import inspect
import warnings

from django.core.exceptions import ImproperlyConfigured
from django.forms import models as model_forms
from django.http import HttpResponseRedirect
from django.utils import six
from django.utils.deprecation import RemovedInDjango20Warning
from django.utils.encoding import force_text
from django.views.generic.base import TemplateResponseMixin, ContextMixin, View
from django.views.generic.detail import (SingleObjectMixin,
                        SingleObjectTemplateResponseMixin, BaseDetailView)


class FormMixinBase(type):
    def __new__(cls, name, bases, attrs):
        get_form = attrs.get('get_form')
        if get_form and inspect.isfunction(get_form):
            try:
                inspect.getcallargs(get_form, None)
            except TypeError:
                warnings.warn(
                    "`%s.%s.get_form` method must define a default value for "
                    "its `form_class` argument." % (attrs['__module__'], name),
                    RemovedInDjango20Warning, stacklevel=2
                )

                def get_form_with_form_class(self, form_class=None):
                    if form_class is None:
                        form_class = self.get_form_class()
                    return get_form(self, form_class=form_class)
                attrs['get_form'] = get_form_with_form_class
        return super(FormMixinBase, cls).__new__(cls, name, bases, attrs)


class FormMixin(six.with_metaclass(FormMixinBase, ContextMixin)):
    """
    A mixin that provides a way to show and handle a form in a request.
    """

    initial = {}
    form_class = None
    success_url = None
    prefix = None

    def get_initial(self):
        """
        Returns the initial data to use for forms on this view.
        """
        return self.initial.copy()

    def get_prefix(self):
        """
        Returns the prefix to use for forms on this view
        """
        return self.prefix

    def get_form_class(self):
        """
        Returns the form class to use in this view
        """
        return self.form_class

    def get_form(self, form_class=None):
        """
        Returns an instance of the form to be used in this view.
        """
        if form_class is None:
            form_class = self.get_form_class()
        return form_class(**self.get_form_kwargs())

    def get_form_kwargs(self):
        """
        Returns the keyword arguments for instantiating the form.
        """
        kwargs = {
            'initial': self.get_initial(),
            'prefix': self.get_prefix(),
        }

        if self.request.method in ('POST', 'PUT'):
            kwargs.update({
                'data': self.request.POST,
                'files': self.request.FILES,
            })
        return kwargs

    def get_success_url(self):
        """
        Returns the supplied success URL.
        """
        if self.success_url:
            # Forcing possible reverse_lazy evaluation
            url = force_text(self.success_url)
        else:
            raise ImproperlyConfigured(
                "No URL to redirect to. Provide a success_url.")
        return url

    def form_valid(self, form):
        """
        If the form is valid, redirect to the supplied URL.
        """
        return HttpResponseRedirect(self.get_success_url())

    def form_invalid(self, form):
        """
        If the form is invalid, re-render the context data with the
        data-filled form and errors.
        """
        return self.render_to_response(self.get_context_data(form=form))


class ModelFormMixin(FormMixin, SingleObjectMixin):
    """
    A mixin that provides a way to show and handle a modelform in a request.
    """
    fields = None

    def get_form_class(self):
        """
        Returns the form class to use in this view.
        """
        if self.fields is not None and self.form_class:
            raise ImproperlyConfigured(
                "Specifying both 'fields' and 'form_class' is not permitted."
            )
        if self.form_class:
            return self.form_class
        else:
            if self.model is not None:
                # If a model has been explicitly provided, use it
                model = self.model
            elif hasattr(self, 'object') and self.object is not None:
                # If this view is operating on a single object, use
                # the class of that object
                model = self.object.__class__
            else:
                # Try to get a queryset and extract the model class
                # from that
                model = self.get_queryset().model

            if self.fields is None:
                raise ImproperlyConfigured(
                    "Using ModelFormMixin (base class of %s) without "
                    "the 'fields' attribute is prohibited." % self.__class__.__name__
                )

            return model_forms.modelform_factory(model, fields=self.fields)

    def get_form_kwargs(self):
        """
        Returns the keyword arguments for instantiating the form.
        """
        kwargs = super(ModelFormMixin, self).get_form_kwargs()
        if hasattr(self, 'object'):
            kwargs.update({'instance': self.object})
        return kwargs

    def get_success_url(self):
        """
        Returns the supplied URL.
        """
        if self.success_url:
            url = self.success_url % self.object.__dict__
        else:
            try:
                url = self.object.get_absolute_url()
            except AttributeError:
                raise ImproperlyConfigured(
                    "No URL to redirect to.  Either provide a url or define"
                    " a get_absolute_url method on the Model.")
        return url

    def form_valid(self, form):
        """
        If the form is valid, save the associated model.
        """
        self.object = form.save()
        return super(ModelFormMixin, self).form_valid(form)


class ProcessFormView(View):
    """
    A mixin that renders a form on GET and processes it on POST.
    """
    def get(self, request, *args, **kwargs):
        """
        Handles GET requests and instantiates a blank version of the form.
        """
        form = self.get_form()
        return self.render_to_response(self.get_context_data(form=form))

    def post(self, request, *args, **kwargs):
        """
        Handles POST requests, instantiating a form instance with the passed
        POST variables and then checked for validity.
        """
        form = self.get_form()
        if form.is_valid():
            return self.form_valid(form)
        else:
            return self.form_invalid(form)

    # PUT is a valid HTTP verb for creating (with a known URL) or editing an
    # object, note that browsers only support POST for now.
    def put(self, *args, **kwargs):
        return self.post(*args, **kwargs)


class BaseFormView(FormMixin, ProcessFormView):
    """
    A base view for displaying a form
    """


class FormView(TemplateResponseMixin, BaseFormView):
    """
    A view for displaying a form, and rendering a template response.
    """


class BaseCreateView(ModelFormMixin, ProcessFormView):
    """
    Base view for creating an new object instance.

    Using this base class requires subclassing to provide a response mixin.
    """
    def get(self, request, *args, **kwargs):
        self.object = None
        return super(BaseCreateView, self).get(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        self.object = None
        return super(BaseCreateView, self).post(request, *args, **kwargs)


class CreateView(SingleObjectTemplateResponseMixin, BaseCreateView):
    """
    View for creating a new object instance,
    with a response rendered by template.
    """
    template_name_suffix = '_form'


class BaseUpdateView(ModelFormMixin, ProcessFormView):
    """
    Base view for updating an existing object.

    Using this base class requires subclassing to provide a response mixin.
    """
    def get(self, request, *args, **kwargs):
        self.object = self.get_object()
        return super(BaseUpdateView, self).get(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        self.object = self.get_object()
        return super(BaseUpdateView, self).post(request, *args, **kwargs)


class UpdateView(SingleObjectTemplateResponseMixin, BaseUpdateView):
    """
    View for updating an object,
    with a response rendered by template.
    """
    template_name_suffix = '_form'


class DeletionMixin(object):
    """
    A mixin providing the ability to delete objects
    """
    success_url = None

    def delete(self, request, *args, **kwargs):
        """
        Calls the delete() method on the fetched object and then
        redirects to the success URL.
        """
        self.object = self.get_object()
        success_url = self.get_success_url()
        self.object.delete()
        return HttpResponseRedirect(success_url)

    # Add support for browsers which only accept GET and POST for now.
    def post(self, request, *args, **kwargs):
        return self.delete(request, *args, **kwargs)

    def get_success_url(self):
        if self.success_url:
            return self.success_url % self.object.__dict__
        else:
            raise ImproperlyConfigured(
                "No URL to redirect to. Provide a success_url.")


class BaseDeleteView(DeletionMixin, BaseDetailView):
    """
    Base view for deleting an object.

    Using this base class requires subclassing to provide a response mixin.
    """


class DeleteView(SingleObjectTemplateResponseMixin, BaseDeleteView):
    """
    View for deleting an object retrieved with `self.get_object()`,
    with a response rendered by template.
    """
    template_name_suffix = '_confirm_delete'