from django.apps import apps
from django.conf import settings
from django.contrib.auth.models import (
    ContentType,
    Permission
)
from django.db.models import QuerySet


def permission_queryset():
    """Filter Permissions to those used within the application

    Returns:
        list: Filtered queryset that only contains the used permissions
    """

    centurion_apps = [
        'access',
        'accounting',
        'assistance',
        'config_management',
        'core',
        'devops',
        'django_celery_results',
        'human_resources',
        'itam',
        'itim',
        'project_management',
        'settings',
    ]

    exclude_models = [
        'appsettings',
        'chordcounter',
        'comment',
        'groupresult',
        'history',
        'modelnotes',
        'usersettings',
    ]

    exclude_permissions = [
        'add_checkin',
        'add_history',
        'add_organization',
        'add_taskresult',
        'add_ticketcommentaction',
        'change_checkin',
        'change_history',
        'change_organization',
        'change_taskresult',
        'change_ticketcommentaction',
        'delete_checkin',
        'delete_history',
        'delete_organization',
        'delete_taskresult',
        'delete_ticketcommentaction',
        'view_checkin',
        'view_history',
    ]


    if not settings.RUNNING_TESTS:

        try:
        # This blocks purpose is to cater for fresh install
        # so that the app does not crash before the DB is setup.

            models = apps.get_models()

            for model in models:

                if(
                    not str(model._meta.object_name).endswith('AuditHistory')
                    and not str(model._meta.model_name).lower().endswith('history')
                ):
                    # check `endswith('history')` can be removed when the old history models are removed
                    continue

                content_type = ContentType.objects.get(
                    app_label = model._meta.app_label,
                    model = model._meta.model_name
                )

                permissions = Permission.objects.filter(
                    content_type = content_type,
                )

                for permission in permissions:

                    if(
                        not permission.codename == 'view_' + str(model._meta.model_name)
                        and str(model._meta.object_name).endswith('AuditHistory')
                    ):
                        exclude_permissions += [ permission.codename ]

                    elif(
                        not str(model._meta.object_name).endswith('AuditHistory')
                        and str(model._meta.model_name).lower().endswith('history')
                    ):
                        # This `elif` can be removed when the old history models are removed

                        exclude_permissions += [ permission.codename ]


            return Permission.objects.select_related('content_type').filter(
                    content_type__app_label__in = centurion_apps,
                ).exclude(
                    content_type__model__in = exclude_models
                ).exclude(
                    codename__in = exclude_permissions
                )

        except:
            pass

        return QuerySet()

    else:

        return Permission.objects.select_related('content_type').filter(
                content_type__app_label__in = centurion_apps,
            ).exclude(
                content_type__model__in = exclude_models
            ).exclude(
                codename__in = exclude_permissions
            )