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

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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"]
  }
]

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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.

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Function summary

FunctionDescription
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

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File organization

To make the code more maintainable, functions in core.py are grouped by responsibility.
SectionResponsibilityFunctions
🔄 File operationsLoad and save task data in JSON formatload_tasks, save_tasks
➕ Task creationAdd new tasks with automatic ID and statusadd_task
📄 Task readingRead and return task datalist_tasks
✅ Task updatesModify the status of taskscomplete_task
✅ Task editModify the status or content of taskscomplete_task, edit_task
❌ Task deletionRemove tasks individually or all at oncedelete_task, clear_tasks

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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