def create_plan():
    """Create an empty plan.

    This function can return whatever data structure you like: it just can't be None.
    Whatever you return from this function will be passed into other functions when
    they are tested.
    """


def add_task(plan, name: str, priority: int, duration: int, 
             dependencies: set[str] = set(), **kwargs):
    """Add a task to a plan.

    Parameters
    ----------
    plan : whatever type you've chosen
      A plan that originally came from create_plan()

    name : str
      A name for this task.
      It should be unique: if a task with this name has already been added, this
      function will return False and the task will not be created.

    priority : int
      A measure of how important this task is. This should be an integer between
      1 (most important) and 5 (least important); if any other integer is passed,
      this function will return False and the task will not be created.

    dependencies : set[str]
      Tasks that must be completed before this one.
      If a task named in this set does not already exist in the plan, this function
      will return False and the task will not be created.

    duration : int
      How long a task will take to complete, in minutes.

    **kwargs : dict
      Other details that should be included in the task.

    Returns
    -------
    True if the task was added successfully or False if there was a problem with the
    arguments passed to the function (e.g., an task with the given name already exists
    """


def get_task(plan, name: str) -> dict | None:
    """Retrieve details about a task.

    This function looks like a task in the given plan. If a task with the given name
    exists, a dictionary is returned that contains its priority, dependencies and any
    other details that were passed to add_task().

    Parameters
    ----------
    plan : whatever type you've chosen
      A plan that originally came from create_plan()

    name : str
      The name of the task to look up. If there is no such tasks, return None.

    Returns
    -------
    Details of a task (as a dictionary) or None (if the named task does not exist in
    the plan).
    """


def complete_task(plan, name: str) -> bool:
    """Mark a task as complete.

    Note that a task is complete. This should only work if the named task exists,
    all of its dependencies are complete and it has not already been marked as complete.

    Parameters
    ----------
    plan : whatever type you've chosen
      A plan that originally came from create_plan()

    name : str
      The name of the task to look up

    Returns
    -------
    Whether or not the task has successfully been marked as complete.
    """


def task_is_available(task: dict) -> bool:
    """Is a task available to be worked on and completed?

    A task is "available" if it is incomplete and has no incomplete dependencies.

    Parameters
    ----------
    task : dict
    """


def task_is_complete(plan, name: str) -> bool:
    """Is a task complete?

    Parameters
    ----------
    plan : whatever type you've chosen
      A plan that originally came from create_plan()

    name : str
      The name of the task to look up

    Returns
    -------
    Whether or not the task exists and is complete.
    """


def get_tasks(plan,
              max_duration: int = 0,
              only_available: bool = False,
              only_complete: bool = False,
              only_incomplete: bool = False):
    """Get tasks that match certain criteria.

    Parameters
    ----------
    plan : whatever type you've chosen
      A plan that originally came from create_plan()

    max_duration : int
      If positive, only return tasks with a duration less than or equal to this value.
      If negative or zero, do not filter by duration.

    only_available : bool
      If true, only return tasks that are available to be completed,
      i.e., incomplete tasks with no uncompleted dependencies

    only_complete : bool
      If true, only return completed tasks

    only_incomplete : bool
      If true, only return incomplete tasks

    Returns
    -------
    An iterable (list, set, etc.) of tasks, as would be returned by get_task()
    """