import 'package:flutter/material.dart';
import "package:collection/collection.dart";

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final _lessons = <Lesson>[
    Lesson(
        startTime: DateTime.utc(2019, 7, 25, 13),
        teacher: "Jacek Graczyk",
        courseCategory: "Matematyka"),
    Lesson(
        startTime: DateTime.utc(2019, 7, 25, 14),
        teacher: "Piotr Konieczny",
        courseCategory: "Historia"),
    Lesson(
        startTime: DateTime.utc(2019, 7, 27, 20),
        teacher: "Marcin Miara",
        courseCategory: "Język angielski"),
  ];

  Widget _buildSingleLessonWidget(Lesson lesson) {
    return Padding(
      padding: EdgeInsets.all(6.0),
      child: Row(children: [
        Icon(
          Icons.cake,
          size: 40.0,
        ),
        Column(
          children: [
            Text(lesson.courseCategory),
            Text(lesson.teacher),
          ],
        ),
        Text(lesson.startTime.hour.toString()),
      ]),
    );
  }

  Widget _buildLessonsWidget(List<Lesson> lessons, String weekDay) {
    final lessonWidgets = lessons.map((Lesson lesson) {
      return _buildSingleLessonWidget(lesson);
    }).toList();
    return Column(
      children: [Text(weekDay), ...lessonWidgets],
    );
  }

  @override
  Widget build(BuildContext context) {
    var newMap = groupBy(_lessons, (_lessons) => _lessons.startTime)
        .map((k, v) =>
            MapEntry(k, _buildLessonsWidget(v, k.toString())))
        .entries
        .toList()
          ..sort((a, b) => a.key.compareTo(b.key))
          ..map((x) => x.value);

    return Scaffold(
      appBar: AppBar(
        title: Text('NauczMnie'),
      ),
      body: Column(children: List<Widget>.from(newMap)),
    );
  }
}

class Lesson {
  final DateTime startTime;
  final String teacher;
  final String courseCategory;

  const Lesson({
    @required this.startTime,
    @required this.teacher,
    @required this.courseCategory,
  })  : assert(startTime != null),
        assert(teacher != null),
        assert(courseCategory != null);
}