Source code for pyflocker.ciphers.backends

from __future__ import annotations

import enum
import typing
from importlib import import_module

from pyflocker.ciphers import exc

_DEFAULT_BACKEND = None

if typing.TYPE_CHECKING:  # pragma: no cover
    import types
    from types import ModuleType




class Backends(enum.Enum):
    """The backends of PyFLocker."""

    CRYPTOGRAPHY = "cryptography"
    CRYPTODOME = "cryptodome"





def load_algorithm(
    name: str, backend: Backends | None = None
) -> types.ModuleType:
    """Load a specific algorithm from the given ``backend``.

    Args:
        name: The name of the algorithm.
        backend: The backend to use.

    Returns:
        module: Algorithm module from the required backend.

    Raises:
        UnsupportedAlgorithm:
            This is raised if the algorithm is not found in the backend.
    """
    _backend = load_backend(backend)
    try:
        return import_module(f".{name}", _backend.__name__)
    except ImportError as e:
        msg = f"{name} is not implemented by backend {backend}."
        raise exc.UnsupportedAlgorithm(msg) from e





def load_backend(
    backend: Backends | None = None,
) -> types.ModuleType:
    """Load a backend.

    Args:
        backend: An attribute from :class:`Backends` class.

    Returns:
        module: The backend module.
    """
    # Rules:
    # 1. if default is present and backend is None: return default
    # 2. if backend is given:
    # 2.1. don't set default
    # 2.2. load that particular backend or raise
    # otherwise find a backend or raise
    # once the backend is found, set it as default
    global _DEFAULT_BACKEND

    if backend is None:
        if _DEFAULT_BACKEND is None:
            _DEFAULT_BACKEND = _find_backend()
        return _DEFAULT_BACKEND  # type: ignore

    # backend is not None
    if not isinstance(backend, Backends):
        msg = "argument backend must be of type Backends."
        raise TypeError(msg)

    if _DEFAULT_BACKEND is None:
        _DEFAULT_BACKEND = _import_helper(backend)
        return _DEFAULT_BACKEND  # noqa: PIE781

    return _import_helper(backend)



def _import_helper(backend: Backends) -> ModuleType:
    return import_module(
        f".{backend.name.lower()}_",
        __spec__.parent,
    )


def _find_backend() -> ModuleType | None:
    errors = 0

    for i in list(Backends):
        try:
            return _import_helper(i)
        except ImportError:
            errors += 1

    if errors == len(Backends):
        msg = "No backends found."
        raise ImportError(msg)

    return None