from rest_framework import pagination, serializers


class PaginationSerializer(pagination.PaginationSerializer):
    """
    Custom PaginationSerializer for openedx.

    Adds the following fields:
        - num_pages: total number of pages
        - current_page: the current page being returned
        - start: the index of the first page item within the overall collection
    """
    start_page = 1  # django Paginator.page objects have 1-based indexes
    num_pages = serializers.Field(source='paginator.num_pages')
    current_page = serializers.SerializerMethodField('get_current_page')
    start = serializers.SerializerMethodField('get_start')
    sort_order = serializers.SerializerMethodField('get_sort_order')

    def get_current_page(self, page):
        """Get the current page"""
        return page.number

    def get_start(self, page):
        """Get the index of the first page item within the overall collection"""
        return (self.get_current_page(page) - self.start_page) * page.paginator.per_page

    def get_sort_order(self, page):  # pylint: disable=unused-argument
        """Get the order by which this collection was sorted"""
        return self.context.get('sort_order')


class CollapsedReferenceSerializer(serializers.HyperlinkedModelSerializer):
    """Serializes arbitrary models in a collapsed format, with just an id and url."""
    url = serializers.HyperlinkedIdentityField(view_name='')

    def __init__(self, model_class, view_name, id_source='id', lookup_field=None, *args, **kwargs):
        """Configures the serializer.

        Args:
            model_class (class): Model class to serialize.
            view_name (string): Name of the Django view used to lookup the
                model.
            id_source (string): Optional name of the id field on the model.
                Defaults to 'id'. Also used as the property name of the field
                in the serialized representation.
            lookup_field (string): Optional name of the model field used to
                lookup the model in the view. Defaults to the value of
                id_source.
        """
        if not lookup_field:
            lookup_field = id_source

        self.Meta.model = model_class

        super(CollapsedReferenceSerializer, self).__init__(*args, **kwargs)

        self.fields[id_source] = serializers.CharField(read_only=True, source=id_source)
        self.fields['url'].view_name = view_name
        self.fields['url'].lookup_field = lookup_field

    class Meta(object):
        """Defines meta information for the ModelSerializer.

        model is set dynamically in __init__.
        """
        fields = ("url",)