implementing API graphs and getting frustrated at async stuff

lib/common/widgets/charts/time_series_simple.dart

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+/// Timeseries chart example
+import 'package:charts_flutter/flutter.dart' as charts;
+import 'package:flutter/material.dart';
+
+class SimpleTimeSeriesChart extends StatelessWidget {
+  final List<charts.Series> seriesList;
+  final bool animate;
+
+  SimpleTimeSeriesChart(this.seriesList, {this.animate});
+
+  /// Creates a [TimeSeriesChart] with sample data and no transition.
+  factory SimpleTimeSeriesChart.withSampleData() {
+    return new SimpleTimeSeriesChart(
+      _createSampleData(),
+      // Disable animations for image tests.
+      animate: true,
+    );
+  }
+
+
+  @override
+  Widget build(BuildContext context) {
+    return new charts.TimeSeriesChart(
+      seriesList,
+      animate: animate,
+      // Optionally pass in a [DateTimeFactory] used by the chart. The factory
+      // should create the same type of [DateTime] as the data provided. If none
+      // specified, the default creates local date time.
+      dateTimeFactory: const charts.LocalDateTimeFactory(),
+    );
+  }
+
+  /// Create one series with sample hard coded data.
+  static List<charts.Series<TimeSeriesSales, DateTime>> _createSampleData() {
+    final data = [
+      new TimeSeriesSales(new DateTime(2017, 9, 19), 5),
+      new TimeSeriesSales(new DateTime(2017, 9, 26), 25),
+      new TimeSeriesSales(new DateTime(2017, 10, 3), 100),
+      new TimeSeriesSales(new DateTime(2017, 10, 10), 75),
+    ];
+
+    return [
+      new charts.Series<TimeSeriesSales, DateTime>(
+        id: 'Sales',
+        colorFn: (_, __) => charts.MaterialPalette.blue.shadeDefault,
+        domainFn: (TimeSeriesSales sales, _) => sales.time,
+        measureFn: (TimeSeriesSales sales, _) => sales.sales,
+        data: data,
+      )
+    ];
+  }
+}
+
+/// Sample time series data type.
+class TimeSeriesSales {
+  final DateTime time;
+  final int sales;
+
+  TimeSeriesSales(this.time, this.sales);
+}