# Copyright 2014 Budapest University of Technology and Economics (BME IK)
#
# This file is part of CIRCLE Cloud.
#
# CIRCLE is free software: you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# CIRCLE is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
# details.
#
# You should have received a copy of the GNU General Public License along
# with CIRCLE.  If not, see <http://www.gnu.org/licenses/>.
from __future__ import unicode_literals, absolute_import

import json
import logging
import re
from collections import OrderedDict
from urlparse import urljoin

from django.conf import settings
from django.contrib import messages
from django.contrib.auth import REDIRECT_FIELD_NAME, login as auth_login
from django.contrib.auth.forms import AuthenticationForm
from django.contrib.auth.models import User, Group
from django.contrib.auth.views import redirect_to_login
from django.contrib.sites.shortcuts import get_current_site
from django.core import signing
from django.core.exceptions import PermissionDenied, SuspiciousOperation
from django.core.urlresolvers import reverse
from django.db.models import Q, Count, Sum
from django.http import (
    HttpResponse, Http404, HttpResponseRedirect, JsonResponse
)
from django.shortcuts import redirect, render, resolve_url
from django.utils.http import is_safe_url
from django.utils.translation import ugettext_lazy as _, ugettext_noop

from django.utils.decorators import method_decorator
from django.views.decorators.cache import never_cache
from django.views.decorators.csrf import csrf_protect
from django.views.decorators.debug import sensitive_post_parameters
from django.views.generic import DetailView, View, DeleteView, FormView
from django.views.generic.detail import SingleObjectMixin

from braces.views import LoginRequiredMixin
from braces.views._access import AccessMixin
from celery.exceptions import TimeoutError

from common.models import HumanReadableException, HumanReadableObject
from ..models import GroupProfile, Profile
from ..forms import TransferOwnershipForm


logger = logging.getLogger(__name__)
saml_available = hasattr(settings, "SAML_CONFIG")


class RedirectToLoginMixin(AccessMixin):

    redirect_exception_classes = (PermissionDenied, )

    def dispatch(self, request, *args, **kwargs):
        try:
            return super(RedirectToLoginMixin, self).dispatch(
                request, *args, **kwargs)
        except self.redirect_exception_classes:
            if not request.user.is_authenticated():
                return redirect_to_login(request.get_full_path(),
                                         self.get_login_url(),
                                         self.get_redirect_field_name())
            else:
                raise


def search_user(keyword):
    try:
        return User.objects.get(username=keyword)
    except User.DoesNotExist:
        try:
            return User.objects.get(profile__org_id__iexact=keyword)
        except User.DoesNotExist:
            return User.objects.get(email=keyword)


class FilterMixin(object):

    def get_queryset_filters(self):
        filters = {}
        excludes = {}

        for key, value in self.request.GET.items():
            if not key:
                continue
            exclude = key.startswith('!')
            key = key.lstrip('!')
            if key not in self.allowed_filters:
                continue

            filter_field = self.allowed_filters[key]
            value = (value.split(",")
                     if filter_field.endswith("__in") else
                     value)
            if exclude:
                excludes[filter_field] = value
            else:
                filters[filter_field] = value

        return filters, excludes

    def get_queryset(self):
        return super(FilterMixin,
                     self).get_queryset().filter(**self.get_queryset_filters())

    def create_fake_get(self):
        self.request.GET = self._parse_get(self.request.GET)

    def _parse_get(self, GET_dict):
        """
        Returns a new dict from request's GET dict to filter the vm list
        For example: "name:xy node:1" updates the GET dict
                     to resemble this URL ?name=xy&node=1

        "name:xy node:1".split(":") becomes ["name", "xy node", "1"]
        we pop the the first element and use it as the first dict key
        then we iterate over the rest of the list and split by the last
        whitespace, the first part of this list will be the previous key's
        value, then last part of the list will be the next key.
        The final dict looks like this: {'name': xy, 'node':1}

        >>> f = FilterMixin()
        >>> o = f._parse_get({'s': "hello"}).items()
        >>> sorted(o) # doctest: +ELLIPSIS
        [(u'name', u'hello'), (...)]
        >>> o = f._parse_get({'s': "name:hello owner:test"}).items()
        >>> sorted(o) # doctest: +ELLIPSIS
        [(u'name', u'hello'), (u'owner', u'test'), (...)]
        >>> o = f._parse_get({'s': "name:hello ws node:node 3 oh"}).items()
        >>> sorted(o) # doctest: +ELLIPSIS
        [(u'name', u'hello ws'), (u'node', u'node 3 oh'), (...)]
        >>> o = f._parse_get({'s': "!hello:szia"}).items()
        >>> sorted(o) # doctest: +ELLIPSIS
        [(u'!hello', u'szia'), (...)]
        """
        s = GET_dict.get("s")
        fake = GET_dict.copy()
        if s:
            s = s.split(":")
            if len(s) < 2:  # if there is no ':' in the string, filter by name
                got = {'name': s[0]}
            else:
                latest = s.pop(0)
                got = {'%s' % latest: None}
                for i in s[:-1]:
                    new = i.rsplit(" ", 1)
                    got[latest] = new[0]
                    latest = new[1] if len(new) > 1 else None
                got[latest] = s[-1]

            # generate a new GET request, that is kinda fake
            for k, v in got.iteritems():
                fake[k] = v
        return fake

    def create_acl_queryset(self, model):
        cleaned_data = self.search_form.cleaned_data
        stype = cleaned_data.get('stype', 'all')
        superuser = stype == 'all'
        shared = stype == 'shared' or stype == 'all'
        level = 'owner' if stype == 'owned' else 'user'
        user = self.request.user
        queryset = model.get_objects_with_level(
            level, user, group_also=shared, disregard_superuser=not superuser)
        if stype == 'owned':
            queryset = queryset.filter(owner=user)
        elif stype == 'shared':
            queryset = queryset.filter(owner=user)

            pk_list = []
            for record in queryset:
                count = record.object_level_set.annotate(
                    Count('users'), Count('groups')).aggregate(
                        Sum('users__count'), Sum('groups__count'))
                if (count['users__count__sum'] > 1 or
                   count['groups__count__sum'] > 0):

                    pk_list.append(record.pk)

            queryset = queryset.filter(pk__in=pk_list)
        elif stype == 'shared_with_me':
            queryset = queryset.exclude(owner=user)
        return queryset


class CheckedDetailView(LoginRequiredMixin, DetailView):
    read_level = 'user'

    def get_has_level(self):
        return self.object.has_level

    def get_context_data(self, **kwargs):
        context = super(CheckedDetailView, self).get_context_data(**kwargs)
        if not self.get_has_level()(self.request.user, self.read_level):
            raise PermissionDenied()
        return context


class OperationView(RedirectToLoginMixin, DetailView):

    template_name = 'dashboard/operate.html'
    show_in_toolbar = True
    effect = None
    wait_for_result = None
    with_reload = False

    @property
    def name(self):
        return self.get_op().name

    @property
    def description(self):
        return self.get_op().description

    def is_preferred(self):
        return self.get_op().is_preferred()

    @classmethod
    def get_urlname(cls):
        return 'dashboard.%s.op.%s' % (cls.model._meta.model_name, cls.op)

    @classmethod
    def get_instance_url(cls, pk, key=None, *args, **kwargs):
        url = reverse(cls.get_urlname(), args=(pk, ) + args, kwargs=kwargs)
        if key is None:
            return url
        else:
            return "%s?k=%s" % (url, key)

    def get_url(self, **kwargs):
        return self.get_instance_url(self.get_object().pk, **kwargs)

    def get_template_names(self):
        if self.request.is_ajax():
            return ['dashboard/_modal.html']
        else:
            return ['dashboard/_base.html']

    @classmethod
    def get_op_by_object(cls, obj):
        return getattr(obj, cls.op)

    def get_op(self):
        if not hasattr(self, '_opobj'):
            setattr(self, '_opobj', getattr(self.get_object(), self.op))
        return self._opobj

    @classmethod
    def get_operation_class(cls):
        return cls.model.get_operation_class(cls.op)

    def get_context_data(self, **kwargs):
        ctx = super(OperationView, self).get_context_data(**kwargs)
        ctx['op'] = self.get_op()
        ctx['opview'] = self
        url = self.request.path
        if self.request.GET:
            url += '?' + self.request.GET.urlencode()
        ctx['url'] = url
        ctx['template'] = super(OperationView, self).get_template_names()[0]
        return ctx

    def check_auth(self):
        logger.debug("OperationView.check_auth(%s)", unicode(self))
        self.get_op().check_auth(self.request.user)

    @classmethod
    def check_perms(cls, user):
        cls.get_operation_class().check_perms(user)

    def get(self, request, *args, **kwargs):
        self.check_auth()
        return super(OperationView, self).get(request, *args, **kwargs)

    def get_response_data(self, result, done, extra=None, **kwargs):
        """Return serializable data to return to agents requesting json
        response to POST"""

        if extra is None:
            extra = {}
        extra["success"] = not isinstance(result, Exception)
        extra["done"] = done
        if isinstance(result, HumanReadableObject):
            extra["message"] = result.get_user_text()
        return extra

    def post(self, request, extra=None, *args, **kwargs):
        self.check_auth()
        self.object = self.get_object()
        if extra is None:
            extra = {}
        result = None
        done = False
        try:
            task = self.get_op().async(user=request.user, **extra)
        except HumanReadableException as e:
            e.send_message(request)
            logger.exception("Could not start operation")
            result = e
        except Exception as e:
            messages.error(request, _('Could not start operation.'))
            logger.exception("Could not start operation")
            result = e
        else:
            wait = self.wait_for_result
            if wait:
                try:
                    result = task.get(timeout=wait,
                                      interval=min((wait / 5, .5)))
                except TimeoutError:
                    logger.debug("Result didn't arrive in %ss",
                                 self.wait_for_result, exc_info=True)
                except HumanReadableException as e:
                    e.send_message(request)
                    logger.exception(e)
                    result = e
                except Exception as e:
                    messages.error(request, _('Operation failed.'))
                    logger.debug("Operation failed.", exc_info=True)
                    result = e
                else:
                    done = True
                    messages.success(request, _('Operation succeeded.'))
            if result is None and not done:
                messages.success(request, _('Operation is started.'))

        if "/json" in request.META.get("HTTP_ACCEPT", ""):
            data = self.get_response_data(result, done,
                                          post_extra=extra, **kwargs)
            return HttpResponse(json.dumps(data),
                                content_type="application/json")
        else:
            return HttpResponseRedirect("%s#activity" %
                                        self.object.get_absolute_url())

    @classmethod
    def factory(cls, op, icon='cog', effect='info', extra_bases=(), **kwargs):
        kwargs.update({'op': op, 'icon': icon, 'effect': effect})
        return type(str(cls.__name__ + op),
                    tuple(list(extra_bases) + [cls]), kwargs)

    @classmethod
    def bind_to_object(cls, instance, **kwargs):
        me = cls()
        me.get_object = lambda: instance
        for key, value in kwargs.iteritems():
            setattr(me, key, value)
        return me


class AjaxOperationMixin(object):

    def post(self, request, extra=None, *args, **kwargs):
        resp = super(AjaxOperationMixin, self).post(
            request, extra, *args, **kwargs)
        if request.is_ajax():
            if not self.with_reload:
                store = messages.get_messages(request)
                store.used = True
            else:
                store = []
            return JsonResponse({'success': True,
                                 'with_reload': self.with_reload,
                                 'messages': [unicode(m) for m in store]})
        else:
            return resp


class FormOperationMixin(object):

    form_class = None

    def get_form_kwargs(self):
        return {}

    def get_context_data(self, **kwargs):
        ctx = super(FormOperationMixin, self).get_context_data(**kwargs)
        if self.request.method == 'POST':
            ctx['form'] = self.form_class(self.request.POST,
                                          **self.get_form_kwargs())
        else:
            ctx['form'] = self.form_class(**self.get_form_kwargs())
        return ctx

    def post(self, request, extra=None, *args, **kwargs):
        if extra is None:
            extra = {}
        form = self.form_class(self.request.POST, **self.get_form_kwargs())
        if form.is_valid():
            extra.update(form.cleaned_data)
            resp = super(FormOperationMixin, self).post(
                request, extra, *args, **kwargs)
            if request.is_ajax():
                return JsonResponse({'success': True,
                                     'with_reload': self.with_reload})
            else:
                return resp
        else:
            return self.get(request)


class RequestFormOperationMixin(FormOperationMixin):

    def get_form_kwargs(self):
        val = super(RequestFormOperationMixin, self).get_form_kwargs()
        val.update({'request': self.request})
        return val


class AclUpdateView(LoginRequiredMixin, View, SingleObjectMixin):
    def send_success_message(self, whom, old_level, new_level):
        if old_level and new_level:
            msg = _("Acl user/group %(w)s successfully modified.")
        elif not old_level and new_level:
            msg = _("Acl user/group %(w)s successfully added.")
        elif old_level and not new_level:
            msg = _("Acl user/group %(w)s successfully removed.")
        if msg:
            messages.success(self.request, msg % {'w': whom})

    def get_level(self, whom):
        for u, level in self.acl_data:
            if u == whom:
                return level
        return None

    @classmethod
    def get_acl_data(cls, obj, user, url):
        levels = obj.ACL_LEVELS
        allowed_levels = list(l for l in OrderedDict(levels)
                              if cls.has_next_level(user, obj, l))
        is_owner = 'owner' in allowed_levels

        allowed_users = cls.get_allowed_users(user)
        allowed_groups = (set(cls.get_allowed_groups(user)) |
                          set(user.groups.all()))

        user_levels = list(
            {'user': u, 'level': l} for u, l in obj.get_users_with_level()
            if is_owner or u == user or u in allowed_users)

        group_levels = list(
            {'group': g, 'level': l} for g, l in obj.get_groups_with_level()
            if is_owner or g in allowed_groups)

        return {'users': user_levels,
                'groups': group_levels,
                'levels': levels,
                'allowed_levels': allowed_levels,
                'url': reverse(url, args=[obj.pk])}

    @classmethod
    def has_next_level(self, user, instance, level):
        levels = OrderedDict(instance.ACL_LEVELS).keys()
        next_levels = dict(zip([None] + levels, levels + levels[-1:]))
        # {None: 'user', 'user': 'operator', 'operator: 'owner',
        #  'owner: 'owner'}
        next_level = next_levels[level]
        return instance.has_level(user, next_level)

    @classmethod
    def get_allowed_groups(cls, user):
        if user.has_perm('dashboard.use_autocomplete'):
            return Group.objects.all()
        else:
            profiles = GroupProfile.get_objects_with_level('owner', user)
            return Group.objects.filter(groupprofile__in=profiles).distinct()

    @classmethod
    def get_allowed_users(cls, user):
        if user.has_perm('dashboard.use_autocomplete'):
            return User.objects.all()
        else:
            groups = cls.get_allowed_groups(user)
            return User.objects.filter(
                Q(groups__in=groups) | Q(pk=user.pk)).distinct()

    def check_auth(self, whom, old_level, new_level):
        if isinstance(whom, Group):
            if (not self.is_owner and whom not in
                    AclUpdateView.get_allowed_groups(self.request.user)):
                return False
        elif isinstance(whom, User):
            if (not self.is_owner and whom not in
                    AclUpdateView.get_allowed_users(self.request.user)):
                return False
        return (
            AclUpdateView.has_next_level(self.request.user,
                                         self.instance, new_level) and
            AclUpdateView.has_next_level(self.request.user,
                                         self.instance, old_level))

    def set_level(self, whom, new_level):
        user = self.request.user
        old_level = self.get_level(whom)
        if old_level == new_level:
            return

        if getattr(self.instance, "owner", None) == whom:
            logger.info("Tried to set owner's acl level for %s by %s.",
                        unicode(self.instance), unicode(user))
            msg = _("The original owner cannot be removed, however "
                    "you can transfer ownership.")
            if not getattr(self, 'hide_messages', False):
                messages.warning(self.request, msg)
        elif self.check_auth(whom, old_level, new_level):
            logger.info(
                u"Set %s's acl level for %s to %s by %s.", unicode(whom),
                unicode(self.instance), new_level, unicode(user))
            if not getattr(self, 'hide_messages', False):
                self.send_success_message(whom, old_level, new_level)
            self.instance.set_level(whom, new_level)
        else:
            logger.warning(
                u"Tried to set %s's acl_level for %s (%s->%s) by %s.",
                unicode(whom), unicode(self.instance), old_level, new_level,
                unicode(user))

    def set_or_remove_levels(self):
        for key, value in self.request.POST.items():
            m = re.match('(perm|remove)-([ug])-(\d+)', key)
            if m:
                cmd, typ, id = m.groups()
                if cmd == 'remove':
                    value = None
                entity = {'u': User, 'g': Group}[typ].objects.get(id=id)
                self.set_level(entity, value)

    def add_levels(self):
        name = self.request.POST.get('name', None)
        level = self.request.POST.get('level', None)
        if not name or not level:
            return
        try:
            entity = search_user(name)
            if self.instance.object_level_set.filter(users__in=[entity]):
                messages.warning(
                    self.request, _('User "%s" has already '
                                    'access to this object.') % name)
                return
        except User.DoesNotExist:
            entity = None
            try:
                entity = Group.objects.get(name=name)
                if self.instance.object_level_set.filter(groups__in=[entity]):
                    messages.warning(
                        self.request, _('Group "%s" has already '
                                        'access to this object.') % name)
                    return
            except Group.DoesNotExist:
                messages.warning(
                    self.request, _('User or group "%s" not found.') % name)
                return
        self.set_level(entity, level)

    def post(self, request, *args, **kwargs):
        self.instance = self.get_object()
        self.is_owner = self.instance.has_level(request.user, 'owner')
        self.acl_data = (self.instance.get_users_with_level() +
                         self.instance.get_groups_with_level())
        self.set_or_remove_levels()
        self.add_levels()
        return redirect("%s#access" % self.instance.get_absolute_url())


class GraphMixin(object):
    graph_time_options = [
        {'time': "1h", 'name': _("1 hour")},
        {'time': "6h", 'name': _("6 hours")},
        {'time': "1d", 'name': _("1 day")},
        {'time': "1w", 'name': _("1 week")},
        {'time': "30d", 'name': _("1 month")},
        {'time': "26w", 'name': _("6 months")},
    ]
    default_graph_time = "6h"

    def get_context_data(self, *args, **kwargs):
        context = super(GraphMixin, self).get_context_data(*args, **kwargs)
        graph_time = self.request.GET.get("graph_time",
                                          self.default_graph_time)
        if not re.match("^[0-9]{1,2}[hdwy]$", graph_time):
            messages.warning(self.request, _("Bad graph time format, "
                                             "available periods are: "
                                             "h, d, w, and y."))
            graph_time = self.default_graph_time
        context['graph_time'] = graph_time
        context['graph_time_options'] = self.graph_time_options
        return context


def absolute_url(url):
    return urljoin(settings.DJANGO_URL, url)


class TransferOwnershipView(CheckedDetailView, DetailView):
    def get_template_names(self):
        if self.request.is_ajax():
            return ['dashboard/_modal.html']
        else:
            return ['dashboard/nojs-wrapper.html']

    def get_context_data(self, *args, **kwargs):
        context = super(TransferOwnershipView, self).get_context_data(
            *args, **kwargs)
        context['form'] = TransferOwnershipForm()
        context.update({
            'box_title': _("Transfer ownership"),
            'ajax_title': True,
            'template': self.template,
        })
        return context

    def post(self, request, *args, **kwargs):
        form = TransferOwnershipForm(request.POST)
        if not form.is_valid():
            return self.get(request)
        try:
            new_owner = search_user(request.POST['name'])
        except User.DoesNotExist:
            messages.error(request, _('Can not find specified user.'))
            return self.get(request, *args, **kwargs)
        except KeyError:
            raise SuspiciousOperation()

        obj = self.get_object()
        if not (obj.owner == request.user or
                request.user.is_superuser):
            raise PermissionDenied()

        token = signing.dumps(
            (obj.pk, new_owner.pk),
            salt=self.confirm_view.get_salt())
        token_path = reverse(self.token_url, args=[token])
        try:
            new_owner.profile.notify(
                ugettext_noop('Ownership offer'),
                self.notification_msg,
                {'instance': obj, 'token': token_path, 'owner': request.user})
        except Profile.DoesNotExist:
            messages.error(request, _('Can not notify selected user.'))
        else:
            messages.success(request,
                             _('User %s is notified about the offer.') % (
                                 unicode(new_owner), ))

        return redirect(obj.get_absolute_url())


class TransferOwnershipConfirmView(LoginRequiredMixin, View):
    """User can accept an ownership offer."""

    max_age = 3 * 24 * 3600
    success_message = _("Ownership successfully transferred to you.")

    @classmethod
    def get_salt(cls):
        return unicode(cls) + unicode(cls.model)

    def get(self, request, key, *args, **kwargs):
        """Confirm ownership transfer based on token.
        """
        logger.debug('Confirm dialog for token %s.', key)
        try:
            instance, new_owner = self.get_instance(key, request.user)
        except PermissionDenied:
            messages.error(request, _('This token is for an other user.'))
            raise
        except SuspiciousOperation:
            messages.error(request, _('This token is invalid or has expired.'))
            raise PermissionDenied()
        return render(request, self.template,
                      dictionary={'instance': instance, 'key': key})

    def change_owner(self, instance, new_owner):
        instance.owner = new_owner
        instance.clean()
        instance.save()

    def post(self, request, key, *args, **kwargs):
        """Really transfer ownership based on token.
        """
        instance, owner = self.get_instance(key, request.user)

        old = instance.owner
        self.change_owner(instance, request.user)
        messages.success(request, self.success_message)
        logger.info('Ownership of %s transferred from %s to %s.',
                    unicode(instance), unicode(old), unicode(request.user))
        if old.profile:
            old.profile.notify(
                ugettext_noop('Ownership accepted'),
                ugettext_noop('Your ownership offer of %(instance)s has been '
                              'accepted by %(owner)s.'),
                {'instance': instance, 'owner': request.user})
        return redirect(instance.get_absolute_url())

    def get_instance(self, key, user):
        """Get object based on signed token.
        """
        try:
            instance, new_owner = (
                signing.loads(key, max_age=self.max_age,
                              salt=self.get_salt()))
        except (signing.BadSignature, ValueError, TypeError) as e:
            logger.error('Tried invalid token. Token: %s, user: %s. %s',
                         key, unicode(user), unicode(e))
            raise SuspiciousOperation()

        try:
            instance = self.model.objects.get(id=instance)
        except self.model.DoesNotExist as e:
            logger.error('Tried token to nonexistent instance %d. '
                         'Token: %s, user: %s. %s',
                         instance, key, unicode(user), unicode(e))
            raise Http404()

        if new_owner != user.pk:
            logger.error('%s (%d) tried the token for %s. Token: %s.',
                         unicode(user), user.pk, new_owner, key)
            raise PermissionDenied()
        return (instance, new_owner)


class DeleteViewBase(LoginRequiredMixin, DeleteView):
    level = 'owner'

    def get_template_names(self):
        if self.request.is_ajax():
            return ['dashboard/confirm/ajax-delete.html']
        else:
            return ['dashboard/confirm/base-delete.html']

    def check_auth(self):
        if not self.get_object().has_level(self.request.user, self.level):
            raise PermissionDenied()

    def get(self, request, *args, **kwargs):
        try:
            self.check_auth()
        except PermissionDenied:
            message = _("Only the owners can delete the selected object.")
            if request.is_ajax():
                raise PermissionDenied()
            else:
                messages.warning(request, message)
                return redirect(self.get_success_url())
        return super(DeleteViewBase, self).get(request, *args, **kwargs)

    def delete_obj(self, request, *args, **kwargs):
        self.get_object().delete()

    def delete(self, request, *args, **kwargs):
        self.check_auth()
        self.delete_obj(request, *args, **kwargs)

        if request.is_ajax():
            return HttpResponse(
                json.dumps({'message': self.success_message}),
                content_type="application/json",
            )
        else:
            messages.success(request, self.success_message)
            return HttpResponseRedirect(self.get_success_url())


# only in Django 1.9
class LoginView(FormView):
    """
    Displays the login form and handles the login action.
    """
    form_class = AuthenticationForm
    authentication_form = None
    redirect_field_name = REDIRECT_FIELD_NAME
    template_name = 'registration/login.html'
    redirect_authenticated_user = False
    extra_context = None

    @method_decorator(sensitive_post_parameters())
    @method_decorator(csrf_protect)
    @method_decorator(never_cache)
    def dispatch(self, request, *args, **kwargs):
        if (self.redirect_authenticated_user and
                self.request.user.is_authenticated):
            redirect_to = self.get_success_url()
            if redirect_to == self.request.path:
                raise ValueError(
                    "Redirection loop for authenticated user detected. Check "
                    "your LOGIN_REDIRECT_URL doesn't point to a login page."
                )
            return HttpResponseRedirect(redirect_to)
        return super(LoginView, self).dispatch(request, *args, **kwargs)

    def get_success_url(self):
        """Ensure the user-originating redirection URL is safe."""
        redirect_to = self.request.POST.get(
            self.redirect_field_name,
            self.request.GET.get(self.redirect_field_name, '')
        )
        if not is_safe_url(url=redirect_to, host=self.request.get_host()):
            return resolve_url(settings.LOGIN_REDIRECT_URL)
        return redirect_to

    def get_form_class(self):
        return self.authentication_form or self.form_class

    def form_valid(self, form):
        """Security check complete. Log the user in."""
        auth_login(self.request, form.get_user())
        return HttpResponseRedirect(self.get_success_url())

    def get_context_data(self, **kwargs):
        context = super(LoginView, self).get_context_data(**kwargs)
        current_site = get_current_site(self.request)
        context.update({
            self.redirect_field_name: self.get_success_url(),
            'site': current_site,
            'site_name': current_site.name,
        })
        if self.extra_context is not None:
            context.update(self.extra_context)
        return context
