from typing import Callable
import secrets
import base64

import django
from django.core.management.utils import get_random_secret_key
from django.utils.crypto import get_random_string

if django.VERSION[0] > 3 or \
        (django.VERSION[0] == 3 and django.VERSION[1] >= 2):
    # RANDOM_STRING_CHARS was only introduced in django 3.2
    from django.utils.crypto import RANDOM_STRING_CHARS
else:
    RANDOM_STRING_CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"  # pragma: no cover


def gen_django_secret_key() -> str:
    """
    Generate a cryptographically secure random string that can safely be used as a SECRET_KEY in django
    """
    return get_random_secret_key()


def gen_random_string(length: int, allowed_chars: str = RANDOM_STRING_CHARS) -> Callable[[], str]:
    """
    Create a parameterized generator which generates a cryptographically secure random string of the given length
    containing the given characters.
    """

    def _gen_random_string() -> str:
        return get_random_string(length, allowed_chars)

    return _gen_random_string


def gen_bytes(length: int, encoding: str) -> Callable[[], str]:
    """
    Create a parameterized generator which generates a cryptographically secure random assortments of bytes of the given
    length and encoded in the given format

    :param length: How many bytes should be generated. Not how long the encoded string will be.
    :param encoding: How the generated bytes should be encoded.
        Accepted values are "base64", "base64_urlsafe" and "hex" (case is ignored)
    """
    encoding = encoding.lower()
    if encoding not in ("base64", "base64_urlsafe", "hex"):
        raise ValueError(f"Cannot gen_bytes with encoding '{encoding}'. Valid encodings are 'base64', 'base64_urlsafe'"
                         f" and 'hex'")

    def _gen_bytes() -> str:
        b = secrets.token_bytes(length)
        if encoding == "base64":
            return base64.standard_b64encode(b).decode("ASCII")
        elif encoding == "base64_urlsafe":
            return base64.urlsafe_b64encode(b).decode("ASCII")
        elif encoding == "hex":
            return b.hex().upper()

    return _gen_bytes