Manager storage data on json file

pubspec.yaml

dependencies:
  path_provider: ^1.6.10

storage.dart

import 'dart:io';
import 'dart:convert';
import 'package:path_provider/path_provider.dart';

///  Storage storage = new Storage();
class Storage {
  Map<String, dynamic> _lastRemoved;
  int _lastRemovedIdx;

  Future<File> _getFile() async {
    final directory = await getApplicationDocumentsDirectory();

    return File('${directory.path}/data.json');
  }

  Future<File> saveData(List list) async {
    String data = json.encode(list);
    final file = await _getFile();

    return file.writeAsString(data);
  }

  /// @usage on initState();
  ///    storage.readData().then((data) {
  ///      setState(() {
  ///        _history = json.decode(data);
  ///        _history.sort((a, b) {
  ///          DateTime aDate = DateTime.parse(a['date']);
  ///          DateTime bDate = DateTime.parse(b['date']);
  ///
  ///          if (aDate.millisecondsSinceEpoch == bDate.millisecondsSinceEpoch) {
  ///            return 0;
  ///          }
  ///
  ///          return aDate.millisecondsSinceEpoch > bDate.millisecondsSinceEpoch ? -1 : 1;
  ///        });
  ///      });
  ///    });
  ///
  /// @usage on RefreshIndicator::onRefresh;
  ///    storage.readData().then((data) {
  ///      setState(() {
  ///        _history = json.decode(data);
  ///        _history.sort((a, b) {
  ///          DateTime aDate = DateTime.parse(a['date']);
  ///          DateTime bDate = DateTime.parse(b['date']);
  ///
  ///          if (aDate.millisecondsSinceEpoch == bDate.millisecondsSinceEpoch) {
  ///            return 0;
  ///          }
  ///
  ///          return aDate.millisecondsSinceEpoch > bDate.millisecondsSinceEpoch ? -1 : 1;
  ///        });
  ///
  ///        storage.saveData(_history);
  ///      });
  ///    });
  Future<String> readData() async {
    try {
      final file = await _getFile();

      return file.readAsString();
    } catch(e) {
      return null;
    }
  }

  /// @usage
  ///    Map<String, dynamic> entry = Map();
  ///    entry['name'] = name;
  ///    entry['...'] = ...;
  ///
  ///    storage.add(entry).then((value) {
  ///      setState(() {
  ///        _resultSaved = true;
  ///
  ///        final snack = SnackBar(
  ///          content: Text('Dados salvo com sucesso!'),
  ///          duration: Duration(seconds: 3),
  ///        );
  ///
  ///        _scaffoldKey.currentState.removeCurrentSnackBar();
  ///        _scaffoldKey.currentState.showSnackBar(snack);
  ///      });
  ///    });
  Future<File> add(Map entry) {
    return this.readData().then((data) {
      List history = [];

      history = json.decode(data);
      history.add(entry);

      return saveData(history);
    });
  }

  /// @usage
  ///        storage.removeAt(index).then((file) {
  ///          file.readAsString().then((data) {
  ///            setState(() {
  ///              _history = json.decode(data);
  ///
  ///              final snack = SnackBar(
  ///                content: Text('Dados removidos com sucesso!'),
  ///                duration: Duration(seconds: 3),
  ///                action: SnackBarAction(
  ///                  label: 'Desfazer',
  ///                  onPressed: () {
  ///                    storage.insertLastRemoved().then((file) {
  ///                      file.readAsString().then((data) {
  ///                        setState(() {
  ///                          _history = json.decode(data);
  ///                        });
  ///                      });
  ///                    });
  ///                  },
  ///                ),
  ///              );
  ///
  ///              _scaffoldKey.currentState.removeCurrentSnackBar();
  ///              _scaffoldKey.currentState.showSnackBar(snack);
  ///            });
  ///          });
  ///        });
  Future<File> removeAt(int index) {
    return this.readData().then((data) {
      List history = [];

      history = json.decode(data);

      _lastRemoved = Map.from(history[index]);
      _lastRemovedIdx = index;
      history.removeAt(index);

      return saveData(history);
    });
  }

  Future<File> insertLastRemoved() {
    return this.readData().then((data) {
      List history = [];

      history = json.decode(data);
      history.insert(_lastRemovedIdx, _lastRemoved);

      return saveData(history);
    });
  }
}