fix: 4301 - new "up-to-date" provider for product list

New files:
* `up_to_date_interest.dart`: Management of the interest for a key.
* `up_to_date_product_list_mixin.dart`: Provides the most up-to-date local product list data for a StatefulWidget.
* `up_to_date_product_list_provider.dart`: Provider that reflects the latest barcode lists on ProductLists.

Impacted files:
* `dao_product_list.dart`: made public method `getKey`; refreshes the provider
* `local_database.dart`: added a new `UpToDateProductListProvider`
* `product_list_page.dart`: now extends `UpToDateProductListMixin
* `up_to_date_product_provider.dart`: refactored using a `UpToDateInterest`
* `user_preferences_account.dart`: removed redundant access to product list page

packages/smooth_app/lib/data_models/up_to_date_interest.dart

@@ -0,0 +1,28 @@
+/// Management of the interest for a key.
+class UpToDateInterest {
+  /// Number of time an interest was shown for a given key.
+  final Map<String, int> _interestCounts = <String, int>{};
+
+  /// Shows an interest for a key.
+  void add(final String key) {
+    final int result = (_interestCounts[key] ?? 0) + 1;
+    _interestCounts[key] = result;
+  }
+
+  /// Loses an interest for a key.
+  ///
+  /// Returns true if completely lost interest.
+  bool remove(final String key) {
+    final int result = (_interestCounts[key] ?? 0) - 1;
+    if (result <= 0) {
+      _interestCounts.remove(key);
+      return true;
+    }
+    _interestCounts[key] = result;
+    return false;
+  }
+
+  bool get isEmpty => _interestCounts.isEmpty;
+
+  bool containsKey(final String key) => _interestCounts.containsKey(key);
+}

packages/smooth_app/lib/data_models/up_to_date_product_list_mixin.dart

@@ -0,0 +1,55 @@
+import 'package:flutter/material.dart';
+import 'package:smooth_app/data_models/product_list.dart';
+import 'package:smooth_app/database/dao_product_list.dart';
+import 'package:smooth_app/database/local_database.dart';
+
+/// Provides the most up-to-date local product list data for a StatefulWidget.
+@optionalTypeArgs
+mixin UpToDateProductListMixin<T extends StatefulWidget> on State<T> {
+  /// To be used in the `initState` method.
+  void initUpToDate(
+    final ProductList initialProductList,
+    final LocalDatabase localDatabase,
+  ) {
+    _productList = initialProductList;
+    _localDatabase = localDatabase;
+    _localDatabase.upToDateProductList.showInterest(initialProductList);
+    _localDatabase.upToDateProductList.setLocalUpToDate(
+      DaoProductList.getKey(_productList),
+      _productList.barcodes,
+    );
+  }
+
+  late final LocalDatabase _localDatabase;
+
+  late ProductList _productList;
+
+  ProductList get productList => _productList;
+
+  set productList(final ProductList productList) {
+    final ProductList previous = _productList;
+    _productList = productList;
+    _localDatabase.upToDateProductList.showInterest(_productList);
+    _localDatabase.upToDateProductList.loseInterest(previous);
+    _localDatabase.upToDateProductList.setLocalUpToDate(
+      DaoProductList.getKey(_productList),
+      _productList.barcodes,
+    );
+  }
+
+  @override
+  void dispose() {
+    _localDatabase.upToDateProductList.loseInterest(_productList);
+    super.dispose();
+  }
+
+  /// Refreshes [upToDateProduct] with the latest available local data.
+  ///
+  /// To be used in the `build` method, after a call to
+  /// `context.watch<LocalDatabase>()`.
+  void refreshUpToDate() {
+    final List<String> barcodes =
+        _localDatabase.upToDateProductList.getLocalUpToDate(_productList);
+    _productList.set(barcodes);
+  }
+}

packages/smooth_app/lib/data_models/up_to_date_product_list_provider.dart

@@ -0,0 +1,54 @@
+import 'package:smooth_app/data_models/product_list.dart';
+import 'package:smooth_app/data_models/up_to_date_interest.dart';
+import 'package:smooth_app/database/dao_product_list.dart';
+import 'package:smooth_app/database/local_database.dart';
+
+/// Provider that reflects the latest barcode lists on [ProductList]s.
+class UpToDateProductListProvider {
+  UpToDateProductListProvider(this.localDatabase);
+
+  final LocalDatabase localDatabase;
+
+  /// Product lists currently displayed in the app.
+  ///
+  /// We need to know which product lists are "interesting" because we need to
+  /// cache barcode lists in memory for instant access. And we should cache only
+  /// them, because we cannot cache all product lists in memory.
+  final UpToDateInterest _interest = UpToDateInterest();
+
+  final Map<String, List<String>> _barcodes = <String, List<String>>{};
+
+  /// Shows an interest for a product list.
+  ///
+  /// Typically, to be used by a widget in `initState`.
+  void showInterest(final ProductList productList) =>
+      _interest.add(_getKey(productList));
+
+  /// Loses interest for a product list.
+  ///
+  /// Typically, to be used by a widget in `dispose`.
+  void loseInterest(final ProductList productList) {
+    final String key = _getKey(productList);
+    if (!_interest.remove(key)) {
+      return;
+    }
+    _barcodes.remove(key);
+  }
+
+  String _getKey(final ProductList productList) =>
+      DaoProductList.getKey(productList);
+
+  void setLocalUpToDate(
+    final String key,
+    final List<String> barcodes,
+  ) {
+    if (!_interest.containsKey(key)) {
+      return;
+    }
+    _barcodes[key] = List<String>.from(barcodes); // need to copy
+  }
+
+  /// Returns the latest barcodes.
+  List<String> getLocalUpToDate(final ProductList productList) =>
+      _barcodes[_getKey(productList)] ?? <String>[];
+}

packages/smooth_app/lib/data_models/up_to_date_product_provider.dart

@@ -2,6 +2,7 @@ import 'dart:convert';
 
 import 'package:openfoodfacts/openfoodfacts.dart';
 import 'package:smooth_app/data_models/up_to_date_changes.dart';
+import 'package:smooth_app/data_models/up_to_date_interest.dart';
 import 'package:smooth_app/database/dao_transient_operation.dart';
 import 'package:smooth_app/database/local_database.dart';
 
@@ -26,7 +27,7 @@ class UpToDateProductProvider {
   /// We need to know which barcodes are "interesting" because we need to cache
   /// products in memory for instant access. And we should cache only them,
   /// because we cannot cache all products in memory.
-  final Map<String, int> _interestingBarcodes = <String, int>{};
+  final UpToDateInterest _interest = UpToDateInterest();
 
   /// Returns true if at least one barcode was refreshed after the [timestamp].
   bool needsRefresh(final int? latestTimestamp, final List<String> barcodes) {
@@ -46,23 +47,18 @@ class UpToDateProductProvider {
   /// Shows an interest for a barcode.
   ///
   /// Typically, to be used by a widget in `initState`.
-  void showInterest(final String barcode) {
-    final int result = (_interestingBarcodes[barcode] ?? 0) + 1;
-    _interestingBarcodes[barcode] = result;
-  }
+  void showInterest(final String barcode) => _interest.add(barcode);
 
   /// Loses interest for a barcode.
   ///
   /// Typically, to be used by a widget in `dispose`.
   void loseInterest(final String barcode) {
-    final int result = (_interestingBarcodes[barcode] ?? 0) - 1;
-    if (result <= 0) {
-      _interestingBarcodes.remove(barcode);
-      _latestDownloadedProducts.remove(barcode);
-      _timestamps.remove(barcode);
-    } else {
-      _interestingBarcodes[barcode] = result;
+    final bool lostInterest = _interest.remove(barcode);
+    if (!lostInterest) {
+      return;
     }
+    _latestDownloadedProducts.remove(barcode);
+    _timestamps.remove(barcode);
   }
 
   /// Typical use-case: a product page is refreshed through a pull-gesture.
@@ -82,12 +78,12 @@ class UpToDateProductProvider {
     final Iterable<Product> products, {
     final bool notify = true,
   }) {
-    if (_interestingBarcodes.isEmpty) {
+    if (_interest.isEmpty) {
       return;
     }
     bool atLeastOne = false;
     for (final Product product in products) {
-      if (_interestingBarcodes.containsKey(product.barcode)) {
+      if (_interest.containsKey(product.barcode!)) {
         atLeastOne = true;
         setLatestDownloadedProduct(product, notify: false);
       }

packages/smooth_app/lib/database/dao_product_list.dart

@@ -84,8 +84,16 @@ class DaoProductList extends AbstractDao {
 
   LazyBox<_BarcodeList> _getBox() => Hive.lazyBox<_BarcodeList>(_hiveBoxName);
 
-  Future<_BarcodeList?> _get(final ProductList productList) =>
-      _getBox().get(_getKey(productList));
+  Future<_BarcodeList?> _get(final ProductList productList) async {
+    final _BarcodeList? result = await _getBox().get(getKey(productList));
+    if (result != null) {
+      localDatabase.upToDateProductList.setLocalUpToDate(
+        getKey(productList),
+        result.barcodes,
+      );
+    }
+    return result;
+  }
 
   Future<int?> getTimestamp(final ProductList productList) async =>
       (await _get(productList))?.timestamp;
@@ -95,7 +103,7 @@ class DaoProductList extends AbstractDao {
   // Encoding the parameter part in base64 makes us safe regarding ASCII.
   // As it's a list of keywords, there's a fairly high probability
   // that we'll be under the 255 character length.
-  static String _getKey(final ProductList productList) =>
+  static String getKey(final ProductList productList) =>
       '${productList.listType.key}'
       '$_keySeparator'
       '${base64.encode(utf8.encode(productList.getParametersKey()))}';
@@ -126,15 +134,21 @@ class DaoProductList extends AbstractDao {
     throw Exception('Unknown product list type: "$value" from "$key"');
   }
 
-  Future<void> _put(final String key, final _BarcodeList barcodeList) async =>
-      _getBox().put(key, barcodeList);
+  Future<void> _put(final String key, final _BarcodeList barcodeList) async {
+    await _getBox().put(key, barcodeList);
+    localDatabase.upToDateProductList.setLocalUpToDate(
+      key,
+      barcodeList.barcodes,
+    );
+  }
 
   Future<void> put(final ProductList productList) async =>
-      _put(_getKey(productList), _BarcodeList.fromProductList(productList));
+      _put(getKey(productList), _BarcodeList.fromProductList(productList));
 
   Future<bool> delete(final ProductList productList) async {
     final LazyBox<_BarcodeList> box = _getBox();
-    final String key = _getKey(productList);
+    final String key = getKey(productList);
+    localDatabase.upToDateProductList.setLocalUpToDate(key, <String>[]);
     if (!box.containsKey(key)) {
       return false;
     }
@@ -182,12 +196,12 @@ class DaoProductList extends AbstractDao {
     barcodes.remove(barcode); // removes a potential duplicate
     barcodes.add(barcode);
     final _BarcodeList newList = _BarcodeList.now(barcodes);
-    await _put(_getKey(productList), newList);
+    await _put(getKey(productList), newList);
   }
 
   Future<void> clear(final ProductList productList) async {
     final _BarcodeList newList = _BarcodeList.now(<String>[]);
-    await _put(_getKey(productList), newList);
+    await _put(getKey(productList), newList);
   }
 
   /// Adds or removes a barcode within a product list (depending on [include])
@@ -217,7 +231,7 @@ class DaoProductList extends AbstractDao {
       barcodes.add(barcode);
     }
     final _BarcodeList newList = _BarcodeList.now(barcodes);
-    await _put(_getKey(productList), newList);
+    await _put(getKey(productList), newList);
     return true;
   }
 
@@ -249,7 +263,7 @@ class DaoProductList extends AbstractDao {
     }
 
     final _BarcodeList newList = _BarcodeList.now(allBarcodes);
-    await _put(_getKey(productList), newList);
+    await _put(getKey(productList), newList);
   }
 
   Future<ProductList> rename(
@@ -259,7 +273,7 @@ class DaoProductList extends AbstractDao {
     final ProductList newList = ProductList.user(newName);
     final _BarcodeList list =
         await _get(initialList) ?? _BarcodeList.now(<String>[]);
-    await _put(_getKey(newList), list);
+    await _put(getKey(newList), list);
     await delete(initialList);
     await get(newList);
     return newList;

packages/smooth_app/lib/database/local_database.dart

@@ -6,6 +6,7 @@ import 'package:hive_flutter/hive_flutter.dart';
 import 'package:path/path.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:smooth_app/background/background_task_manager.dart';
+import 'package:smooth_app/data_models/up_to_date_product_list_provider.dart';
 import 'package:smooth_app/data_models/up_to_date_product_provider.dart';
 import 'package:smooth_app/database/abstract_dao.dart';
 import 'package:smooth_app/database/dao_hive_product.dart';
@@ -25,14 +26,18 @@ import 'package:sqflite/sqflite.dart';
 class LocalDatabase extends ChangeNotifier {
   LocalDatabase._(final Database database) : _database = database {
     _upToDateProductProvider = UpToDateProductProvider(this);
+    _upToDateProductListProvider = UpToDateProductListProvider(this);
   }
 
   final Database _database;
   late final UpToDateProductProvider _upToDateProductProvider;
+  late final UpToDateProductListProvider _upToDateProductListProvider;
 
   Database get database => _database;
 
   UpToDateProductProvider get upToDate => _upToDateProductProvider;
+  UpToDateProductListProvider get upToDateProductList =>
+      _upToDateProductListProvider;
 
   @override
   void notifyListeners() {