import sys

from django.apps import apps
from django.contrib.auth.models import Permission
from django.contrib.contenttypes.models import ContentType
from django.db.models import Q
from django.dispatch import Signal

from ..utils.autoupdate import Element, inform_changed_elements


# This signal is send when the migrate command is done. That means it is sent
# after post_migrate sending and creating all Permission objects. Don't use it
# for other things than dealing with Permission objects.
post_permission_creation = Signal()

# This signal is sent if a permission is changed (e. g. a group gets a new
# permission). Connected receivers may yield Collections.
permission_change = Signal()


def delete_django_app_permissions(sender, **kwargs):
    """
    Deletes the permissions, Django creates by default. Only required
    for auth, contenttypes and sessions.
    """
    contenttypes = ContentType.objects.filter(
        Q(app_label="auth") | Q(app_label="contenttypes") | Q(app_label="sessions")
    )
    Permission.objects.filter(content_type__in=contenttypes).delete()


def get_permission_change_data(sender, permissions, **kwargs):
    """
    Yields all necessary Cachables if the respective permissions change.
    """
    core_app = apps.get_app_config(app_label="core")
    for permission in permissions:
        if permission.content_type.app_label == core_app.label:
            if permission.codename == "can_see_projector":
                yield core_app.get_model("Projector")
            elif permission.codename == "can_manage_projector":
                yield core_app.get_model("ProjectorMessage")
                yield core_app.get_model("Countdown")
            elif permission.codename == "can_use_chat":
                yield core_app.get_model("ChatMessage")


def autoupdate_for_many_to_many_relations(sender, instance, **kwargs):
    """
    Send autoupdate for many-to-many related objects if the other side
    is deleted.
    """
    # Hotfix for #4501: Skip autoupdate for many-to-many related objects
    # during migrations.
    if "migrate" in sys.argv:
        return

    m2m_fields = (
        field
        for field in instance._meta.get_fields(include_hidden=True)
        if field.many_to_many and field.auto_created
    )
    for field in m2m_fields:
        queryset = getattr(instance, field.get_accessor_name()).all()
        for related_instance in queryset:
            if hasattr(related_instance, "get_root_rest_element"):
                # The related instance is or has a root rest element.
                # So lets send it via autoupdate.
                root_rest_element = related_instance.get_root_rest_element()
                inform_changed_elements(
                    [
                        Element(
                            collection_string=root_rest_element.get_collection_string(),
                            id=root_rest_element.pk,
                            full_data=None,
                            reload=True,
                        )
                    ]
                )