import datetime

from django.db import transaction
from django.http import HttpResponse
from dry_rest_permissions.generics import DRYPermissions
from rest_framework import viewsets, status
from rest_framework.decorators import detail_route
from rest_framework.response import Response

from course_discovery.apps.api import filters, serializers
from course_discovery.apps.api.pagination import ProxiedPagination
from course_discovery.apps.api.renderers import CourseRunCSVRenderer
from course_discovery.apps.api.v1.views import User, prefetch_related_objects_for_courses
from course_discovery.apps.catalogs.models import Catalog
from course_discovery.apps.course_metadata.models import CourseRun


# pylint: disable=no-member
class CatalogViewSet(viewsets.ModelViewSet):
    """ Catalog resource. """

    filter_backends = (filters.PermissionsFilter,)
    lookup_field = 'id'
    permission_classes = (DRYPermissions,)
    queryset = Catalog.objects.all()
    serializer_class = serializers.CatalogSerializer

    # Explicitly support PageNumberPagination and LimitOffsetPagination. Future
    # versions of this API should only support the system default, PageNumberPagination.
    pagination_class = ProxiedPagination

    @transaction.atomic
    def create(self, request, *args, **kwargs):
        """ Create a new catalog. """
        data = request.data.copy()
        usernames = request.data.get('viewers', ())

        # Add support for parsing a comma-separated list from Swagger
        if isinstance(usernames, str):
            usernames = usernames.split(',')
            data.setlist('viewers', usernames)

        # Ensure the users exist
        for username in usernames:
            User.objects.get_or_create(username=username)

        serializer = self.get_serializer(data=data)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)

    def destroy(self, request, *args, **kwargs):
        """ Destroy a catalog. """
        return super(CatalogViewSet, self).destroy(request, *args, **kwargs)

    def list(self, request, *args, **kwargs):
        """ Retrieve a list of all catalogs.
        ---
        parameters:
            - name: username
              description: User whose catalogs should be retrieved.
              required: false
              type: string
              paramType: query
              multiple: false
        """
        return super(CatalogViewSet, self).list(request, *args, **kwargs)

    def partial_update(self, request, *args, **kwargs):
        """ Update one, or more, fields for a catalog. """
        return super(CatalogViewSet, self).partial_update(request, *args, **kwargs)

    def retrieve(self, request, *args, **kwargs):
        """ Retrieve details for a catalog. """
        return super(CatalogViewSet, self).retrieve(request, *args, **kwargs)

    def update(self, request, *args, **kwargs):
        """ Update a catalog. """
        return super(CatalogViewSet, self).update(request, *args, **kwargs)

    @detail_route()
    def courses(self, request, id=None):  # pylint: disable=redefined-builtin,unused-argument
        """
        Retrieve the list of courses contained within this catalog.

        Only courses with active course runs are returned. A course run is considered active if it is currently
        open for enrollment, or will open in the future.
        ---
        serializer: serializers.CourseSerializerExcludingClosedRuns
        """

        catalog = self.get_object()
        queryset = catalog.courses().active()
        queryset = prefetch_related_objects_for_courses(queryset)

        page = self.paginate_queryset(queryset)
        serializer = serializers.CourseSerializerExcludingClosedRuns(page, many=True, context={'request': request})
        return self.get_paginated_response(serializer.data)

    @detail_route()
    def contains(self, request, id=None):  # pylint: disable=redefined-builtin,unused-argument
        """
        Determine if this catalog contains the provided courses.

        A dictionary mapping course IDs to booleans, indicating course presence, will be returned.
        ---
        serializer: serializers.ContainedCoursesSerializer
        parameters:
            - name: course_id
              description: Course IDs to check for existence in the Catalog.
              required: true
              type: string
              paramType: query
              multiple: true
        """
        course_ids = request.query_params.get('course_id')
        course_ids = course_ids.split(',')

        catalog = self.get_object()
        courses = catalog.contains(course_ids)

        instance = {'courses': courses}
        serializer = serializers.ContainedCoursesSerializer(instance)
        return Response(serializer.data)

    @detail_route()
    def csv(self, request, id=None):  # pylint: disable=redefined-builtin,unused-argument
        """
        Retrieve a CSV containing the course runs contained within this catalog.

        Only active course runs are returned. A course run is considered active if it is currently
        open for enrollment, or will be open for enrollment in the future.
        ---
        serializer: serializers.FlattenedCourseRunWithCourseSerializer
        """
        catalog = self.get_object()
        courses = catalog.courses()
        course_runs = CourseRun.objects.filter(course__in=courses).active().marketable()

        # We use select_related and prefetch_related to decrease our database query count
        course_runs = course_runs.select_related(*serializers.SELECT_RELATED_FIELDS['course_run'])
        prefetch_fields = ['course__' + field for field in serializers.PREFETCH_FIELDS['course']]
        prefetch_fields += serializers.PREFETCH_FIELDS['course_run']
        course_runs = course_runs.prefetch_related(*prefetch_fields)

        serializer = serializers.FlattenedCourseRunWithCourseSerializer(
            course_runs, many=True, context={'request': request}
        )
        data = CourseRunCSVRenderer().render(serializer.data)

        response = HttpResponse(data, content_type='text/csv')
        response['Content-Disposition'] = 'attachment; filename="catalog_{id}_{date}.csv"'.format(
            id=id, date=datetime.datetime.utcnow().strftime('%Y-%m-%d-%H-%M')
        )
        return response
