todo.py

#   TaskStatus = Not Started | InProgress | Done
#   InProgress = { tags: List[Tag] }
# 
#   Tag

#   UnderReview instance of Tag
#   Blocked instance of Tag

#   TaskPriority = High | Medium | Low

#   Task:
#       status: TaskStatus
#       content: str
#       priority: Optional[TaskPriority]
#       visibility: Visibility = Private
#       
#       mark_done()
#           self._set_status(TaskStatus.Done)
#       
#       mark_started()
#           self._set_status(TaskStatus.InProgress)

#       toggle_priority()
#           self.priority = Some(next state in priority)
#
#       edit_content(new_content: str)
#           self.content = new_content
#       
#       _set_status(new_status: TaskStatus)
#           self.status = new_status
#       
#       change_vis(new_vis: Visibility)
#           self.visibility = new_vis
#
#       

#   TodoListWithHistory derives Shareable and History:
#       tasks: List[Task]
#       get_tasks(priority: Optional[Priority])
#           <implementation>
#       create_task(task: Task)
#           <implementation>
#       remove_task(task: Task)
#           <implementation>

#   TodoList derives Shareable and History:
#       tasks: List[Task]
#       get_tasks(priority: Optional[Priority])
#           <implementation>
#       create_task(task: Task)
#           <implementation>
#       remove_task(task: Task)
#           <implementation>


# trait History
#   created_at
#   updated_at
#
#   If a TodoList implements History, then modify the create and add tasks
#   functions to update the created_at and updated_at
#   Current TodoLists won't implement this trait, so it won't work for them
#   (This feels very ugly)

#   User:
#       username: str
#       friends: list[User]
#       todolist: TodoList

#   Visibility = Public | Private (for tasks)
#   trait Shareable
#       share_with(user: User)
#           <implemenation>
#       stop_sharing_with(user: User)
#           <implemenation>
#       shared_with() -> list[User]
#           <implemenation>


# UI: To view a Friend's todolist could have:
#   - Dropdown of friends
#   - Select a friend, subselect viewable todo lists
#       - Repopulate currently viewed TODO list 
#       - So could just reuse that code
#
#    To extend to show counts, can add a function that counts currently displayed tasks.
#       However, important to only count currently displayed tasks, as then they are guaranteed
#       to be properly permissioned and won't leak any extra information
#       to the user.
#