refactor: #954 - split the nutrition page code for better focus (#1142)

New file:
* `nutrition_container.dart`: Nutrition data, for nutrient order and conversions.
* `tmp_to_off_nutriments.dart`: Nutrient ids supported by `Nutriments`, to be moved to off-dart

Impacted file:
* `nutrition_page_loaded.dart`: moved the nutrient and conversion code to new class `NutritionContainer`

packages/smooth_app/lib/pages/product/nutrition_container.dart

@@ -0,0 +1,318 @@
+import 'package:openfoodfacts/interface/JsonObject.dart';
+import 'package:openfoodfacts/model/Nutriments.dart';
+import 'package:openfoodfacts/model/OrderedNutrient.dart';
+import 'package:openfoodfacts/model/OrderedNutrients.dart';
+import 'package:openfoodfacts/model/Product.dart';
+import 'package:openfoodfacts/utils/UnitHelper.dart';
+import 'package:smooth_app/pages/product/tmp_to_off_nutriments.dart';
+
+/// Nutrition data, for nutrient order and conversions.
+class NutritionContainer {
+  NutritionContainer({
+    required final OrderedNutrients orderedNutrients,
+    required final Product product,
+  }) {
+    _loadNutrients(orderedNutrients.nutrients);
+    final Map<String, dynamic>? json = product.nutriments?.toJson();
+    if (json != null) {
+      _loadUnits(json);
+      _loadValues(json);
+    }
+    _servingSize = product.servingSize;
+    _barcode = product.barcode!;
+  }
+
+  static const String _energyId = 'energy';
+
+  /// special case: present id [OrderedNutrient] but not in [Nutriments] map.
+  static const String _energyKJId = 'energy-kj';
+  static const String _energyKCalId = 'energy-kcal';
+  static const String fakeNutrientIdServingSize = '_servingSize';
+
+  static const Map<Unit, Unit> _nextWeightUnits = <Unit, Unit>{
+    Unit.G: Unit.MILLI_G,
+    Unit.MILLI_G: Unit.MICRO_G,
+    Unit.MICRO_G: Unit.G,
+  };
+
+  // For the moment we only care about "weight or not weight?"
+  // Could be refined with values taken from https://static.openfoodfacts.org/data/taxonomies/nutrients.json
+  // Fun fact: most of them are not supported (yet) by [Nutriments].
+  static const Map<String, Unit> _defaultNotWeightUnits = <String, Unit>{
+    _energyId: Unit.KJ,
+    _energyKCalId: Unit.KCAL,
+    'alcohol': Unit.PERCENT,
+    'cocoa': Unit.PERCENT,
+    'collagen-meat-protein-ratio': Unit.PERCENT,
+    'fruits-vegetables-nuts': Unit.PERCENT,
+    'fruits-vegetables-nuts-dried': Unit.PERCENT,
+    'fruits-vegetables-nuts-estimate': Unit.PERCENT,
+  };
+
+  /// All the nutrients (country-related).
+  final List<OrderedNutrient> _nutrients = <OrderedNutrient>[];
+
+  /// Nutrient values for 100g and serving.
+  final Map<String, double> _values = <String, double>{};
+
+  /// Nutrient units.
+  final Map<String, Unit> _units = <String, Unit>{};
+
+  /// Nutrient Ids added by the end-user
+  final Set<String> _added = <String>{};
+
+  String? _servingSize;
+
+  String? get servingSize => _servingSize;
+
+  late final String _barcode;
+
+  /// Returns the not interesting nutrients, for a "Please add me!" list.
+  Iterable<OrderedNutrient> getLeftoverNutrients() => _nutrients.where(
+        (final OrderedNutrient element) => _isNotRelevant(element),
+      );
+
+  /// Returns the interesting nutrients that need to be displayed.
+  Iterable<OrderedNutrient> getDisplayableNutrients() => _nutrients.where(
+        (final OrderedNutrient element) => !_isNotRelevant(element),
+      );
+
+  /// Returns true if the [OrderedNutrient] is not relevant.
+  bool _isNotRelevant(final OrderedNutrient orderedNutrient) {
+    final String nutrientId = orderedNutrient.id;
+    final double? value100g = getValue(getValueKey(nutrientId, false));
+    final double? valueServing = getValue(getValueKey(nutrientId, true));
+    return value100g == null &&
+        valueServing == null &&
+        (!orderedNutrient.important) &&
+        (!_added.contains(nutrientId));
+  }
+
+  /// Returns a [Product] with only nutrients data.
+  Product getProduct() => Product(
+        barcode: _barcode,
+        nutriments: _getNutriments(),
+        servingSize: _servingSize,
+      );
+
+  /// Converts all the data to a [Nutriments].
+  Nutriments _getNutriments() {
+    /// Converts a (weight) value to grams (before sending a value to the BE)
+    double? _convertWeightToG(final double? value, final Unit unit) {
+      if (value == null) {
+        return null;
+      }
+      if (unit == Unit.MILLI_G) {
+        return value / 1E3;
+      }
+      if (unit == Unit.MICRO_G) {
+        return value / 1E6;
+      }
+      return value;
+    }
+
+    final Map<String, dynamic> map = <String, dynamic>{};
+    for (final OrderedNutrient orderedNutrient in getDisplayableNutrients()) {
+      final String nutrientId = orderedNutrient.id;
+      final String key100g = getValueKey(nutrientId, false);
+      final String keyServing = getValueKey(nutrientId, true);
+      final double? value100g = getValue(key100g);
+      final double? valueServing = getValue(keyServing);
+      if (value100g == null && valueServing == null) {
+        continue;
+      }
+      final Unit unit = getUnit(nutrientId);
+      if (value100g != null) {
+        map[key100g] = _convertWeightToG(value100g, unit);
+      }
+      if (valueServing != null) {
+        //map[keyServing] = _convertWeightToG(valueServing, unit);
+      }
+      map[_getNutrimentsUnitKey(nutrientId)] = UnitHelper.unitToString(unit);
+    }
+
+    return Nutriments.fromJson(map);
+  }
+
+  /// Returns the stored product nutrient's value.
+  double? getValue(final String valueKey) => _values[valueKey];
+
+  /// Stores the text from the end-user input.
+  void setControllerText(final String controllerKey, final String text) {
+    if (controllerKey == fakeNutrientIdServingSize) {
+      _servingSize = text.trim().isEmpty ? null : text;
+      return;
+    }
+
+    double? value;
+    if (text.isNotEmpty) {
+      try {
+        value = double.parse(text.replaceAll(',', '.'));
+      } catch (e) {
+        //
+      }
+    }
+    if (value == null) {
+      _values.remove(controllerKey);
+    } else {
+      _values[controllerKey] = value;
+    }
+  }
+
+  /// Typical use-case: should we make the [Unit] button clickable?
+  static bool isEditableWeight(final OrderedNutrient orderedNutrient) =>
+      _getDefaultUnit(orderedNutrient.id) == null;
+
+  /// Typical use-case: [Unit] button action.
+  void setNextWeightUnit(final OrderedNutrient orderedNutrient) {
+    final Unit unit = getUnit(orderedNutrient.id);
+    _setUnit(orderedNutrient.id, _nextWeightUnits[unit] ?? unit);
+  }
+
+  /// Returns the nutrient [Unit], after possible alterations.
+  Unit getUnit(String nutrientId) {
+    nutrientId = _fixNutrientId(nutrientId);
+    switch (nutrientId) {
+      case _energyId:
+      case _energyKJId:
+        return Unit.KJ;
+      case _energyKCalId:
+        return Unit.KCAL;
+      default:
+        return _units[nutrientId] ?? _getDefaultUnit(nutrientId) ?? Unit.G;
+    }
+  }
+
+  /// Stores the nutrient [Unit].
+  void _setUnit(final String nutrientId, final Unit unit) =>
+      _units[_fixNutrientId(nutrientId)] = unit;
+
+  static Unit? _getDefaultUnit(final String nutrientId) =>
+      _defaultNotWeightUnits[_fixNutrientId(nutrientId)];
+
+  /// To be used when an [OrderedNutrient] is added to the input list
+  void add(final OrderedNutrient orderedNutrient) =>
+      _added.add(orderedNutrient.id);
+
+  /// Returns the [Nutriments] map key for the nutrient value.
+  ///
+  /// * [perServing] true: per serving.
+  /// * [perServing] false: per 100g.
+  static String getValueKey(
+    String nutrientId,
+    final bool perServing,
+  ) {
+    nutrientId = _fixNutrientId(nutrientId);
+    // 'energy-kcal' is directly for serving (no 'energy-kcal_serving')
+    if (nutrientId == _energyKCalId && perServing) {
+      return _energyKCalId;
+    }
+    return '$nutrientId${perServing ? '_serving' : '_100g'}';
+  }
+
+  /// Returns a vertical list of nutrients from a tree structure.
+  ///
+  /// Typical use-case: to be used from BE's tree nutrients in order to get
+  /// a simple one-dimension list, easier to display and parse.
+  /// For some countries, there's energy or energyKJ, or both
+  /// cf. https://github.com/openfoodfacts/openfoodfacts-server/blob/main/lib/ProductOpener/Food.pm
+  /// Regarding our list of nutrients here, we need one and only one of them.
+  void _loadNutrients(
+    final List<OrderedNutrient> nutrients,
+  ) {
+    bool alreadyEnergyKJ = false;
+
+    // inner method, in order to use alreadyEnergyKJ without a private variable.
+    void _populateOrderedNutrientList(final List<OrderedNutrient> list) {
+      for (final OrderedNutrient nutrient in list) {
+        if (nutrient.id != _energyKJId &&
+            !TmpToOffNutriments.supportedNutrientIds.contains(nutrient.id)) {
+          continue;
+        }
+        final bool nowEnergy =
+            nutrient.id == _energyId || nutrient.id == _energyKJId;
+        bool addNutrient = true;
+        if (nowEnergy) {
+          if (alreadyEnergyKJ) {
+            addNutrient = false;
+          }
+          alreadyEnergyKJ = true;
+        }
+        if (addNutrient) {
+          _nutrients.add(nutrient);
+        }
+        if (nutrient.subNutrients != null) {
+          _populateOrderedNutrientList(nutrient.subNutrients!);
+        }
+      }
+    }
+
+    _populateOrderedNutrientList(nutrients);
+
+    if (!alreadyEnergyKJ) {
+      throw Exception('no energy or energyKJ found: very suspicious!');
+    }
+  }
+
+  /// Returns the unit key according to [Nutriments] json map.
+  static String _getNutrimentsUnitKey(final String nutrientId) =>
+      '${_fixNutrientId(nutrientId)}_unit';
+
+  static String _fixNutrientId(final String nutrientId) =>
+      nutrientId == _energyKJId ? _energyId : nutrientId;
+
+  /// Loads product nutrient units into a map.
+  ///
+  /// Needs nutrients to be loaded first.
+  void _loadUnits(final Map<String, dynamic> json) {
+    for (final OrderedNutrient orderedNutrient in _nutrients) {
+      final String nutrientId = orderedNutrient.id;
+      final String unitKey = _getNutrimentsUnitKey(nutrientId);
+      final dynamic value = json[unitKey];
+      if (value == null || value is! String) {
+        continue;
+      }
+      final Unit? unit = UnitHelper.stringToUnit(value);
+      if (unit != null) {
+        _setUnit(nutrientId, unit);
+      }
+    }
+  }
+
+  /// Loads product nutrients into a map.
+  ///
+  /// Needs nutrients and units to be loaded first.
+  void _loadValues(final Map<String, dynamic> json) {
+    /// Converts a double (weight) value from grams.
+    ///
+    /// Typical use-case: after receiving a value from the BE.
+    double? _convertWeightFromG(final double? value, final Unit unit) {
+      if (value == null) {
+        return null;
+      }
+      if (unit == Unit.MILLI_G) {
+        return value * 1E3;
+      }
+      if (unit == Unit.MICRO_G) {
+        return value * 1E6;
+      }
+      return value;
+    }
+
+    for (final OrderedNutrient orderedNutrient in _nutrients) {
+      final String nutrientId = orderedNutrient.id;
+      final Unit unit = getUnit(nutrientId);
+      for (int i = 0; i < 2; i++) {
+        final bool perServing = i == 0;
+        final String valueKey = getValueKey(nutrientId, perServing);
+        final double? value = _convertWeightFromG(
+          JsonObject.parseDouble(json[valueKey]),
+          unit,
+        );
+        if (value != null) {
+          _values[valueKey] = value;
+        }
+      }
+    }
+  }
+}