"""
Helper functions for creating Form classes from Django models
and database field objects.
"""

from __future__ import unicode_literals

from collections import OrderedDict
from itertools import chain

from django.core.exceptions import (
    ImproperlyConfigured, ValidationError, NON_FIELD_ERRORS, FieldError)
from django.forms.fields import Field, ChoiceField
from django.forms.forms import DeclarativeFieldsMetaclass, BaseForm
from django.forms.formsets import BaseFormSet, formset_factory
from django.forms.utils import ErrorList
from django.forms.widgets import (SelectMultiple, HiddenInput,
    MultipleHiddenInput)
from django.utils import six
from django.utils.encoding import smart_text, force_text
from django.utils.text import get_text_list, capfirst
from django.utils.translation import ugettext_lazy as _, ugettext


__all__ = (
    'ModelForm', 'BaseModelForm', 'model_to_dict', 'fields_for_model',
    'save_instance', 'ModelChoiceField', 'ModelMultipleChoiceField',
    'ALL_FIELDS', 'BaseModelFormSet', 'modelformset_factory',
    'BaseInlineFormSet', 'inlineformset_factory', 'modelform_factory',
)

ALL_FIELDS = '__all__'


def construct_instance(form, instance, fields=None, exclude=None):
    """
    Constructs and returns a model instance from the bound ``form``'s
    ``cleaned_data``, but does not save the returned instance to the
    database.
    """
    from django.db import models
    opts = instance._meta

    cleaned_data = form.cleaned_data
    file_field_list = []
    for f in opts.fields:
        if not f.editable or isinstance(f, models.AutoField) \
                or f.name not in cleaned_data:
            continue
        if fields is not None and f.name not in fields:
            continue
        if exclude and f.name in exclude:
            continue
        # Defer saving file-type fields until after the other fields, so a
        # callable upload_to can use the values from other fields.
        if isinstance(f, models.FileField):
            file_field_list.append(f)
        else:
            f.save_form_data(instance, cleaned_data[f.name])

    for f in file_field_list:
        f.save_form_data(instance, cleaned_data[f.name])

    return instance


def save_instance(form, instance, fields=None, fail_message='saved',
                  commit=True, exclude=None, construct=True):
    """
    Saves bound Form ``form``'s cleaned_data into model instance ``instance``.

    If commit=True, then the changes to ``instance`` will be saved to the
    database. Returns ``instance``.

    If construct=False, assume ``instance`` has already been constructed and
    just needs to be saved.
    """
    if construct:
        instance = construct_instance(form, instance, fields, exclude)
    opts = instance._meta
    if form.errors:
        raise ValueError("The %s could not be %s because the data didn't"
                         " validate." % (opts.object_name, fail_message))

    # Wrap up the saving of m2m data as a function.
    def save_m2m():
        cleaned_data = form.cleaned_data
        # Note that for historical reasons we want to include also
        # virtual_fields here. (GenericRelation was previously a fake
        # m2m field).
        for f in chain(opts.many_to_many, opts.virtual_fields):
            if not hasattr(f, 'save_form_data'):
                continue
            if fields and f.name not in fields:
                continue
            if exclude and f.name in exclude:
                continue
            if f.name in cleaned_data:
                f.save_form_data(instance, cleaned_data[f.name])
    if commit:
        # If we are committing, save the instance and the m2m data immediately.
        instance.save()
        save_m2m()
    else:
        # We're not committing. Add a method to the form to allow deferred
        # saving of m2m data.
        form.save_m2m = save_m2m
    return instance


# ModelForms #################################################################

def model_to_dict(instance, fields=None, exclude=None):
    """
    Returns a dict containing the data in ``instance`` suitable for passing as
    a Form's ``initial`` keyword argument.

    ``fields`` is an optional list of field names. If provided, only the named
    fields will be included in the returned dict.

    ``exclude`` is an optional list of field names. If provided, the named
    fields will be excluded from the returned dict, even if they are listed in
    the ``fields`` argument.
    """
    # avoid a circular import
    from django.db.models.fields.related import ManyToManyField
    opts = instance._meta
    data = {}
    for f in chain(opts.concrete_fields, opts.virtual_fields, opts.many_to_many):
        if not getattr(f, 'editable', False):
            continue
        if fields and f.name not in fields:
            continue
        if exclude and f.name in exclude:
            continue
        if isinstance(f, ManyToManyField):
            # If the object doesn't have a primary key yet, just use an empty
            # list for its m2m fields. Calling f.value_from_object will raise
            # an exception.
            if instance.pk is None:
                data[f.name] = []
            else:
                # MultipleChoiceWidget needs a list of pks, not object instances.
                qs = f.value_from_object(instance)
                if qs._result_cache is not None:
                    data[f.name] = [item.pk for item in qs]
                else:
                    data[f.name] = list(qs.values_list('pk', flat=True))
        else:
            data[f.name] = f.value_from_object(instance)
    return data


def fields_for_model(model, fields=None, exclude=None, widgets=None,
                     formfield_callback=None, localized_fields=None,
                     labels=None, help_texts=None, error_messages=None):
    """
    Returns a ``OrderedDict`` containing form fields for the given model.

    ``fields`` is an optional list of field names. If provided, only the named
    fields will be included in the returned fields.

    ``exclude`` is an optional list of field names. If provided, the named
    fields will be excluded from the returned fields, even if they are listed
    in the ``fields`` argument.

    ``widgets`` is a dictionary of model field names mapped to a widget.

    ``localized_fields`` is a list of names of fields which should be localized.

    ``labels`` is a dictionary of model field names mapped to a label.

    ``help_texts`` is a dictionary of model field names mapped to a help text.

    ``error_messages`` is a dictionary of model field names mapped to a
    dictionary of error messages.

    ``formfield_callback`` is a callable that takes a model field and returns
    a form field.
    """
    field_list = []
    ignored = []
    opts = model._meta
    # Avoid circular import
    from django.db.models.fields import Field as ModelField
    sortable_virtual_fields = [f for f in opts.virtual_fields
                               if isinstance(f, ModelField)]
    for f in sorted(chain(opts.concrete_fields, sortable_virtual_fields, opts.many_to_many)):
        if not getattr(f, 'editable', False):
            continue
        if fields is not None and f.name not in fields:
            continue
        if exclude and f.name in exclude:
            continue

        kwargs = {}
        if widgets and f.name in widgets:
            kwargs['widget'] = widgets[f.name]
        if localized_fields == ALL_FIELDS or (localized_fields and f.name in localized_fields):
            kwargs['localize'] = True
        if labels and f.name in labels:
            kwargs['label'] = labels[f.name]
        if help_texts and f.name in help_texts:
            kwargs['help_text'] = help_texts[f.name]
        if error_messages and f.name in error_messages:
            kwargs['error_messages'] = error_messages[f.name]

        if formfield_callback is None:
            formfield = f.formfield(**kwargs)
        elif not callable(formfield_callback):
            raise TypeError('formfield_callback must be a function or callable')
        else:
            formfield = formfield_callback(f, **kwargs)

        if formfield:
            field_list.append((f.name, formfield))
        else:
            ignored.append(f.name)
    field_dict = OrderedDict(field_list)
    if fields:
        field_dict = OrderedDict(
            [(f, field_dict.get(f)) for f in fields
                if ((not exclude) or (exclude and f not in exclude)) and (f not in ignored)]
        )
    return field_dict


class ModelFormOptions(object):
    def __init__(self, options=None):
        self.model = getattr(options, 'model', None)
        self.fields = getattr(options, 'fields', None)
        self.exclude = getattr(options, 'exclude', None)
        self.widgets = getattr(options, 'widgets', None)
        self.localized_fields = getattr(options, 'localized_fields', None)
        self.labels = getattr(options, 'labels', None)
        self.help_texts = getattr(options, 'help_texts', None)
        self.error_messages = getattr(options, 'error_messages', None)


class ModelFormMetaclass(DeclarativeFieldsMetaclass):
    def __new__(mcs, name, bases, attrs):
        formfield_callback = attrs.pop('formfield_callback', None)

        new_class = super(ModelFormMetaclass, mcs).__new__(mcs, name, bases, attrs)

        if bases == (BaseModelForm,):
            return new_class

        opts = new_class._meta = ModelFormOptions(getattr(new_class, 'Meta', None))

        # We check if a string was passed to `fields` or `exclude`,
        # which is likely to be a mistake where the user typed ('foo') instead
        # of ('foo',)
        for opt in ['fields', 'exclude', 'localized_fields']:
            value = getattr(opts, opt)
            if isinstance(value, six.string_types) and value != ALL_FIELDS:
                msg = ("%(model)s.Meta.%(opt)s cannot be a string. "
                       "Did you mean to type: ('%(value)s',)?" % {
                           'model': new_class.__name__,
                           'opt': opt,
                           'value': value,
                       })
                raise TypeError(msg)

        if opts.model:
            # If a model is defined, extract form fields from it.
            if opts.fields is None and opts.exclude is None:
                raise ImproperlyConfigured(
                    "Creating a ModelForm without either the 'fields' attribute "
                    "or the 'exclude' attribute is prohibited; form %s "
                    "needs updating." % name
                )

            if opts.fields == ALL_FIELDS:
                # Sentinel for fields_for_model to indicate "get the list of
                # fields from the model"
                opts.fields = None

            fields = fields_for_model(opts.model, opts.fields, opts.exclude,
                                      opts.widgets, formfield_callback,
                                      opts.localized_fields, opts.labels,
                                      opts.help_texts, opts.error_messages)

            # make sure opts.fields doesn't specify an invalid field
            none_model_fields = [k for k, v in six.iteritems(fields) if not v]
            missing_fields = (set(none_model_fields) -
                              set(new_class.declared_fields.keys()))
            if missing_fields:
                message = 'Unknown field(s) (%s) specified for %s'
                message = message % (', '.join(missing_fields),
                                     opts.model.__name__)
                raise FieldError(message)
            # Override default model fields with any custom declared ones
            # (plus, include all the other declared fields).
            fields.update(new_class.declared_fields)
        else:
            fields = new_class.declared_fields

        new_class.base_fields = fields

        return new_class


class BaseModelForm(BaseForm):
    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                 initial=None, error_class=ErrorList, label_suffix=None,
                 empty_permitted=False, instance=None):
        opts = self._meta
        if opts.model is None:
            raise ValueError('ModelForm has no model class specified.')
        if instance is None:
            # if we didn't get an instance, instantiate a new one
            self.instance = opts.model()
            object_data = {}
        else:
            self.instance = instance
            object_data = model_to_dict(instance, opts.fields, opts.exclude)
        # if initial was provided, it should override the values from instance
        if initial is not None:
            object_data.update(initial)
        # self._validate_unique will be set to True by BaseModelForm.clean().
        # It is False by default so overriding self.clean() and failing to call
        # super will stop validate_unique from being called.
        self._validate_unique = False
        super(BaseModelForm, self).__init__(data, files, auto_id, prefix, object_data,
                                            error_class, label_suffix, empty_permitted)
        # Apply ``limit_choices_to`` to each field.
        for field_name in self.fields:
            formfield = self.fields[field_name]
            if hasattr(formfield, 'queryset') and hasattr(formfield, 'get_limit_choices_to'):
                limit_choices_to = formfield.get_limit_choices_to()
                if limit_choices_to is not None:
                    formfield.queryset = formfield.queryset.complex_filter(limit_choices_to)

    def _get_validation_exclusions(self):
        """
        For backwards-compatibility, several types of fields need to be
        excluded from model validation. See the following tickets for
        details: #12507, #12521, #12553
        """
        exclude = []
        # Build up a list of fields that should be excluded from model field
        # validation and unique checks.
        for f in self.instance._meta.fields:
            field = f.name
            # Exclude fields that aren't on the form. The developer may be
            # adding these values to the model after form validation.
            if field not in self.fields:
                exclude.append(f.name)

            # Don't perform model validation on fields that were defined
            # manually on the form and excluded via the ModelForm's Meta
            # class. See #12901.
            elif self._meta.fields and field not in self._meta.fields:
                exclude.append(f.name)
            elif self._meta.exclude and field in self._meta.exclude:
                exclude.append(f.name)

            # Exclude fields that failed form validation. There's no need for
            # the model fields to validate them as well.
            elif field in self._errors.keys():
                exclude.append(f.name)

            # Exclude empty fields that are not required by the form, if the
            # underlying model field is required. This keeps the model field
            # from raising a required error. Note: don't exclude the field from
            # validation if the model field allows blanks. If it does, the blank
            # value may be included in a unique check, so cannot be excluded
            # from validation.
            else:
                form_field = self.fields[field]
                field_value = self.cleaned_data.get(field, None)
                if not f.blank and not form_field.required and field_value in form_field.empty_values:
                    exclude.append(f.name)
        return exclude

    def clean(self):
        self._validate_unique = True
        return self.cleaned_data

    def _update_errors(self, errors):
        # Override any validation error messages defined at the model level
        # with those defined at the form level.
        opts = self._meta
        for field, messages in errors.error_dict.items():
            if (field == NON_FIELD_ERRORS and opts.error_messages and
                    NON_FIELD_ERRORS in opts.error_messages):
                error_messages = opts.error_messages[NON_FIELD_ERRORS]
            elif field in self.fields:
                error_messages = self.fields[field].error_messages
            else:
                continue

            for message in messages:
                if (isinstance(message, ValidationError) and
                        message.code in error_messages):
                    message.message = error_messages[message.code]

        self.add_error(None, errors)

    def _post_clean(self):
        opts = self._meta

        exclude = self._get_validation_exclusions()
        # a subset of `exclude` which won't have the InlineForeignKeyField
        # if we're adding a new object since that value doesn't exist
        # until after the new instance is saved to the database.
        construct_instance_exclude = list(exclude)

        # Foreign Keys being used to represent inline relationships
        # are excluded from basic field value validation. This is for two
        # reasons: firstly, the value may not be supplied (#12507; the
        # case of providing new values to the admin); secondly the
        # object being referred to may not yet fully exist (#12749).
        # However, these fields *must* be included in uniqueness checks,
        # so this can't be part of _get_validation_exclusions().
        for name, field in self.fields.items():
            if isinstance(field, InlineForeignKeyField):
                if self.cleaned_data.get(name) is not None and self.cleaned_data[name]._state.adding:
                    construct_instance_exclude.append(name)
                exclude.append(name)

        # Update the model instance with self.cleaned_data.
        self.instance = construct_instance(self, self.instance, opts.fields, construct_instance_exclude)

        try:
            self.instance.full_clean(exclude=exclude, validate_unique=False)
        except ValidationError as e:
            self._update_errors(e)

        # Validate uniqueness if needed.
        if self._validate_unique:
            self.validate_unique()

    def validate_unique(self):
        """
        Calls the instance's validate_unique() method and updates the form's
        validation errors if any were raised.
        """
        exclude = self._get_validation_exclusions()
        try:
            self.instance.validate_unique(exclude=exclude)
        except ValidationError as e:
            self._update_errors(e)

    def save(self, commit=True):
        """
        Saves this ``form``'s cleaned_data into model instance
        ``self.instance``.

        If commit=True, then the changes to ``instance`` will be saved to the
        database. Returns ``instance``.
        """
        if self.instance.pk is None:
            fail_message = 'created'
        else:
            fail_message = 'changed'
        return save_instance(self, self.instance, self._meta.fields,
                             fail_message, commit, self._meta.exclude,
                             construct=False)

    save.alters_data = True


class ModelForm(six.with_metaclass(ModelFormMetaclass, BaseModelForm)):
    pass


def modelform_factory(model, form=ModelForm, fields=None, exclude=None,
                      formfield_callback=None, widgets=None, localized_fields=None,
                      labels=None, help_texts=None, error_messages=None):
    """
    Returns a ModelForm containing form fields for the given model.

    ``fields`` is an optional list of field names. If provided, only the named
    fields will be included in the returned fields. If omitted or '__all__',
    all fields will be used.

    ``exclude`` is an optional list of field names. If provided, the named
    fields will be excluded from the returned fields, even if they are listed
    in the ``fields`` argument.

    ``widgets`` is a dictionary of model field names mapped to a widget.

    ``localized_fields`` is a list of names of fields which should be localized.

    ``formfield_callback`` is a callable that takes a model field and returns
    a form field.

    ``labels`` is a dictionary of model field names mapped to a label.

    ``help_texts`` is a dictionary of model field names mapped to a help text.

    ``error_messages`` is a dictionary of model field names mapped to a
    dictionary of error messages.
    """
    # Create the inner Meta class. FIXME: ideally, we should be able to
    # construct a ModelForm without creating and passing in a temporary
    # inner class.

    # Build up a list of attributes that the Meta object will have.
    attrs = {'model': model}
    if fields is not None:
        attrs['fields'] = fields
    if exclude is not None:
        attrs['exclude'] = exclude
    if widgets is not None:
        attrs['widgets'] = widgets
    if localized_fields is not None:
        attrs['localized_fields'] = localized_fields
    if labels is not None:
        attrs['labels'] = labels
    if help_texts is not None:
        attrs['help_texts'] = help_texts
    if error_messages is not None:
        attrs['error_messages'] = error_messages

    # If parent form class already has an inner Meta, the Meta we're
    # creating needs to inherit from the parent's inner meta.
    parent = (object,)
    if hasattr(form, 'Meta'):
        parent = (form.Meta, object)
    Meta = type(str('Meta'), parent, attrs)

    # Give this new form class a reasonable name.
    class_name = model.__name__ + str('Form')

    # Class attributes for the new form class.
    form_class_attrs = {
        'Meta': Meta,
        'formfield_callback': formfield_callback
    }

    if (getattr(Meta, 'fields', None) is None and
            getattr(Meta, 'exclude', None) is None):
        raise ImproperlyConfigured(
            "Calling modelform_factory without defining 'fields' or "
            "'exclude' explicitly is prohibited."
        )

    # Instantiate type(form) in order to use the same metaclass as form.
    return type(form)(class_name, (form,), form_class_attrs)


# ModelFormSets ##############################################################

class BaseModelFormSet(BaseFormSet):
    """
    A ``FormSet`` for editing a queryset and/or adding new objects to it.
    """
    model = None

    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                 queryset=None, **kwargs):
        self.queryset = queryset
        self.initial_extra = kwargs.pop('initial', None)
        defaults = {'data': data, 'files': files, 'auto_id': auto_id, 'prefix': prefix}
        defaults.update(kwargs)
        super(BaseModelFormSet, self).__init__(**defaults)

    def initial_form_count(self):
        """Returns the number of forms that are required in this FormSet."""
        if not (self.data or self.files):
            return len(self.get_queryset())
        return super(BaseModelFormSet, self).initial_form_count()

    def _existing_object(self, pk):
        if not hasattr(self, '_object_dict'):
            self._object_dict = {o.pk: o for o in self.get_queryset()}
        return self._object_dict.get(pk)

    def _get_to_python(self, field):
        """
        If the field is a related field, fetch the concrete field's (that
        is, the ultimate pointed-to field's) to_python.
        """
        while field.rel is not None:
            field = field.rel.get_related_field()
        return field.to_python

    def _construct_form(self, i, **kwargs):
        if self.is_bound and i < self.initial_form_count():
            pk_key = "%s-%s" % (self.add_prefix(i), self.model._meta.pk.name)
            pk = self.data[pk_key]
            pk_field = self.model._meta.pk
            to_python = self._get_to_python(pk_field)
            pk = to_python(pk)
            kwargs['instance'] = self._existing_object(pk)
        if i < self.initial_form_count() and 'instance' not in kwargs:
            kwargs['instance'] = self.get_queryset()[i]
        if i >= self.initial_form_count() and self.initial_extra:
            # Set initial values for extra forms
            try:
                kwargs['initial'] = self.initial_extra[i - self.initial_form_count()]
            except IndexError:
                pass
        return super(BaseModelFormSet, self)._construct_form(i, **kwargs)

    def get_queryset(self):
        if not hasattr(self, '_queryset'):
            if self.queryset is not None:
                qs = self.queryset
            else:
                qs = self.model._default_manager.get_queryset()

            # If the queryset isn't already ordered we need to add an
            # artificial ordering here to make sure that all formsets
            # constructed from this queryset have the same form order.
            if not qs.ordered:
                qs = qs.order_by(self.model._meta.pk.name)

            # Removed queryset limiting here. As per discussion re: #13023
            # on django-dev, max_num should not prevent existing
            # related objects/inlines from being displayed.
            self._queryset = qs
        return self._queryset

    def save_new(self, form, commit=True):
        """Saves and returns a new model instance for the given form."""
        return form.save(commit=commit)

    def save_existing(self, form, instance, commit=True):
        """Saves and returns an existing model instance for the given form."""
        return form.save(commit=commit)

    def save(self, commit=True):
        """Saves model instances for every form, adding and changing instances
        as necessary, and returns the list of instances.
        """
        if not commit:
            self.saved_forms = []

            def save_m2m():
                for form in self.saved_forms:
                    form.save_m2m()
            self.save_m2m = save_m2m
        return self.save_existing_objects(commit) + self.save_new_objects(commit)

    save.alters_data = True

    def clean(self):
        self.validate_unique()

    def validate_unique(self):
        # Collect unique_checks and date_checks to run from all the forms.
        all_unique_checks = set()
        all_date_checks = set()
        forms_to_delete = self.deleted_forms
        valid_forms = [form for form in self.forms if form.is_valid() and form not in forms_to_delete]
        for form in valid_forms:
            exclude = form._get_validation_exclusions()
            unique_checks, date_checks = form.instance._get_unique_checks(exclude=exclude)
            all_unique_checks = all_unique_checks.union(set(unique_checks))
            all_date_checks = all_date_checks.union(set(date_checks))

        errors = []
        # Do each of the unique checks (unique and unique_together)
        for uclass, unique_check in all_unique_checks:
            seen_data = set()
            for form in valid_forms:
                # get data for each field of each of unique_check
                row_data = (form.cleaned_data[field]
                            for field in unique_check if field in form.cleaned_data)
                # Reduce Model instances to their primary key values
                row_data = tuple(d._get_pk_val() if hasattr(d, '_get_pk_val') else d
                                 for d in row_data)
                if row_data and None not in row_data:
                    # if we've already seen it then we have a uniqueness failure
                    if row_data in seen_data:
                        # poke error messages into the right places and mark
                        # the form as invalid
                        errors.append(self.get_unique_error_message(unique_check))
                        form._errors[NON_FIELD_ERRORS] = self.error_class([self.get_form_error()])
                        # remove the data from the cleaned_data dict since it was invalid
                        for field in unique_check:
                            if field in form.cleaned_data:
                                del form.cleaned_data[field]
                    # mark the data as seen
                    seen_data.add(row_data)
        # iterate over each of the date checks now
        for date_check in all_date_checks:
            seen_data = set()
            uclass, lookup, field, unique_for = date_check
            for form in valid_forms:
                # see if we have data for both fields
                if (form.cleaned_data and form.cleaned_data[field] is not None
                        and form.cleaned_data[unique_for] is not None):
                    # if it's a date lookup we need to get the data for all the fields
                    if lookup == 'date':
                        date = form.cleaned_data[unique_for]
                        date_data = (date.year, date.month, date.day)
                    # otherwise it's just the attribute on the date/datetime
                    # object
                    else:
                        date_data = (getattr(form.cleaned_data[unique_for], lookup),)
                    data = (form.cleaned_data[field],) + date_data
                    # if we've already seen it then we have a uniqueness failure
                    if data in seen_data:
                        # poke error messages into the right places and mark
                        # the form as invalid
                        errors.append(self.get_date_error_message(date_check))
                        form._errors[NON_FIELD_ERRORS] = self.error_class([self.get_form_error()])
                        # remove the data from the cleaned_data dict since it was invalid
                        del form.cleaned_data[field]
                    # mark the data as seen
                    seen_data.add(data)

        if errors:
            raise ValidationError(errors)

    def get_unique_error_message(self, unique_check):
        if len(unique_check) == 1:
            return ugettext("Please correct the duplicate data for %(field)s.") % {
                "field": unique_check[0],
            }
        else:
            return ugettext("Please correct the duplicate data for %(field)s, "
                "which must be unique.") % {
                "field": get_text_list(unique_check, six.text_type(_("and"))),
            }

    def get_date_error_message(self, date_check):
        return ugettext("Please correct the duplicate data for %(field_name)s "
            "which must be unique for the %(lookup)s in %(date_field)s.") % {
            'field_name': date_check[2],
            'date_field': date_check[3],
            'lookup': six.text_type(date_check[1]),
        }

    def get_form_error(self):
        return ugettext("Please correct the duplicate values below.")

    def save_existing_objects(self, commit=True):
        self.changed_objects = []
        self.deleted_objects = []
        if not self.initial_forms:
            return []

        saved_instances = []
        forms_to_delete = self.deleted_forms
        for form in self.initial_forms:
            obj = form.instance
            if form in forms_to_delete:
                # If the pk is None, it means that the object can't be
                # deleted again. Possible reason for this is that the
                # object was already deleted from the DB. Refs #14877.
                if obj.pk is None:
                    continue
                self.deleted_objects.append(obj)
                if commit:
                    obj.delete()
            elif form.has_changed():
                self.changed_objects.append((obj, form.changed_data))
                saved_instances.append(self.save_existing(form, obj, commit=commit))
                if not commit:
                    self.saved_forms.append(form)
        return saved_instances

    def save_new_objects(self, commit=True):
        self.new_objects = []
        for form in self.extra_forms:
            if not form.has_changed():
                continue
            # If someone has marked an add form for deletion, don't save the
            # object.
            if self.can_delete and self._should_delete_form(form):
                continue
            self.new_objects.append(self.save_new(form, commit=commit))
            if not commit:
                self.saved_forms.append(form)
        return self.new_objects

    def add_fields(self, form, index):
        """Add a hidden field for the object's primary key."""
        from django.db.models import AutoField, OneToOneField, ForeignKey
        self._pk_field = pk = self.model._meta.pk
        # If a pk isn't editable, then it won't be on the form, so we need to
        # add it here so we can tell which object is which when we get the
        # data back. Generally, pk.editable should be false, but for some
        # reason, auto_created pk fields and AutoField's editable attribute is
        # True, so check for that as well.

        def pk_is_not_editable(pk):
            return ((not pk.editable) or (pk.auto_created or isinstance(pk, AutoField))
                or (pk.rel and pk.rel.parent_link and pk_is_not_editable(pk.rel.to._meta.pk)))
        if pk_is_not_editable(pk) or pk.name not in form.fields:
            if form.is_bound:
                pk_value = form.instance.pk
            else:
                try:
                    if index is not None:
                        pk_value = self.get_queryset()[index].pk
                    else:
                        pk_value = None
                except IndexError:
                    pk_value = None
            if isinstance(pk, OneToOneField) or isinstance(pk, ForeignKey):
                qs = pk.rel.to._default_manager.get_queryset()
            else:
                qs = self.model._default_manager.get_queryset()
            qs = qs.using(form.instance._state.db)
            if form._meta.widgets:
                widget = form._meta.widgets.get(self._pk_field.name, HiddenInput)
            else:
                widget = HiddenInput
            form.fields[self._pk_field.name] = ModelChoiceField(qs, initial=pk_value, required=False, widget=widget)
        super(BaseModelFormSet, self).add_fields(form, index)


def modelformset_factory(model, form=ModelForm, formfield_callback=None,
                         formset=BaseModelFormSet, extra=1, can_delete=False,
                         can_order=False, max_num=None, fields=None, exclude=None,
                         widgets=None, validate_max=False, localized_fields=None,
                         labels=None, help_texts=None, error_messages=None,
                         min_num=None, validate_min=False):
    """
    Returns a FormSet class for the given Django model class.
    """
    meta = getattr(form, 'Meta', None)
    if meta is None:
        meta = type(str('Meta'), (object,), {})
    if (getattr(meta, 'fields', fields) is None and
            getattr(meta, 'exclude', exclude) is None):
        raise ImproperlyConfigured(
            "Calling modelformset_factory without defining 'fields' or "
            "'exclude' explicitly is prohibited."
        )

    form = modelform_factory(model, form=form, fields=fields, exclude=exclude,
                             formfield_callback=formfield_callback,
                             widgets=widgets, localized_fields=localized_fields,
                             labels=labels, help_texts=help_texts, error_messages=error_messages)
    FormSet = formset_factory(form, formset, extra=extra, min_num=min_num, max_num=max_num,
                              can_order=can_order, can_delete=can_delete,
                              validate_min=validate_min, validate_max=validate_max)
    FormSet.model = model
    return FormSet


# InlineFormSets #############################################################

class BaseInlineFormSet(BaseModelFormSet):
    """A formset for child objects related to a parent."""
    def __init__(self, data=None, files=None, instance=None,
                 save_as_new=False, prefix=None, queryset=None, **kwargs):
        if instance is None:
            self.instance = self.fk.rel.to()
        else:
            self.instance = instance
        self.save_as_new = save_as_new
        if queryset is None:
            queryset = self.model._default_manager
        if self.instance.pk is not None:
            qs = queryset.filter(**{self.fk.name: self.instance})
        else:
            qs = queryset.none()
        super(BaseInlineFormSet, self).__init__(data, files, prefix=prefix,
                                                queryset=qs, **kwargs)

    def initial_form_count(self):
        if self.save_as_new:
            return 0
        return super(BaseInlineFormSet, self).initial_form_count()

    def _construct_form(self, i, **kwargs):
        form = super(BaseInlineFormSet, self)._construct_form(i, **kwargs)
        if self.save_as_new:
            # Remove the primary key from the form's data, we are only
            # creating new instances
            form.data[form.add_prefix(self._pk_field.name)] = None

            # Remove the foreign key from the form's data
            form.data[form.add_prefix(self.fk.name)] = None

        # Set the fk value here so that the form can do its validation.
        fk_value = self.instance.pk
        if self.fk.rel.field_name != self.fk.rel.to._meta.pk.name:
            fk_value = getattr(self.instance, self.fk.rel.field_name)
            fk_value = getattr(fk_value, 'pk', fk_value)
        setattr(form.instance, self.fk.get_attname(), fk_value)
        return form

    @classmethod
    def get_default_prefix(cls):
        return cls.fk.rel.get_accessor_name(model=cls.model).replace('+', '')

    def save_new(self, form, commit=True):
        # Use commit=False so we can assign the parent key afterwards, then
        # save the object.
        obj = form.save(commit=False)
        pk_value = getattr(self.instance, self.fk.rel.field_name)
        setattr(obj, self.fk.get_attname(), getattr(pk_value, 'pk', pk_value))
        if commit:
            obj.save()
        # form.save_m2m() can be called via the formset later on if commit=False
        if commit and hasattr(form, 'save_m2m'):
            form.save_m2m()
        return obj

    def add_fields(self, form, index):
        super(BaseInlineFormSet, self).add_fields(form, index)
        if self._pk_field == self.fk:
            name = self._pk_field.name
            kwargs = {'pk_field': True}
        else:
            # The foreign key field might not be on the form, so we poke at the
            # Model field to get the label, since we need that for error messages.
            name = self.fk.name
            kwargs = {
                'label': getattr(form.fields.get(name), 'label', capfirst(self.fk.verbose_name))
            }
            if self.fk.rel.field_name != self.fk.rel.to._meta.pk.name:
                kwargs['to_field'] = self.fk.rel.field_name

        form.fields[name] = InlineForeignKeyField(self.instance, **kwargs)

        # Add the generated field to form._meta.fields if it's defined to make
        # sure validation isn't skipped on that field.
        if form._meta.fields:
            if isinstance(form._meta.fields, tuple):
                form._meta.fields = list(form._meta.fields)
            form._meta.fields.append(self.fk.name)

    def get_unique_error_message(self, unique_check):
        unique_check = [field for field in unique_check if field != self.fk.name]
        return super(BaseInlineFormSet, self).get_unique_error_message(unique_check)


def _get_foreign_key(parent_model, model, fk_name=None, can_fail=False):
    """
    Finds and returns the ForeignKey from model to parent if there is one
    (returns None if can_fail is True and no such field exists). If fk_name is
    provided, assume it is the name of the ForeignKey field. Unless can_fail is
    True, an exception is raised if there is no ForeignKey from model to
    parent_model.
    """
    # avoid circular import
    from django.db.models import ForeignKey
    opts = model._meta
    if fk_name:
        fks_to_parent = [f for f in opts.fields if f.name == fk_name]
        if len(fks_to_parent) == 1:
            fk = fks_to_parent[0]
            if not isinstance(fk, ForeignKey) or \
                    (fk.rel.to != parent_model and
                     fk.rel.to not in parent_model._meta.get_parent_list()):
                raise ValueError(
                    "fk_name '%s' is not a ForeignKey to '%s.%s'."
                    % (fk_name, parent_model._meta.app_label, parent_model._meta.object_name))
        elif len(fks_to_parent) == 0:
            raise ValueError(
                "'%s.%s' has no field named '%s'."
                % (model._meta.app_label, model._meta.object_name, fk_name))
    else:
        # Try to discover what the ForeignKey from model to parent_model is
        fks_to_parent = [
            f for f in opts.fields
            if isinstance(f, ForeignKey)
            and (f.rel.to == parent_model
                or f.rel.to in parent_model._meta.get_parent_list())
        ]
        if len(fks_to_parent) == 1:
            fk = fks_to_parent[0]
        elif len(fks_to_parent) == 0:
            if can_fail:
                return
            raise ValueError(
                "'%s.%s' has no ForeignKey to '%s.%s'." % (
                    model._meta.app_label,
                    model._meta.object_name,
                    parent_model._meta.app_label,
                    parent_model._meta.object_name,
                )
            )
        else:
            raise ValueError(
                "'%s.%s' has more than one ForeignKey to '%s.%s'." % (
                    model._meta.app_label,
                    model._meta.object_name,
                    parent_model._meta.app_label,
                    parent_model._meta.object_name,
                )
            )
    return fk


def inlineformset_factory(parent_model, model, form=ModelForm,
                          formset=BaseInlineFormSet, fk_name=None,
                          fields=None, exclude=None, extra=3, can_order=False,
                          can_delete=True, max_num=None, formfield_callback=None,
                          widgets=None, validate_max=False, localized_fields=None,
                          labels=None, help_texts=None, error_messages=None,
                          min_num=None, validate_min=False):
    """
    Returns an ``InlineFormSet`` for the given kwargs.

    You must provide ``fk_name`` if ``model`` has more than one ``ForeignKey``
    to ``parent_model``.
    """
    fk = _get_foreign_key(parent_model, model, fk_name=fk_name)
    # enforce a max_num=1 when the foreign key to the parent model is unique.
    if fk.unique:
        max_num = 1
    kwargs = {
        'form': form,
        'formfield_callback': formfield_callback,
        'formset': formset,
        'extra': extra,
        'can_delete': can_delete,
        'can_order': can_order,
        'fields': fields,
        'exclude': exclude,
        'min_num': min_num,
        'max_num': max_num,
        'widgets': widgets,
        'validate_min': validate_min,
        'validate_max': validate_max,
        'localized_fields': localized_fields,
        'labels': labels,
        'help_texts': help_texts,
        'error_messages': error_messages,
    }
    FormSet = modelformset_factory(model, **kwargs)
    FormSet.fk = fk
    return FormSet


# Fields #####################################################################

class InlineForeignKeyField(Field):
    """
    A basic integer field that deals with validating the given value to a
    given parent instance in an inline.
    """
    widget = HiddenInput
    default_error_messages = {
        'invalid_choice': _('The inline foreign key did not match the parent instance primary key.'),
    }

    def __init__(self, parent_instance, *args, **kwargs):
        self.parent_instance = parent_instance
        self.pk_field = kwargs.pop("pk_field", False)
        self.to_field = kwargs.pop("to_field", None)
        if self.parent_instance is not None:
            if self.to_field:
                kwargs["initial"] = getattr(self.parent_instance, self.to_field)
            else:
                kwargs["initial"] = self.parent_instance.pk
        kwargs["required"] = False
        super(InlineForeignKeyField, self).__init__(*args, **kwargs)

    def clean(self, value):
        if value in self.empty_values:
            if self.pk_field:
                return None
            # if there is no value act as we did before.
            return self.parent_instance
        # ensure the we compare the values as equal types.
        if self.to_field:
            orig = getattr(self.parent_instance, self.to_field)
        else:
            orig = self.parent_instance.pk
        if force_text(value) != force_text(orig):
            raise ValidationError(self.error_messages['invalid_choice'], code='invalid_choice')
        return self.parent_instance

    def has_changed(self, initial, data):
        return False


class ModelChoiceIterator(object):
    def __init__(self, field):
        self.field = field
        self.queryset = field.queryset

    def __iter__(self):
        if self.field.empty_label is not None:
            yield ("", self.field.empty_label)
        for obj in self.queryset.iterator():
            yield self.choice(obj)

    def __len__(self):
        return (len(self.queryset) +
            (1 if self.field.empty_label is not None else 0))

    def choice(self, obj):
        return (self.field.prepare_value(obj), self.field.label_from_instance(obj))


class ModelChoiceField(ChoiceField):
    """A ChoiceField whose choices are a model QuerySet."""
    # This class is a subclass of ChoiceField for purity, but it doesn't
    # actually use any of ChoiceField's implementation.
    default_error_messages = {
        'invalid_choice': _('Select a valid choice. That choice is not one of'
                            ' the available choices.'),
    }

    def __init__(self, queryset, empty_label="---------",
                 required=True, widget=None, label=None, initial=None,
                 help_text='', to_field_name=None, limit_choices_to=None,
                 *args, **kwargs):
        if required and (initial is not None):
            self.empty_label = None
        else:
            self.empty_label = empty_label

        # Call Field instead of ChoiceField __init__() because we don't need
        # ChoiceField.__init__().
        Field.__init__(self, required, widget, label, initial, help_text,
                       *args, **kwargs)
        self.queryset = queryset
        self.limit_choices_to = limit_choices_to   # limit the queryset later.
        self.to_field_name = to_field_name

    def get_limit_choices_to(self):
        """
        Returns ``limit_choices_to`` for this form field.

        If it is a callable, it will be invoked and the result will be
        returned.
        """
        if callable(self.limit_choices_to):
            return self.limit_choices_to()
        return self.limit_choices_to

    def __deepcopy__(self, memo):
        result = super(ChoiceField, self).__deepcopy__(memo)
        # Need to force a new ModelChoiceIterator to be created, bug #11183
        result.queryset = result.queryset
        return result

    def _get_queryset(self):
        return self._queryset

    def _set_queryset(self, queryset):
        self._queryset = queryset
        self.widget.choices = self.choices

    queryset = property(_get_queryset, _set_queryset)

    # this method will be used to create object labels by the QuerySetIterator.
    # Override it to customize the label.
    def label_from_instance(self, obj):
        """
        This method is used to convert objects into strings; it's used to
        generate the labels for the choices presented by this object. Subclasses
        can override this method to customize the display of the choices.
        """
        return smart_text(obj)

    def _get_choices(self):
        # If self._choices is set, then somebody must have manually set
        # the property self.choices. In this case, just return self._choices.
        if hasattr(self, '_choices'):
            return self._choices

        # Otherwise, execute the QuerySet in self.queryset to determine the
        # choices dynamically. Return a fresh ModelChoiceIterator that has not been
        # consumed. Note that we're instantiating a new ModelChoiceIterator *each*
        # time _get_choices() is called (and, thus, each time self.choices is
        # accessed) so that we can ensure the QuerySet has not been consumed. This
        # construct might look complicated but it allows for lazy evaluation of
        # the queryset.
        return ModelChoiceIterator(self)

    choices = property(_get_choices, ChoiceField._set_choices)

    def prepare_value(self, value):
        if hasattr(value, '_meta'):
            if self.to_field_name:
                return value.serializable_value(self.to_field_name)
            else:
                return value.pk
        return super(ModelChoiceField, self).prepare_value(value)

    def to_python(self, value):
        if value in self.empty_values:
            return None
        try:
            key = self.to_field_name or 'pk'
            value = self.queryset.get(**{key: value})
        except (ValueError, TypeError, self.queryset.model.DoesNotExist):
            raise ValidationError(self.error_messages['invalid_choice'], code='invalid_choice')
        return value

    def validate(self, value):
        return Field.validate(self, value)

    def has_changed(self, initial, data):
        initial_value = initial if initial is not None else ''
        data_value = data if data is not None else ''
        return force_text(self.prepare_value(initial_value)) != force_text(data_value)


class ModelMultipleChoiceField(ModelChoiceField):
    """A MultipleChoiceField whose choices are a model QuerySet."""
    widget = SelectMultiple
    hidden_widget = MultipleHiddenInput
    default_error_messages = {
        'list': _('Enter a list of values.'),
        'invalid_choice': _('Select a valid choice. %(value)s is not one of the'
                            ' available choices.'),
        'invalid_pk_value': _('"%(pk)s" is not a valid value for a primary key.')
    }

    def __init__(self, queryset, required=True, widget=None, label=None,
                 initial=None, help_text='', *args, **kwargs):
        super(ModelMultipleChoiceField, self).__init__(queryset, None,
            required, widget, label, initial, help_text, *args, **kwargs)

    def to_python(self, value):
        if not value:
            return []
        return list(self._check_values(value))

    def clean(self, value):
        if self.required and not value:
            raise ValidationError(self.error_messages['required'], code='required')
        elif not self.required and not value:
            return self.queryset.none()
        if not isinstance(value, (list, tuple)):
            raise ValidationError(self.error_messages['list'], code='list')
        qs = self._check_values(value)
        # Since this overrides the inherited ModelChoiceField.clean
        # we run custom validators here
        self.run_validators(value)
        return qs

    def _check_values(self, value):
        """
        Given a list of possible PK values, returns a QuerySet of the
        corresponding objects. Raises a ValidationError if a given value is
        invalid (not a valid PK, not in the queryset, etc.)
        """
        key = self.to_field_name or 'pk'
        # deduplicate given values to avoid creating many querysets or
        # requiring the database backend deduplicate efficiently.
        try:
            value = frozenset(value)
        except TypeError:
            # list of lists isn't hashable, for example
            raise ValidationError(
                self.error_messages['list'],
                code='list',
            )
        for pk in value:
            try:
                self.queryset.filter(**{key: pk})
            except (ValueError, TypeError):
                raise ValidationError(
                    self.error_messages['invalid_pk_value'],
                    code='invalid_pk_value',
                    params={'pk': pk},
                )
        qs = self.queryset.filter(**{'%s__in' % key: value})
        pks = set(force_text(getattr(o, key)) for o in qs)
        for val in value:
            if force_text(val) not in pks:
                raise ValidationError(
                    self.error_messages['invalid_choice'],
                    code='invalid_choice',
                    params={'value': val},
                )
        return qs

    def prepare_value(self, value):
        if (hasattr(value, '__iter__') and
                not isinstance(value, six.text_type) and
                not hasattr(value, '_meta')):
            return [super(ModelMultipleChoiceField, self).prepare_value(v) for v in value]
        return super(ModelMultipleChoiceField, self).prepare_value(value)

    def has_changed(self, initial, data):
        if initial is None:
            initial = []
        if data is None:
            data = []
        if len(initial) != len(data):
            return True
        initial_set = set(force_text(value) for value in self.prepare_value(initial))
        data_set = set(force_text(value) for value in data)
        return data_set != initial_set


def modelform_defines_fields(form_class):
    return (form_class is not None and (
            hasattr(form_class, '_meta') and
            (form_class._meta.fields is not None or
             form_class._meta.exclude is not None)
            ))
