import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ReorderItems(topTen: ['EPL', 'MLS', 'LLG']);
  }
}

/// Holding the common data as a singleton to avoid excessive rebuilds.
/// Usually this should be replaced with a manager or bloc or changenotifier class
class DataHolder {
  List<String> parentKeys;

  Map<String, List<String>> childMap;

  DataHolder._privateConstructor();

  static final DataHolder _dataHolder = DataHolder._privateConstructor();

  static DataHolder get instance => _dataHolder;

  factory DataHolder.initialize({@required parentKeys}) {
    _dataHolder.parentKeys = parentKeys;
    _dataHolder.childMap = {};
    for (String key in parentKeys) {
      _dataHolder.childMap.putIfAbsent(
          key, () => ['${key}child_1', '${key}child_2', '${key}child_3']);
    }
    return _dataHolder;
  }
}

class ReorderItems extends StatefulWidget {
  final List<String> topTen;
  ReorderItems({this.topTen});
  @override
  _ReorderItemsState createState() => _ReorderItemsState();
}

class _ReorderItemsState extends State<ReorderItems> {
  @override
  void initState() {
    super.initState();
    // initialize the children for the Expansion tile
    // This initialization can be replaced with any logic like network fetch or something else.
    DataHolder.initialize(parentKeys: widget.topTen);
  }

  @override
  Widget build(BuildContext context) {
    return PrimaryScrollController(
      key: ValueKey(widget.topTen.toString()),
      controller: ScrollController(),
      child: ReorderableListView(
        onReorder: onReorder,
        children: getListItem(),
      ),
    );
  }

  List<ExpansionTile> getListItem() => DataHolder.instance.parentKeys
      .asMap()
      .map((index, item) => MapEntry(index, buildTenableListTile(item, index)))
      .values
      .toList();

  ExpansionTile buildTenableListTile(String mapKey, int index) => ExpansionTile(
        key: ValueKey(mapKey),
        title: Text(mapKey),
        leading: Icon(Icons.list),
        backgroundColor: Colors.blue,
        children: [
          Container(
            key: ValueKey('$mapKey$index'),
            height: 400,
            child: Container(
              padding: EdgeInsets.only(left: 20.0),
              child: ReorderList(
                parentMapKey: mapKey,
              ),
            ),
          ),
        ],
      );

  void onReorder(int oldIndex, int newIndex) {
    if (newIndex > oldIndex) {
      newIndex -= 1;
    }
    setState(() {
      String game = widget.topTen[oldIndex];
      DataHolder.instance.parentKeys.removeAt(oldIndex);
      DataHolder.instance.parentKeys.insert(newIndex, game);
    });
  }
}

class ReorderList extends StatefulWidget {
  final String parentMapKey;
  ReorderList({this.parentMapKey});
  @override
  _ReorderListState createState() => _ReorderListState();
}

class _ReorderListState extends State<ReorderList> {
  @override
  Widget build(BuildContext context) {
    return PrimaryScrollController(
      controller: ScrollController(),
      child: ReorderableListView(
        // scrollController: ScrollController(),
        onReorder: onReorder,
        children: DataHolder.instance.childMap[widget.parentMapKey]
            .map(
              (String child) => ListTile(
                key: ValueKey(child),
                leading: Icon(Icons.done_all),
                title: Text(child),
              ),
            )
            .toList(),
      ),
    );
  }

  void onReorder(int oldIndex, int newIndex) {
    if (newIndex > oldIndex) {
      newIndex -= 1;
    }
    List<String> children = DataHolder.instance.childMap[widget.parentMapKey];
    String game = children[oldIndex];
    children.removeAt(oldIndex);
    children.insert(newIndex, game);
    DataHolder.instance.childMap[widget.parentMapKey] = children;
    // Need to set state to rebuild the children.
    setState(() {});
  }
}