from django.contrib.auth import login as auth_login
from django.contrib.auth import logout as auth_logout
from django.contrib.auth.forms import AuthenticationForm
from django.utils.encoding import force_text
from django.utils.translation import ugettext as _
from django.utils.translation import ugettext_lazy

from ..core.config import config
from ..utils.rest_api import (
    ModelViewSet,
    Response,
    SimpleMetadata,
    ValidationError,
    detail_route,
    status,
)
from ..utils.views import APIView, PDFView
from .access_permissions import UserAccessPermissions
from .models import Group, User
from .pdf import users_passwords_to_pdf, users_to_pdf
from .serializers import GroupSerializer


# Viewsets for the REST API

class UserViewSet(ModelViewSet):
    """
    API endpoint for users.

    There are the following views: metadata, list, retrieve, create,
    partial_update, update, destroy and reset_password.
    """
    access_permissions = UserAccessPermissions()
    queryset = User.objects.all()

    def check_view_permissions(self):
        """
        Returns True if the user has required permissions.
        """
        if self.action in ('list', 'retrieve'):
            result = self.get_access_permissions().check_permissions(self.request.user)
        elif self.action in ('metadata', 'update', 'partial_update'):
            result = self.request.user.has_perm('users.can_see_name')
        elif self.action in ('create', 'destroy', 'reset_password'):
            result = (self.request.user.has_perm('users.can_see_name') and
                      self.request.user.has_perm('users.can_see_extra_data') and
                      self.request.user.has_perm('users.can_manage'))
        else:
            result = False
        return result

    def update(self, request, *args, **kwargs):
        """
        Customized view endpoint to update an user.

        Checks also whether the requesting user can update the user. He
        needs at least the permissions 'users.can_see_name' (see
        self.check_view_permissions()). Also it is evaluated whether he
        wants to update himself or is manager.
        """
        # Check manager perms
        if (request.user.has_perm('users.can_see_extra_data') and
                request.user.has_perm('users.can_manage')):
            if request.data.get('is_active') is False and self.get_object() == request.user:
                # A user can not deactivate himself.
                raise ValidationError({'detail': _('You can not deactivate yourself.')})
        else:
            # Check permissions only to update yourself.
            if str(request.user.pk) != self.kwargs['pk']:
                self.permission_denied(request)
        response = super().update(request, *args, **kwargs)
        return response

    def destroy(self, request, *args, **kwargs):
        """
        Customized view endpoint to delete an user.

        Ensures that no one can delete himself.
        """
        instance = self.get_object()
        if instance == self.request.user:
            raise ValidationError({'detail': _('You can not delete yourself.')})
        self.perform_destroy(instance)
        return Response(status=status.HTTP_204_NO_CONTENT)

    @detail_route(methods=['post'])
    def reset_password(self, request, pk=None):
        """
        View to reset the password using the requested password.
        """
        user = self.get_object()
        if isinstance(request.data.get('password'), str):
            user.set_password(request.data.get('password'))
            user.save()
            return Response({'detail': _('Password successfully reset.')})
        else:
            raise ValidationError({'detail': 'Password has to be a string.'})


class GroupViewSetMetadata(SimpleMetadata):
    """
    Customized metadata class for OPTIONS requests.
    """
    def get_field_info(self, field):
        """
        Customized method to change the display name of permission choices.
        """
        field_info = super().get_field_info(field)
        if field.field_name == 'permissions':
            field_info['choices'] = [
                {
                    'value': choice_value,
                    'display_name': force_text(choice_name, strings_only=True).split(' | ')[2]
                }
                for choice_value, choice_name in field.choices.items()
            ]
        return field_info


class GroupViewSet(ModelViewSet):
    """
    API endpoint for groups.

    There are the following views: metadata, list, retrieve, create,
    partial_update, update and destroy.
    """
    metadata_class = GroupViewSetMetadata
    queryset = Group.objects.prefetch_related('permissions', 'permissions__content_type')
    serializer_class = GroupSerializer

    def check_view_permissions(self):
        """
        Returns True if the user has required permissions.
        """
        if self.action in ('metadata', 'list', 'retrieve'):
            # Every authenticated user can see the metadata and list or
            # retrieve groups. Anonymous users can do so if they are enabled.
            result = self.request.user.is_authenticated() or config['general_system_enable_anonymous']
        elif self.action in ('create', 'partial_update', 'update', 'destroy'):
            # Users with all app permissions can edit groups.
            result = (self.request.user.has_perm('users.can_see_name') and
                      self.request.user.has_perm('users.can_see_extra_data') and
                      self.request.user.has_perm('users.can_manage'))
        else:
            # Deny request in any other case.
            result = False
        return result

    def destroy(self, request, *args, **kwargs):
        """
        Protects builtin groups 'Default' (pk=1) from being deleted.
        """
        instance = self.get_object()
        if instance.pk == 1:
            self.permission_denied(request)
        self.perform_destroy(instance)
        return Response(status=status.HTTP_204_NO_CONTENT)


# Special API views

class UserLoginView(APIView):
    """
    Login the user.
    """
    http_method_names = ['get', 'post']

    def post(self, *args, **kwargs):
        form = AuthenticationForm(self.request, data=self.request.data)
        if not form.is_valid():
            raise ValidationError({'detail': _('Username or password is not correct.')})
        self.user = form.get_user()
        auth_login(self.request, self.user)
        return super().post(*args, **kwargs)

    def get_context_data(self, **context):
        """
        Adds some context.

        For GET requests adds login info text to context. This info text is
        taken from the config. If this value is empty, a special text is used
        if the admin user has the password 'admin'.

        For POST requests adds the id of the current user to the context.
        """
        if self.request.method == 'GET':
            if config['general_login_info_text']:
                context['info_text'] = config['general_login_info_text']
            else:
                try:
                    user = User.objects.get(username='admin')
                except User.DoesNotExist:
                    context['info_text'] = ''
                else:
                    if user.check_password('admin'):
                        context['info_text'] = _(
                            'Installation was successfully. Use {username} and '
                            '{password} for first login. Important: Please change '
                            'your password!').format(
                                username='<strong>admin</strong>',
                                password='<strong>admin</strong>')
                    else:
                        context['info_text'] = ''
        else:
            # self.request.method == 'POST'
            context['user_id'] = self.user.pk
        return super().get_context_data(**context)


class UserLogoutView(APIView):
    """
    Logout the user.
    """
    http_method_names = ['post']

    def post(self, *args, **kwargs):
        if not self.request.user.is_authenticated():
            raise ValidationError({'detail': _('You are not authenticated.')})
        auth_logout(self.request)
        return super().post(*args, **kwargs)


class WhoAmIView(APIView):
    """
    Returns the id of the requesting user.
    """
    http_method_names = ['get']

    def get_context_data(self, **context):
        """
        Appends the user id to the context. Uses None for the anonymous
        user. Appends also a flag if guest users are enabled in the config.
        """
        return super().get_context_data(
            user_id=self.request.user.pk,
            guest_enabled=config['general_system_enable_anonymous'],
            **context)


class SetPasswordView(APIView):
    """
    Users can set a new password for themselves.
    """
    http_method_names = ['post']

    def post(self, request, *args, **kwargs):
        user = request.user
        if user.check_password(request.data['old_password']):
            user.set_password(request.data['new_password'])
            user.save()
        else:
            raise ValidationError({'detail': _('Old password does not match.')})
        return super().post(request, *args, **kwargs)


# Views to generate PDFs

class UsersListPDF(PDFView):
    """
    Generate a list of all users as PDF.
    """
    required_permission = 'users.can_see_extra_data'
    filename = ugettext_lazy('user-list')
    document_title = ugettext_lazy('List of users')

    def append_to_pdf(self, pdf):
        """
        Append PDF objects.
        """
        users_to_pdf(pdf)


class UsersPasswordsPDF(PDFView):
    """
    Generate the access data welcome paper for all users as PDF.
    """
    required_permission = 'users.can_manage'
    filename = ugettext_lazy('user-access-data')
    top_space = 0

    def build_document(self, pdf_document, story):
        pdf_document.build(story)

    def append_to_pdf(self, pdf):
        """
        Append PDF objects.
        """
        users_passwords_to_pdf(pdf)