Simple Todo Application

A command-line todo list manager with persistent JSON storage.

Overview

This is a simple yet complete todo application that demonstrates:

• Functional requirements implementation (CRUD operations)
• Non-functional requirements (persistence, validation, performance, error handling)
• Clean code architecture with proper error handling
• Data persistence using JSON

Requirements Implemented

Functional Requirements

• REQ-001: Create Todo Items - Add new todos with title and optional description
• REQ-002: List Todo Items - Display all todos with status and metadata
• REQ-003: Mark Todo as Complete - Toggle completion status on/off
• REQ-004: Delete Todo Items - Remove todos from the list permanently
• REQ-005: Edit Todo Items - Update title and description of existing todos

Non-Functional Requirements

• REQ-006: Data Persistence - All todos saved to todos.json file
• REQ-007: Input Validation - Titles validated (non-empty, max 200 chars)
• REQ-008: Performance - All operations complete within 100ms
• REQ-009: Code Quality - Comprehensive error handling with descriptive messages
• REQ-010: User Interface - Simple CLI with menu-driven interface

Features

✅ Create, Read, Update, Delete (CRUD) todos ✅ Toggle completion status ✅ Persistent storage (JSON) ✅ Input validation ✅ Error handling ✅ Clear CLI interface ✅ Timestamps for created/updated dates

Usage

python app.py

Menu Options

1. Create new todo          - Add a new todo item
2. List all todos          - View all todos with status
3. Mark todo complete      - Toggle todo completion status
4. Edit todo               - Update title or description
5. Delete todo             - Remove a todo permanently
6. Exit                    - Save and quit application

Data Storage

All todos are persisted in todos.json with the following structure:

[
  {
    "id": 1,
    "title": "Buy groceries",
    "description": "Milk, eggs, bread",
    "completed": false,
    "created_at": "2025-12-09T10:30:00",
    "updated_at": "2025-12-09T10:30:00"
  }
]

File Structure

simple_app/
├── requirements.md    - 10 requirements for the application
├── app.py            - Main application implementation
└── README.md         - This file

Requirements Traceability

Each requirement is implemented and can be traced in the code:

REQ ID	Feature	Implementation	Status
REQ-001	Create todos	create_todo() method	✅
REQ-002	List todos	list_todos() method	✅
REQ-003	Mark complete	mark_complete() method	✅
REQ-004	Delete todos	delete_todo() method	✅
REQ-005	Edit todos	edit_todo() method	✅
REQ-006	Data persistence	_load_todos(), _save_todos()	✅
REQ-007	Input validation	_validate_title() method	✅
REQ-008	Performance	JSON operations, efficient filtering	✅
REQ-009	Error handling	Try-except blocks, error messages	✅
REQ-010	CLI interface	show_menu(), run() methods	✅

Example Session

🚀 Welcome to the Simple Todo Application!

════════════════════════════════════════════════════════════════════
📝 Todo Application
════════════════════════════════════════════════════════════════════
1. Create new todo
2. List all todos
3. Mark todo complete/incomplete
4. Edit todo
5. Delete todo
6. Exit
════════════════════════════════════════════════════════════════════
Enter your choice (1-6): 1
Enter todo title: Buy groceries
Enter description (optional): Milk, eggs, bread
✅ Todo created: 'Buy groceries'

📋 Your Todos:
════════════════════════════════════════════════════════════════════

  ○ [1] [TODO] Buy groceries
      Description: Milk, eggs, bread
      Created: 2025-12-09

════════════════════════════════════════════════════════════════════

Error Handling

The application provides clear error messages for:

• Empty titles
• Titles exceeding 200 characters
• Invalid todo IDs
• File I/O errors
• Invalid menu selections

Performance

All operations are optimized:

• JSON file read on startup only
• Linear search for todo lookups (acceptable for typical use)
• Single file write per operation
• No external dependencies

Code Quality

• Type hints for all function parameters
• Comprehensive docstrings
• Clear variable names
• Proper error handling throughout
• Separation of concerns (UI, data, logic)