[GSoC] Add Use new backend (persistent) preference (#11977)

* Add `Use the new backend` (persistent) preference
And remove the old temporary "Use V16 backend" preference
* Add a stronger warning before changing to the new backend

AnkiDroid/src/main/java/com/ichi2/anki/AnkiDroidApp.java

@@ -173,6 +173,15 @@ public class AnkiDroidApp extends Application {
         // Get preferences
         SharedPreferences preferences = getSharedPrefs(this);
 
+        // TODO remove the following if-block once AnkiDroid uses the new schema by default
+        if (BuildConfig.LEGACY_SCHEMA) {
+            boolean isNewSchemaEnabledByPref = preferences.getBoolean(getString(R.string.pref_rust_backend_key), false);
+            if (isNewSchemaEnabledByPref) {
+                Timber.i("New schema enabled by preference");
+                BackendFactory.setDefaultLegacySchema(false);
+            }
+        }
+
         CrashReportService.initialize(this);
 
         if (BuildConfig.DEBUG) {

AnkiDroid/src/main/java/com/ichi2/anki/preferences/AdvancedSettingsFragment.kt

@@ -22,6 +22,7 @@ import android.content.Context
 import android.content.Intent
 import android.content.pm.PackageManager
 import android.net.Uri
+import androidx.annotation.StringRes
 import androidx.preference.EditTextPreference
 import androidx.preference.Preference
 import androidx.preference.SwitchPreference
@@ -30,6 +31,7 @@ import com.ichi2.anki.*
 import com.ichi2.anki.exception.StorageAccessException
 import com.ichi2.anki.provider.CardContentProvider
 import com.ichi2.compat.CompatHelper
+import net.ankiweb.rsdroid.BackendFactory
 import timber.log.Timber
 
 class AdvancedSettingsFragment : SettingsFragment() {
@@ -110,6 +112,45 @@ class AdvancedSettingsFragment : SettingsFragment() {
             }
             requireActivity().packageManager.setComponentEnabledSetting(providerName, state, PackageManager.DONT_KILL_APP)
         }
+        // Use V16 backend
+        requirePreference<SwitchPreference>(R.string.pref_rust_backend_key).apply {
+            if (!BuildConfig.LEGACY_SCHEMA) {
+                title = "New schema already enabled on local.properties"
+                isEnabled = false
+            }
+            setOnPreferenceChangeListener { newValue ->
+                if (newValue == true) {
+                    confirmExperimentalChange(
+                        R.string.use_rust_backend_title,
+                        R.string.use_rust_backend_warning,
+                        onCancel = { isChecked = false },
+                        onConfirm = {
+                            BackendFactory.defaultLegacySchema = false
+                            (requireActivity() as Preferences).restartWithNewDeckPicker()
+                        }
+                    )
+                } else {
+                    BackendFactory.defaultLegacySchema = true
+                    (requireActivity() as Preferences).restartWithNewDeckPicker()
+                }
+            }
+        }
+    }
+
+    /**
+     * Shows a dialog to confirm if the user wants to enable an experimental preference
+     */
+    private fun confirmExperimentalChange(@StringRes prefTitle: Int, @StringRes message: Int? = null, onCancel: () -> Unit, onConfirm: () -> Unit) {
+        val prefTitleString = getString(prefTitle)
+        val dialogTitle = getString(R.string.experimental_pref_confirmation, prefTitleString)
+
+        MaterialDialog(requireContext()).show {
+            title(text = dialogTitle)
+            message(message)
+            positiveButton(R.string.dialog_ok) { onConfirm() }
+            negativeButton(R.string.dialog_cancel) { onCancel() }
+            cancelOnTouchOutside(false) // to avoid `onCancel` not being triggered on outside cancels
+        }
     }
 
     private fun removeUnnecessaryAdvancedPrefs() {

AnkiDroid/src/main/java/com/ichi2/anki/preferences/DevOptionsFragment.kt

@@ -22,7 +22,6 @@ import androidx.preference.SwitchPreference
 import com.afollestad.materialdialogs.MaterialDialog
 import com.ichi2.anki.*
 import com.ichi2.anki.analytics.UsageAnalytics
-import net.ankiweb.rsdroid.BackendFactory
 import timber.log.Timber
 
 /**
@@ -74,15 +73,6 @@ class DevOptionsFragment : SettingsFragment() {
             OnboardingUtils.reset(requireContext())
             true
         }
-        // Use V16 Backend
-        requirePreference<Preference>(getString(R.string.pref_rust_backend_key)).apply {
-            setDefaultValue(!BackendFactory.defaultLegacySchema)
-            setOnPreferenceClickListener {
-                BackendFactory.defaultLegacySchema = false
-                (requireActivity() as Preferences).restartWithNewDeckPicker()
-                true
-            }
-        }
         // Use scoped storage
         requirePreference<Preference>(getString(R.string.pref_scoped_storage_key)).apply {
             setDefaultValue(AnkiDroidApp.TESTING_SCOPED_STORAGE)

AnkiDroid/src/main/res/values/10-preferences.xml

@@ -333,6 +333,13 @@ this formatter is used if the bind only applies to both the question and the ans
     Keys cannot be translated yet.">Remove ‘%s’</string>
     <string name="bindings_already_bound">Already bound to ‘%s’</string>
 
+    <!-- Advanced -->
+    <string name="pref_cat_experimental" maxLength="41">Experimental</string>
+    <string name="experimental_pref_confirmation" maxLength="41">Enable ‘%s’</string>
+    <string name="use_rust_backend_title" maxLength="41">Use the new backend</string>
+    <string name="use_rust_backend_summary">Enables newer Anki features, such as the v3 scheduler\nUNSTABLE. Do not use on a collection you care about. NOT reverted on app close</string>
+    <string name="use_rust_backend_warning">There is a chance this could corrupt your installation completely, requiring app uninstall and deletion of the AnkiDroid folder, and has a chance of propagating corruption via sync to AnkiWeb.\n\nWe welcome the testing, but please make sure you have a valid non-AnkiWeb backup.</string>
+
     <!-- Developer options -->
     <string name="pref_cat_dev_options" maxLength="41">Developer options</string>
     <string name="dev_options_enabled_pref" maxLength="41">Enable developer options</string>

AnkiDroid/src/main/res/xml/preferences_advanced.xml

@@ -147,4 +147,12 @@
                 android:title="@string/thirdparty_apps_title">
             </Preference>
         </PreferenceCategory>
+        <PreferenceCategory
+            android:title="@string/pref_cat_experimental">
+            <SwitchPreference
+                android:key="@string/pref_rust_backend_key"
+                android:title="@string/use_rust_backend_title"
+                android:summary="@string/use_rust_backend_summary"
+                android:defaultValue="false"/>
+        </PreferenceCategory>
 </PreferenceScreen>

AnkiDroid/src/main/res/xml/preferences_dev_options.xml

@@ -46,16 +46,12 @@
         android:summary="@string/show_onboarding_desc"
         android:key="@string/pref_show_onboarding_key"
         android:defaultValue="false"/>
-    <Preference
-        android:title="@string/reset_onboarding"
-        android:summary="@string/reset_onboarding_desc"
-        android:key="@string/pref_reset_onboarding_key"/>
-    <Preference
-        android:title="Use V16 Backend"
-        android:summary="UNSTABLE. DO NOT USE ON A COLLECTION YOU CARE ABOUT. REVERTED ON APP CLOSE"
-        android:key="@string/pref_rust_backend_key"/>
     <Preference
         android:title="Enable Scoped Storage"
         android:summary="UNSTABLE. DO NOT USE ON A COLLECTION YOU CARE ABOUT. REVERTED ON APP CLOSE"
         android:key="@string/pref_scoped_storage_key"/>
+    <Preference
+        android:title="@string/reset_onboarding"
+        android:summary="@string/reset_onboarding_desc"
+        android:key="@string/pref_reset_onboarding_key"/>
 </PreferenceScreen>