Project: Todo CLI App in Dart

Project Goal

Build a command-line Todo app that persists tasks to a JSON file. Users can add, list, complete, delete, and filter tasks by status. This project covers file I/O, JSON serialization, CLI argument parsing, and OOP design.

Design

• Task model class with fromJson/toJson
• TodoRepository for CRUD and persistence
• TodoCLI for command routing

Full Code

import 'dart:io';
import 'dart:convert';

class Task {
  final int id;
  String title;
  bool completed;
  final DateTime createdAt;

  Task({required this.id, required this.title, this.completed = false, DateTime? createdAt})
      : createdAt = createdAt ?? DateTime.now();

  factory Task.fromJson(Map<String, dynamic> j) => Task(
    id: j['id'],
    title: j['title'],
    completed: j['completed'] ?? false,
    createdAt: DateTime.parse(j['created_at']),
  );

  Map<String, dynamic> toJson() => {
    'id': id,
    'title': title,
    'completed': completed,
    'created_at': createdAt.toIso8601String(),
  };

  @override
  String toString() {
    var status = completed ? '✓' : '○';
    var date = '$${createdAt.month}/$${createdAt.day}';
    return '[$status] #$id $title ($date)';
  }
}

class TodoRepository {
  final String _path;
  List<Task> _tasks = [];

  TodoRepository([this._path = 'todos.json']);

  void load() {
    var file = File(_path);
    if (file.existsSync()) {
      var data = jsonDecode(file.readAsStringSync()) as List;
      _tasks = data.map((j) => Task.fromJson(j)).toList();
    }
  }

  void _save() => File(_path).writeAsStringSync(
      JsonEncoder.withIndent('  ').convert(_tasks.map((t) => t.toJson()).toList()));

  Task add(String title) {
    var id = _tasks.isEmpty ? 1 : _tasks.map((t) => t.id).reduce((a, b) => a > b ? a : b) + 1;
    var task = Task(id: id, title: title);
    _tasks.add(task);
    _save();
    return task;
  }

  List<Task> getAll({bool? completed}) =>
      completed == null ? _tasks : _tasks.where((t) => t.completed == completed).toList();

  bool complete(int id) {
    var task = _tasks.cast<Task?>().firstWhere((t) => t?.id == id, orElse: () => null);
    if (task == null) return false;
    task.completed = true;
    _save();
    return true;
  }

  bool delete(int id) {
    var before = _tasks.length;
    _tasks.removeWhere((t) => t.id == id);
    if (_tasks.length < before) { _save(); return true; }
    return false;
  }

  void clearCompleted() {
    _tasks.removeWhere((t) => t.completed);
    _save();
  }
}

void printHelp() {
  print('''
Usage: todo <command> [args]
  add <title>    Add a new task
  list           List all tasks
  list pending   List pending tasks
  list done      List completed tasks
  done <id>      Mark task as completed
  delete <id>   Delete a task
  clear          Remove all completed tasks
  help           Show this help
''');
}

void main(List<String> args) {
  var repo = TodoRepository()..load();
  if (args.isEmpty) { printHelp(); return; }

  switch (args[0]) {
    case 'add':
      if (args.length < 2) { print('Usage: todo add <title>'); return; }
      var task = repo.add(args.skip(1).join(' '));
      print('Added: $task');
    case 'list':
      bool? filter = args.length > 1 ? (args[1] == 'done') : null;
      var tasks = repo.getAll(completed: filter);
      if (tasks.isEmpty) { print('No tasks.'); return; }
      tasks.forEach(print);
      print('\nTotal: $${tasks.length}');
    case 'done':
      if (args.length < 2) { print('Usage: todo done <id>'); return; }
      var ok = repo.complete(int.parse(args[1]));
      print(ok ? 'Completed #$${args[1]}' : 'Task #$${args[1]} not found');
    case 'delete':
      if (args.length < 2) { print('Usage: todo delete <id>'); return; }
      var ok = repo.delete(int.parse(args[1]));
      print(ok ? 'Deleted #$${args[1]}' : 'Task #$${args[1]} not found');
    case 'clear':
      repo.clearCompleted();
      print('Cleared completed tasks');
    default:
      printHelp();
  }
}

Running

dart run todo.dart add "Learn Dart generics"
dart run todo.dart add "Build a Flutter app"
dart run todo.dart list
dart run todo.dart done 1
dart run todo.dart list pending
dart run todo.dart clear

Challenges

• Add priority levels (low, medium, high)
• Add due dates and overdue detection
• Add search by keyword
• Add categories/tags