feature: 3263 - new BackgroundTaskManager that always works

Deleted file:
* `background_task_helper.dart`

New files:
* `background_task_manager.dart`: Management of background tasks: single thread, block, restart, display.
* `dao_instant_string.dart`: Where we store strings that need INSTANT access (= not lazy, no await).

Impacted fles:
* `abstract_background_task.dart`: refactored
* `background_task_details.dart`: refactored around the changes in `AbstractBackgroundTask`
* `background_task_image.dart`: refactored around the changes in `AbstractBackgroundTask`
* `dao_string_list.dart`: refactoring around now managing several lists; removed unnecessary `await` for a non-lazy dao
* `local_database.dart`: added the new class `DaoInstantString`; relaunch the background task manager at every refresh
* `main.dart`: minor refactoring
* `new_crop_page.dart`: unrelated bug fix
* `offline_tasks_page.dart`: refactored around the new `BackgroundTaskManager`
* `operation_type.dart`: added helper methods
* `product_image_gallery_view.dart`: minor refactoring
* `product_image_viewer.dart`: unrelated bug fix - the product was not refreshed, and so wasn't the image even after a successful download
* `pubspec.lock`: wtf
* `pubspec.yaml`: removed `flutter_task_manager`
* `search_history_view.dart`: minor refactoring now that we have several lists in `DaoStringList`
* `search_page.dart`: minor refactoring now that we have several lists in `DaoStringList`
* `up_to_date_changes.dart`: minor refactoring
* `up_to_date_product_provider.dart`: minor refactoring

packages/smooth_app/lib/background/abstract_background_task.dart

@@ -1,14 +1,17 @@
 import 'dart:convert';
 
 import 'package:flutter/material.dart';
+import 'package:flutter_gen/gen_l10n/app_localizations.dart';
 import 'package:openfoodfacts/openfoodfacts.dart';
 import 'package:openfoodfacts/utils/CountryHelper.dart';
+import 'package:provider/provider.dart';
 import 'package:smooth_app/background/background_task_details.dart';
 import 'package:smooth_app/background/background_task_image.dart';
+import 'package:smooth_app/background/background_task_manager.dart';
 import 'package:smooth_app/database/dao_product.dart';
 import 'package:smooth_app/database/local_database.dart';
+import 'package:smooth_app/generic_lib/duration_constants.dart';
 import 'package:smooth_app/query/product_query.dart';
-import 'package:task_manager/task_manager.dart';
 
 /// Abstract background task.
 abstract class AbstractBackgroundTask {
@@ -34,29 +37,61 @@ abstract class AbstractBackgroundTask {
   final String user;
   final String country;
 
-  @protected
   Map<String, dynamic> toJson();
 
   /// Returns the deserialized background task if possible, or null.
-  static AbstractBackgroundTask? fromTask(final Task task) =>
-      BackgroundTaskDetails.fromTask(task) ??
-      BackgroundTaskImage.fromTask(task);
+  static AbstractBackgroundTask? fromJson(final Map<String, dynamic> map) =>
+      BackgroundTaskDetails.fromJson(map) ?? BackgroundTaskImage.fromJson(map);
 
   /// Response code sent by the server in case of a success.
   @protected
   static const int SUCCESS_CODE = 1;
 
   /// Executes the background task: upload, download, update locally.
-  Future<TaskResult> execute(final LocalDatabase localDatabase) async {
+  Future<void> execute(final LocalDatabase localDatabase) async {
     await upload();
     await _downloadAndRefresh(localDatabase);
-    return TaskResult.success;
   }
 
+  /// Runs _instantly_ temporary code in order to "fake" the background task.
+  ///
+  /// For instance, here we can pretend that we've changed the product name
+  /// by doing it locally, but the background task that talks to the server
+  /// is not even started.
+  Future<void> preExecute(final LocalDatabase localDatabase);
+
+  /// Cleans the temporary data changes performed in [preExecute].
+  Future<void> postExecute(final LocalDatabase localDatabase);
+
   /// Uploads data changes.
   @protected
   Future<void> upload();
 
+  /// SnackBar message when we add the task, like "Added to the task queue!"
+  @protected
+  String getSnackBarMessage(final AppLocalizations appLocalizations);
+
+  /// Adds this task to the [BackgroundTaskManager].
+  @protected
+  Future<void> addToManager(final State<StatefulWidget> widget) async {
+    if (!widget.mounted) {
+      return;
+    }
+    final LocalDatabase localDatabase = widget.context.read<LocalDatabase>();
+    await BackgroundTaskManager(localDatabase).add(this);
+    if (!widget.mounted) {
+      return;
+    }
+    ScaffoldMessenger.of(widget.context).showSnackBar(
+      SnackBar(
+        content: Text(
+          getSnackBarMessage(AppLocalizations.of(widget.context)),
+        ),
+        duration: SnackBarDuration.medium,
+      ),
+    );
+  }
+
   @protected
   OpenFoodFactsLanguage getLanguage() => LanguageHelper.fromJson(languageCode);
 
@@ -84,37 +119,9 @@ abstract class AbstractBackgroundTask {
         await daoProduct.put(product);
         localDatabase.upToDate.setLatestDownloadedProduct(product);
         localDatabase.notifyListeners();
+        return;
       }
     }
-  }
-
-  /// Generates a unique id for the background task.
-  ///
-  /// This ensures that the background task is unique and also
-  /// ensures that in case of conflicts, the background task is replaced.
-  /// Example: 8901072002478_B_en_in_username
-  @protected
-  static String generateUniqueId(
-    String barcode,
-    String processIdentifier, {
-    final bool appendTimestamp = false,
-  }) {
-    final StringBuffer stringBuffer = StringBuffer();
-    stringBuffer
-      ..write(barcode)
-      ..write('_')
-      ..write(processIdentifier)
-      ..write('_')
-      ..write(ProductQuery.getLanguage().code)
-      ..write('_')
-      ..write(ProductQuery.getCountry()!.iso2Code)
-      ..write('_')
-      ..write(ProductQuery.getUser().userId);
-    if (appendTimestamp) {
-      stringBuffer
-        ..write('_')
-        ..write(DateTime.now().millisecondsSinceEpoch);
-    }
-    return stringBuffer.toString();
+    throw Exception('Could not download product!');
   }
 }

packages/smooth_app/lib/background/background_task_details.dart

@@ -5,10 +5,9 @@ import 'package:openfoodfacts/openfoodfacts.dart';
 import 'package:openfoodfacts/utils/CountryHelper.dart';
 import 'package:provider/provider.dart';
 import 'package:smooth_app/background/abstract_background_task.dart';
+import 'package:smooth_app/data_models/operation_type.dart';
 import 'package:smooth_app/database/local_database.dart';
-import 'package:smooth_app/generic_lib/duration_constants.dart';
 import 'package:smooth_app/query/product_query.dart';
-import 'package:task_manager/task_manager.dart';
 
 /// Background task that changes product details (data, but no image upload).
 class BackgroundTaskDetails extends AbstractBackgroundTask {
@@ -36,6 +35,8 @@ class BackgroundTaskDetails extends AbstractBackgroundTask {
   /// Task ID.
   static const String _PROCESS_NAME = 'PRODUCT_EDIT';
 
+  static const OperationType _operationType = OperationType.details;
+
   /// Serialized product.
   final String inputMap;
 
@@ -51,10 +52,9 @@ class BackgroundTaskDetails extends AbstractBackgroundTask {
       };
 
   /// Returns the deserialized background task if possible, or null.
-  static AbstractBackgroundTask? fromTask(final Task task) {
+  static BackgroundTaskDetails? fromJson(final Map<String, dynamic> map) {
     try {
-      final AbstractBackgroundTask result =
-          BackgroundTaskDetails._fromJson(task.data!);
+      final BackgroundTaskDetails result = BackgroundTaskDetails._fromJson(map);
       if (result.processName == _PROCESS_NAME) {
         return result;
       }
@@ -65,44 +65,34 @@ class BackgroundTaskDetails extends AbstractBackgroundTask {
   }
 
   @override
-  Future<TaskResult> execute(final LocalDatabase localDatabase) async {
-    try {
-      await super.execute(localDatabase);
-    } catch (e) {
-      //
-    } finally {
+  Future<void> preExecute(final LocalDatabase localDatabase) async =>
+      localDatabase.upToDate.addChange(uniqueId, _product);
+
+  @override
+  Future<void> postExecute(final LocalDatabase localDatabase) async =>
       localDatabase.upToDate.terminate(uniqueId);
-    }
-    return TaskResult.success;
-  }
 
   /// Adds the background task about changing a product.
   static Future<void> addTask(
     final Product minimalistProduct, {
     required final State<StatefulWidget> widget,
   }) async {
     final LocalDatabase localDatabase = widget.context.read<LocalDatabase>();
-    final String uniqueId =
-        await localDatabase.upToDate.addChange(minimalistProduct);
-    final BackgroundTaskDetails backgroundTask = _getNewTask(
+    final String uniqueId = await _operationType.getNewKey(
+      localDatabase,
+      minimalistProduct.barcode!,
+    );
+    final AbstractBackgroundTask task = _getNewTask(
       minimalistProduct,
       uniqueId,
     );
-    // TODO(monsieurtanuki): currently we run the task immediately and just once - if it fails we rollback the changes.
-    backgroundTask.execute(localDatabase); // async
-    if (!widget.mounted) {
-      return;
-    }
-    ScaffoldMessenger.of(widget.context).showSnackBar(
-      SnackBar(
-        content: Text(
-          AppLocalizations.of(widget.context).product_task_background_schedule,
-        ),
-        duration: SnackBarDuration.medium,
-      ),
-    );
+    await task.addToManager(widget);
   }
 
+  @override
+  String getSnackBarMessage(final AppLocalizations appLocalizations) =>
+      appLocalizations.product_task_background_schedule;
+
   /// Returns a new background task about changing a product.
   static BackgroundTaskDetails _getNewTask(
     final Product minimalistProduct,
@@ -118,16 +108,16 @@ class BackgroundTaskDetails extends AbstractBackgroundTask {
         country: ProductQuery.getCountry()!.iso2Code,
       );
 
+  Product get _product =>
+      Product.fromJson(json.decode(inputMap) as Map<String, dynamic>);
+
   /// Uploads the product changes.
   @override
   Future<void> upload() async {
-    final Map<String, dynamic> productMap =
-        json.decode(inputMap) as Map<String, dynamic>;
-
     // TODO(AshAman999): check returned Status
     await OpenFoodAPIClient.saveProduct(
       getUser(),
-      Product.fromJson(productMap),
+      _product,
       language: getLanguage(),
       country: getCountry(),
     );

packages/smooth_app/lib/background/background_task_image.dart

@@ -7,11 +7,10 @@ import 'package:openfoodfacts/openfoodfacts.dart';
 import 'package:openfoodfacts/utils/CountryHelper.dart';
 import 'package:provider/provider.dart';
 import 'package:smooth_app/background/abstract_background_task.dart';
+import 'package:smooth_app/data_models/operation_type.dart';
 import 'package:smooth_app/database/local_database.dart';
 import 'package:smooth_app/database/transient_file.dart';
-import 'package:smooth_app/generic_lib/duration_constants.dart';
 import 'package:smooth_app/query/product_query.dart';
-import 'package:task_manager/task_manager.dart';
 
 /// Background task about product image upload.
 class BackgroundTaskImage extends AbstractBackgroundTask {
@@ -41,6 +40,8 @@ class BackgroundTaskImage extends AbstractBackgroundTask {
   /// Task ID.
   static const String _PROCESS_NAME = 'IMAGE_UPLOAD';
 
+  static const OperationType _operationType = OperationType.image;
+
   final String imageField;
   final String imagePath;
 
@@ -57,10 +58,9 @@ class BackgroundTaskImage extends AbstractBackgroundTask {
       };
 
   /// Returns the deserialized background task if possible, or null.
-  static AbstractBackgroundTask? fromTask(final Task task) {
+  static AbstractBackgroundTask? fromJson(final Map<String, dynamic> map) {
     try {
-      final AbstractBackgroundTask result =
-          BackgroundTaskImage._fromJson(task.data!);
+      final AbstractBackgroundTask result = BackgroundTaskImage._fromJson(map);
       if (result.processName == _PROCESS_NAME) {
         return result;
       }
@@ -78,55 +78,57 @@ class BackgroundTaskImage extends AbstractBackgroundTask {
     required final State<StatefulWidget> widget,
   }) async {
     final LocalDatabase localDatabase = widget.context.read<LocalDatabase>();
-    // For "OTHER" images we randomize the id with timestamp
-    // so that it runs separately.
-    final String uniqueId = AbstractBackgroundTask.generateUniqueId(
+    final String uniqueId = await _operationType.getNewKey(
+      localDatabase,
       barcode,
-      imageField.value,
-      appendTimestamp: imageField == ImageField.OTHER,
-    );
-    TransientFile.putImage(imageField, barcode, localDatabase, imageFile);
-    final BackgroundTaskImage backgroundTask = BackgroundTaskImage._(
-      uniqueId: uniqueId,
-      barcode: barcode,
-      processName: _PROCESS_NAME,
-      imageField: imageField.value,
-      imagePath: imageFile.path,
-      languageCode: ProductQuery.getLanguage().code,
-      user: jsonEncode(ProductQuery.getUser().toJson()),
-      country: ProductQuery.getCountry()!.iso2Code,
     );
-    // TODO(monsieurtanuki): currently we run the task immediately and just once - if it fails we rollback the changes.
-    backgroundTask.execute(localDatabase); // async
-    if (!widget.mounted) {
-      return;
-    }
-    ScaffoldMessenger.of(widget.context).showSnackBar(
-      SnackBar(
-        content: Text(
-          AppLocalizations.of(widget.context).image_upload_queued,
-        ),
-        duration: SnackBarDuration.medium,
-      ),
+    final AbstractBackgroundTask task = _getNewTask(
+      barcode,
+      imageField,
+      imageFile,
+      uniqueId,
     );
+    await task.addToManager(widget);
   }
 
   @override
-  Future<TaskResult> execute(final LocalDatabase localDatabase) async {
-    try {
-      await super.execute(localDatabase);
-    } catch (e) {
-      //
-    } finally {
+  String getSnackBarMessage(final AppLocalizations appLocalizations) =>
+      appLocalizations.image_upload_queued;
+
+  /// Returns a new background task about changing a product.
+  static BackgroundTaskImage _getNewTask(
+    final String barcode,
+    final ImageField imageField,
+    final File imageFile,
+    final String uniqueId,
+  ) =>
+      BackgroundTaskImage._(
+        uniqueId: uniqueId,
+        barcode: barcode,
+        processName: _PROCESS_NAME,
+        imageField: imageField.value,
+        imagePath: imageFile.path,
+        languageCode: ProductQuery.getLanguage().code,
+        user: jsonEncode(ProductQuery.getUser().toJson()),
+        country: ProductQuery.getCountry()!.iso2Code,
+      );
+
+  @override
+  Future<void> preExecute(final LocalDatabase localDatabase) async =>
+      TransientFile.putImage(
+        ImageFieldExtension.getType(imageField),
+        barcode,
+        localDatabase,
+        File(imagePath),
+      );
+
+  @override
+  Future<void> postExecute(final LocalDatabase localDatabase) async =>
       TransientFile.removeImage(
         ImageFieldExtension.getType(imageField),
         barcode,
         localDatabase,
       );
-      localDatabase.notifyListeners();
-    }
-    return TaskResult.success;
-  }
 
   /// Uploads the product image.
   @override