubmitButtonClicked
 
-    private val _dismissSheet = MutableLiveData<Event<Unit>>()
-    val dismissSheet: LiveData<Event<Unit>> = _dismissSheet
-
     private val _uiState = MutableLiveData<List<PrepublishingHomeItemUiState>>()
     private var _socialUiState: MutableLiveData<SocialUiState> = MutableLiveData(SocialUiState.Hidden)
 
@@ -72,12 +69,11 @@ class PrepublishingHomeViewModel @Inject constructor(
     fun start(editPostRepository: EditPostRepository, site: SiteModel) {
         this.editPostRepository = editPostRepository
         if (isStarted) return
-        // The sheet is a DialogFragment, so the FragmentManager can restore it after a config
-        // change or process death before the host activity has loaded a post. Close the sheet
-        // rather than building its UI against an empty repository.
+        // PrepublishingViewModel already dismisses the sheet when the host has no post, but that
+        // dismissal is asynchronous and the FragmentManager can restore this fragment and create its
+        // view before it commits. Skip the UI rather than reading a post that isn't there.
         if (!editPostRepository.hasPost()) {
-            AppLog.e(AppLog.T.POSTS, "Prepublishing sheet opened without a post; dismissing.")
-            _dismissSheet.postValue(Event(Unit))
+            AppLog.e(AppLog.T.POSTS, "Prepublishing home started without a post; skipping setup.")
             return
         }
         isStarted = true

WordPress/src/test/java/org/wordpress/android/ui/posts/EditPostRepositoryTest.kt

@@ -19,7 +19,6 @@ import org.wordpress.android.fluxc.model.post.PostLocation
 import org.wordpress.android.fluxc.model.post.PostStatus.DRAFT
 import org.wordpress.android.fluxc.model.post.PostStatus.PENDING
 import org.wordpress.android.fluxc.model.post.PostStatus.PUBLISHED
-import org.wordpress.android.fluxc.model.post.PostStatus.UNKNOWN
 import org.wordpress.android.fluxc.store.PostStore
 import org.wordpress.android.ui.posts.EditPostRepository.UpdatePostResult
 import org.wordpress.android.util.LocaleManagerWrapper
@@ -70,11 +69,6 @@ class EditPostRepositoryTest : BaseUnitTest() {
         assertThat(editPostRepository.isPostPublishable()).isFalse()
     }
 
-    @Test
-    fun `status is UNKNOWN before initialization`() {
-        assertThat(editPostRepository.status).isEqualTo(UNKNOWN)
-    }
-
     @Test
     fun `reads post for undo correctly`() {
         val post = PostModel()

WordPress/src/test/java/org/wordpress/android/ui/posts/PrepublishingHomeViewModelTest.kt

@@ -399,18 +399,31 @@ class PrepublishingHomeViewModelTest : BaseUnitTest() {
     }
 
     @Test
-    fun `given a repository with no post, when the viewModel is started, then the sheet is dismissed`() {
+    fun `given a repository with no post, when the viewModel is started, then no ui state is built`() {
         // arrange
         whenever(editPostRepository.hasPost()).thenReturn(false)
 
         // act
         viewModel.start(editPostRepository, site)
 
         // assert
-        assertThat(viewModel.dismissSheet.value?.peekContent()).isNotNull
         assertThat(viewModel.uiState.value).isNull()
     }
 
+    @Test
+    fun `given a start with no post, when started again once the post loads, then the ui state is built`() {
+        // arrange
+        whenever(editPostRepository.hasPost()).thenReturn(false)
+        viewModel.start(editPostRepository, site)
+
+        // act - the guard must not latch isStarted, or the sheet would stay empty forever
+        whenever(editPostRepository.hasPost()).thenReturn(true)
+        viewModel.start(editPostRepository, site)
+
+        // assert
+        assertThat(viewModel.uiState.value).isNotNull
+    }
+
     private fun getHeaderUiState() = viewModel.uiState.value?.filterIsInstance(HeaderUiState::class.java)?.first()
 
     private fun getButtonUiState(): ButtonUiState? {

WordPress/src/test/java/org/wordpress/android/ui/posts/prepublishing/PrepublishingViewModelTest.kt

@@ -54,6 +54,30 @@ class PrepublishingViewModelTest : BaseUnitTest() {
         assertThat(event?.peekContent()?.targetScreen).isEqualTo(expectedScreen)
     }
 
+    @Test
+    fun `when viewModel start is called without a post, dismiss the sheet instead of navigating`() {
+        var dismissEvent: Event<Unit>? = null
+        var navigationEvent: Event<PrepublishingNavigationTarget>? = null
+        viewModel.dismissBottomSheet.observeForever { dismissEvent = it }
+        viewModel.navigationTarget.observeForever { navigationEvent = it }
+
+        // TAGS rather than HOME because a restored sheet can land on any screen
+        viewModel.start(mock(), TAGS, hasPost = false)
+
+        assertThat(dismissEvent).isNotNull
+        assertThat(navigationEvent).isNull()
+    }
+
+    @Test
+    fun `when viewModel start is called with a post, don't dismiss the sheet`() {
+        var dismissEvent: Event<Unit>? = null
+        viewModel.dismissBottomSheet.observeForever { dismissEvent = it }
+
+        viewModel.start(mock(), TAGS, hasPost = true)
+
+        assertThat(dismissEvent).isNull()
+    }
+
     @Test
     fun `when onBackClicked is pressed and currentScreen isn't HOME, navigate to HOME`() {
         val expectedScreen = HOME