from django.contrib.auth.tokens import default_token_generator
from django.contrib.contenttypes.models import ContentType
from django.contrib.sites.models import Site
from django.utils.encoding import force_bytes
from django.utils.http import urlsafe_base64_encode
from rest_framework.exceptions import PermissionDenied


def encode_pk(resource):
    """Encode the primary key of a resource with Base64 for usage in URLs."""
    return urlsafe_base64_encode(force_bytes(resource.pk))


class AlreadyConfirmed(Exception):
    """The given resource has already been confirmed."""

    pass


class Confirmation:
    """
    Base class for handling a confirmation process.
    """

    def __init__(self, user, resource):
        self.user = user
        self.resource = resource

    def check(self):
        if not self.has_permission(self.user, self.resource):
            raise PermissionDenied()
        if self.is_confirmed(self.resource):
            raise AlreadyConfirmed()
        self.confirm(self.resource)

    def confirm(self, resource):
        """Overwrite this method to supply operations to confirm the resource."""
        pass

    def has_permission(self, user, resource) -> bool:
        """Overwrite this method returning if a user may confirm a resource."""
        return False

    def is_confirmed(self, resource) -> bool:
        """Overwrite this method to tell if a resource is confirmed."""
        return False

    def send_request(self):
        if self.is_confirmed(self.resource):
            return

        site = Site.objects.get_current()
        uid = encode_pk(self.user)
        token = default_token_generator.make_token(self.user)
        obj_type = ContentType.objects.get_for_model(self.resource)
        type_id = encode_pk(obj_type)
        obj_id = encode_pk(self.resource)
        confirmation_url = (
            f"https://{site.domain}/confirm/{uid}/{token}/{type_id}/{obj_id}"
        )
        self.user.email_user(
            f"{site.name}: Bestätigung der Anfrage",
            f"Bitte bestätige, dass du deine E-Mail-Adresse auf der Seite {site.name} ({site.domain}) eingegeben hast. "
            f"Kopiere dazu folgende URL in deinen Webbrowser:\n\n{confirmation_url}",
        )