Add firebase support to web_dashboard (#421)

* add mock data, app state, model classes

* Set up app without ChangeNotifier

* refactor

* add experiments to experimental/

* Add project-agnostic Firebase authentication code

* add sign in button

* add stub firebase API

* add firestore

* refactor code for google_sign_in

* update pubspec.lock

* switch to mocks for non-firebase version

* Add firebase instructions to the README

* fix README

* sign in silently if the user is already signed in

* add json_serializable

* update README

* ignore 'id' field on types

* Implement FirebaseItemApi

* Add build_runner instructions to README

* remove experiments directory

* add EditItemForm

* move types.dart into api.dart

* move mock and firebase configuration into the constructor

* add main_mock entrypoint

* add copyright checks to grinder script

* fix fix-copyright task

* run grind fix-copyright

* add run and generate tasks

* add run tasks to grind script

* add fillWithMockData() fix delete() in mock API

* add edit / new form dialogs

* Add charts that display entries from Firebase

* Add Entries list without editing

* refactor home page

* format

* Add entries page functionality

* Show current day in charts

* cleanup: pubspec.lock, remove type annotation

* Remove _selectedItem from Home page

Add ItemsDropdown
Use ItemsDropdown in NewEntryDialog / NewEntryForm

* rename item-category

* don't wait to show snackbar on delete

* fix circular progress indicator

* Move dialogs into dialogs.dart

* run grind fix-copyright

* remove unused import

* Refactor entry total calculation, add chart_utils library

* fix bug in chart_utils.dart

* convert CategoryChart to a stateless widget

* use a const for number of days in chart

* code review updates

- rename stream -> subscribe
- timeStamp -> timestamp
- remove latest() from API
- use FutureBuilder and StreamBuilder instead of stateful widget
- rename variables in mock_service_test.dart

* use a single collection reference in firebase API

* remove reference to stream in mock API

* Use a new type,  _EntriesEvent to improve filtering in mock API

* add analysis_options.yaml and fix (most) issues

* fix avoid_types_on_closure_parameters lint warnings

* use spread operator in dashboard.dart

* handle case where selected item in the category dropdown goes away

* use StreamBuilder + FutureBuilder on Entries page

* rename method

* use fake firebase configuration

* update pubspec.lock

* update README

* Change categories_dropdown to FutureBuilder + StreamBuilder

* Update minSdkVersion in build.gradle

SDK version 16 was failing: "The number of method references in a .dex
file cannot exceed 64K."

* update README

* Use a collection reference in FirebaseEntryApi

Already added to FirebaseCategoryApi

* Invoke onSelected in CategoriesDropdown when necessary

Also, avoid calling onSelected during a build.

* fix misnamed var

* remove unused import

* Use relative imports

* Use extension methods for DateTime utilities

* remove forms.dart

* Make Firebase instructions specific for this sample

* add copyright headers

* fix grammar

* dartfmt

* avoid setState() during build phase in CategoryDropdown

* add empty test to material_theme_builder

experimental/web_dashboard/lib/src/utils/chart_utils.dart

@@ -0,0 +1,65 @@
+// Copyright 2020, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../api/api.dart';
+import 'day_helpers.dart';
+
+/// The total value of one or more [Entry]s on a given day.
+class EntryTotal {
+  final DateTime day;
+  int value;
+
+  EntryTotal(this.day, this.value);
+}
+
+/// Returns a list of [EntryTotal] objects. Each [EntryTotal] is the sum of
+/// the values of all the entries on a given day.
+List<EntryTotal> entryTotalsByDay(List<Entry> entries, int daysAgo,
+    {DateTime today}) {
+  today ??= DateTime.now();
+  return _entryTotalsByDay(entries, daysAgo, today).toList();
+}
+
+Iterable<EntryTotal> _entryTotalsByDay(
+    List<Entry> entries, int daysAgo, DateTime today) sync* {
+  var start = today.subtract(Duration(days: daysAgo));
+  var entriesByDay = _entriesInRange(start, today, entries);
+
+  for (var i = 0; i < entriesByDay.length; i++) {
+    var list = entriesByDay[i];
+    var entryTotal = EntryTotal(start.add(Duration(days: i)), 0);
+
+    for (var entry in list) {
+      entryTotal.value += entry.value;
+    }
+
+    yield entryTotal;
+  }
+}
+
+/// Groups entries by day between [start] and [end]. The result is a list of
+/// lists. The outer list represents the number of days since [start], and the
+/// inner list is the group of entries on that day.
+List<List<Entry>> _entriesInRange(
+        DateTime start, DateTime end, List<Entry> entries) =>
+    _entriesInRangeImpl(start, end, entries).toList();
+
+Iterable<List<Entry>> _entriesInRangeImpl(
+    DateTime start, DateTime end, List<Entry> entries) sync* {
+  start = start.atMidnight;
+  end = end.atMidnight;
+  var d = start;
+
+  while (d.compareTo(end) <= 0) {
+    var es = <Entry>[];
+    for (var entry in entries) {
+      if (d.isSameDay(entry.time.atMidnight)) {
+        es.add(entry);
+      }
+    }
+
+    yield es;
+    d = d.add(Duration(days: 1));
+  }
+}

experimental/web_dashboard/lib/src/utils/day_helpers.dart

@@ -0,0 +1,15 @@
+// Copyright 2020, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+extension DayUtils on DateTime {
+  /// The UTC date portion of a datetime, without the minutes, seconds, etc.
+  DateTime get atMidnight {
+    return DateTime.utc(year, month, day);
+  }
+
+  /// Checks that the two [DateTime]s share the same date.
+  bool isSameDay(DateTime d2) {
+    return this.year == d2.year && this.month == d2.month && this.day == d2.day;
+  }
+}