Core logic explanation

This page contains the business logic for the Todo CLI application.
All core operations like adding, listing, marking, and clearing tasks are defined here.

Storage

• Tasks are stored in a file: todo_data.json
• The format is JSON, with a list of objects:

JSON

[
  {
    "id": 1,
    "text": "Buy milk",
    "done": false,
    "priority": "medium",
    "created": "2025-06-01T10:00:00+00:00",
    "due": "2025-06-10",
    "tags": ["shopping", "errands"]
  }
]

Task structure

Each task is defined using a TypedDict for type safety and readability:

Python

class TaskDict(TypedDict):
  id: int
  text: str
  done: bool
  priority: Literal["low", "medium", "high"]
  created: str
  due: Optional[str]
  tags: Optional[list[str]]

• The default priority for new tasks is “medium”.
• The created field is always generated automatically.
• The due field is optional and can be left blank.

Function summary

Function	Description
load_tasks()	Load tasks from the JSON file
save_tasks(tasks)	Save tasks to the JSON file
add_task(text)	Add a new task with optional priority and due date
list_tasks()	Return all existing tasks
complete_task(id)	Mark a task as completed by ID
delete_task(id)	Delete a task by ID
edit_task(...)	Edit an existing task’s text, priority, due date or tags
clear_tasks()	Remove all tasks from the list

File organization

To make the code more maintainable, functions in core.py are grouped by responsibility.

Section	Responsibility	Functions
🔄 File operations	Load and save task data in JSON format	load_tasks, save_tasks
➕ Task creation	Add new tasks with automatic ID and status	add_task
📄 Task reading	Read and return task data	list_tasks
✅ Task updates	Modify the status of tasks	complete_task
✅ Task edit	Modify the status or content of tasks	complete_task, edit_task
❌ Task deletion	Remove tasks individually or all at once	delete_task, clear_tasks

---

Notes

• Task IDs are incremented automatically.
• If the storage file is missing or invalid, an empty list is returned.
• All tasks are stored in JSON with indent=2 and ensure_ascii=False.
• The design is modular and easy to extend to:
  • Tags or categories
  • Date reminders or recurring tasks
  • Database or cloud backends