classDiagram
    class TodoItem {
        -int id
        -str title
        -str description
        -str due_date
        -bool completed
        -str created_at
        +__init__(id: int, title: str, description: str = "", due_date: str = "", completed: bool = False, created_at: str = "")
        +to_dict() dict
        +from_dict(data: dict) TodoItem
    }
    class Storage {
        -str file_path
        +__init__(file_path: str)
        +load() list[dict]
        +save(data: list[dict]) None
    }
    class TodoManager {
        -list[TodoItem] items
        -Storage storage
        -int next_id
        +__init__(storage: Storage)
        +add(title: str, description: str = "", due_date: str = "") TodoItem
        +list_all() list[TodoItem]
        +list_by_status(completed: bool) list[TodoItem]
        +mark_done(item_id: int) bool
        +mark_undone(item_id: int) bool
        +delete(item_id: int) bool
        +edit(item_id: int, title: str = None, description: str = None, due_date: str = None, completed: bool = None) bool
        +_load() None
        +_save() None
        +_find_by_id(item_id: int) TodoItem | None
    }
    class TodoCLI {
        -TodoManager manager
        -argparse.ArgumentParser parser
        +__init__(manager: TodoManager)
        +run(args: list[str] = None) None
        +_setup_parser() None
        +_handle_add(args) None
        +_handle_list(args) None
        +_handle_done(args) None
        +_handle_delete(args) None
        +_handle_edit(args) None
    }
    TodoCLI --> TodoManager
    TodoManager --> Storage
    TodoManager --> TodoItem
    Storage ..> TodoItem : uses to_dict/from_dict