"""Utility functions."""

from operator import itemgetter
from typing import Callable, Collection, Hashable, TypeVar, cast


__all__ = ['has_duplicates']


T = TypeVar('T')


def has_duplicates(items: Collection[T], key: str | Callable[[T], Hashable] | None = None) -> bool:
    """Check if a collection contains any duplicate elements based on a key.

    Args:
        items: A collection of elements.
        key: The key to use for finding duplicates. It Can be a string (for dict-like objects),
        a callable, or None (to use the item itself).

    Returns:
        True if the collection contains duplicates, False otherwise.

    """
    key_func: Callable[[T], Hashable]
    if key is not None:
        if isinstance(key, str):
            # Use `cast` to tell mypy that we know itemgetter is a valid
            # callable for this context. This resolves the error.
            key_func = cast(Callable[[T], Hashable], itemgetter(key))
        else:
            key_func = key
    else:
        # If no key, the item itself is used. It must be hashable.
        key_func = lambda o: cast(Hashable, o)  # noqa: E731

    seen: set[Hashable] = set()
    for item in items:
        key_item = key_func(item)
        if key_item in seen:
            return True
        seen.add(key_item)

    return False