fix(browse): col reopen & language change

* After a collection change, `setActiveBrowserColumns` is reset
* After a language change, column headers need to be updated

Due to the language change, the activity goes through `onCreate`,
so pick up this change on `onRestoreInstanceState`

This was a good opportunity to decouple the column data and the column
headings in the View

Fixes 17803
Fixes 17367

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

@@ -59,19 +59,18 @@ import com.ichi2.anki.browser.BrowserColumnCollection
 import com.ichi2.anki.browser.BrowserColumnSelectionFragment
 import com.ichi2.anki.browser.BrowserMultiColumnAdapter
 import com.ichi2.anki.browser.BrowserRowCollection
-import com.ichi2.anki.browser.CardBrowserColumn
 import com.ichi2.anki.browser.CardBrowserLaunchOptions
 import com.ichi2.anki.browser.CardBrowserViewModel
 import com.ichi2.anki.browser.CardBrowserViewModel.SearchState
 import com.ichi2.anki.browser.CardBrowserViewModel.SearchState.Initializing
 import com.ichi2.anki.browser.CardBrowserViewModel.SearchState.Searching
 import com.ichi2.anki.browser.CardOrNoteId
+import com.ichi2.anki.browser.ColumnHeading
 import com.ichi2.anki.browser.PreviewerIdsFile
 import com.ichi2.anki.browser.RepositionCardsRequest.ContainsNonNewCardsError
 import com.ichi2.anki.browser.RepositionCardsRequest.RepositionData
 import com.ichi2.anki.browser.SaveSearchResult
 import com.ichi2.anki.browser.SharedPreferencesLastDeckIdRepository
-import com.ichi2.anki.browser.getLabel
 import com.ichi2.anki.browser.toCardBrowserLaunchOptions
 import com.ichi2.anki.dialogs.BrowserOptionsDialog
 import com.ichi2.anki.dialogs.CardBrowserMySearchesDialog
@@ -455,27 +454,8 @@ open class CardBrowser :
         fun onSelectedRowsChanged(rows: Set<Any>) = onSelectionChanged()
 
         fun onColumnsChanged(columnCollection: BrowserColumnCollection) {
+            Timber.d("columns changed")
             notifyDataSetChanged()
-
-            if (!viewModel.columnNamesLoaded) return
-
-            // reset headings
-            val headingsContainer =
-                browserColumnHeadings.apply {
-                    removeAllViews()
-                }
-
-            val layoutInflater = LayoutInflater.from(headingsContainer.context)
-            for (column in columnCollection.columns) {
-                Timber.d("setting up column %s", column)
-                layoutInflater.inflate(R.layout.browse_column_heading, headingsContainer, false).apply {
-                    headingsContainer.addView(this)
-                    (this as TextView).text =
-                        viewModel
-                            .namedColumns[CardBrowserColumn.entries.indexOf(column)]
-                            .getLabel(viewModel.cardsOrNotes)
-                }
-            }
         }
 
         fun onFilterQueryChanged(filterQuery: String) {
@@ -540,6 +520,25 @@ open class CardBrowser :
             }
         }
 
+        fun onColumnNamesChanged(columnCollection: List<ColumnHeading>) {
+            Timber.d("column names changed")
+            // reset headings
+            val headingsContainer =
+                browserColumnHeadings.apply {
+                    removeAllViews()
+                }
+
+            // set up the new columns
+            val layoutInflater = LayoutInflater.from(headingsContainer.context)
+            for (column in columnCollection) {
+                Timber.d("setting up column %s", column)
+                layoutInflater.inflate(R.layout.browse_column_heading, headingsContainer, false).apply {
+                    headingsContainer.addView(this)
+                    (this as TextView).text = column.label
+                }
+            }
+        }
+
         viewModel.flowOfIsTruncated.launchCollectionInLifecycleScope(::onIsTruncatedChanged)
         viewModel.flowOfSearchQueryExpanded.launchCollectionInLifecycleScope(::onSearchQueryExpanded)
         viewModel.flowOfSelectedRows.launchCollectionInLifecycleScope(::onSelectedRowsChanged)
@@ -550,6 +549,7 @@ open class CardBrowser :
         viewModel.flowOfIsInMultiSelectMode.launchCollectionInLifecycleScope(::isInMultiSelectModeChanged)
         viewModel.flowOfCardsUpdated.launchCollectionInLifecycleScope(::cardsUpdatedChanged)
         viewModel.flowOfSearchState.launchCollectionInLifecycleScope(::searchStateChanged)
+        viewModel.flowOfColumnHeadings.launchCollectionInLifecycleScope(::onColumnNamesChanged)
     }
 
     // Finish initializing the activity after the collection has been correctly loaded
@@ -1552,6 +1552,7 @@ open class CardBrowser :
 
     public override fun onRestoreInstanceState(savedInstanceState: Bundle) {
         super.onRestoreInstanceState(savedInstanceState)
+        viewModel.onReinit()
         viewModel.launchSearchForCards(
             savedInstanceState.getString("mSearchTerms", ""),
             forceRefresh = false,

AnkiDroid/src/main/java/com/ichi2/anki/browser/CardBrowserViewModel.kt

@@ -64,6 +64,7 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.combineTransform
 import kotlinx.coroutines.flow.filter
@@ -138,6 +139,13 @@ class CardBrowserViewModel(
     private val reverseDirectionFlow = MutableStateFlow(ReverseDirection(orderAsc = false))
     val orderAsc get() = reverseDirectionFlow.value.orderAsc
 
+    /**
+     * A map from column backend key to backend column definition
+     *
+     * @see [flowOfColumnHeadings]
+     */
+    private val flowOfAllColumns = MutableSharedFlow<Map<String, BrowserColumns.Column>>()
+
     val flowOfActiveColumns =
         MutableStateFlow(
             BrowserColumnCollection(
@@ -152,9 +160,6 @@ class CardBrowserViewModel(
     val activeColumns
         get() = flowOfActiveColumns.value.columns
 
-    /** Available columns with names */
-    lateinit var namedColumns: List<BrowserColumns.Column>
-
     val flowOfSearchQueryExpanded = MutableStateFlow(false)
 
     private val searchQueryInputFlow = MutableStateFlow<String?>(null)
@@ -241,8 +246,16 @@ class CardBrowserViewModel(
 
     val flowOfInitCompleted = MutableStateFlow(false)
 
-    val columnNamesLoaded
-        get() = ::namedColumns.isInitialized
+    val flowOfColumnHeadings: StateFlow<List<ColumnHeading>> =
+        combine(flowOfActiveColumns, flowOfCardsOrNotes, flowOfAllColumns) { activeColumns, cardsOrNotes, allColumns ->
+            Timber.d("updated headings for %d columns", activeColumns.count)
+            activeColumns.columns.map {
+                ColumnHeading(
+                    label = allColumns[it.ankiColumnKey]!!.getLabel(cardsOrNotes),
+                )
+            }
+            // stateIn is requires for tests
+        }.stateIn(viewModelScope, SharingStarted.Eagerly, initialValue = emptyList())
 
     /**
      * Whether the task launched from CardBrowserViewModel.init has completed.
@@ -305,19 +318,21 @@ class CardBrowserViewModel(
             .onEach { sortType -> withCol { sortType.save(config, sharedPrefs()) } }
             .launchIn(viewModelScope)
 
+        flowOfCardsOrNotes
+            .onEach { cardsOrNotes ->
+                Timber.d("loading columns for %s mode", cardsOrNotes)
+                updateActiveColumns(BrowserColumnCollection.load(sharedPrefs(), cardsOrNotes))
+            }.launchIn(viewModelScope)
+
         viewModelScope.launch {
             val initialDeckId = if (selectAllDecks) ALL_DECKS_ID else getInitialDeck()
             // PERF: slightly inefficient if the source was lastDeckId
             setDeckId(initialDeckId)
+            refreshBackendColumns()
+
             val cardsOrNotes = withCol { CardsOrNotes.fromCollection(this@withCol) }
             flowOfCardsOrNotes.update { cardsOrNotes }
 
-            val allColumns = withCol { allBrowserColumns() }.associateBy { it.key }
-            namedColumns =
-                CardBrowserColumn.entries.map { allColumns[it.ankiColumnKey]!! }
-
-            setupColumns(cardsOrNotes)
-
             withCol {
                 sortTypeFlow.update { SortType.fromCol(config, cardsOrNotes, sharedPrefs()) }
                 reverseDirectionFlow.update { ReverseDirection.fromConfig(config) }
@@ -331,11 +346,41 @@ class CardBrowserViewModel(
         }
     }
 
-    private suspend fun setupColumns(cardsOrNotes: CardsOrNotes) {
-        Timber.d("loading columns columns for %s mode", cardsOrNotes)
-        val columns = BrowserColumnCollection.load(sharedPrefs(), cardsOrNotes)
-        flowOfActiveColumns.update { columns }
+    /**
+     * Called if `onCreate` is called again, which may be due to the collection being reopened
+     *
+     * If this is the case, the backend has lost the active columns state, which is required for
+     * [transformBrowserRow]
+     */
+    fun onReinit() {
+        // this can occur after process death, if so, the ViewModel starts normally
+        if (!initCompleted) return
+
+        Timber.d("onReinit: executing")
+
+        // we currently have no way to test whether setActiveBrowserColumns was called
+        // so set it again. This needs to be done immediately to ensure that the RecyclerView
+        // gets correct values when initialized
+        CollectionManager
+            .getBackend()
+            .setActiveBrowserColumns(flowOfActiveColumns.value.backendKeys)
+
+        // if the language has changed, the backend column labels may have changed
+        viewModelScope.launch {
+            refreshBackendColumns()
+        }
+    }
+
+    /** Handles an update to the list of backend columns */
+    private suspend fun refreshBackendColumns() {
+        flowOfAllColumns.emit(withCol { allBrowserColumns() }.associateBy { it.key })
+    }
+
+    /** Handles an update of the visible columns */
+    private suspend fun updateActiveColumns(columns: BrowserColumnCollection) {
+        Timber.d("updating active columns")
         withCol { backend.setActiveBrowserColumns(columns.backendKeys) }
+        flowOfActiveColumns.update { columns }
     }
 
     @VisibleForTesting
@@ -398,7 +443,6 @@ class CardBrowserViewModel(
                 newValue.saveToCollection(this@withCol)
             }
             flowOfCardsOrNotes.update { newValue }
-            setupColumns(newValue)
         }
 
     fun setTruncated(value: Boolean) {
@@ -553,10 +597,8 @@ class CardBrowserViewModel(
         Timber.d("editing columns for current headings: %b", isEditingCurrentHeadings)
 
         if (isEditingCurrentHeadings) {
-            Timber.d("updating active columns")
             viewModelScope.launch {
-                withCol { backend.setActiveBrowserColumns(columnCollection.backendKeys) }
-                flowOfActiveColumns.update { columnCollection }
+                updateActiveColumns(columnCollection)
             }
         }
 
@@ -1074,3 +1116,7 @@ sealed class RepositionCardsRequest {
 }
 
 fun BrowserColumns.Column.getLabel(cardsOrNotes: CardsOrNotes): String = if (cardsOrNotes == CARDS) cardsModeLabel else notesModeLabel
+
+data class ColumnHeading(
+    val label: String,
+)