import copy
import json
import operator
import re
from collections import OrderedDict
from functools import partial, reduce, update_wrapper
from urllib.parse import quote as urlquote

from django import forms
from django.conf import settings
from django.contrib import messages
from django.contrib.admin import helpers, widgets
from django.contrib.admin.checks import (
    BaseModelAdminChecks, InlineModelAdminChecks, ModelAdminChecks,
)
from django.contrib.admin.exceptions import DisallowedModelAdminToField
from django.contrib.admin.templatetags.admin_urls import add_preserved_filters
from django.contrib.admin.utils import (
    NestedObjects, construct_change_message, flatten_fieldsets,
    get_deleted_objects, lookup_needs_distinct, model_format_dict,
    model_ngettext, quote, unquote,
)
from django.contrib.admin.views.autocomplete import AutocompleteJsonView
from django.contrib.admin.widgets import (
    AutocompleteSelect, AutocompleteSelectMultiple,
)
from django.contrib.auth import get_permission_codename
from django.core.exceptions import (
    FieldDoesNotExist, FieldError, PermissionDenied, ValidationError,
)
from django.core.paginator import Paginator
from django.db import models, router, transaction
from django.db.models.constants import LOOKUP_SEP
from django.db.models.fields import BLANK_CHOICE_DASH
from django.forms.formsets import DELETION_FIELD_NAME, all_valid
from django.forms.models import (
    BaseInlineFormSet, inlineformset_factory, modelform_defines_fields,
    modelform_factory, modelformset_factory,
)
from django.forms.widgets import CheckboxSelectMultiple, SelectMultiple
from django.http import HttpResponseRedirect
from django.http.response import HttpResponseBase
from django.template.response import SimpleTemplateResponse, TemplateResponse
from django.urls import reverse
from django.utils.decorators import method_decorator
from django.utils.html import format_html
from django.utils.http import urlencode
from django.utils.inspect import get_func_args
from django.utils.safestring import mark_safe
from django.utils.text import capfirst, format_lazy, get_text_list
from django.utils.translation import gettext as _, ngettext
from django.views.decorators.csrf import csrf_protect
from django.views.generic import RedirectView

IS_POPUP_VAR = '_popup'
TO_FIELD_VAR = '_to_field'


HORIZONTAL, VERTICAL = 1, 2


def get_content_type_for_model(obj):
    # Since this module gets imported in the application's root package,
    # it cannot import models from other applications at the module level.
    from django.contrib.contenttypes.models import ContentType
    return ContentType.objects.get_for_model(obj, for_concrete_model=False)


def get_ul_class(radio_style):
    return 'radiolist' if radio_style == VERTICAL else 'radiolist inline'


class IncorrectLookupParameters(Exception):
    pass


# Defaults for formfield_overrides. ModelAdmin subclasses can change this
# by adding to ModelAdmin.formfield_overrides.

FORMFIELD_FOR_DBFIELD_DEFAULTS = {
    models.DateTimeField: {
        'form_class': forms.SplitDateTimeField,
        'widget': widgets.AdminSplitDateTime
    },
    models.DateField: {'widget': widgets.AdminDateWidget},
    models.TimeField: {'widget': widgets.AdminTimeWidget},
    models.TextField: {'widget': widgets.AdminTextareaWidget},
    models.URLField: {'widget': widgets.AdminURLFieldWidget},
    models.IntegerField: {'widget': widgets.AdminIntegerFieldWidget},
    models.BigIntegerField: {'widget': widgets.AdminBigIntegerFieldWidget},
    models.CharField: {'widget': widgets.AdminTextInputWidget},
    models.ImageField: {'widget': widgets.AdminFileWidget},
    models.FileField: {'widget': widgets.AdminFileWidget},
    models.EmailField: {'widget': widgets.AdminEmailInputWidget},
    models.UUIDField: {'widget': widgets.AdminUUIDInputWidget},
}

csrf_protect_m = method_decorator(csrf_protect)


class BaseModelAdmin(metaclass=forms.MediaDefiningClass):
    """Functionality common to both ModelAdmin and InlineAdmin."""

    autocomplete_fields = ()
    raw_id_fields = ()
    fields = None
    exclude = None
    fieldsets = None
    form = forms.ModelForm
    filter_vertical = ()
    filter_horizontal = ()
    radio_fields = {}
    prepopulated_fields = {}
    formfield_overrides = {}
    readonly_fields = ()
    ordering = None
    sortable_by = None
    view_on_site = True
    show_full_result_count = True
    checks_class = BaseModelAdminChecks

    def check(self, **kwargs):
        return self.checks_class().check(self, **kwargs)

    def __init__(self):
        # Merge FORMFIELD_FOR_DBFIELD_DEFAULTS with the formfield_overrides
        # rather than simply overwriting.
        overrides = copy.deepcopy(FORMFIELD_FOR_DBFIELD_DEFAULTS)
        for k, v in self.formfield_overrides.items():
            overrides.setdefault(k, {}).update(v)
        self.formfield_overrides = overrides

    def formfield_for_dbfield(self, db_field, request, **kwargs):
        """
        Hook for specifying the form Field instance for a given database Field
        instance.

        If kwargs are given, they're passed to the form Field's constructor.
        """
        # If the field specifies choices, we don't need to look for special
        # admin widgets - we just need to use a select widget of some kind.
        if db_field.choices:
            return self.formfield_for_choice_field(db_field, request, **kwargs)

        # ForeignKey or ManyToManyFields
        if isinstance(db_field, (models.ForeignKey, models.ManyToManyField)):
            # Combine the field kwargs with any options for formfield_overrides.
            # Make sure the passed in **kwargs override anything in
            # formfield_overrides because **kwargs is more specific, and should
            # always win.
            if db_field.__class__ in self.formfield_overrides:
                kwargs = {**self.formfield_overrides[db_field.__class__], **kwargs}

            # Get the correct formfield.
            if isinstance(db_field, models.ForeignKey):
                formfield = self.formfield_for_foreignkey(db_field, request, **kwargs)
            elif isinstance(db_field, models.ManyToManyField):
                formfield = self.formfield_for_manytomany(db_field, request, **kwargs)

            # For non-raw_id fields, wrap the widget with a wrapper that adds
            # extra HTML -- the "add other" interface -- to the end of the
            # rendered output. formfield can be None if it came from a
            # OneToOneField with parent_link=True or a M2M intermediary.
            if formfield and db_field.name not in self.raw_id_fields:
                related_modeladmin = self.admin_site._registry.get(db_field.remote_field.model)
                wrapper_kwargs = {}
                if related_modeladmin:
                    wrapper_kwargs.update(
                        can_add_related=related_modeladmin.has_add_permission(request),
                        can_change_related=related_modeladmin.has_change_permission(request),
                        can_delete_related=related_modeladmin.has_delete_permission(request),
                        can_view_related=related_modeladmin.has_view_permission(request),
                    )
                formfield.widget = widgets.RelatedFieldWidgetWrapper(
                    formfield.widget, db_field.remote_field, self.admin_site, **wrapper_kwargs
                )

            return formfield

        # If we've got overrides for the formfield defined, use 'em. **kwargs
        # passed to formfield_for_dbfield override the defaults.
        for klass in db_field.__class__.mro():
            if klass in self.formfield_overrides:
                kwargs = {**copy.deepcopy(self.formfield_overrides[klass]), **kwargs}
                return db_field.formfield(**kwargs)

        # For any other type of field, just call its formfield() method.
        return db_field.formfield(**kwargs)

    def formfield_for_choice_field(self, db_field, request, **kwargs):
        """
        Get a form Field for a database Field that has declared choices.
        """
        # If the field is named as a radio_field, use a RadioSelect
        if db_field.name in self.radio_fields:
            # Avoid stomping on custom widget/choices arguments.
            if 'widget' not in kwargs:
                kwargs['widget'] = widgets.AdminRadioSelect(attrs={
                    'class': get_ul_class(self.radio_fields[db_field.name]),
                })
            if 'choices' not in kwargs:
                kwargs['choices'] = db_field.get_choices(
                    include_blank=db_field.blank,
                    blank_choice=[('', _('None'))]
                )
        return db_field.formfield(**kwargs)

    def get_field_queryset(self, db, db_field, request):
        """
        If the ModelAdmin specifies ordering, the queryset should respect that
        ordering.  Otherwise don't specify the queryset, let the field decide
        (return None in that case).
        """
        related_admin = self.admin_site._registry.get(db_field.remote_field.model)
        if related_admin is not None:
            ordering = related_admin.get_ordering(request)
            if ordering is not None and ordering != ():
                return db_field.remote_field.model._default_manager.using(db).order_by(*ordering)
        return None

    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        """
        Get a form Field for a ForeignKey.
        """
        db = kwargs.get('using')

        if 'widget' not in kwargs:
            if db_field.name in self.get_autocomplete_fields(request):
                kwargs['widget'] = AutocompleteSelect(db_field.remote_field, self.admin_site, using=db)
            elif db_field.name in self.raw_id_fields:
                kwargs['widget'] = widgets.ForeignKeyRawIdWidget(db_field.remote_field, self.admin_site, using=db)
            elif db_field.name in self.radio_fields:
                kwargs['widget'] = widgets.AdminRadioSelect(attrs={
                    'class': get_ul_class(self.radio_fields[db_field.name]),
                })
                kwargs['empty_label'] = _('None') if db_field.blank else None

        if 'queryset' not in kwargs:
            queryset = self.get_field_queryset(db, db_field, request)
            if queryset is not None:
                kwargs['queryset'] = queryset

        return db_field.formfield(**kwargs)

    def formfield_for_manytomany(self, db_field, request, **kwargs):
        """
        Get a form Field for a ManyToManyField.
        """
        # If it uses an intermediary model that isn't auto created, don't show
        # a field in admin.
        if not db_field.remote_field.through._meta.auto_created:
            return None
        db = kwargs.get('using')

        autocomplete_fields = self.get_autocomplete_fields(request)
        if db_field.name in autocomplete_fields:
            kwargs['widget'] = AutocompleteSelectMultiple(db_field.remote_field, self.admin_site, using=db)
        elif db_field.name in self.raw_id_fields:
            kwargs['widget'] = widgets.ManyToManyRawIdWidget(db_field.remote_field, self.admin_site, using=db)
        elif db_field.name in [*self.filter_vertical, *self.filter_horizontal]:
            kwargs['widget'] = widgets.FilteredSelectMultiple(
                db_field.verbose_name,
                db_field.name in self.filter_vertical
            )

        if 'queryset' not in kwargs:
            queryset = self.get_field_queryset(db, db_field, request)
            if queryset is not None:
                kwargs['queryset'] = queryset

        form_field = db_field.formfield(**kwargs)
        if (isinstance(form_field.widget, SelectMultiple) and
                not isinstance(form_field.widget, (CheckboxSelectMultiple, AutocompleteSelectMultiple))):
            msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
            help_text = form_field.help_text
            form_field.help_text = format_lazy('{} {}', help_text, msg) if help_text else msg
        return form_field

    def get_autocomplete_fields(self, request):
        """
        Return a list of ForeignKey and/or ManyToMany fields which should use
        an autocomplete widget.
        """
        return self.autocomplete_fields

    def get_view_on_site_url(self, obj=None):
        if obj is None or not self.view_on_site:
            return None

        if callable(self.view_on_site):
            return self.view_on_site(obj)
        elif self.view_on_site and hasattr(obj, 'get_absolute_url'):
            # use the ContentType lookup if view_on_site is True
            return reverse('admin:view_on_site', kwargs={
                'content_type_id': get_content_type_for_model(obj).pk,
                'object_id': obj.pk
            })

    def get_empty_value_display(self):
        """
        Return the empty_value_display set on ModelAdmin or AdminSite.
        """
        try:
            return mark_safe(self.empty_value_display)
        except AttributeError:
            return mark_safe(self.admin_site.empty_value_display)

    def get_exclude(self, request, obj=None):
        """
        Hook for specifying exclude.
        """
        return self.exclude

    def get_fields(self, request, obj=None):
        """
        Hook for specifying fields.
        """
        if self.fields:
            return self.fields
        # _get_form_for_get_fields() is implemented in subclasses.
        form = self._get_form_for_get_fields(request, obj)
        return [*form.base_fields, *self.get_readonly_fields(request, obj)]

    def get_fieldsets(self, request, obj=None):
        """
        Hook for specifying fieldsets.
        """
        if self.fieldsets:
            return self.fieldsets
        return [(None, {'fields': self.get_fields(request, obj)})]

    def get_ordering(self, request):
        """
        Hook for specifying field ordering.
        """
        return self.ordering or ()  # otherwise we might try to *None, which is bad ;)

    def get_readonly_fields(self, request, obj=None):
        """
        Hook for specifying custom readonly fields.
        """
        return self.readonly_fields

    def get_prepopulated_fields(self, request, obj=None):
        """
        Hook for specifying custom prepopulated fields.
        """
        return self.prepopulated_fields

    def get_queryset(self, request):
        """
        Return a QuerySet of all model instances that can be edited by the
        admin site. This is used by changelist_view.
        """
        qs = self.model._default_manager.get_queryset()
        # TODO: this should be handled by some parameter to the ChangeList.
        ordering = self.get_ordering(request)
        if ordering:
            qs = qs.order_by(*ordering)
        return qs

    def get_sortable_by(self, request):
        """Hook for specifying which fields can be sorted in the changelist."""
        return self.sortable_by if self.sortable_by is not None else self.get_list_display(request)

    def lookup_allowed(self, lookup, value):
        from django.contrib.admin.filters import SimpleListFilter

        model = self.model
        # Check FKey lookups that are allowed, so that popups produced by
        # ForeignKeyRawIdWidget, on the basis of ForeignKey.limit_choices_to,
        # are allowed to work.
        for fk_lookup in model._meta.related_fkey_lookups:
            # As ``limit_choices_to`` can be a callable, invoke it here.
            if callable(fk_lookup):
                fk_lookup = fk_lookup()
            if (lookup, value) in widgets.url_params_from_lookup_dict(fk_lookup).items():
                return True

        relation_parts = []
        prev_field = None
        for part in lookup.split(LOOKUP_SEP):
            try:
                field = model._meta.get_field(part)
            except FieldDoesNotExist:
                # Lookups on nonexistent fields are ok, since they're ignored
                # later.
                break
            # It is allowed to filter on values that would be found from local
            # model anyways. For example, if you filter on employee__department__id,
            # then the id value would be found already from employee__department_id.
            if not prev_field or (prev_field.is_relation and
                                  field not in prev_field.get_path_info()[-1].target_fields):
                relation_parts.append(part)
            if not getattr(field, 'get_path_info', None):
                # This is not a relational field, so further parts
                # must be transforms.
                break
            prev_field = field
            model = field.get_path_info()[-1].to_opts.model

        if len(relation_parts) <= 1:
            # Either a local field filter, or no fields at all.
            return True
        valid_lookups = {self.date_hierarchy}
        for filter_item in self.list_filter:
            if isinstance(filter_item, type) and issubclass(filter_item, SimpleListFilter):
                valid_lookups.add(filter_item.parameter_name)
            elif isinstance(filter_item, (list, tuple)):
                valid_lookups.add(filter_item[0])
            else:
                valid_lookups.add(filter_item)

        # Is it a valid relational lookup?
        return not {
            LOOKUP_SEP.join(relation_parts),
            LOOKUP_SEP.join(relation_parts + [part])
        }.isdisjoint(valid_lookups)

    def to_field_allowed(self, request, to_field):
        """
        Return True if the model associated with this admin should be
        allowed to be referenced by the specified field.
        """
        opts = self.model._meta

        try:
            field = opts.get_field(to_field)
        except FieldDoesNotExist:
            return False

        # Always allow referencing the primary key since it's already possible
        # to get this information from the change view URL.
        if field.primary_key:
            return True

        # Allow reverse relationships to models defining m2m fields if they
        # target the specified field.
        for many_to_many in opts.many_to_many:
            if many_to_many.m2m_target_field_name() == to_field:
                return True

        # Make sure at least one of the models registered for this site
        # references this field through a FK or a M2M relationship.
        registered_models = set()
        for model, admin in self.admin_site._registry.items():
            registered_models.add(model)
            for inline in admin.inlines:
                registered_models.add(inline.model)

        related_objects = (
            f for f in opts.get_fields(include_hidden=True)
            if (f.auto_created and not f.concrete)
        )
        for related_object in related_objects:
            related_model = related_object.related_model
            remote_field = related_object.field.remote_field
            if (any(issubclass(model, related_model) for model in registered_models) and
                    hasattr(remote_field, 'get_related_field') and
                    remote_field.get_related_field() == field):
                return True

        return False

    def has_add_permission(self, request):
        """
        Return True if the given request has permission to add an object.
        Can be overridden by the user in subclasses.
        """
        opts = self.opts
        codename = get_permission_codename('add', opts)
        return request.user.has_perm("%s.%s" % (opts.app_label, codename))

    def has_change_permission(self, request, obj=None):
        """
        Return True if the given request has permission to change the given
        Django model instance, the default implementation doesn't examine the
        `obj` parameter.

        Can be overridden by the user in subclasses. In such case it should
        return True if the given request has permission to change the `obj`
        model instance. If `obj` is None, this should return True if the given
        request has permission to change *any* object of the given type.
        """
        opts = self.opts
        codename = get_permission_codename('change', opts)
        return request.user.has_perm("%s.%s" % (opts.app_label, codename))

    def has_delete_permission(self, request, obj=None):
        """
        Return True if the given request has permission to change the given
        Django model instance, the default implementation doesn't examine the
        `obj` parameter.

        Can be overridden by the user in subclasses. In such case it should
        return True if the given request has permission to delete the `obj`
        model instance. If `obj` is None, this should return True if the given
        request has permission to delete *any* object of the given type.
        """
        opts = self.opts
        codename = get_permission_codename('delete', opts)
        return request.user.has_perm("%s.%s" % (opts.app_label, codename))

    def has_view_permission(self, request, obj=None):
        """
        Return True if the given request has permission to view the given
        Django model instance. The default implementation doesn't examine the
        `obj` parameter.

        If overridden by the user in subclasses, it should return True if the
        given request has permission to view the `obj` model instance. If `obj`
        is None, it should return True if the request has permission to view
        any object of the given type.
        """
        opts = self.opts
        codename_view = get_permission_codename('view', opts)
        codename_change = get_permission_codename('change', opts)
        return (
            request.user.has_perm('%s.%s' % (opts.app_label, codename_view)) or
            request.user.has_perm('%s.%s' % (opts.app_label, codename_change))
        )

    def has_view_or_change_permission(self, request, obj=None):
        return self.has_view_permission(request, obj) or self.has_change_permission(request, obj)

    def has_module_permission(self, request):
        """
        Return True if the given request has any permission in the given
        app label.

        Can be overridden by the user in subclasses. In such case it should
        return True if the given request has permission to view the module on
        the admin index page and access the module's index page. Overriding it
        does not restrict access to the add, change or delete views. Use
        `ModelAdmin.has_(add|change|delete)_permission` for that.
        """
        return request.user.has_module_perms(self.opts.app_label)


class ModelAdmin(BaseModelAdmin):
    """Encapsulate all admin options and functionality for a given model."""

    list_display = ('__str__',)
    list_display_links = ()
    list_filter = ()
    list_select_related = False
    list_per_page = 100
    list_max_show_all = 200
    list_editable = ()
    search_fields = ()
    date_hierarchy = None
    save_as = False
    save_as_continue = True
    save_on_top = False
    paginator = Paginator
    preserve_filters = True
    inlines = []

    # Custom templates (designed to be over-ridden in subclasses)
    add_form_template = None
    change_form_template = None
    change_list_template = None
    delete_confirmation_template = None
    delete_selected_confirmation_template = None
    object_history_template = None
    popup_response_template = None

    # Actions
    actions = []
    action_form = helpers.ActionForm
    actions_on_top = True
    actions_on_bottom = False
    actions_selection_counter = True
    checks_class = ModelAdminChecks

    def __init__(self, model, admin_site):
        self.model = model
        self.opts = model._meta
        self.admin_site = admin_site
        super().__init__()

    def __str__(self):
        return "%s.%s" % (self.model._meta.app_label, self.__class__.__name__)

    def get_inline_instances(self, request, obj=None):
        inline_instances = []
        for inline_class in self.inlines:
            inline = inline_class(self.model, self.admin_site)
            if request:
                inline_has_add_permission = inline._has_add_permission(request, obj)
                if not (inline.has_view_or_change_permission(request, obj) or
                        inline_has_add_permission or
                        inline.has_delete_permission(request, obj)):
                    continue
                if not inline_has_add_permission:
                    inline.max_num = 0
            inline_instances.append(inline)

        return inline_instances

    def get_urls(self):
        from django.urls import path

        def wrap(view):
            def wrapper(*args, **kwargs):
                return self.admin_site.admin_view(view)(*args, **kwargs)
            wrapper.model_admin = self
            return update_wrapper(wrapper, view)

        info = self.model._meta.app_label, self.model._meta.model_name

        urlpatterns = [
            path('', wrap(self.changelist_view), name='%s_%s_changelist' % info),
            path('add/', wrap(self.add_view), name='%s_%s_add' % info),
            path('autocomplete/', wrap(self.autocomplete_view), name='%s_%s_autocomplete' % info),
            path('<path:object_id>/history/', wrap(self.history_view), name='%s_%s_history' % info),
            path('<path:object_id>/delete/', wrap(self.delete_view), name='%s_%s_delete' % info),
            path('<path:object_id>/change/', wrap(self.change_view), name='%s_%s_change' % info),
            # For backwards compatibility (was the change url before 1.9)
            path('<path:object_id>/', wrap(RedirectView.as_view(
                pattern_name='%s:%s_%s_change' % ((self.admin_site.name,) + info)
            ))),
        ]
        return urlpatterns

    @property
    def urls(self):
        return self.get_urls()

    @property
    def media(self):
        extra = '' if settings.DEBUG else '.min'
        js = [
            'vendor/jquery/jquery%s.js' % extra,
            'jquery.init.js',
            'core.js',
            'admin/RelatedObjectLookups.js',
            'actions%s.js' % extra,
            'urlify.js',
            'prepopulate%s.js' % extra,
            'vendor/xregexp/xregexp%s.js' % extra,
        ]
        return forms.Media(js=['admin/js/%s' % url for url in js])

    def get_model_perms(self, request):
        """
        Return a dict of all perms for this model. This dict has the keys
        ``add``, ``change``, ``delete``, and ``view`` mapping to the True/False
        for each of those actions.
        """
        return {
            'add': self.has_add_permission(request),
            'change': self.has_change_permission(request),
            'delete': self.has_delete_permission(request),
            'view': self.has_view_permission(request),
        }

    def _get_form_for_get_fields(self, request, obj):
        return self.get_form(request, obj, fields=None)

    def get_form(self, request, obj=None, change=False, **kwargs):
        """
        Return a Form class for use in the admin add view. This is used by
        add_view and change_view.
        """
        if 'fields' in kwargs:
            fields = kwargs.pop('fields')
        else:
            fields = flatten_fieldsets(self.get_fieldsets(request, obj))
        excluded = self.get_exclude(request, obj)
        exclude = [] if excluded is None else list(excluded)
        readonly_fields = self.get_readonly_fields(request, obj)
        exclude.extend(readonly_fields)
        # Exclude all fields if it's a change form and the user doesn't have
        # the change permission.
        if change and hasattr(request, 'user') and not self.has_change_permission(request, obj):
            exclude.extend(fields)
        if excluded is None and hasattr(self.form, '_meta') and self.form._meta.exclude:
            # Take the custom ModelForm's Meta.exclude into account only if the
            # ModelAdmin doesn't define its own.
            exclude.extend(self.form._meta.exclude)
        # if exclude is an empty list we pass None to be consistent with the
        # default on modelform_factory
        exclude = exclude or None

        # Remove declared form fields which are in readonly_fields.
        new_attrs = OrderedDict.fromkeys(
            f for f in readonly_fields
            if f in self.form.declared_fields
        )
        form = type(self.form.__name__, (self.form,), new_attrs)

        defaults = {
            'form': form,
            'fields': fields,
            'exclude': exclude,
            'formfield_callback': partial(self.formfield_for_dbfield, request=request),
            **kwargs,
        }

        if defaults['fields'] is None and not modelform_defines_fields(defaults['form']):
            defaults['fields'] = forms.ALL_FIELDS

        try:
            return modelform_factory(self.model, **defaults)
        except FieldError as e:
            raise FieldError(
                '%s. Check fields/fieldsets/exclude attributes of class %s.'
                % (e, self.__class__.__name__)
            )

    def get_changelist(self, request, **kwargs):
        """
        Return the ChangeList class for use on the changelist page.
        """
        from django.contrib.admin.views.main import ChangeList
        return ChangeList

    def get_changelist_instance(self, request):
        """
        Return a `ChangeList` instance based on `request`. May raise
        `IncorrectLookupParameters`.
        """
        list_display = self.get_list_display(request)
        list_display_links = self.get_list_display_links(request, list_display)
        # Add the action checkboxes if any actions are available.
        if self.get_actions(request):
            list_display = ['action_checkbox', *list_display]
        sortable_by = self.get_sortable_by(request)
        ChangeList = self.get_changelist(request)
        return ChangeList(
            request,
            self.model,
            list_display,
            list_display_links,
            self.get_list_filter(request),
            self.date_hierarchy,
            self.get_search_fields(request),
            self.get_list_select_related(request),
            self.list_per_page,
            self.list_max_show_all,
            self.list_editable,
            self,
            sortable_by,
        )

    def get_object(self, request, object_id, from_field=None):
        """
        Return an instance matching the field and value provided, the primary
        key is used if no field is provided. Return ``None`` if no match is
        found or the object_id fails validation.
        """
        queryset = self.get_queryset(request)
        model = queryset.model
        field = model._meta.pk if from_field is None else model._meta.get_field(from_field)
        try:
            object_id = field.to_python(object_id)
            return queryset.get(**{field.name: object_id})
        except (model.DoesNotExist, ValidationError, ValueError):
            return None

    def get_changelist_form(self, request, **kwargs):
        """
        Return a Form class for use in the Formset on the changelist page.
        """
        defaults = {
            'formfield_callback': partial(self.formfield_for_dbfield, request=request),
            **kwargs,
        }
        if defaults.get('fields') is None and not modelform_defines_fields(defaults.get('form')):
            defaults['fields'] = forms.ALL_FIELDS

        return modelform_factory(self.model, **defaults)

    def get_changelist_formset(self, request, **kwargs):
        """
        Return a FormSet class for use on the changelist page if list_editable
        is used.
        """
        defaults = {
            'formfield_callback': partial(self.formfield_for_dbfield, request=request),
            **kwargs,
        }
        return modelformset_factory(
            self.model, self.get_changelist_form(request), extra=0,
            fields=self.list_editable, **defaults
        )

    def get_formsets_with_inlines(self, request, obj=None):
        """
        Yield formsets and the corresponding inlines.
        """
        for inline in self.get_inline_instances(request, obj):
            yield inline.get_formset(request, obj), inline

    def get_paginator(self, request, queryset, per_page, orphans=0, allow_empty_first_page=True):
        return self.paginator(queryset, per_page, orphans, allow_empty_first_page)

    def log_addition(self, request, object, message):
        """
        Log that an object has been successfully added.

        The default implementation creates an admin LogEntry object.
        """
        from django.contrib.admin.models import LogEntry, ADDITION
        return LogEntry.objects.log_action(
            user_id=request.user.pk,
            content_type_id=get_content_type_for_model(object).pk,
            object_id=object.pk,
            object_repr=str(object),
            action_flag=ADDITION,
            change_message=message,
        )

    def log_change(self, request, object, message):
        """
        Log that an object has been successfully changed.

        The default implementation creates an admin LogEntry object.
        """
        from django.contrib.admin.models import LogEntry, CHANGE
        return LogEntry.objects.log_action(
            user_id=request.user.pk,
            content_type_id=get_content_type_for_model(object).pk,
            object_id=object.pk,
            object_repr=str(object),
            action_flag=CHANGE,
            change_message=message,
        )

    def log_deletion(self, request, object, object_repr):
        """
        Log that an object will be deleted. Note that this method must be
        called before the deletion.

        The default implementation creates an admin LogEntry object.
        """
        from django.contrib.admin.models import LogEntry, DELETION
        return LogEntry.objects.log_action(
            user_id=request.user.pk,
            content_type_id=get_content_type_for_model(object).pk,
            object_id=object.pk,
            object_repr=object_repr,
            action_flag=DELETION,
        )

    def action_checkbox(self, obj):
        """
        A list_display column containing a checkbox widget.
        """
        return helpers.checkbox.render(helpers.ACTION_CHECKBOX_NAME, str(obj.pk))
    action_checkbox.short_description = mark_safe('<input type="checkbox" id="action-toggle">')

    def _get_base_actions(self):
        """Return the list of actions, prior to any request-based filtering."""
        actions = []

        # Gather actions from the admin site first
        for (name, func) in self.admin_site.actions:
            description = getattr(func, 'short_description', name.replace('_', ' '))
            actions.append((func, name, description))
        # Add actions from this ModelAdmin.
        actions.extend(self.get_action(action) for action in self.actions or [])
        # get_action might have returned None, so filter any of those out.
        return filter(None, actions)

    def _filter_actions_by_permissions(self, request, actions):
        """Filter out any actions that the user doesn't have access to."""
        filtered_actions = []
        for action in actions:
            callable = action[0]
            if not hasattr(callable, 'allowed_permissions'):
                filtered_actions.append(action)
                continue
            permission_checks = (
                getattr(self, 'has_%s_permission' % permission)
                for permission in callable.allowed_permissions
            )
            if any(has_permission(request) for has_permission in permission_checks):
                filtered_actions.append(action)
        return filtered_actions

    def get_actions(self, request):
        """
        Return a dictionary mapping the names of all actions for this
        ModelAdmin to a tuple of (callable, name, description) for each action.
        """
        # If self.actions is set to None that means actions are disabled on
        # this page.
        if self.actions is None or IS_POPUP_VAR in request.GET:
            return OrderedDict()
        actions = self._filter_actions_by_permissions(request, self._get_base_actions())
        # Convert the actions into an OrderedDict keyed by name.
        return OrderedDict(
            (name, (func, name, desc))
            for func, name, desc in actions
        )

    def get_action_choices(self, request, default_choices=BLANK_CHOICE_DASH):
        """
        Return a list of choices for use in a form object.  Each choice is a
        tuple (name, description).
        """
        choices = [] + default_choices
        for func, name, description in self.get_actions(request).values():
            choice = (name, description % model_format_dict(self.opts))
            choices.append(choice)
        return choices

    def get_action(self, action):
        """
        Return a given action from a parameter, which can either be a callable,
        or the name of a method on the ModelAdmin.  Return is a tuple of
        (callable, name, description).
        """
        # If the action is a callable, just use it.
        if callable(action):
            func = action
            action = action.__name__

        # Next, look for a method. Grab it off self.__class__ to get an unbound
        # method instead of a bound one; this ensures that the calling
        # conventions are the same for functions and methods.
        elif hasattr(self.__class__, action):
            func = getattr(self.__class__, action)

        # Finally, look for a named method on the admin site
        else:
            try:
                func = self.admin_site.get_action(action)
            except KeyError:
                return None

        if hasattr(func, 'short_description'):
            description = func.short_description
        else:
            description = capfirst(action.replace('_', ' '))
        return func, action, description

    def get_list_display(self, request):
        """
        Return a sequence containing the fields to be displayed on the
        changelist.
        """
        return self.list_display

    def get_list_display_links(self, request, list_display):
        """
        Return a sequence containing the fields to be displayed as links
        on the changelist. The list_display parameter is the list of fields
        returned by get_list_display().
        """
        if self.list_display_links or self.list_display_links is None or not list_display:
            return self.list_display_links
        else:
            # Use only the first item in list_display as link
            return list(list_display)[:1]

    def get_list_filter(self, request):
        """
        Return a sequence containing the fields to be displayed as filters in
        the right sidebar of the changelist page.
        """
        return self.list_filter

    def get_list_select_related(self, request):
        """
        Return a list of fields to add to the select_related() part of the
        changelist items query.
        """
        return self.list_select_related

    def get_search_fields(self, request):
        """
        Return a sequence containing the fields to be searched whenever
        somebody submits a search query.
        """
        return self.search_fields

    def get_search_results(self, request, queryset, search_term):
        """
        Return a tuple containing a queryset to implement the search
        and a boolean indicating if the results may contain duplicates.
        """
        # Apply keyword searches.
        def construct_search(field_name):
            if field_name.startswith('^'):
                return "%s__istartswith" % field_name[1:]
            elif field_name.startswith('='):
                return "%s__iexact" % field_name[1:]
            elif field_name.startswith('@'):
                return "%s__search" % field_name[1:]
            # Use field_name if it includes a lookup.
            opts = queryset.model._meta
            lookup_fields = field_name.split(LOOKUP_SEP)
            # Go through the fields, following all relations.
            prev_field = None
            for path_part in lookup_fields:
                if path_part == 'pk':
                    path_part = opts.pk.name
                try:
                    field = opts.get_field(path_part)
                except FieldDoesNotExist:
                    # Use valid query lookups.
                    if prev_field and prev_field.get_lookup(path_part):
                        return field_name
                else:
                    prev_field = field
                    if hasattr(field, 'get_path_info'):
                        # Update opts to follow the relation.
                        opts = field.get_path_info()[-1].to_opts
            # Otherwise, use the field with icontains.
            return "%s__icontains" % field_name

        use_distinct = False
        search_fields = self.get_search_fields(request)
        if search_fields and search_term:
            orm_lookups = [construct_search(str(search_field))
                           for search_field in search_fields]
            for bit in search_term.split():
                or_queries = [models.Q(**{orm_lookup: bit})
                              for orm_lookup in orm_lookups]
                queryset = queryset.filter(reduce(operator.or_, or_queries))
            use_distinct |= any(lookup_needs_distinct(self.opts, search_spec) for search_spec in orm_lookups)

        return queryset, use_distinct

    def get_preserved_filters(self, request):
        """
        Return the preserved filters querystring.
        """
        match = request.resolver_match
        if self.preserve_filters and match:
            opts = self.model._meta
            current_url = '%s:%s' % (match.app_name, match.url_name)
            changelist_url = 'admin:%s_%s_changelist' % (opts.app_label, opts.model_name)
            if current_url == changelist_url:
                preserved_filters = request.GET.urlencode()
            else:
                preserved_filters = request.GET.get('_changelist_filters')

            if preserved_filters:
                return urlencode({'_changelist_filters': preserved_filters})
        return ''

    def construct_change_message(self, request, form, formsets, add=False):
        """
        Construct a JSON structure describing changes from a changed object.
        """
        return construct_change_message(form, formsets, add)

    def message_user(self, request, message, level=messages.INFO, extra_tags='',
                     fail_silently=False):
        """
        Send a message to the user. The default implementation
        posts a message using the django.contrib.messages backend.

        Exposes almost the same API as messages.add_message(), but accepts the
        positional arguments in a different order to maintain backwards
        compatibility. For convenience, it accepts the `level` argument as
        a string rather than the usual level number.
        """
        if not isinstance(level, int):
            # attempt to get the level if passed a string
            try:
                level = getattr(messages.constants, level.upper())
            except AttributeError:
                levels = messages.constants.DEFAULT_TAGS.values()
                levels_repr = ', '.join('`%s`' % l for l in levels)
                raise ValueError(
                    'Bad message level string: `%s`. Possible values are: %s'
                    % (level, levels_repr)
                )

        messages.add_message(request, level, message, extra_tags=extra_tags, fail_silently=fail_silently)

    def save_form(self, request, form, change):
        """
        Given a ModelForm return an unsaved instance. ``change`` is True if
        the object is being changed, and False if it's being added.
        """
        return form.save(commit=False)

    def save_model(self, request, obj, form, change):
        """
        Given a model instance save it to the database.
        """
        obj.save()

    def delete_model(self, request, obj):
        """
        Given a model instance delete it from the database.
        """
        obj.delete()

    def delete_queryset(self, request, queryset):
        """Given a queryset, delete it from the database."""
        queryset.delete()

    def save_formset(self, request, form, formset, change):
        """
        Given an inline formset save it to the database.
        """
        formset.save()

    def save_related(self, request, form, formsets, change):
        """
        Given the ``HttpRequest``, the parent ``ModelForm`` instance, the
        list of inline formsets and a boolean value based on whether the
        parent is being added or changed, save the related objects to the
        database. Note that at this point save_form() and save_model() have
        already been called.
        """
        form.save_m2m()
        for formset in formsets:
            self.save_formset(request, form, formset, change=change)

    def render_change_form(self, request, context, add=False, change=False, form_url='', obj=None):
        opts = self.model._meta
        app_label = opts.app_label
        preserved_filters = self.get_preserved_filters(request)
        form_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, form_url)
        view_on_site_url = self.get_view_on_site_url(obj)
        has_editable_inline_admin_formsets = False
        for inline in context['inline_admin_formsets']:
            if inline.has_add_permission or inline.has_change_permission or inline.has_delete_permission:
                has_editable_inline_admin_formsets = True
                break
        context.update({
            'add': add,
            'change': change,
            'has_view_permission': self.has_view_permission(request, obj),
            'has_add_permission': self.has_add_permission(request),
            'has_change_permission': self.has_change_permission(request, obj),
            'has_delete_permission': self.has_delete_permission(request, obj),
            'has_editable_inline_admin_formsets': has_editable_inline_admin_formsets,
            'has_file_field': context['adminform'].form.is_multipart() or any(
                admin_formset.formset.form().is_multipart()
                for admin_formset in context['inline_admin_formsets']
            ),
            'has_absolute_url': view_on_site_url is not None,
            'absolute_url': view_on_site_url,
            'form_url': form_url,
            'opts': opts,
            'content_type_id': get_content_type_for_model(self.model).pk,
            'save_as': self.save_as,
            'save_on_top': self.save_on_top,
            'to_field_var': TO_FIELD_VAR,
            'is_popup_var': IS_POPUP_VAR,
            'app_label': app_label,
        })
        if add and self.add_form_template is not None:
            form_template = self.add_form_template
        else:
            form_template = self.change_form_template

        request.current_app = self.admin_site.name

        return TemplateResponse(request, form_template or [
            "admin/%s/%s/change_form.html" % (app_label, opts.model_name),
            "admin/%s/change_form.html" % app_label,
            "admin/change_form.html"
        ], context)

    def response_add(self, request, obj, post_url_continue=None):
        """
        Determine the HttpResponse for the add_view stage.
        """
        opts = obj._meta
        preserved_filters = self.get_preserved_filters(request)
        obj_url = reverse(
            'admin:%s_%s_change' % (opts.app_label, opts.model_name),
            args=(quote(obj.pk),),
            current_app=self.admin_site.name,
        )
        # Add a link to the object's change form if the user can edit the obj.
        if self.has_change_permission(request, obj):
            obj_repr = format_html('<a href="{}">{}</a>', urlquote(obj_url), obj)
        else:
            obj_repr = str(obj)
        msg_dict = {
            'name': opts.verbose_name,
            'obj': obj_repr,
        }
        # Here, we distinguish between different save types by checking for
        # the presence of keys in request.POST.

        if IS_POPUP_VAR in request.POST:
            to_field = request.POST.get(TO_FIELD_VAR)
            if to_field:
                attr = str(to_field)
            else:
                attr = obj._meta.pk.attname
            value = obj.serializable_value(attr)
            popup_response_data = json.dumps({
                'value': str(value),
                'obj': str(obj),
            })
            return TemplateResponse(request, self.popup_response_template or [
                'admin/%s/%s/popup_response.html' % (opts.app_label, opts.model_name),
                'admin/%s/popup_response.html' % opts.app_label,
                'admin/popup_response.html',
            ], {
                'popup_response_data': popup_response_data,
            })

        elif "_continue" in request.POST or (
                # Redirecting after "Save as new".
                "_saveasnew" in request.POST and self.save_as_continue and
                self.has_change_permission(request, obj)
        ):
            msg = _('The {name} "{obj}" was added successfully.')
            if self.has_change_permission(request, obj):
                msg += ' ' + _('You may edit it again below.')
            self.message_user(request, format_html(msg, **msg_dict), messages.SUCCESS)
            if post_url_continue is None:
                post_url_continue = obj_url
            post_url_continue = add_preserved_filters(
                {'preserved_filters': preserved_filters, 'opts': opts},
                post_url_continue
            )
            return HttpResponseRedirect(post_url_continue)

        elif "_addanother" in request.POST:
            msg = format_html(
                _('The {name} "{obj}" was added successfully. You may add another {name} below.'),
                **msg_dict
            )
            self.message_user(request, msg, messages.SUCCESS)
            redirect_url = request.path
            redirect_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, redirect_url)
            return HttpResponseRedirect(redirect_url)

        else:
            msg = format_html(
                _('The {name} "{obj}" was added successfully.'),
                **msg_dict
            )
            self.message_user(request, msg, messages.SUCCESS)
            return self.response_post_save_add(request, obj)

    def response_change(self, request, obj):
        """
        Determine the HttpResponse for the change_view stage.
        """

        if IS_POPUP_VAR in request.POST:
            opts = obj._meta
            to_field = request.POST.get(TO_FIELD_VAR)
            attr = str(to_field) if to_field else opts.pk.attname
            value = request.resolver_match.kwargs['object_id']
            new_value = obj.serializable_value(attr)
            popup_response_data = json.dumps({
                'action': 'change',
                'value': str(value),
                'obj': str(obj),
                'new_value': str(new_value),
            })
            return TemplateResponse(request, self.popup_response_template or [
                'admin/%s/%s/popup_response.html' % (opts.app_label, opts.model_name),
                'admin/%s/popup_response.html' % opts.app_label,
                'admin/popup_response.html',
            ], {
                'popup_response_data': popup_response_data,
            })

        opts = self.model._meta
        preserved_filters = self.get_preserved_filters(request)

        msg_dict = {
            'name': opts.verbose_name,
            'obj': format_html('<a href="{}">{}</a>', urlquote(request.path), obj),
        }
        if "_continue" in request.POST:
            msg = format_html(
                _('The {name} "{obj}" was changed successfully. You may edit it again below.'),
                **msg_dict
            )
            self.message_user(request, msg, messages.SUCCESS)
            redirect_url = request.path
            redirect_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, redirect_url)
            return HttpResponseRedirect(redirect_url)

        elif "_saveasnew" in request.POST:
            msg = format_html(
                _('The {name} "{obj}" was added successfully. You may edit it again below.'),
                **msg_dict
            )
            self.message_user(request, msg, messages.SUCCESS)
            redirect_url = reverse('admin:%s_%s_change' %
                                   (opts.app_label, opts.model_name),
                                   args=(obj.pk,),
                                   current_app=self.admin_site.name)
            redirect_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, redirect_url)
            return HttpResponseRedirect(redirect_url)

        elif "_addanother" in request.POST:
            msg = format_html(
                _('The {name} "{obj}" was changed successfully. You may add another {name} below.'),
                **msg_dict
            )
            self.message_user(request, msg, messages.SUCCESS)
            redirect_url = reverse('admin:%s_%s_add' %
                                   (opts.app_label, opts.model_name),
                                   current_app=self.admin_site.name)
            redirect_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, redirect_url)
            return HttpResponseRedirect(redirect_url)

        else:
            msg = format_html(
                _('The {name} "{obj}" was changed successfully.'),
                **msg_dict
            )
            self.message_user(request, msg, messages.SUCCESS)
            return self.response_post_save_change(request, obj)

    def _response_post_save(self, request, obj):
        opts = self.model._meta
        if self.has_view_or_change_permission(request):
            post_url = reverse('admin:%s_%s_changelist' %
                               (opts.app_label, opts.model_name),
                               current_app=self.admin_site.name)
            preserved_filters = self.get_preserved_filters(request)
            post_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, post_url)
        else:
            post_url = reverse('admin:index',
                               current_app=self.admin_site.name)
        return HttpResponseRedirect(post_url)

    def response_post_save_add(self, request, obj):
        """
        Figure out where to redirect after the 'Save' button has been pressed
        when adding a new object.
        """
        return self._response_post_save(request, obj)

    def response_post_save_change(self, request, obj):
        """
        Figure out where to redirect after the 'Save' button has been pressed
        when editing an existing object.
        """
        return self._response_post_save(request, obj)

    def response_action(self, request, queryset):
        """
        Handle an admin action. This is called if a request is POSTed to the
        changelist; it returns an HttpResponse if the action was handled, and
        None otherwise.
        """

        # There can be multiple action forms on the page (at the top
        # and bottom of the change list, for example). Get the action
        # whose button was pushed.
        try:
            action_index = int(request.POST.get('index', 0))
        except ValueError:
            action_index = 0

        # Construct the action form.
        data = request.POST.copy()
        data.pop(helpers.ACTION_CHECKBOX_NAME, None)
        data.pop("index", None)

        # Use the action whose button was pushed
        try:
            data.update({'action': data.getlist('action')[action_index]})
        except IndexError:
            # If we didn't get an action from the chosen form that's invalid
            # POST data, so by deleting action it'll fail the validation check
            # below. So no need to do anything here
            pass

        action_form = self.action_form(data, auto_id=None)
        action_form.fields['action'].choices = self.get_action_choices(request)

        # If the form's valid we can handle the action.
        if action_form.is_valid():
            action = action_form.cleaned_data['action']
            select_across = action_form.cleaned_data['select_across']
            func = self.get_actions(request)[action][0]

            # Get the list of selected PKs. If nothing's selected, we can't
            # perform an action on it, so bail. Except we want to perform
            # the action explicitly on all objects.
            selected = request.POST.getlist(helpers.ACTION_CHECKBOX_NAME)
            if not selected and not select_across:
                # Reminder that something needs to be selected or nothing will happen
                msg = _("Items must be selected in order to perform "
                        "actions on them. No items have been changed.")
                self.message_user(request, msg, messages.WARNING)
                return None

            if not select_across:
                # Perform the action only on the selected objects
                queryset = queryset.filter(pk__in=selected)

            response = func(self, request, queryset)

            # Actions may return an HttpResponse-like object, which will be
            # used as the response from the POST. If not, we'll be a good
            # little HTTP citizen and redirect back to the changelist page.
            if isinstance(response, HttpResponseBase):
                return response
            else:
                return HttpResponseRedirect(request.get_full_path())
        else:
            msg = _("No action selected.")
            self.message_user(request, msg, messages.WARNING)
            return None

    def response_delete(self, request, obj_display, obj_id):
        """
        Determine the HttpResponse for the delete_view stage.
        """
        opts = self.model._meta

        if IS_POPUP_VAR in request.POST:
            popup_response_data = json.dumps({
                'action': 'delete',
                'value': str(obj_id),
            })
            return TemplateResponse(request, self.popup_response_template or [
                'admin/%s/%s/popup_response.html' % (opts.app_label, opts.model_name),
                'admin/%s/popup_response.html' % opts.app_label,
                'admin/popup_response.html',
            ], {
                'popup_response_data': popup_response_data,
            })

        self.message_user(
            request,
            _('The %(name)s "%(obj)s" was deleted successfully.') % {
                'name': opts.verbose_name,
                'obj': obj_display,
            },
            messages.SUCCESS,
        )

        if self.has_change_permission(request, None):
            post_url = reverse(
                'admin:%s_%s_changelist' % (opts.app_label, opts.model_name),
                current_app=self.admin_site.name,
            )
            preserved_filters = self.get_preserved_filters(request)
            post_url = add_preserved_filters(
                {'preserved_filters': preserved_filters, 'opts': opts}, post_url
            )
        else:
            post_url = reverse('admin:index', current_app=self.admin_site.name)
        return HttpResponseRedirect(post_url)

    def render_delete_form(self, request, context):
        opts = self.model._meta
        app_label = opts.app_label

        request.current_app = self.admin_site.name
        context.update(
            to_field_var=TO_FIELD_VAR,
            is_popup_var=IS_POPUP_VAR,
            media=self.media,
        )

        return TemplateResponse(
            request,
            self.delete_confirmation_template or [
                "admin/{}/{}/delete_confirmation.html".format(app_label, opts.model_name),
                "admin/{}/delete_confirmation.html".format(app_label),
                "admin/delete_confirmation.html",
            ],
            context,
        )

    def get_inline_formsets(self, request, formsets, inline_instances, obj=None):
        # Edit permissions on parent model are required for editable inlines.
        can_edit_parent = self.has_change_permission(request, obj) if obj else self.has_add_permission(request)
        inline_admin_formsets = []
        for inline, formset in zip(inline_instances, formsets):
            fieldsets = list(inline.get_fieldsets(request, obj))
            readonly = list(inline.get_readonly_fields(request, obj))
            if can_edit_parent:
                has_add_permission = inline._has_add_permission(request, obj)
                has_change_permission = inline.has_change_permission(request, obj)
                has_delete_permission = inline.has_delete_permission(request, obj)
            else:
                # Disable all edit-permissions, and overide formset settings.
                has_add_permission = has_change_permission = has_delete_permission = False
                formset.extra = formset.max_num = 0
            has_view_permission = inline.has_view_permission(request, obj)
            prepopulated = dict(inline.get_prepopulated_fields(request, obj))
            inline_admin_formset = helpers.InlineAdminFormSet(
                inline, formset, fieldsets, prepopulated, readonly, model_admin=self,
                has_add_permission=has_add_permission, has_change_permission=has_change_permission,
                has_delete_permission=has_delete_permission, has_view_permission=has_view_permission,
            )
            inline_admin_formsets.append(inline_admin_formset)
        return inline_admin_formsets

    def get_changeform_initial_data(self, request):
        """
        Get the initial form data from the request's GET params.
        """
        initial = dict(request.GET.items())
        for k in initial:
            try:
                f = self.model._meta.get_field(k)
            except FieldDoesNotExist:
                continue
            # We have to special-case M2Ms as a list of comma-separated PKs.
            if isinstance(f, models.ManyToManyField):
                initial[k] = initial[k].split(",")
        return initial

    def _get_obj_does_not_exist_redirect(self, request, opts, object_id):
        """
        Create a message informing the user that the object doesn't exist
        and return a redirect to the admin index page.
        """
        msg = _("""%(name)s with ID "%(key)s" doesn't exist. Perhaps it was deleted?""") % {
            'name': opts.verbose_name,
            'key': unquote(object_id),
        }
        self.message_user(request, msg, messages.WARNING)
        url = reverse('admin:index', current_app=self.admin_site.name)
        return HttpResponseRedirect(url)

    @csrf_protect_m
    def changeform_view(self, request, object_id=None, form_url='', extra_context=None):
        with transaction.atomic(using=router.db_for_write(self.model)):
            return self._changeform_view(request, object_id, form_url, extra_context)

    def _changeform_view(self, request, object_id, form_url, extra_context):
        to_field = request.POST.get(TO_FIELD_VAR, request.GET.get(TO_FIELD_VAR))
        if to_field and not self.to_field_allowed(request, to_field):
            raise DisallowedModelAdminToField("The field %s cannot be referenced." % to_field)

        model = self.model
        opts = model._meta

        if request.method == 'POST' and '_saveasnew' in request.POST:
            object_id = None

        add = object_id is None

        if add:
            if not self.has_add_permission(request):
                raise PermissionDenied
            obj = None

        else:
            obj = self.get_object(request, unquote(object_id), to_field)

            if request.method == 'POST':
                if not self.has_change_permission(request, obj):
                    raise PermissionDenied
            else:
                if not self.has_view_or_change_permission(request, obj):
                    raise PermissionDenied

            if obj is None:
                return self._get_obj_does_not_exist_redirect(request, opts, object_id)

        ModelForm = self.get_form(request, obj, change=not add)
        if request.method == 'POST':
            form = ModelForm(request.POST, request.FILES, instance=obj)
            form_validated = form.is_valid()
            if form_validated:
                new_object = self.save_form(request, form, change=not add)
            else:
                new_object = form.instance
            formsets, inline_instances = self._create_formsets(request, new_object, change=not add)
            if all_valid(formsets) and form_validated:
                self.save_model(request, new_object, form, not add)
                self.save_related(request, form, formsets, not add)
                change_message = self.construct_change_message(request, form, formsets, add)
                if add:
                    self.log_addition(request, new_object, change_message)
                    return self.response_add(request, new_object)
                else:
                    self.log_change(request, new_object, change_message)
                    return self.response_change(request, new_object)
            else:
                form_validated = False
        else:
            if add:
                initial = self.get_changeform_initial_data(request)
                form = ModelForm(initial=initial)
                formsets, inline_instances = self._create_formsets(request, form.instance, change=False)
            else:
                form = ModelForm(instance=obj)
                formsets, inline_instances = self._create_formsets(request, obj, change=True)

        if not add and not self.has_change_permission(request, obj):
            readonly_fields = flatten_fieldsets(self.get_fieldsets(request, obj))
        else:
            readonly_fields = self.get_readonly_fields(request, obj)
        adminForm = helpers.AdminForm(
            form,
            list(self.get_fieldsets(request, obj)),
            # Clear prepopulated fields on a view-only form to avoid a crash.
            self.get_prepopulated_fields(request, obj) if add or self.has_change_permission(request, obj) else {},
            readonly_fields,
            model_admin=self)
        media = self.media + adminForm.media

        inline_formsets = self.get_inline_formsets(request, formsets, inline_instances, obj)
        for inline_formset in inline_formsets:
            media = media + inline_formset.media

        if add:
            title = _('Add %s')
        elif self.has_change_permission(request, obj):
            title = _('Change %s')
        else:
            title = _('View %s')
        context = {
            **self.admin_site.each_context(request),
            'title': title % opts.verbose_name,
            'adminform': adminForm,
            'object_id': object_id,
            'original': obj,
            'is_popup': IS_POPUP_VAR in request.POST or IS_POPUP_VAR in request.GET,
            'to_field': to_field,
            'media': media,
            'inline_admin_formsets': inline_formsets,
            'errors': helpers.AdminErrorList(form, formsets),
            'preserved_filters': self.get_preserved_filters(request),
        }

        # Hide the "Save" and "Save and continue" buttons if "Save as New" was
        # previously chosen to prevent the interface from getting confusing.
        if request.method == 'POST' and not form_validated and "_saveasnew" in request.POST:
            context['show_save'] = False
            context['show_save_and_continue'] = False
            # Use the change template instead of the add template.
            add = False

        context.update(extra_context or {})

        return self.render_change_form(request, context, add=add, change=not add, obj=obj, form_url=form_url)

    def autocomplete_view(self, request):
        return AutocompleteJsonView.as_view(model_admin=self)(request)

    def add_view(self, request, form_url='', extra_context=None):
        return self.changeform_view(request, None, form_url, extra_context)

    def change_view(self, request, object_id, form_url='', extra_context=None):
        return self.changeform_view(request, object_id, form_url, extra_context)

    def _get_edited_object_pks(self, request, prefix):
        """Return POST data values of list_editable primary keys."""
        pk_pattern = re.compile(
            r'{}-\d+-{}$'.format(re.escape(prefix), self.model._meta.pk.name)
        )
        return [value for key, value in request.POST.items() if pk_pattern.match(key)]

    def _get_list_editable_queryset(self, request, prefix):
        """
        Based on POST data, return a queryset of the objects that were edited
        via list_editable.
        """
        object_pks = self._get_edited_object_pks(request, prefix)
        queryset = self.get_queryset(request)
        validate = queryset.model._meta.pk.to_python
        try:
            for pk in object_pks:
                validate(pk)
        except ValidationError:
            # Disable the optimization if the POST data was tampered with.
            return queryset
        return queryset.filter(pk__in=object_pks)

    @csrf_protect_m
    def changelist_view(self, request, extra_context=None):
        """
        The 'change list' admin view for this model.
        """
        from django.contrib.admin.views.main import ERROR_FLAG
        opts = self.model._meta
        app_label = opts.app_label
        if not self.has_view_or_change_permission(request):
            raise PermissionDenied

        try:
            cl = self.get_changelist_instance(request)
        except IncorrectLookupParameters:
            # Wacky lookup parameters were given, so redirect to the main
            # changelist page, without parameters, and pass an 'invalid=1'
            # parameter via the query string. If wacky parameters were given
            # and the 'invalid=1' parameter was already in the query string,
            # something is screwed up with the database, so display an error
            # page.
            if ERROR_FLAG in request.GET:
                return SimpleTemplateResponse('admin/invalid_setup.html', {
                    'title': _('Database error'),
                })
            return HttpResponseRedirect(request.path + '?' + ERROR_FLAG + '=1')

        # If the request was POSTed, this might be a bulk action or a bulk
        # edit. Try to look up an action or confirmation first, but if this
        # isn't an action the POST will fall through to the bulk edit check,
        # below.
        action_failed = False
        selected = request.POST.getlist(helpers.ACTION_CHECKBOX_NAME)

        actions = self.get_actions(request)
        # Actions with no confirmation
        if (actions and request.method == 'POST' and
                'index' in request.POST and '_save' not in request.POST):
            if selected:
                response = self.response_action(request, queryset=cl.get_queryset(request))
                if response:
                    return response
                else:
                    action_failed = True
            else:
                msg = _("Items must be selected in order to perform "
                        "actions on them. No items have been changed.")
                self.message_user(request, msg, messages.WARNING)
                action_failed = True

        # Actions with confirmation
        if (actions and request.method == 'POST' and
                helpers.ACTION_CHECKBOX_NAME in request.POST and
                'index' not in request.POST and '_save' not in request.POST):
            if selected:
                response = self.response_action(request, queryset=cl.get_queryset(request))
                if response:
                    return response
                else:
                    action_failed = True

        if action_failed:
            # Redirect back to the changelist page to avoid resubmitting the
            # form if the user refreshes the browser or uses the "No, take
            # me back" button on the action confirmation page.
            return HttpResponseRedirect(request.get_full_path())

        # If we're allowing changelist editing, we need to construct a formset
        # for the changelist given all the fields to be edited. Then we'll
        # use the formset to validate/process POSTed data.
        formset = cl.formset = None

        # Handle POSTed bulk-edit data.
        if request.method == 'POST' and cl.list_editable and '_save' in request.POST:
            if not self.has_change_permission(request):
                raise PermissionDenied
            FormSet = self.get_changelist_formset(request)
            modified_objects = self._get_list_editable_queryset(request, FormSet.get_default_prefix())
            formset = cl.formset = FormSet(request.POST, request.FILES, queryset=modified_objects)
            if formset.is_valid():
                changecount = 0
                for form in formset.forms:
                    if form.has_changed():
                        obj = self.save_form(request, form, change=True)
                        self.save_model(request, obj, form, change=True)
                        self.save_related(request, form, formsets=[], change=True)
                        change_msg = self.construct_change_message(request, form, None)
                        self.log_change(request, obj, change_msg)
                        changecount += 1

                if changecount:
                    msg = ngettext(
                        "%(count)s %(name)s was changed successfully.",
                        "%(count)s %(name)s were changed successfully.",
                        changecount
                    ) % {
                        'count': changecount,
                        'name': model_ngettext(opts, changecount),
                    }
                    self.message_user(request, msg, messages.SUCCESS)

                return HttpResponseRedirect(request.get_full_path())

        # Handle GET -- construct a formset for display.
        elif cl.list_editable and self.has_change_permission(request):
            FormSet = self.get_changelist_formset(request)
            formset = cl.formset = FormSet(queryset=cl.result_list)

        # Build the list of media to be used by the formset.
        if formset:
            media = self.media + formset.media
        else:
            media = self.media

        # Build the action form and populate it with available actions.
        if actions:
            action_form = self.action_form(auto_id=None)
            action_form.fields['action'].choices = self.get_action_choices(request)
            media += action_form.media
        else:
            action_form = None

        selection_note_all = ngettext(
            '%(total_count)s selected',
            'All %(total_count)s selected',
            cl.result_count
        )

        context = {
            **self.admin_site.each_context(request),
            'module_name': str(opts.verbose_name_plural),
            'selection_note': _('0 of %(cnt)s selected') % {'cnt': len(cl.result_list)},
            'selection_note_all': selection_note_all % {'total_count': cl.result_count},
            'title': cl.title,
            'is_popup': cl.is_popup,
            'to_field': cl.to_field,
            'cl': cl,
            'media': media,
            'has_add_permission': self.has_add_permission(request),
            'opts': cl.opts,
            'action_form': action_form,
            'actions_on_top': self.actions_on_top,
            'actions_on_bottom': self.actions_on_bottom,
            'actions_selection_counter': self.actions_selection_counter,
            'preserved_filters': self.get_preserved_filters(request),
            **(extra_context or {}),
        }

        request.current_app = self.admin_site.name

        return TemplateResponse(request, self.change_list_template or [
            'admin/%s/%s/change_list.html' % (app_label, opts.model_name),
            'admin/%s/change_list.html' % app_label,
            'admin/change_list.html'
        ], context)

    def get_deleted_objects(self, objs, request):
        """
        Hook for customizing the delete process for the delete view and the
        "delete selected" action.
        """
        return get_deleted_objects(objs, request, self.admin_site)

    @csrf_protect_m
    def delete_view(self, request, object_id, extra_context=None):
        with transaction.atomic(using=router.db_for_write(self.model)):
            return self._delete_view(request, object_id, extra_context)

    def _delete_view(self, request, object_id, extra_context):
        "The 'delete' admin view for this model."
        opts = self.model._meta
        app_label = opts.app_label

        to_field = request.POST.get(TO_FIELD_VAR, request.GET.get(TO_FIELD_VAR))
        if to_field and not self.to_field_allowed(request, to_field):
            raise DisallowedModelAdminToField("The field %s cannot be referenced." % to_field)

        obj = self.get_object(request, unquote(object_id), to_field)

        if not self.has_delete_permission(request, obj):
            raise PermissionDenied

        if obj is None:
            return self._get_obj_does_not_exist_redirect(request, opts, object_id)

        # Populate deleted_objects, a data structure of all related objects that
        # will also be deleted.
        deleted_objects, model_count, perms_needed, protected = self.get_deleted_objects([obj], request)

        if request.POST and not protected:  # The user has confirmed the deletion.
            if perms_needed:
                raise PermissionDenied
            obj_display = str(obj)
            attr = str(to_field) if to_field else opts.pk.attname
            obj_id = obj.serializable_value(attr)
            self.log_deletion(request, obj, obj_display)
            self.delete_model(request, obj)

            return self.response_delete(request, obj_display, obj_id)

        object_name = str(opts.verbose_name)

        if perms_needed or protected:
            title = _("Cannot delete %(name)s") % {"name": object_name}
        else:
            title = _("Are you sure?")

        context = {
            **self.admin_site.each_context(request),
            'title': title,
            'object_name': object_name,
            'object': obj,
            'deleted_objects': deleted_objects,
            'model_count': dict(model_count).items(),
            'perms_lacking': perms_needed,
            'protected': protected,
            'opts': opts,
            'app_label': app_label,
            'preserved_filters': self.get_preserved_filters(request),
            'is_popup': IS_POPUP_VAR in request.POST or IS_POPUP_VAR in request.GET,
            'to_field': to_field,
            **(extra_context or {}),
        }

        return self.render_delete_form(request, context)

    def history_view(self, request, object_id, extra_context=None):
        "The 'history' admin view for this model."
        from django.contrib.admin.models import LogEntry
        # First check if the user can see this history.
        model = self.model
        obj = self.get_object(request, unquote(object_id))
        if obj is None:
            return self._get_obj_does_not_exist_redirect(request, model._meta, object_id)

        if not self.has_view_or_change_permission(request, obj):
            raise PermissionDenied

        # Then get the history for this object.
        opts = model._meta
        app_label = opts.app_label
        action_list = LogEntry.objects.filter(
            object_id=unquote(object_id),
            content_type=get_content_type_for_model(model)
        ).select_related().order_by('action_time')

        context = {
            **self.admin_site.each_context(request),
            'title': _('Change history: %s') % obj,
            'action_list': action_list,
            'module_name': str(capfirst(opts.verbose_name_plural)),
            'object': obj,
            'opts': opts,
            'preserved_filters': self.get_preserved_filters(request),
            **(extra_context or {}),
        }

        request.current_app = self.admin_site.name

        return TemplateResponse(request, self.object_history_template or [
            "admin/%s/%s/object_history.html" % (app_label, opts.model_name),
            "admin/%s/object_history.html" % app_label,
            "admin/object_history.html"
        ], context)

    def _create_formsets(self, request, obj, change):
        "Helper function to generate formsets for add/change_view."
        formsets = []
        inline_instances = []
        prefixes = {}
        get_formsets_args = [request]
        if change:
            get_formsets_args.append(obj)
        for FormSet, inline in self.get_formsets_with_inlines(*get_formsets_args):
            prefix = FormSet.get_default_prefix()
            prefixes[prefix] = prefixes.get(prefix, 0) + 1
            if prefixes[prefix] != 1 or not prefix:
                prefix = "%s-%s" % (prefix, prefixes[prefix])
            formset_params = {
                'instance': obj,
                'prefix': prefix,
                'queryset': inline.get_queryset(request),
            }
            if request.method == 'POST':
                formset_params.update({
                    'data': request.POST.copy(),
                    'files': request.FILES,
                    'save_as_new': '_saveasnew' in request.POST
                })
            formset = FormSet(**formset_params)

            def user_deleted_form(request, obj, formset, index):
                """Return whether or not the user deleted the form."""
                return (
                    inline.has_delete_permission(request, obj) and
                    '{}-{}-DELETE'.format(formset.prefix, index) in request.POST
                )

            # Bypass validation of each view-only inline form (since the form's
            # data won't be in request.POST), unless the form was deleted.
            if not inline.has_change_permission(request, obj if change else None):
                for index, form in enumerate(formset.initial_forms):
                    if user_deleted_form(request, obj, formset, index):
                        continue
                    form._errors = {}
                    form.cleaned_data = form.initial
            formsets.append(formset)
            inline_instances.append(inline)
        return formsets, inline_instances


class InlineModelAdmin(BaseModelAdmin):
    """
    Options for inline editing of ``model`` instances.

    Provide ``fk_name`` to specify the attribute name of the ``ForeignKey``
    from ``model`` to its parent. This is required if ``model`` has more than
    one ``ForeignKey`` to its parent.
    """
    model = None
    fk_name = None
    formset = BaseInlineFormSet
    extra = 3
    min_num = None
    max_num = None
    template = None
    verbose_name = None
    verbose_name_plural = None
    can_delete = True
    show_change_link = False
    checks_class = InlineModelAdminChecks
    classes = None

    def __init__(self, parent_model, admin_site):
        self.admin_site = admin_site
        self.parent_model = parent_model
        self.opts = self.model._meta
        self.has_registered_model = admin_site.is_registered(self.model)
        super().__init__()
        if self.verbose_name is None:
            self.verbose_name = self.model._meta.verbose_name
        if self.verbose_name_plural is None:
            self.verbose_name_plural = self.model._meta.verbose_name_plural

    @property
    def media(self):
        extra = '' if settings.DEBUG else '.min'
        js = ['vendor/jquery/jquery%s.js' % extra, 'jquery.init.js',
              'inlines%s.js' % extra]
        if self.filter_vertical or self.filter_horizontal:
            js.extend(['SelectBox.js', 'SelectFilter2.js'])
        if self.classes and 'collapse' in self.classes:
            js.append('collapse%s.js' % extra)
        return forms.Media(js=['admin/js/%s' % url for url in js])

    def _has_add_permission(self, request, obj):
        # RemovedInDjango30Warning: obj will be a required argument.
        args = get_func_args(self.has_add_permission)
        return self.has_add_permission(request, obj) if 'obj' in args else self.has_add_permission(request)

    def get_extra(self, request, obj=None, **kwargs):
        """Hook for customizing the number of extra inline forms."""
        return self.extra

    def get_min_num(self, request, obj=None, **kwargs):
        """Hook for customizing the min number of inline forms."""
        return self.min_num

    def get_max_num(self, request, obj=None, **kwargs):
        """Hook for customizing the max number of extra inline forms."""
        return self.max_num

    def get_formset(self, request, obj=None, **kwargs):
        """Return a BaseInlineFormSet class for use in admin add/change views."""
        if 'fields' in kwargs:
            fields = kwargs.pop('fields')
        else:
            fields = flatten_fieldsets(self.get_fieldsets(request, obj))
        excluded = self.get_exclude(request, obj)
        exclude = [] if excluded is None else list(excluded)
        exclude.extend(self.get_readonly_fields(request, obj))
        if excluded is None and hasattr(self.form, '_meta') and self.form._meta.exclude:
            # Take the custom ModelForm's Meta.exclude into account only if the
            # InlineModelAdmin doesn't define its own.
            exclude.extend(self.form._meta.exclude)
        # If exclude is an empty list we use None, since that's the actual
        # default.
        exclude = exclude or None
        can_delete = self.can_delete and self.has_delete_permission(request, obj)
        defaults = {
            'form': self.form,
            'formset': self.formset,
            'fk_name': self.fk_name,
            'fields': fields,
            'exclude': exclude,
            'formfield_callback': partial(self.formfield_for_dbfield, request=request),
            'extra': self.get_extra(request, obj, **kwargs),
            'min_num': self.get_min_num(request, obj, **kwargs),
            'max_num': self.get_max_num(request, obj, **kwargs),
            'can_delete': can_delete,
            **kwargs,
        }

        base_model_form = defaults['form']
        can_change = self.has_change_permission(request, obj) if request else True
        can_add = self._has_add_permission(request, obj) if request else True

        class DeleteProtectedModelForm(base_model_form):

            def hand_clean_DELETE(self):
                """
                We don't validate the 'DELETE' field itself because on
                templates it's not rendered using the field information, but
                just using a generic "deletion_field" of the InlineModelAdmin.
                """
                if self.cleaned_data.get(DELETION_FIELD_NAME, False):
                    using = router.db_for_write(self._meta.model)
                    collector = NestedObjects(using=using)
                    if self.instance._state.adding:
                        return
                    collector.collect([self.instance])
                    if collector.protected:
                        objs = []
                        for p in collector.protected:
                            objs.append(
                                # Translators: Model verbose name and instance representation,
                                # suitable to be an item in a list.
                                _('%(class_name)s %(instance)s') % {
                                    'class_name': p._meta.verbose_name,
                                    'instance': p}
                            )
                        params = {
                            'class_name': self._meta.model._meta.verbose_name,
                            'instance': self.instance,
                            'related_objects': get_text_list(objs, _('and')),
                        }
                        msg = _("Deleting %(class_name)s %(instance)s would require "
                                "deleting the following protected related objects: "
                                "%(related_objects)s")
                        raise ValidationError(msg, code='deleting_protected', params=params)

            def is_valid(self):
                result = super().is_valid()
                self.hand_clean_DELETE()
                return result

            def has_changed(self):
                # Protect against unauthorized edits.
                if not can_change and not self.instance._state.adding:
                    return False
                if not can_add and self.instance._state.adding:
                    return False
                return super().has_changed()

        defaults['form'] = DeleteProtectedModelForm

        if defaults['fields'] is None and not modelform_defines_fields(defaults['form']):
            defaults['fields'] = forms.ALL_FIELDS

        return inlineformset_factory(self.parent_model, self.model, **defaults)

    def _get_form_for_get_fields(self, request, obj=None):
        return self.get_formset(request, obj, fields=None).form

    def get_queryset(self, request):
        queryset = super().get_queryset(request)
        if not self.has_view_or_change_permission(request):
            queryset = queryset.none()
        return queryset

    def _has_any_perms_for_target_model(self, request, perms):
        """
        This method is called only when the ModelAdmin's model is for an
        ManyToManyField's implicit through model (if self.opts.auto_created).
        Return True if the user has any of the given permissions ('add',
        'change', etc.) for the model that points to the through model.
        """
        opts = self.opts
        # Find the target model of an auto-created many-to-many relationship.
        for field in opts.fields:
            if field.remote_field and field.remote_field.model != self.parent_model:
                opts = field.remote_field.model._meta
                break
        return any(
            request.user.has_perm('%s.%s' % (opts.app_label, get_permission_codename(perm, opts)))
            for perm in perms
        )

    def has_add_permission(self, request, obj=None):
        # RemovedInDjango30Warning: obj becomes a mandatory argument.
        if self.opts.auto_created:
            # Auto-created intermediate models don't have their own
            # permissions. The user needs to have the change permission for the
            # related model in order to be able to do anything with the
            # intermediate model.
            return self._has_any_perms_for_target_model(request, ['change'])
        return super().has_add_permission(request)

    def has_change_permission(self, request, obj=None):
        if self.opts.auto_created:
            # Same comment as has_add_permission().
            return self._has_any_perms_for_target_model(request, ['change'])
        return super().has_change_permission(request)

    def has_delete_permission(self, request, obj=None):
        if self.opts.auto_created:
            # Same comment as has_add_permission().
            return self._has_any_perms_for_target_model(request, ['change'])
        return super().has_delete_permission(request, obj)

    def has_view_permission(self, request, obj=None):
        if self.opts.auto_created:
            # Same comment as has_add_permission(). The 'change' permission
            # also implies the 'view' permission.
            return self._has_any_perms_for_target_model(request, ['view', 'change'])
        return super().has_view_permission(request)


class StackedInline(InlineModelAdmin):
    template = 'admin/edit_inline/stacked.html'


class TabularInline(InlineModelAdmin):
    template = 'admin/edit_inline/tabular.html'
