Support backend undo

Can be tested by importing an apkg from the deck list, then choosing
the undo option.

- If a backend undo entry is present, it takes priority over the old
undo system to ensure data integrity. AD's reviewer saves config vars and
decks as part of the review process, and it was triggering undo entries
for those changes, which prevent the v2 scheduler review from being undone.
The calls have been updated to clear the backend undo, so that the review
takes precedence. The desktop code has the same problem, and it will be
avoidable once updating to the v3 scheduler.
- Introduce a helper to await a job in unit tests, to avoid race
conditions

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

@@ -44,6 +44,7 @@ import androidx.annotation.StringRes
 import androidx.annotation.VisibleForTesting
 import androidx.coordinatorlayout.widget.CoordinatorLayout
 import androidx.webkit.WebViewAssetLoader
+import anki.collection.OpChanges
 import com.afollestad.materialdialogs.MaterialDialog
 import com.drakeet.drawer.FullDraggableContainer
 import com.google.android.material.snackbar.Snackbar
@@ -98,6 +99,8 @@ import com.ichi2.utils.HashUtil.HashSetInit
 import com.ichi2.utils.KotlinCleanup
 import com.ichi2.utils.MaxExecFunction
 import com.ichi2.utils.WebViewDebugging.initializeDebugging
+import kotlinx.coroutines.Job
+import net.ankiweb.rsdroid.BackendFactory
 import net.ankiweb.rsdroid.RustCleanup
 import timber.log.Timber
 import java.io.*
@@ -120,7 +123,8 @@ abstract class AbstractFlashcardViewer :
     TagsDialogListener,
     WhiteboardMultiTouchMethods,
     AutomaticallyAnswered,
-    OnPageFinishedCallback {
+    OnPageFinishedCallback,
+    ChangeManager.Subscriber {
     private var mTtsInitialized = false
     private var mReplayOnTtsInit = false
     private var mAnkiDroidJsAPI: AnkiDroidJsAPI? = null
@@ -277,6 +281,10 @@ abstract class AbstractFlashcardViewer :
         displayCardAnswer()
     }
 
+    init {
+        ChangeManager.subscribe(this)
+    }
+
     // Event handler for eases (answer buttons)
     inner class SelectEaseHandler : View.OnClickListener, OnTouchListener {
         private var mPrevCard: Card? = null
@@ -826,21 +834,33 @@ abstract class AbstractFlashcardViewer :
         }
     }
 
-    open fun undo() {
+    open fun undo(): Job? {
         if (isUndoAvailable) {
             val res = resources
             val undoName = col.undoName(res)
-            Undo().runWithHandler(
-                answerCardHandler(false)
-                    .alsoExecuteAfter {
-                        showThemedToast(
-                            this@AbstractFlashcardViewer,
-                            res.getString(R.string.undo_succeeded, undoName),
-                            true
-                        )
+            fun legacyUndo() {
+                Undo().runWithHandler(
+                    answerCardHandler(false)
+                        .alsoExecuteAfter {
+                            showThemedToast(
+                                this@AbstractFlashcardViewer,
+                                res.getString(R.string.undo_succeeded, undoName),
+                                true
+                            )
+                        }
+                )
+            }
+            if (BackendFactory.defaultLegacySchema) {
+                legacyUndo()
+            } else {
+                return launchCatchingCollectionTask { col ->
+                    if (!backendUndoAndShowPopup(col)) {
+                        legacyUndo()
                     }
-            )
+                }
+            }
         }
+        return null
     }
 
     private fun finishNoStorageAvailable() {
@@ -2559,6 +2579,15 @@ abstract class AbstractFlashcardViewer :
         return AnkiDroidJsAPI(this)
     }
 
+    override fun opExecuted(changes: OpChanges, handler: Any?) {
+        if ((changes.studyQueues || changes.noteText || changes.card) && handler !== this) {
+            // executing this only for the refresh side effects; there may be a better way
+            Undo().runWithHandler(
+                answerCardHandler(false)
+            )
+        }
+    }
+
     companion object {
         /**
          * Result codes that are returned when this activity finishes.

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

@@ -0,0 +1,47 @@
+/***************************************************************************************
+ * Copyright (c) 2022 Ankitects Pty Ltd <https://apps.ankiweb.net>                       *
+ *                                                                                      *
+ * This program is free software; you can redistribute it and/or modify it under        *
+ * the terms of the GNU General Public License as published by the Free Software        *
+ * Foundation; either version 3 of the License, or (at your option) any later           *
+ * version.                                                                             *
+ *                                                                                      *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY      *
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A      *
+ * PARTICULAR PURPOSE. See the GNU General Public License for more details.             *
+ *                                                                                      *
+ * You should have received a copy of the GNU General Public License along with         *
+ * this program.  If not, see <http://www.gnu.org/licenses/>.                           *
+ ****************************************************************************************/
+
+package com.ichi2.anki
+
+import com.ichi2.anki.UIUtils.showSimpleSnackbar
+import com.ichi2.libanki.CollectionV16
+import com.ichi2.libanki.undoNew
+import com.ichi2.libanki.undoableOp
+import net.ankiweb.rsdroid.BackendException
+
+suspend fun AnkiActivity.backendUndoAndShowPopup(col: CollectionV16): Boolean {
+    return try {
+        val changes = runInBackgroundWithProgress() {
+            undoableOp {
+                col.undoNew()
+            }
+        }
+        showSimpleSnackbar(
+            this,
+            col.tr.undoActionUndone(changes.operation),
+            false
+        )
+        true
+    } catch (exc: BackendException) {
+        // FIXME: -Backend module should export this as a separate Exception
+        if (exc.localizedMessage == "UndoEmpty") {
+            // backend undo queue empty
+            false
+        } else {
+            throw exc
+        }
+    }
+}

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

@@ -33,6 +33,7 @@ import androidx.activity.result.contract.ActivityResultContracts.StartActivityFo
 import androidx.annotation.CheckResult
 import androidx.annotation.VisibleForTesting
 import androidx.appcompat.widget.SearchView
+import anki.collection.OpChanges
 import com.afollestad.materialdialogs.list.SingleChoiceListener
 import com.google.android.material.snackbar.Snackbar
 import com.ichi2.anim.ActivityTransitionAnimation
@@ -96,6 +97,7 @@ import com.ichi2.utils.HashUtil.HashMapInit
 import com.ichi2.utils.Permissions.hasStorageAccessPermission
 import com.ichi2.utils.TagsUtil.getUpdatedTags
 import com.ichi2.widget.WidgetStatus.update
+import net.ankiweb.rsdroid.BackendFactory
 import net.ankiweb.rsdroid.RustCleanup
 import timber.log.Timber
 import java.lang.Exception
@@ -112,7 +114,12 @@ import kotlin.math.min
 @Suppress("LeakingThis") // The class is only 'open' due to testing
 @KotlinCleanup("scan through this class and add attributes - not started")
 @KotlinCleanup("Add TextUtils.isNotNullOrEmpty accepting nulls and use it. Remove TextUtils import")
-open class CardBrowser : NavigationDrawerActivity(), SubtitleListener, DeckSelectionListener, TagsDialogListener {
+open class CardBrowser :
+    NavigationDrawerActivity(),
+    SubtitleListener,
+    DeckSelectionListener,
+    TagsDialogListener,
+    ChangeManager.Subscriber {
     @KotlinCleanup("using ?. and let keyword would be good here")
     override fun onDeckSelected(deck: SelectableDeck?) {
         if (deck == null) {
@@ -255,6 +262,10 @@ open class CardBrowser : NavigationDrawerActivity(), SubtitleListener, DeckSelec
     private var mUnmountReceiver: BroadcastReceiver? = null
     private val orderSingleChoiceDialogListener: SingleChoiceListener = { _, index: Int, _ -> changeCardOrder(index) }
 
+    init {
+        ChangeManager.subscribe(this)
+    }
+
     @VisibleForTesting(otherwise = VisibleForTesting.PROTECTED)
     fun changeCardOrder(which: Int) {
         if (which != mOrder) {
@@ -1255,7 +1266,15 @@ open class CardBrowser : NavigationDrawerActivity(), SubtitleListener, DeckSelec
     @VisibleForTesting
     fun onUndo() {
         if (col.undoAvailable()) {
-            Undo().runWithHandler(mUndoHandler)
+            if (BackendFactory.defaultLegacySchema) {
+                Undo().runWithHandler(mUndoHandler)
+            } else {
+                launchCatchingCollectionTask { col ->
+                    if (!backendUndoAndShowPopup(col)) {
+                        Undo().runWithHandler(mUndoHandler)
+                    }
+                }
+            }
         }
     }
 
@@ -2612,6 +2631,19 @@ open class CardBrowser : NavigationDrawerActivity(), SubtitleListener, DeckSelec
         searchCards()
     }
 
+    override fun opExecuted(changes: OpChanges, handler: Any?) {
+        if ((
+            changes.browserSidebar ||
+                changes.browserTable ||
+                changes.noteText ||
+                changes.card
+            ) && handler !== this
+        ) {
+            // executing this only for the refresh side effects; there may be a better way
+            Undo().runWithHandler(mUndoHandler)
+        }
+    }
+
     companion object {
         @JvmField
         var sCardBrowserCard: Card? = null

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

@@ -99,7 +99,7 @@ suspend fun <T> Backend.withProgress(
 
 /**
  * Run the provided operation in the background, showing a progress
- * window.
+ * window. Progress info is polled from the backend.
  */
 suspend fun <T> AnkiActivity.runInBackgroundWithProgress(
     backend: Backend,
@@ -122,6 +122,24 @@ suspend fun <T> AnkiActivity.runInBackgroundWithProgress(
     }
 }
 
+/**
+ * Run the provided operation in the background, showing a progress
+ * window with the provided message.
+ */
+suspend fun <T> AnkiActivity.runInBackgroundWithProgress(
+    message: String = "",
+    op: suspend () -> T
+): T = withProgressDialog(
+    context = this@runInBackgroundWithProgress,
+    onCancel = null
+) { dialog ->
+    @Suppress("Deprecation") // ProgressDialog deprecation
+    dialog.setMessage(message)
+    runInBackground {
+        op()
+    }
+}
+
 private suspend fun <T> withProgressDialog(
     context: AnkiActivity,
     onCancel: (() -> Unit)?,

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

@@ -147,7 +147,7 @@ open class DeckPicker :
     MediaCheckDialogListener,
     OnRequestPermissionsResultCallback,
     CustomStudyListener,
-    ChangeManager.ChangeSubscriber {
+    ChangeManager.Subscriber {
     // Short animation duration from system
     private var mShortAnimDuration = 0
     private var mBackButtonPressedToExit = false
@@ -1222,9 +1222,20 @@ open class DeckPicker :
 
     private fun undo() {
         Timber.i("undo()")
-        val undoReviewString = resources.getString(R.string.undo_action_review)
-        val isReview = undoReviewString == col.undoName(resources)
-        Undo().runWithHandler(undoTaskListener(isReview))
+        fun legacyUndo() {
+            val undoReviewString = resources.getString(R.string.undo_action_review)
+            val isReview = undoReviewString == col.undoName(resources)
+            Undo().runWithHandler(undoTaskListener(isReview))
+        }
+        if (BackendFactory.defaultLegacySchema) {
+            legacyUndo()
+        } else {
+            launchCatchingCollectionTask { col ->
+                if (!backendUndoAndShowPopup(col)) {
+                    legacyUndo()
+                }
+            }
+        }
     }
 
     // Show dialogs to deal with database loading issues etc
@@ -2623,6 +2634,7 @@ open class DeckPicker :
 
     override fun opExecuted(changes: OpChanges, handler: Any?) {
         if (changes.studyQueues && handler !== this) {
+            invalidateOptionsMenu()
             updateDeckList()
         }
     }

AnkiDroid/src/main/java/com/ichi2/libanki/BackendUndo.kt

@@ -0,0 +1,73 @@
+/***************************************************************************************
+ * Copyright (c) 2022 Ankitects Pty Ltd <https://apps.ankiweb.net>                       *
+ *                                                                                      *
+ * This program is free software; you can redistribute it and/or modify it under        *
+ * the terms of the GNU General Public License as published by the Free Software        *
+ * Foundation; either version 3 of the License, or (at your option) any later           *
+ * version.                                                                             *
+ *                                                                                      *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY      *
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A      *
+ * PARTICULAR PURPOSE. See the GNU General Public License for more details.             *
+ *                                                                                      *
+ * You should have received a copy of the GNU General Public License along with         *
+ * this program.  If not, see <http://www.gnu.org/licenses/>.                           *
+ ****************************************************************************************/
+
+package com.ichi2.libanki
+
+import anki.collection.OpChangesAfterUndo
+import net.ankiweb.rsdroid.RustCleanup
+import anki.collection.UndoStatus as UndoStatusProto
+
+/**
+ * If undo/redo available, a localized string describing the action will be set.
+ */
+data class UndoStatus(
+    val undo: String?,
+    val redo: String?,
+    // not currently used
+    val lastStep: Int
+) {
+    companion object {
+        fun from(proto: UndoStatusProto): UndoStatus {
+            return UndoStatus(
+                undo = proto.undo.ifEmpty { null },
+                redo = proto.redo.ifEmpty { null },
+                lastStep = proto.lastStep
+            )
+        }
+    }
+}
+
+/**
+ * Undo the last backend operation.
+ *
+ * Should be called via collection.op(), which will notify
+ * [ChangeManager.Subscriber] of the changes.
+ *
+ * Will throw if no undo operation is possible (due to legacy code
+ * directly mutating the database).
+ */
+@RustCleanup("Once fully migrated, and v2 scheduler dropped, rename to undo()")
+fun CollectionV16.undoNew(): OpChangesAfterUndo {
+    val changes = backend.undo()
+    // clear legacy undo log
+    clearUndo()
+    return changes
+}
+
+/** Redoes the previously-undone operation. See the docs for
+[CollectionV16.undoOperation]
+ */
+fun CollectionV16.redo(): OpChangesAfterUndo {
+    val changes = backend.redo()
+    // clear legacy undo log
+    clearUndo()
+    return changes
+}
+
+/** See [UndoStatus] */
+fun CollectionV16.undoStatus(): UndoStatus {
+    return UndoStatus.from(backend.getUndoStatus())
+}

AnkiDroid/src/main/java/com/ichi2/libanki/Collection.kt

@@ -1440,17 +1440,17 @@ open class Collection(
         } else null
     }
 
-    fun undoName(res: Resources?): String {
+    open fun undoName(res: Resources): String {
         val type = undoType()
-        return type?.name(res!!) ?: ""
+        return type?.name(res) ?: ""
     }
 
-    fun undoAvailable(): Boolean {
+    open fun undoAvailable(): Boolean {
         Timber.d("undoAvailable() undo size: %s", undo.size)
         return !undo.isEmpty()
     }
 
-    fun undo(): Card? {
+    open fun undo(): Card? {
         val lastUndo: UndoAction = undo.removeLast()
         Timber.d("undo() of type %s", lastUndo.javaClass)
         return lastUndo.undo(this)