Adds veggieseasons preferences, tweaks styles + list page (#37)

veggieseasons/lib/data/preferences.dart

@@ -0,0 +1,82 @@
+// Copyright 2018 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:scoped_model/scoped_model.dart';
+import 'package:veggieseasons/data/veggie.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// A model class that mirrors the options in [SettingsScreen] and stores data
+/// in shared preferences.
+class Preferences extends Model {
+  Preferences() {
+    _loadingFuture = _load();
+  }
+
+  // Keys to use with shared preferences.
+  static const _caloriesKey = 'calories';
+  static const _preferredCategoriesKey = 'preferredCategories';
+
+  // Indicates whether a call to [_load] is in progress;
+  Future<void> _loadingFuture;
+
+  int _desiredCalories = 2000;
+
+  Set<VeggieCategory> _preferredCategories = Set<VeggieCategory>();
+
+  Future<int> get desiredCalories async {
+    await _loadingFuture;
+    return _desiredCalories;
+  }
+
+  Future<Set<VeggieCategory>> get preferredCategories async {
+    await _loadingFuture;
+    return Set.from(_preferredCategories);
+  }
+
+  void addPreferredCategory(VeggieCategory category) {
+    _preferredCategories.add(category);
+    _save();
+    notifyListeners();
+  }
+
+  void removePreferredCategory(VeggieCategory category) {
+    _preferredCategories.remove(category);
+    _save();
+    notifyListeners();
+  }
+
+  void setDesiredCalories(int calories) {
+    _desiredCalories = calories;
+    _save();
+    notifyListeners();
+  }
+
+  Future<void> _save() async {
+    final prefs = await SharedPreferences.getInstance();
+    prefs.setInt(_caloriesKey, _desiredCalories);
+
+    // Store preferred categories as a comma-separated string containing their
+    // indices.
+    prefs.setString(_preferredCategoriesKey,
+        _preferredCategories.map((c) => c.index.toString()).join(','));
+  }
+
+  Future<void> _load() async {
+    final prefs = await SharedPreferences.getInstance();
+    _desiredCalories = prefs.getInt(_caloriesKey) ?? 2000;
+    _preferredCategories.clear();
+    final names = prefs.getString(_preferredCategoriesKey) ?? '';
+
+    for (final name in names.split(',')) {
+      final index = int.parse(name) ?? 0;
+      if (VeggieCategory.values[index] != null) {
+        _preferredCategories.add(VeggieCategory.values[index]);
+      }
+    }
+
+    notifyListeners();
+  }
+}