connection.py

import re
from collections import Iterable, OrderedDict
from functools import partial

import six

from graphql_relay import connection_from_list

from ..types import Boolean, Int, List, String
from ..types.field import Field
from ..types.objecttype import ObjectType, ObjectTypeMeta
from ..types.options import Options
from ..types.utils import get_fields_in_type, yank_fields_from_attrs
from ..utils.is_base_type import is_base_type
from ..utils.props import props
from .node import Node, is_node


class PageInfo(ObjectType):
    has_next_page = Boolean(
        required=True,
        name='hasNextPage',
        description='When paginating forwards, are there more items?',
    )

    has_previous_page = Boolean(
        required=True,
        name='hasPreviousPage',
        description='When paginating backwards, are there more items?',
    )

    start_cursor = String(
        name='startCursor',
        description='When paginating backwards, the cursor to continue.',
    )

    end_cursor = String(
        name='endCursor',
        description='When paginating forwards, the cursor to continue.',
    )


class ConnectionMeta(ObjectTypeMeta):

    def __new__(cls, name, bases, attrs):
        # Also ensure initialization is only performed for subclasses of Model
        # (excluding Model class itself).
        if not is_base_type(bases, ConnectionMeta):
            return type.__new__(cls, name, bases, attrs)

        options = Options(
            attrs.pop('Meta', None),
            name=None,
            description=None,
            node=None,
        )
        options.interfaces = ()

        assert options.node, 'You have to provide a node in {}.Meta'.format(cls.__name__)
        assert issubclass(options.node, (Node, ObjectType)), (
            'Received incompatible node "{}" for Connection {}.'
        ).format(options.node, name)

        base_name = re.sub('Connection$', '', name)
        if not options.name:
            options.name = '{}Connection'.format(base_name)

        edge_class = attrs.pop('Edge', None)
        edge_fields = OrderedDict([
            ('node', Field(options.node, description='The item at the end of the edge')),
            ('cursor', Field(String, required=True, description='A cursor for use in pagination'))
        ])
        edge_attrs = props(edge_class) if edge_class else OrderedDict()
        extended_edge_fields = get_fields_in_type(ObjectType, edge_attrs)
        edge_fields.update(extended_edge_fields)
        edge_meta = type('Meta', (object, ), {
            'fields': edge_fields,
            'name': '{}Edge'.format(base_name)
        })
        yank_fields_from_attrs(edge_attrs, extended_edge_fields)
        edge = type('Edge', (ObjectType,), dict(edge_attrs, Meta=edge_meta))

        options.local_fields = OrderedDict([
            ('page_info', Field(PageInfo, name='pageInfo', required=True)),
            ('edges', Field(List(edge)))
        ])
        typed_fields = get_fields_in_type(ObjectType, attrs)
        options.local_fields.update(typed_fields)
        options.fields = options.local_fields
        yank_fields_from_attrs(attrs, typed_fields)

        return type.__new__(cls, name, bases, dict(attrs, _meta=options, Edge=edge))


class Connection(six.with_metaclass(ConnectionMeta, ObjectType)):
    pass


class IterableConnectionField(Field):

    def __init__(self, type, *args, **kwargs):
        super(IterableConnectionField, self).__init__(
            type,
            *args,
            before=String(),
            after=String(),
            first=Int(),
            last=Int(),
            **kwargs
        )

    @property
    def type(self):
        type = super(IterableConnectionField, self).type
        if is_node(type):
            connection_type = type.Connection
        else:
            connection_type = type
        assert issubclass(connection_type, Connection), (
            '{} type have to be a subclass of Connection. Received "{}".'
        ).format(str(self), connection_type)
        return connection_type

    @staticmethod
    def connection_resolver(resolver, connection, root, args, context, info):
        iterable = resolver(root, args, context, info)
        assert isinstance(iterable, Iterable), (
            'Resolved value from the connection field have to be iterable. '
            'Received "{}"'
        ).format(iterable)
        connection = connection_from_list(
            iterable,
            args,
            connection_type=connection,
            edge_type=connection.Edge,
            pageinfo_type=PageInfo
        )
        return connection

    def get_resolver(self, parent_resolver):
        return partial(self.connection_resolver, parent_resolver, self.type)

ConnectionField = IterableConnectionField