"""
ViewSets are essentially just a type of class based view, that doesn't provide
any method handlers, such as `get()`, `post()`, etc... but instead has actions,
such as `list()`, `retrieve()`, `create()`, etc...

Actions are only bound to methods at the point of instantiating the views.

    user_list = UserViewSet.as_view({'get': 'list'})
    user_detail = UserViewSet.as_view({'get': 'retrieve'})

Typically, rather than instantiate views from viewsets directly, you'll
regsiter the viewset with a router and let the URL conf be determined
automatically.

    router = DefaultRouter()
    router.register(r'users', UserViewSet, 'user')
    urlpatterns = router.urls
"""
from __future__ import unicode_literals

from functools import update_wrapper
from django.utils.decorators import classonlymethod
from rest_framework import views, generics, mixins


class ViewSetMixin(object):
    """
    This is the magic.

    Overrides `.as_view()` so that it takes an `actions` keyword that performs
    the binding of HTTP methods to actions on the Resource.

    For example, to create a concrete view binding the 'GET' and 'POST' methods
    to the 'list' and 'create' actions...

    view = MyViewSet.as_view({'get': 'list', 'post': 'create'})
    """

    @classonlymethod
    def as_view(cls, actions=None, **initkwargs):
        """
        Because of the way class based views create a closure around the
        instantiated view, we need to totally reimplement `.as_view`,
        and slightly modify the view function that is created and returned.
        """
        # The suffix initkwarg is reserved for identifing the viewset type
        # eg. 'List' or 'Instance'.
        cls.suffix = None

        # sanitize keyword arguments
        for key in initkwargs:
            if key in cls.http_method_names:
                raise TypeError("You tried to pass in the %s method name as a "
                                "keyword argument to %s(). Don't do that."
                                % (key, cls.__name__))
            if not hasattr(cls, key):
                raise TypeError("%s() received an invalid keyword %r" % (
                    cls.__name__, key))

        def view(request, *args, **kwargs):
            self = cls(**initkwargs)
            # We also store the mapping of request methods to actions,
            # so that we can later set the action attribute.
            # eg. `self.action = 'list'` on an incoming GET request.
            self.action_map = actions

            # Bind methods to actions
            # This is the bit that's different to a standard view
            for method, action in actions.items():
                handler = getattr(self, action)
                setattr(self, method, handler)

            # Patch this in as it's otherwise only present from 1.5 onwards
            if hasattr(self, 'get') and not hasattr(self, 'head'):
                self.head = self.get

            # And continue as usual
            return self.dispatch(request, *args, **kwargs)

        # take name and docstring from class
        update_wrapper(view, cls, updated=())

        # and possible attributes set by decorators
        # like csrf_exempt from dispatch
        update_wrapper(view, cls.dispatch, assigned=())

        # We need to set these on the view function, so that breadcrumb
        # generation can pick out these bits of information from a
        # resolved URL.
        view.cls = cls
        view.suffix = initkwargs.get('suffix', None)
        return view

    def initialize_request(self, request, *args, **kargs):
        """
        Set the `.action` attribute on the view,
        depending on the request method.
        """
        request = super(ViewSetMixin, self).initialize_request(request, *args, **kargs)
        self.action = self.action_map.get(request.method.lower())
        return request


class ViewSet(ViewSetMixin, views.APIView):
    """
    The base ViewSet class does not provide any actions by default.
    """
    pass


class ReadOnlyModelViewSet(mixins.RetrieveModelMixin,
                           mixins.ListModelMixin,
                           ViewSetMixin,
                           generics.GenericAPIView):
    """
    A viewset that provides default `list()` and `retrieve()` actions.
    """
    pass


class ModelViewSet(mixins.CreateModelMixin,
                    mixins.RetrieveModelMixin,
                    mixins.UpdateModelMixin,
                    mixins.DestroyModelMixin,
                    mixins.ListModelMixin,
                    ViewSetMixin,
                    generics.GenericAPIView):
    """
    A viewset that provides default `create()`, `retrieve()`, `update()`,
    `partial_update()`, `destroy()` and `list()` actions.
    """
    pass