refactor(deck-picker): deleteDeck => viewModel

* inline confirmDeckDeletion
  * removing unnecessary 'dismiss' calls
* extract `deleteDeck`
* introduce `DeckDeletionResult`

AnkiDroid/src/main/java/com/ichi2/anki/DeckPicker.kt

@@ -105,6 +105,7 @@ import com.ichi2.anki.android.input.ShortcutGroup
 import com.ichi2.anki.android.input.shortcut
 import com.ichi2.anki.deckpicker.BITMAP_BYTES_PER_PIXEL
 import com.ichi2.anki.deckpicker.BackgroundImage
+import com.ichi2.anki.deckpicker.DeckDeletionResult
 import com.ichi2.anki.deckpicker.DeckPickerViewModel
 import com.ichi2.anki.dialogs.AsyncDialogFragment
 import com.ichi2.anki.dialogs.BackupPromptDialog
@@ -168,7 +169,6 @@ import com.ichi2.libanki.Decks
 import com.ichi2.libanki.MediaCheckResult
 import com.ichi2.libanki.exception.ConfirmModSchemaException
 import com.ichi2.libanki.sched.DeckNode
-import com.ichi2.libanki.undoableOp
 import com.ichi2.libanki.utils.TimeManager
 import com.ichi2.ui.AccessibleSearchView
 import com.ichi2.ui.BadgeDrawableBuilder
@@ -617,6 +617,18 @@ open class DeckPicker :
                 .build(),
             onReceiveContentListener,
         )
+
+        setupFlows()
+    }
+
+    private fun setupFlows() {
+        fun onDeckDeleted(result: DeckDeletionResult) {
+            showSnackbar(result.toHumanReadableString(), Snackbar.LENGTH_SHORT) {
+                setAction(R.string.undo) { undo() }
+            }
+        }
+
+        viewModel.deckDeletedNotification.launchCollectionInLifecycleScope(::onDeckDeleted)
     }
 
     private val onReceiveContentListener =
@@ -654,8 +666,10 @@ open class DeckPicker :
                 /* we can only disable the shortcut for now as it is restricted by Google https://issuetracker.google.com/issues/68949561?pli=1#comment4
                  * if fixed or given free hand to delete the shortcut with the help of API update this method and use the new one
                  */
+                // TODO: it feels buggy that this is not called on all deck deletion paths
                 disableDeckAndChildrenShortcuts(deckId)
-                confirmDeckDeletion(deckId)
+                dismissAllDialogFragments()
+                deleteDeck(deckId)
             }
             DeckPickerContextMenuOption.DECK_OPTIONS -> {
                 Timber.i("ContextMenu: Open deck options selected")
@@ -1150,8 +1164,9 @@ open class DeckPicker :
             }
             R.id.action_deck_delete -> {
                 launchCatchingTask {
-                    val targetDeckId = withCol { decks.selected() }
-                    confirmDeckDeletion(targetDeckId)
+                    withProgress(resources.getString(R.string.delete_deck)) {
+                        viewModel.deleteSelectedDeck().join()
+                    }
                 }
                 return true
             }
@@ -2398,31 +2413,14 @@ open class DeckPicker :
         createDeckDialog.showDialog()
     }
 
-    fun confirmDeckDeletion(did: DeckId): Job {
-        // No confirmation required, as undoable
-        dismissAllDialogFragments()
-        return deleteDeck(did)
-    }
-
     /**
-     * Deletes the provided deck, child decks. and all cards inside.
-     * Use [.confirmDeckDeletion] for a confirmation dialog
-     * @param did the deck to delete
+     * Deletes the provided deck, child decks, and all cards inside.
+     * @param did ID of the deck to delete
      */
-    fun deleteDeck(did: DeckId): Job =
+    fun deleteDeck(did: DeckId) =
         launchCatchingTask {
-            val deckName = withCol { decks.get(did)!!.name }
-            val changes =
-                withProgress(resources.getString(R.string.delete_deck)) {
-                    undoableOp {
-                        decks.remove(listOf(did))
-                    }
-                }
-            // After deletion: decks.current() reverts to Default, necessitating `focusedDeck`
-            // to match and avoid unnecessary scrolls in `renderPage()`.
-            viewModel.focusedDeck = Consts.DEFAULT_DECK_ID
-            showSnackbar(TR.browsingCardsDeletedWithDeckname(changes.count, deckName), Snackbar.LENGTH_SHORT) {
-                setAction(R.string.undo) { undo() }
+            withProgress(resources.getString(R.string.delete_deck)) {
+                viewModel.deleteDeck(did).join()
             }
         }
 

AnkiDroid/src/main/java/com/ichi2/anki/deckpicker/DeckPickerViewModel.kt

@@ -16,17 +16,82 @@
 
 package com.ichi2.anki.deckpicker
 
+import androidx.annotation.CheckResult
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import anki.i18n.GeneratedTranslations
+import com.ichi2.anki.CollectionManager.TR
+import com.ichi2.anki.CollectionManager.withCol
 import com.ichi2.anki.DeckPicker
+import com.ichi2.libanki.Consts
 import com.ichi2.libanki.DeckId
+import com.ichi2.libanki.undoableOp
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.launch
 
 /** ViewModel for [DeckPicker] */
 class DeckPickerViewModel : ViewModel() {
+    /**
+     * @see deleteDeck
+     * @see DeckDeletionResult
+     */
+    val deckDeletedNotification = MutableSharedFlow<DeckDeletionResult>()
+
     /**
      * Keep track of which deck was last given focus in the deck list. If we find that this value
      * has changed between deck list refreshes, we need to recenter the deck list to the new current
      * deck.
      */
     // TODO: This should later be handled as a Flow
     var focusedDeck: DeckId = 0
+
+    /**
+     * Deletes the provided deck, child decks. and all cards inside.
+     *
+     * This is a slow operation and should be inside `withProgress`
+     *
+     * @param did ID of the deck to delete
+     */
+    @CheckResult // This is a slow operation and should be inside `withProgress`
+    fun deleteDeck(did: DeckId) =
+        viewModelScope.launch {
+            val deckName = withCol { decks.get(did)!!.name }
+            val changes = undoableOp { decks.remove(listOf(did)) }
+            // After deletion: decks.current() reverts to Default, necessitating `focusedDeck`
+            // to match and avoid unnecessary scrolls in `renderPage()`.
+            focusedDeck = Consts.DEFAULT_DECK_ID
+
+            deckDeletedNotification.emit(
+                DeckDeletionResult(deckName = deckName, cardsDeleted = changes.count),
+            )
+        }
+
+    /**
+     * Deletes the currently selected deck
+     *
+     * This is a slow operation and should be inside `withProgress`
+     */
+    @CheckResult
+    fun deleteSelectedDeck() =
+        viewModelScope.launch {
+            val targetDeckId = withCol { decks.selected() }
+            deleteDeck(targetDeckId).join()
+        }
+}
+
+/** Result of [DeckPickerViewModel.deleteDeck] */
+data class DeckDeletionResult(
+    val deckName: String,
+    val cardsDeleted: Int,
+) {
+    /**
+     * @see GeneratedTranslations.browsingCardsDeletedWithDeckname
+     */
+    // TODO: Somewhat questionable meaning: {count} cards deleted from {deck_name}.
+    @CheckResult
+    fun toHumanReadableString() =
+        TR.browsingCardsDeletedWithDeckname(
+            count = cardsDeleted,
+            deckName = deckName,
+        )
 }

AnkiDroid/src/test/java/com/ichi2/anki/DeckPickerTest.kt

@@ -209,8 +209,7 @@ class DeckPickerTest : RobolectricTest() {
                     DeckPicker::class.java,
                     Intent(),
                 )
-            deckPicker.confirmDeckDeletion(did)
-            advanceRobolectricLooperWithSleep()
+            deckPicker.viewModel.deleteDeck(did).join()
             assertThat("deck was deleted", col.decks.count(), equalTo(1))
         }
 

AnkiDroid/src/test/java/com/ichi2/anki/dialogs/CreateDeckDialogTest.kt

@@ -196,7 +196,7 @@ class CreateDeckDialogTest : RobolectricTest() {
 
                 // After the last deck was created, delete a deck
                 if (decksCount() >= 10) {
-                    deckPicker.confirmDeckDeletion(did)
+                    deckPicker.viewModel.deleteDeck(did).join()
                     assertEquals(deckCounter.decrementAndGet(), decksCount())
 
                     assertEquals(deckCounter.get(), decksCount())