refactor: background tasks with classes (openfoodfacts#2994)

New files:
* `abstract_background_task.dart`: Abstract background task.
* `background_task_details.dart`: Background task that changes product details (data, but no image upload).
* `background_task_image.dart`: Background task about product image upload.

Impacted files:
* `add_basic_details_page.dart`: refactored the call to background task; minor refactoring
* `background_task_helper.dart`: moved most of the code to new classes `AbstractBackgroundTask` and offsprings.
* `edit_ingredients_page.dart`: refactored the call to background task
* `nutrition_page_loaded.dart`: refactored the call to background task
* `picture_capture_helper.dart`: refactored the call to background task
* `simple_input_page.dart`: refactored the call to background task
* `simple_input_page_helpers.dart`: added and implemented method `getTask`

packages/smooth_app/lib/background/abstract_background_task.dart

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+import 'package:flutter/material.dart';
+import 'package:openfoodfacts/openfoodfacts.dart';
+import 'package:openfoodfacts/utils/CountryHelper.dart';
+import 'package:smooth_app/background/background_task_details.dart';
+import 'package:smooth_app/background/background_task_image.dart';
+import 'package:smooth_app/database/local_database.dart';
+import 'package:smooth_app/query/product_query.dart';
+import 'package:task_manager/task_manager.dart';
+
+/// Abstract background task.
+abstract class AbstractBackgroundTask {
+  const AbstractBackgroundTask({
+    required this.processName,
+    required this.uniqueId,
+    required this.barcode,
+    required this.languageCode,
+    required this.user,
+    required this.country,
+  });
+
+  /// Typically, similar to the name of the class that extends this one.
+  ///
+  /// To be used when deserializing, in order to check who is who.
+  final String processName;
+
+  /// Unique task identifier, needed e.g. for task overwriting.
+  final String uniqueId;
+
+  final String barcode;
+  final String languageCode;
+  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);
+
+  /// Response code sent by the server in case of a success.
+  @protected
+  static const int SUCCESS_CODE = 1;
+
+  /// Executes the background task.
+  Future<TaskResult> execute(final LocalDatabase localDatabase);
+
+  @protected
+  OpenFoodFactsLanguage getLanguage() => LanguageHelper.fromJson(languageCode);
+
+  @protected
+  OpenFoodFactsCountry? getCountry() => CountryHelper.fromJson(country);
+
+  /// 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();
+  }
+}

packages/smooth_app/lib/background/background_task_details.dart

@@ -0,0 +1,171 @@
+import 'dart:convert';
+
+import 'package:openfoodfacts/openfoodfacts.dart';
+import 'package:openfoodfacts/utils/CountryHelper.dart';
+import 'package:smooth_app/background/abstract_background_task.dart';
+import 'package:smooth_app/database/dao_product.dart';
+import 'package:smooth_app/database/local_database.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 {
+  const BackgroundTaskDetails._({
+    required super.processName,
+    required super.uniqueId,
+    required super.barcode,
+    required super.languageCode,
+    required super.user,
+    required super.country,
+    required this.inputMap,
+  });
+
+  BackgroundTaskDetails._fromJson(Map<String, dynamic> json)
+      : this._(
+          processName: json['processName'] as String,
+          uniqueId: json['uniqueId'] as String,
+          barcode: json['barcode'] as String,
+          languageCode: json['languageCode'] as String,
+          user: json['user'] as String,
+          country: json['country'] as String,
+          inputMap: json['inputMap'] as String,
+        );
+
+  /// Task ID.
+  static const String _PROCESS_NAME = 'PRODUCT_EDIT';
+
+  /// Serialized product.
+  final String inputMap;
+
+  @override
+  Map<String, dynamic> toJson() => <String, dynamic>{
+        'processName': processName,
+        'uniqueId': uniqueId,
+        'barcode': barcode,
+        'languageCode': languageCode,
+        'user': user,
+        'country': country,
+        'inputMap': inputMap,
+      };
+
+  /// Returns the deserialized background task if possible, or null.
+  static AbstractBackgroundTask? fromTask(final Task task) {
+    try {
+      final AbstractBackgroundTask result =
+          BackgroundTaskDetails._fromJson(task.data!);
+      if (result.processName == _PROCESS_NAME) {
+        return result;
+      }
+    } catch (e) {
+      //
+    }
+    return null;
+  }
+
+  /// Adds the background task about changing a product.
+  ///
+  /// Either [productEditTask] or [productEditTasks] must be populated;
+  /// we need that for classification purpose (and unique id computation).
+  static Future<void> addTask(
+    final Product minimalistProduct, {
+    final List<ProductEditTask>? productEditTasks,
+    final ProductEditTask? productEditTask,
+  }) async {
+    final String code;
+    if (productEditTask != null) {
+      if (productEditTasks != null) {
+        throw Exception();
+      }
+      code = productEditTask.code;
+    } else {
+      if (productEditTasks == null || productEditTasks.isEmpty) {
+        throw Exception();
+      }
+      final StringBuffer buffer = StringBuffer();
+      for (final ProductEditTask task in productEditTasks) {
+        buffer.write(task.code);
+      }
+      code = buffer.toString();
+    }
+    final String uniqueId = AbstractBackgroundTask.generateUniqueId(
+      minimalistProduct.barcode!,
+      code,
+    );
+    final BackgroundTaskDetails backgroundTask = BackgroundTaskDetails._(
+      uniqueId: uniqueId,
+      processName: _PROCESS_NAME,
+      barcode: minimalistProduct.barcode!,
+      languageCode: ProductQuery.getLanguage().code,
+      inputMap: jsonEncode(minimalistProduct.toJson()),
+      user: jsonEncode(ProductQuery.getUser().toJson()),
+      country: ProductQuery.getCountry()!.iso2Code,
+    );
+    await TaskManager().addTask(
+      Task(
+        data: backgroundTask.toJson(),
+        uniqueId: uniqueId,
+      ),
+    );
+  }
+
+  /// Uploads the product changes, downloads the whole product, updates locally.
+  @override
+  Future<TaskResult> execute(final LocalDatabase localDatabase) async {
+    final Map<String, dynamic> productMap =
+        json.decode(inputMap) as Map<String, dynamic>;
+    final User user =
+        User.fromJson(jsonDecode(this.user) as Map<String, dynamic>);
+
+    await OpenFoodAPIClient.saveProduct(
+      user,
+      Product.fromJson(productMap),
+      language: getLanguage(),
+      country: getCountry(),
+    );
+
+    final DaoProduct daoProduct = DaoProduct(localDatabase);
+    final ProductQueryConfiguration configuration = ProductQueryConfiguration(
+      barcode,
+      fields: ProductQuery.fields,
+      language: getLanguage(),
+      country: getCountry(),
+    );
+
+    final ProductResult queryResult =
+        await OpenFoodAPIClient.getProduct(configuration);
+
+    if (queryResult.status == AbstractBackgroundTask.SUCCESS_CODE) {
+      final Product? product = queryResult.product;
+      if (product != null) {
+        await daoProduct.put(product);
+        localDatabase.notifyListeners();
+      }
+    }
+
+    // Returns true to let platform know that the task is completed
+    return TaskResult.success;
+  }
+}
+
+/// Product edit single tasks.
+///
+/// Used for classification (and unique id computation).
+enum ProductEditTask {
+  nutrition('N'),
+  packaging('P'),
+  ingredient('I'),
+  basic('B'),
+  store('S'),
+  origin('O'),
+  emb('E'),
+  label('L'),
+  category('K'),
+  country('C');
+
+  const ProductEditTask(this.code);
+
+  /// Code used to distinguish the tasks.
+  ///
+  /// Of course there shouldn't be duplicates.
+  final String code;
+}

packages/smooth_app/lib/background/background_task_image.dart

@@ -0,0 +1,137 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:openfoodfacts/openfoodfacts.dart';
+import 'package:openfoodfacts/utils/CountryHelper.dart';
+import 'package:smooth_app/background/abstract_background_task.dart';
+import 'package:smooth_app/database/dao_product.dart';
+import 'package:smooth_app/database/local_database.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 {
+  const BackgroundTaskImage._({
+    required super.processName,
+    required super.uniqueId,
+    required super.barcode,
+    required super.languageCode,
+    required super.user,
+    required super.country,
+    required this.imageField,
+    required this.imagePath,
+  });
+
+  BackgroundTaskImage._fromJson(Map<String, dynamic> json)
+      : this._(
+          processName: json['processName'] as String,
+          uniqueId: json['uniqueId'] as String,
+          barcode: json['barcode'] as String,
+          languageCode: json['languageCode'] as String,
+          user: json['user'] as String,
+          country: json['country'] as String,
+          imageField: json['imageField'] as String,
+          imagePath: json['imagePath'] as String,
+        );
+
+  /// Task ID.
+  static const String _PROCESS_NAME = 'IMAGE_UPLOAD';
+
+  final String imageField;
+  final String imagePath;
+
+  @override
+  Map<String, dynamic> toJson() => <String, dynamic>{
+        'processName': processName,
+        'uniqueId': uniqueId,
+        'barcode': barcode,
+        'languageCode': languageCode,
+        'user': user,
+        'country': country,
+        'imageField': imageField,
+        'imagePath': imagePath,
+      };
+
+  /// Returns the deserialized background task if possible, or null.
+  static AbstractBackgroundTask? fromTask(final Task task) {
+    try {
+      final AbstractBackgroundTask result =
+          BackgroundTaskImage._fromJson(task.data!);
+      if (result.processName == _PROCESS_NAME) {
+        return result;
+      }
+    } catch (e) {
+      //
+    }
+    return null;
+  }
+
+  /// Adds the background task about uploading a product image.
+  static Future<void> addTask(
+    final String barcode, {
+    required final ImageField imageField,
+    required final File imageFile,
+  }) async {
+    // For "OTHER" images we randomize the id with timestamp
+    // so that it runs separately.
+    final String uniqueId = AbstractBackgroundTask.generateUniqueId(
+      barcode,
+      imageField.value,
+      appendTimestamp: imageField == ImageField.OTHER,
+    );
+    final BackgroundTaskImage backgroundImageInputData = 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,
+    );
+    await TaskManager().addTask(
+      Task(
+        data: backgroundImageInputData.toJson(),
+        uniqueId: uniqueId,
+      ),
+    );
+  }
+
+  /// Uploads the product image, downloads the whole product, updates locally.
+  @override
+  Future<TaskResult> execute(final LocalDatabase localDatabase) async {
+    final User user =
+        User.fromJson(jsonDecode(this.user) as Map<String, dynamic>);
+
+    final SendImage image = SendImage(
+      lang: getLanguage(),
+      barcode: barcode,
+      imageField: ImageFieldExtension.getType(imageField),
+      imageUri: Uri.parse(imagePath),
+    );
+
+    await OpenFoodAPIClient.addProductImage(user, image);
+
+    // Go to the file system and delete the file that was uploaded
+    File(imagePath).deleteSync();
+    final DaoProduct daoProduct = DaoProduct(localDatabase);
+    final ProductQueryConfiguration configuration = ProductQueryConfiguration(
+      barcode,
+      fields: ProductQuery.fields,
+      language: getLanguage(),
+      country: getCountry(),
+    );
+
+    final ProductResult queryResult =
+        await OpenFoodAPIClient.getProduct(configuration);
+    if (queryResult.status == AbstractBackgroundTask.SUCCESS_CODE) {
+      final Product? product = queryResult.product;
+      if (product != null) {
+        await daoProduct.put(product);
+        localDatabase.notifyListeners();
+      }
+    }
+
+    return TaskResult.success;
+  }
+}