import re
from typing import List

import jsonschema
from django.conf import settings
from django.contrib.auth import get_user_model
from django.core.exceptions import ValidationError as DjangoValidationError
from django.db import IntegrityError, transaction
from django.db.models.deletion import ProtectedError
from django.http.request import QueryDict
from django.utils.translation import ugettext as _, ugettext_noop
from rest_framework import status

from ..core.config import config
from ..core.models import Tag
from ..utils.auth import has_perm, in_some_groups
from ..utils.autoupdate import inform_changed_data, inform_deleted_data
from ..utils.exceptions import OpenSlidesError
from ..utils.rest_api import (
    CreateModelMixin,
    DestroyModelMixin,
    GenericViewSet,
    ModelViewSet,
    Response,
    ReturnDict,
    UpdateModelMixin,
    ValidationError,
    detail_route,
    list_route,
)
from .access_permissions import (
    CategoryAccessPermissions,
    MotionAccessPermissions,
    MotionBlockAccessPermissions,
    MotionChangeRecommendationAccessPermissions,
    MotionCommentSectionAccessPermissions,
    StatuteParagraphAccessPermissions,
    WorkflowAccessPermissions,
)
from .exceptions import WorkflowError
from .models import (
    Category,
    Motion,
    MotionBlock,
    MotionChangeRecommendation,
    MotionComment,
    MotionCommentSection,
    MotionPoll,
    State,
    StatuteParagraph,
    Submitter,
    Workflow,
)
from .serializers import MotionPollSerializer, StateSerializer


# Viewsets for the REST API

class MotionViewSet(ModelViewSet):
    """
    API endpoint for motions.

    There are a lot of views. See check_view_permissions().
    """
    access_permissions = MotionAccessPermissions()
    queryset = Motion.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', 'partial_update', 'update', 'destroy'):
            result = has_perm(self.request.user, 'motions.can_see')
            # For partial_update, update and destroy requests the rest of the check is
            # done in the update method. See below.
        elif self.action == 'create':
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_create') and
                      (not config['motions_stop_submitting'] or
                       has_perm(self.request.user, 'motions.can_manage')))
        elif self.action in ('set_state', 'set_recommendation', 'manage_multiple_recommendation',
                             'follow_recommendation', 'manage_submitters',
                             'sort_submitters', 'manage_multiple_submitters',
                             'manage_multiple_tags', 'create_poll'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage_metadata'))
        elif self.action in ('sort', 'manage_comments'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        elif self.action == 'support':
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_support'))
        else:
            result = False
        return result

    def destroy(self, request, *args, **kwargs):
        """
        Destroy is allowed if the user has manage permissions, or he is the submitter and
        the current state allows to edit the motion.
        """
        motion = self.get_object()

        if not ((has_perm(request.user, 'motions.can_manage') or
                motion.is_submitter(request.user) and motion.state.allow_submitter_edit)):
            self.permission_denied(request)

        result = super().destroy(request, *args, **kwargs)

        # Fire autoupdate again to save information to OpenSlides history.
        inform_deleted_data(
            [(motion.get_collection_string(), motion.pk)],
            information='Motion deleted',
            user_id=request.user.pk)

        return result

    def create(self, request, *args, **kwargs):
        """
        Customized view endpoint to create a new motion.
        """
        # This is a hack to make request.data mutable. Otherwise fields can not be deleted.
        if isinstance(request.data, QueryDict):
            request.data._mutable = True

        # Check if parent motion exists.
        if request.data.get('parent_id') is not None:
            try:
                parent_motion = Motion.objects.get(pk=request.data['parent_id'])
            except Motion.DoesNotExist:
                raise ValidationError({'detail': _('The parent motion does not exist.')})
        else:
            parent_motion = None

        # Check permission to send some data.
        if not has_perm(request.user, 'motions.can_manage'):
            # Remove fields that the user is not allowed to send.
            # The list() is required because we want to use del inside the loop.
            keys = list(request.data.keys())
            whitelist = [
                'title',
                'text',
                'reason',
                'category_id',
            ]
            if parent_motion is not None:
                # For creating amendments.
                whitelist.extend([
                    'parent_id',
                    'amendment_paragraphs',
                    'motion_block_id',  # This and the category_id will be set to the matching
                                        # values from parent_motion.
                ])
                request.data['category_id'] = parent_motion.category_id
                request.data['motion_block_id'] = parent_motion.motion_block_id
            for key in keys:
                if key not in whitelist:
                    del request.data[key]

        # Validate data and create motion.
        # Attention: Even user without permission can_manage_metadata is allowed
        # to create a new motion and set such metadata like category, motion block and origin.
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        motion = serializer.save(request_user=request.user)

        # Check for submitters and make ids unique
        if isinstance(request.data, QueryDict):
            submitters_id = request.data.getlist('submitters_id')
        else:
            submitters_id = request.data.get('submitters_id')
            if submitters_id is None:
                submitters_id = []
        if not isinstance(submitters_id, list):
            raise ValidationError({'detail': _('If submitters_id is given, it has to be a list.')})

        submitters_id_unique = set()
        for id in submitters_id:
            try:
                submitters_id_unique.add(int(id))
            except ValueError:
                continue

        submitters = []
        for submitter_id in submitters_id_unique:
            try:
                submitters.append(get_user_model().objects.get(pk=submitter_id))
            except get_user_model().DoesNotExist:
                continue  # Do not add users that do not exist

        # Add the request user, if he is authenticated and no submitters were given:
        if len(submitters) == 0 and request.user.is_authenticated:
            submitters.append(request.user)

        # create all submitters
        for submitter in submitters:
            Submitter.objects.add(submitter, motion)

        # Write the log message and initiate response.
        motion.write_log([ugettext_noop('Motion created')], request.user)

        # Send new submitters and supporters via autoupdate because users
        # without permission to see users may not have them but can get it now.
        new_users = list(motion.submitters.all())
        new_users.extend(motion.supporters.all())
        inform_changed_data(new_users)

        headers = self.get_success_headers(serializer.data)
        # Strip out response data so nobody gets unrestricted data.
        data = ReturnDict(
            id=serializer.data.get('id'),
            serializer=serializer
        )
        return Response(data, status=status.HTTP_201_CREATED, headers=headers)

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

        Checks also whether the requesting user can update the motion. He
        needs at least the permissions 'motions.can_see' (see
        self.check_view_permissions()). Also check manage permission or
        submitter and state.
        """
        # This is a hack to make request.data mutable. Otherwise fields can not be deleted.
        if isinstance(request.data, QueryDict):
            request.data._mutable = True

        # Get motion.
        motion = self.get_object()

        # Check permissions.
        if (not has_perm(request.user, 'motions.can_manage') and
                not has_perm(request.user, 'motions.can_manage_metadata') and
                not (motion.is_submitter(request.user) and motion.state.allow_submitter_edit)):
            self.permission_denied(request)

        # Check permission to send only some data.
        # Attention: Users with motions.can_manage permission can change all
        #            fields even if they do not have motions.can_manage_metadata
        #            permission.
        if not has_perm(request.user, 'motions.can_manage'):
            # Remove fields that the user is not allowed to change.
            # The list() is required because we want to use del inside the loop.
            keys = list(request.data.keys())
            whitelist: List[str] = []
            # Add title, text and reason to the whitelist only, if the user is the submitter.
            if motion.is_submitter(request.user) and motion.state.allow_submitter_edit:
                whitelist.extend((
                    'title',
                    'text',
                    'reason',
                ))

            if has_perm(request.user, 'motions.can_manage_metadata'):
                whitelist.extend((
                    'category_id',
                    'motion_block_id',
                    'origin',
                    'supporters_id',
                ))

            for key in keys:
                if key not in whitelist:
                    del request.data[key]

        # Validate data and update motion.
        serializer = self.get_serializer(
            motion,
            data=request.data,
            partial=kwargs.get('partial', False))
        serializer.is_valid(raise_exception=True)
        updated_motion = serializer.save()

        # Write the log message, check removal of supporters and initiate response.
        # TODO: Log if a motion was updated.
        updated_motion.write_log([ugettext_noop('Motion updated')], request.user)
        if (config['motions_remove_supporters'] and updated_motion.state.allow_support and
                not has_perm(request.user, 'motions.can_manage')):
            updated_motion.supporters.clear()
            updated_motion.write_log([ugettext_noop('All supporters removed')], request.user)

        # Send new supporters via autoupdate because users
        # without permission to see users may not have them but can get it now.
        new_users = list(updated_motion.supporters.all())
        inform_changed_data(new_users)

        # Fire autoupdate again to save information to OpenSlides history.
        inform_changed_data(
            updated_motion,
            information='Motion updated',
            user_id=request.user.pk)

        # We do not add serializer.data to response so nobody gets unrestricted data here.
        return Response()

    @list_route(methods=['post'])
    def sort(self, request):
        """
        Sort motions. Also checks sort_parent field to prevent hierarchical loops.

        Note: This view is not tested! Maybe needs to be refactored. Add documentation
        abou the data to be send.
        """
        nodes = request.data.get('nodes', [])
        sort_parent_id = request.data.get('parent_id')
        motions = []
        with transaction.atomic():
            for index, node in enumerate(nodes):
                id = node['id']
                motion = Motion.objects.get(pk=id)
                motion.sort_parent_id = sort_parent_id
                motion.weight = index
                motion.save(skip_autoupdate=True)
                motions.append(motion)

                # Now check consistency. TODO: Try to use less DB queries.
                motion = Motion.objects.get(pk=id)
                ancestor = motion.sort_parent
                while ancestor is not None:
                    if ancestor == motion:
                        raise ValidationError({'detail': _(
                            'There must not be a hierarchical loop.')})
                    ancestor = ancestor.sort_parent

        inform_changed_data(motions)
        return Response({'detail': _('The motions has been sorted.')})

    @detail_route(methods=['POST', 'DELETE'])
    def manage_comments(self, request, pk=None):
        """
        Create, update and delete motion comments.

        Send a POST request with {'section_id': <id>, 'comment': '<comment>'}
        to create a new comment or update an existing comment.

        Send a DELETE request with just {'section_id': <id>} to delete the comment.
        For every request, the user must have read and write permission for the given field.
        """
        motion = self.get_object()

        # Get the comment section
        section_id = request.data.get('section_id')
        if not section_id or not isinstance(section_id, int):
            raise ValidationError({'detail': _('You have to provide a section_id of type int.')})

        try:
            section = MotionCommentSection.objects.get(pk=section_id)
        except MotionCommentSection.DoesNotExist:
            raise ValidationError({'detail': _('A comment section with id {} does not exist').format(section_id)})

        # the request user needs to see and write to the comment section
        if (not in_some_groups(request.user, list(section.read_groups.values_list('pk', flat=True))) or
                not in_some_groups(request.user, list(section.write_groups.values_list('pk', flat=True)))):
            raise ValidationError({'detail': _('You are not allowed to see or write to the comment section.')})

        if request.method == 'POST':  # Create or update
            # validate comment
            comment_value = request.data.get('comment', '')
            if not isinstance(comment_value, str):
                raise ValidationError({'detail': _('The comment should be a string.')})

            comment, created = MotionComment.objects.get_or_create(
                    motion=motion,
                    section=section,
                    defaults={
                        'comment': comment_value})
            if not created:
                comment.comment = comment_value
                comment.save()

            # write log
            motion.write_log(
                [ugettext_noop('Comment {} updated').format(section.name)],
                request.user)
            message = _('Comment {} updated').format(section.name)
        else:  # DELETE
            try:
                comment = MotionComment.objects.get(motion=motion, section=section)
            except MotionComment.DoesNotExist:
                # Be silent about not existing comments, but do not create a log entry.
                pass
            else:
                comment.delete()

                motion.write_log(
                    [ugettext_noop('Comment {} deleted').format(section.name)],
                    request.user)
            message = _('Comment {} deleted').format(section.name)

        return Response({'detail': message})

    @detail_route(methods=['POST', 'DELETE'])
    def manage_submitters(self, request, pk=None):
        """
        POST: Add a user as a submitter to this motion.
        DELETE: Remove the user as a submitter from this motion.
        For both cases provide ['user': <user_id>} for the user to add or remove.
        """
        motion = self.get_object()

        if request.method == 'POST':
            user_id = request.data.get('user')

            # Check permissions and other conditions. Get user instance.
            if user_id is None:
                raise ValidationError({'detail': _('You have to provide a user.')})
            else:
                try:
                    user = get_user_model().objects.get(pk=int(user_id))
                except (ValueError, get_user_model().DoesNotExist):
                    raise ValidationError({'detail': _('User does not exist.')})

            # Try to add the user. This ensurse that a user is not twice a submitter
            try:
                Submitter.objects.add(user, motion)
            except OpenSlidesError as e:
                raise ValidationError({'detail': str(e)})
            message = _('User %s was successfully added as a submitter.') % user

            # Send new submitter via autoupdate because users without permission
            # to see users may not have it but can get it now.
            inform_changed_data(user)

        else:  # DELETE
            user_id = request.data.get('user')

            # Check permissions and other conditions. Get user instance.
            if user_id is None:
                raise ValidationError({'detail': _('You have to provide a user.')})
            else:
                try:
                    user = get_user_model().objects.get(pk=int(user_id))
                except (ValueError, get_user_model().DoesNotExist):
                    raise ValidationError({'detail': _('User does not exist.')})

                queryset = Submitter.objects.filter(motion=motion, user=user)
                try:
                    # We assume that there aren't multiple entries because this
                    # is forbidden by the Manager's add method. We assume that
                    # there is only one submitter instance or none.
                    submitter = queryset.get()
                except Submitter.DoesNotExist:
                    raise ValidationError({'detail': _('The user is not a submitter.')})
                else:
                    name = str(submitter.user)
                    submitter.delete()
                    message = _('User {} successfully removed as a submitter.').format(name)

        # Initiate response.
        return Response({'detail': message})

    @detail_route(methods=['POST'])
    def sort_submitters(self, request, pk=None):
        """
        Special view endpoint to sort the submitters.
        Send {'submitters': [<submitter_id_1>, <submitter_id_2>, ...]} as payload.
        """
        # Retrieve motion.
        motion = self.get_object()

        # Check data
        submitter_ids = request.data.get('submitters')
        if not isinstance(submitter_ids, list):
            raise ValidationError(
                {'detail': _('Invalid data.')})

        # Get all submitters
        submitters = {}
        for submitter in motion.submitters.all():
            submitters[submitter.pk] = submitter

        # Check and sort submitters
        valid_submitters = []
        for submitter_id in submitter_ids:
            if not isinstance(submitter_id, int) or submitters.get(submitter_id) is None:
                raise ValidationError(
                    {'detail': _('Invalid data.')})
            valid_submitters.append(submitters[submitter_id])
        weight = 1
        with transaction.atomic():
            for submitter in valid_submitters:
                submitter.weight = weight
                submitter.save(skip_autoupdate=True)
                weight += 1

        # send autoupdate
        inform_changed_data(motion)

        # Initiate response.
        return Response({'detail': _('Submitters successfully sorted.')})

    @list_route(methods=['post'])
    @transaction.atomic
    def manage_multiple_submitters(self, request):
        """
        Set or reset submitters of multiple motions.

        Send POST {"motions": [... see schema ...]} to changed the submitters.
        """
        motions = request.data.get('motions')

        schema = {
            "$schema": "http://json-schema.org/draft-07/schema#",
            "title": "Motion manage multiple submitters schema",
            "description": "An array of motion ids with the respective user ids that should be set as submitter.",
            "type": "array",
            "items": {
                "type": "object",
                "properties": {
                    "id": {
                        "description": "The id of the motion.",
                        "type": "integer",
                    },
                    "submitters": {
                        "description": "An array of user ids the should become submitters. Use an empty array to clear submitter field.",
                        "type": "array",
                        "items": {
                            "type": "integer",
                        },
                        "uniqueItems": True,
                    },
                },
                "required": ["id", "submitters"],
            },
            "uniqueItems": True,
        }

        # Validate request data.
        try:
            jsonschema.validate(motions, schema)
        except jsonschema.ValidationError as err:
            raise ValidationError({'detail': str(err)})

        motion_result = []
        new_submitters = []
        for item in motions:
            # Get motion.
            try:
                motion = Motion.objects.get(pk=item['id'])
            except Motion.DoesNotExist:
                raise ValidationError({'detail': 'Motion {} does not exist'.format(item['id'])})

            # Remove all submitters.
            Submitter.objects.filter(motion=motion).delete()

            # Set new submitters.
            for submitter_id in item['submitters']:
                try:
                    submitter = get_user_model().objects.get(pk=submitter_id)
                except get_user_model().DoesNotExist:
                    raise ValidationError({'detail': 'Submitter {} does not exist'.format(submitter_id)})
                Submitter.objects.add(submitter, motion)
                new_submitters.append(submitter)

            # Finish motion.
            motion_result.append(motion)

        # Now inform all clients.
        inform_changed_data(motion_result)

        # Also send all new submitters via autoupdate because users without
        # permission to see users may not have them but can get it now.
        # TODO: Skip history.
        inform_changed_data(new_submitters)

        # Send response.
        return Response({
            'detail': _('{number} motions successfully updated.').format(number=len(motion_result)),
        })

    @detail_route(methods=['post', 'delete'])
    def support(self, request, pk=None):
        """
        Special view endpoint to support a motion or withdraw support
        (unsupport).

        Send POST to support and DELETE to unsupport.
        """
        # Retrieve motion and allowed actions.
        motion = self.get_object()

        # Support or unsupport motion.
        if request.method == 'POST':
            # Support motion.
            if not (motion.state.allow_support and
                    config['motions_min_supporters'] > 0 and
                    not motion.is_submitter(request.user) and
                    not motion.is_supporter(request.user)):
                raise ValidationError({'detail': _('You can not support this motion.')})
            motion.supporters.add(request.user)
            motion.write_log([ugettext_noop('Motion supported')], request.user)
            # Send new supporter via autoupdate because users without permission
            # to see users may not have it but can get it now.
            inform_changed_data([request.user])
            message = _('You have supported this motion successfully.')
        else:
            # Unsupport motion.
            # request.method == 'DELETE'
            if not motion.state.allow_support or not motion.is_supporter(request.user):
                raise ValidationError({'detail': _('You can not unsupport this motion.')})
            motion.supporters.remove(request.user)
            motion.write_log([ugettext_noop('Motion unsupported')], request.user)
            message = _('You have unsupported this motion successfully.')

        # Initiate response.
        return Response({'detail': message})

    @detail_route(methods=['put'])
    def set_state(self, request, pk=None):
        """
        Special view endpoint to set and reset a state of a motion.

        Send PUT {'state': <state_id>} to set and just PUT {} to reset the
        state. Only managers can use this view.
        """
        # Retrieve motion and state.
        motion = self.get_object()
        state = request.data.get('state')

        # Set or reset state.
        if state is not None:
            # Check data and set state.
            try:
                state_id = int(state)
            except ValueError:
                raise ValidationError({'detail': _('Invalid data. State must be an integer.')})
            if state_id not in [item.id for item in motion.state.next_states.all()]:
                raise ValidationError(
                    {'detail': _('You can not set the state to %(state_id)d.') % {'state_id': state_id}})
            motion.set_state(state_id)
        else:
            # Reset state.
            motion.reset_state()

        # Save motion.
        motion.save(update_fields=['state', 'identifier', 'identifier_number'], skip_autoupdate=True)
        message = _('The state of the motion was set to %s.') % motion.state.name

        # Write the log message and initiate response.
        motion.write_log(
            message_list=[ugettext_noop('State set to'), ' ', motion.state.name],
            person=request.user,
            skip_autoupdate=True)
        inform_changed_data(motion, information='State set to {}.'.format(motion.state.name))
        return Response({'detail': message})

    @detail_route(methods=['put'])
    def set_recommendation(self, request, pk=None):
        """
        Special view endpoint to set a recommendation of a motion.

        Send PUT {'recommendation': <state_id>} to set and just PUT {} to
        reset the recommendation. Only managers can use this view.
        """
        # Retrieve motion and recommendation state.
        motion = self.get_object()
        recommendation_state = request.data.get('recommendation')

        # Set or reset recommendation.
        if recommendation_state is not None:
            # Check data and set recommendation.
            try:
                recommendation_state_id = int(recommendation_state)
            except ValueError:
                raise ValidationError({'detail': _('Invalid data. Recommendation must be an integer.')})
            recommendable_states = State.objects.filter(workflow=motion.workflow_id, recommendation_label__isnull=False)
            if recommendation_state_id not in [item.id for item in recommendable_states]:
                raise ValidationError(
                    {'detail': _('You can not set the recommendation to {recommendation_state_id}.').format(
                        recommendation_state_id=recommendation_state_id)})
            motion.set_recommendation(recommendation_state_id)
        else:
            # Reset recommendation.
            motion.recommendation = None

        # Save motion.
        motion.save(update_fields=['recommendation'], skip_autoupdate=True)
        label = motion.recommendation.recommendation_label if motion.recommendation else 'None'
        message = _('The recommendation of the motion was set to %s.') % label

        # Write the log message and initiate response.
        motion.write_log(
            message_list=[ugettext_noop('Recommendation set to'), ' ', label],
            person=request.user,
            skip_autoupdate=True)
        inform_changed_data(motion)
        return Response({'detail': message})

    @list_route(methods=['post'])
    @transaction.atomic
    def manage_multiple_recommendation(self, request):
        """
        Set or reset recommendations of multiple motions.

        Send POST {"motions": [... see schema ...]} to changed the recommendations.
        """
        motions = request.data.get('motions')

        schema = {
            "$schema": "http://json-schema.org/draft-07/schema#",
            "title": "Motion manage multiple recommendations schema",
            "description": "An array of motion ids with the respective state ids that should be set as recommendation.",
            "type": "array",
            "items": {
                "type": "object",
                "properties": {
                    "id": {
                        "description": "The id of the motion.",
                        "type": "integer",
                    },
                    "recommendation": {
                        "description": "The state id the should become recommendation. Use 0 to clear recommendation field.",
                        "type": "integer",
                    },
                },
                "required": ["id", "recommendation"],
            },
            "uniqueItems": True,
        }

        # Validate request data.
        try:
            jsonschema.validate(motions, schema)
        except jsonschema.ValidationError as err:
            raise ValidationError({'detail': str(err)})

        motion_result = []
        for item in motions:
            # Get motion.
            try:
                motion = Motion.objects.get(pk=item['id'])
            except Motion.DoesNotExist:
                raise ValidationError({'detail': 'Motion {} does not exist'.format(item['id'])})

            # Set or reset recommendation.
            recommendation_state_id = item['recommendation']
            if recommendation_state_id == 0:
                # Reset recommendation.
                motion.recommendation = None
            else:
                # Check data and set recommendation.
                recommendable_states = State.objects.filter(workflow=motion.workflow_id, recommendation_label__isnull=False)
                if recommendation_state_id not in [item.id for item in recommendable_states]:
                    raise ValidationError(
                        {'detail': _('You can not set the recommendation to {recommendation_state_id}.').format(
                            recommendation_state_id=recommendation_state_id)})
                motion.set_recommendation(recommendation_state_id)

            # Save motion.
            motion.save(update_fields=['recommendation'], skip_autoupdate=True)
            label = motion.recommendation.recommendation_label if motion.recommendation else 'None'

            # Write the log message.
            motion.write_log(
                message_list=[ugettext_noop('Recommendation set to'), ' ', label],
                person=request.user,
                skip_autoupdate=True)

            # Finish motion.
            motion_result.append(motion)

        # Now inform all clients.
        inform_changed_data(motion_result)

        # Send response.
        return Response({
            'detail': _('{number} motions successfully updated.').format(number=len(motion_result)),
        })

    @detail_route(methods=['post'])
    def follow_recommendation(self, request, pk=None):
        motion = self.get_object()
        if motion.recommendation is None:
            raise ValidationError({'detail': _('Cannot set an empty recommendation.')})

        # Set state.
        motion.set_state(motion.recommendation)

        # Set the special state comment.
        extension = request.data.get('state_extension')
        if extension is not None:
            motion.state_extension = extension

        # Save and write log.
        motion.save(
            update_fields=['state', 'identifier', 'identifier_number', 'state_extension'],
            skip_autoupdate=True)
        motion.write_log(
            message_list=[ugettext_noop('State set to'), ' ', motion.state.name],
            person=request.user,
            skip_autoupdate=True)

        # Now send all changes to the clients.
        inform_changed_data(motion)
        return Response({'detail': 'Recommendation followed successfully.'})

    @detail_route(methods=['post'])
    def create_poll(self, request, pk=None):
        """
        View to create a poll. It is a POST request without any data.
        """
        motion = self.get_object()
        if not motion.state.allow_create_poll:
            raise ValidationError({'detail': 'You can not create a poll in this motion state.'})
        try:
            with transaction.atomic():
                poll = motion.create_poll(skip_autoupdate=True)
        except WorkflowError as e:
            raise ValidationError({'detail': e})
        motion.write_log([ugettext_noop('Vote created')], request.user, skip_autoupdate=True)

        inform_changed_data(motion)
        return Response({
            'detail': _('Vote created successfully.'),
            'createdPollId': poll.pk})

    @list_route(methods=['post'])
    @transaction.atomic
    def manage_multiple_tags(self, request):
        """
        Set or reset tags of multiple motions.

        Send POST {"motions": [... see schema ...]} to changed the tags.
        """
        motions = request.data.get('motions')

        schema = {
            "$schema": "http://json-schema.org/draft-07/schema#",
            "title": "Motion manage multiple tags schema",
            "description": "An array of motion ids with the respective tags ids that should be set as tag.",
            "type": "array",
            "items": {
                "type": "object",
                "properties": {
                    "id": {
                        "description": "The id of the motion.",
                        "type": "integer",
                    },
                    "tags": {
                        "description": "An array of tag ids the should become tags. Use an empty array to clear tag field.",
                        "type": "array",
                        "items": {
                            "type": "integer",
                        },
                        "uniqueItems": True,
                    },
                },
                "required": ["id", "tags"],
            },
            "uniqueItems": True,
        }

        # Validate request data.
        try:
            jsonschema.validate(motions, schema)
        except jsonschema.ValidationError as err:
            raise ValidationError({'detail': str(err)})

        motion_result = []
        for item in motions:
            # Get motion.
            try:
                motion = Motion.objects.get(pk=item['id'])
            except Motion.DoesNotExist:
                raise ValidationError({'detail': 'Motion {} does not exist'.format(item['id'])})

            # Set new tags
            for tag_id in item['tags']:
                if not Tag.objects.filter(pk=tag_id).exists():
                    raise ValidationError({'detail': 'Tag {} does not exist'.format(tag_id)})
            motion.tags.set(item['tags'])

            # Finish motion.
            motion_result.append(motion)

        # Now inform all clients.
        inform_changed_data(motion_result)

        # Send response.
        return Response({
            'detail': _('{number} motions successfully updated.').format(number=len(motion_result)),
        })


class MotionPollViewSet(UpdateModelMixin, DestroyModelMixin, GenericViewSet):
    """
    API endpoint for motion polls.

    There are the following views: update, partial_update and destroy.
    """
    queryset = MotionPoll.objects.all()
    serializer_class = MotionPollSerializer

    def check_view_permissions(self):
        """
        Returns True if the user has required permissions.
        """
        return (has_perm(self.request.user, 'motions.can_see') and
                has_perm(self.request.user, 'motions.can_manage_metadata'))

    def update(self, *args, **kwargs):
        """
        Customized view endpoint to update a motion poll.
        """
        response = super().update(*args, **kwargs)
        poll = self.get_object()
        poll.motion.write_log([ugettext_noop('Vote updated')], self.request.user)
        return response

    def destroy(self, *args, **kwargs):
        """
        Customized view endpoint to delete a motion poll.
        """
        poll = self.get_object()
        result = super().destroy(*args, **kwargs)
        poll.motion.write_log([ugettext_noop('Vote deleted')], self.request.user)
        return result


class MotionChangeRecommendationViewSet(ModelViewSet):
    """
    API endpoint for motion change recommendations.

    There are the following views: metadata, list, retrieve, create,
    partial_update, update and destroy.
    """
    access_permissions = MotionChangeRecommendationAccessPermissions()
    queryset = MotionChangeRecommendation.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 == 'metadata':
            result = has_perm(self.request.user, 'motions.can_see')
        elif self.action in ('create', 'destroy', 'partial_update', 'update'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        else:
            result = False
        return result

    def create(self, request, *args, **kwargs):
        """
        Creating a Change Recommendation, custom exception handling
        """
        try:
            return super().create(request, *args, **kwargs)
        except DjangoValidationError as err:
            return Response({'detail': err.message}, status=400)


class MotionCommentSectionViewSet(ModelViewSet):
    """
    API endpoint for motion comment fields.
    """
    access_permissions = MotionCommentSectionAccessPermissions()
    queryset = MotionCommentSection.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 ('create', 'destroy', 'update', 'partial_update'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        else:
            result = False
        return result

    def destroy(self, *args, **kwargs):
        """
        Customized view endpoint to delete a motion comment section. Will return
        an error for the user, if still comments for this section exist.
        """
        try:
            result = super().destroy(*args, **kwargs)
        except ProtectedError as e:
            # The protected objects can just be motion comments.
            motions = ['"' + str(comment.motion) + '"' for comment in e.protected_objects.all()]
            count = len(motions)
            motions_verbose = ', '.join(motions[:3])
            if count > 3:
                motions_verbose += ', ...'

            if count == 1:
                msg = _('This section has still comments in motion {}.').format(motions_verbose)
            else:
                msg = _('This section has still comments in motions {}.').format(motions_verbose)

            msg += ' ' + _('Please remove all comments before deletion.')
            raise ValidationError({'detail': msg})
        return result


class StatuteParagraphViewSet(ModelViewSet):
    """
    API endpoint for statute paragraphs.

    There are the following views: list, retrieve, create,
    partial_update, update and destroy.
    """
    access_permissions = StatuteParagraphAccessPermissions()
    queryset = StatuteParagraph.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 ('create', 'partial_update', 'update', 'destroy'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        else:
            result = False
        return result


class CategoryViewSet(ModelViewSet):
    """
    API endpoint for categories.

    There are the following views: metadata, list, retrieve, create,
    partial_update, update, destroy and numbering.
    """
    access_permissions = CategoryAccessPermissions()
    queryset = Category.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 == 'metadata':
            result = has_perm(self.request.user, 'motions.can_see')
        elif self.action in ('create', 'partial_update', 'update', 'destroy', 'numbering'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        else:
            result = False
        return result

    @detail_route(methods=['post'])
    def numbering(self, request, pk=None):
        """
        Special view endpoint to number all motions in this category.

        Only managers can use this view.

        Send POST {'motions': [<list of motion ids>]} to sort the given
        motions in a special order. Ids of motions which do not belong to
        the category are just ignored. Send just POST {} to sort all
        motions in the category by database id.

        Amendments will get a new identifier prefix if the old prefix matches
        the old parent motion identifier.
        """
        category = self.get_object()
        number = 0
        instances = []

        # If MOTION_IDENTIFIER_WITHOUT_BLANKS is set, don't use blanks when building identifier.
        without_blank = hasattr(settings, 'MOTION_IDENTIFIER_WITHOUT_BLANKS') and settings.MOTION_IDENTIFIER_WITHOUT_BLANKS

        # Prepare ordered list of motions.
        if not category.prefix:
            prefix = ''
        elif without_blank:
            prefix = '%s' % category.prefix
        else:
            prefix = '%s ' % category.prefix
        motions = category.motion_set.all()
        motion_list = request.data.get('motions')
        if motion_list:
            motion_dict = {}
            for motion in motions.filter(id__in=motion_list):
                motion_dict[motion.pk] = motion
            motions = [motion_dict[pk] for pk in motion_list]

        # Change identifiers.
        error_message = None
        try:
            with transaction.atomic():
                # Collect old and new identifiers.
                motions_to_be_sorted = []
                for motion in motions:
                    if motion.is_amendment():
                        parent_identifier = motion.parent.identifier or ''
                        if without_blank:
                            prefix = '%s%s' % (parent_identifier, config['motions_amendments_prefix'])
                        else:
                            prefix = '%s %s ' % (parent_identifier, config['motions_amendments_prefix'])
                    number += 1
                    new_identifier = '%s%s' % (prefix, motion.extend_identifier_number(number))
                    motions_to_be_sorted.append({
                        'motion': motion,
                        'old_identifier': motion.identifier,
                        'new_identifier': new_identifier,
                        'number': number
                    })

                # Remove old identifiers
                for motion in motions:
                    motion.identifier = None
                    # This line is to skip agenda item autoupdate. See agenda/signals.py.
                    motion.agenda_item_update_information['skip_autoupdate'] = True
                    motion.save(skip_autoupdate=True)

                # Set new identifers and change identifiers of amendments.
                for obj in motions_to_be_sorted:
                    if Motion.objects.filter(identifier=obj['new_identifier']).exists():
                        # Set the error message and let the code run into an IntegrityError
                        error_message = _('Numbering aborted because the motion identifier "%s" '
                                          'already exists outside of this category.') % obj['new_identifier']
                    motion = obj['motion']
                    motion.identifier = obj['new_identifier']
                    motion.identifier_number = obj['number']
                    motion.save(skip_autoupdate=True)
                    instances.append(motion)
                    instances.append(motion.agenda_item)
                    # Change identifiers of amendments.
                    for child in motion.get_amendments_deep():
                        if child.identifier and child.identifier.startswith(obj['old_identifier']):
                            child.identifier = re.sub(
                                obj['old_identifier'],
                                obj['new_identifier'],
                                child.identifier,
                                count=1)
                            # This line is to skip agenda item autoupdate. See agenda/signals.py.
                            child.agenda_item_update_information['skip_autoupdate'] = True
                            child.save(skip_autoupdate=True)
                            instances.append(child)
                            instances.append(child.agenda_item)
        except IntegrityError:
            if error_message is None:
                error_message = _('Error: At least one identifier of this category does '
                                  'already exist in another category.')
            response = Response({'detail': error_message}, status=400)
        else:
            inform_changed_data(instances)
            message = _('All motions in category {category} numbered '
                        'successfully.').format(category=category)
            response = Response({'detail': message})
        return response


class MotionBlockViewSet(ModelViewSet):
    """
    API endpoint for motion blocks.

    There are the following views: metadata, list, retrieve, create,
    partial_update, update and destroy.
    """
    access_permissions = MotionBlockAccessPermissions()
    queryset = MotionBlock.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 == 'metadata':
            result = has_perm(self.request.user, 'motions.can_see')
        elif self.action in ('create', 'partial_update', 'update', 'destroy', 'follow_recommendations'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        else:
            result = False
        return result

    @detail_route(methods=['post'])
    def follow_recommendations(self, request, pk=None):
        """
        View to set the states of all motions of this motion block each to
        its recommendation. It is a POST request without any data.
        """
        motion_block = self.get_object()
        instances = []
        with transaction.atomic():
            for motion in motion_block.motion_set.all():
                # Follow recommendation.
                motion.follow_recommendation()
                motion.save(skip_autoupdate=True)
                # Write the log message.
                motion.write_log(
                    message_list=[ugettext_noop('State set to'), ' ', motion.state.name],
                    person=request.user,
                    skip_autoupdate=True)
                instances.append(motion)
        inform_changed_data(instances)
        return Response({'detail': _('Followed recommendations successfully.')})


class ProtectedErrorMessageMixin:
    def getProtectedErrorMessage(self, name, error):
        # The protected objects can just be motions..
        motions = ['"' + str(m) + '"' for m in error.protected_objects.all()]
        count = len(motions)
        motions_verbose = ', '.join(motions[:3])
        if count > 3:
            motions_verbose += ', ...'

        if count == 1:
            msg = _('This {} is assigned to motion {}.').format(name, motions_verbose)
        else:
            msg = _('This {} is assigned to motions {}.').format(name, motions_verbose)
        return msg + ' ' + _('Please remove all assignments before deletion.')


class WorkflowViewSet(ModelViewSet, ProtectedErrorMessageMixin):
    """
    API endpoint for workflows.

    There are the following views: metadata, list, retrieve, create,
    partial_update, update and destroy.
    """
    access_permissions = WorkflowAccessPermissions()
    queryset = Workflow.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 == 'metadata':
            result = has_perm(self.request.user, 'motions.can_see')
        elif self.action in ('create', 'partial_update', 'update', 'destroy'):
            result = (has_perm(self.request.user, 'motions.can_see') and
                      has_perm(self.request.user, 'motions.can_manage'))
        else:
            result = False
        return result

    def destroy(self, *args, **kwargs):
        """
        Customized view endpoint to delete a workflow.
        """
        try:
            result = super().destroy(*args, **kwargs)
        except ProtectedError as e:
            msg = self.getProtectedErrorMessage('workflow', e)
            raise ValidationError({'detail': msg})
        return result


class StateViewSet(CreateModelMixin, UpdateModelMixin, DestroyModelMixin, GenericViewSet,
                   ProtectedErrorMessageMixin):
    """
    API endpoint for workflow states.

    There are the following views: create, update, partial_update and destroy.
    """
    queryset = State.objects.all()
    serializer_class = StateSerializer

    def check_view_permissions(self):
        """
        Returns True if the user has required permissions.
        """
        return (has_perm(self.request.user, 'motions.can_see') and
                has_perm(self.request.user, 'motions.can_manage'))

    def destroy(self, *args, **kwargs):
        """
        Customized view endpoint to delete a state.
        """
        state = self.get_object()
        if state.workflow.first_state.pk == state.pk:  # is this the first state of the workflow?
            raise ValidationError({'detail': _('You cannot delete the first state of the workflow.')})
        try:
            result = super().destroy(*args, **kwargs)
        except ProtectedError as e:
            msg = self.getProtectedErrorMessage('workflow', e)
            raise ValidationError({'detail': msg})
        return result