from rest_framework.permissions import BasePermission
from rest_framework.exceptions import MethodNotAllowed
from rest_framework.compat import is_authenticated


class EventSpecificPermissions(BasePermission):

    perms_map = {
        'GET': [],
        'OPTIONS': [],
        'HEAD': [],
        'POST': ['%(prefix)sadd_%(model_name)s'],
        'PUT': ['%(prefix)schange_%(model_name)s'],
        'PATCH': ['%(prefix)schange_%(model_name)s'],
        'DELETE': ['%(prefix)sdelete_%(model_name)s'],
    }

    def get_required_permissions(self, method, view, model_cls):

        if view.event:
            kwargs = {
                'prefix': "event_",
                'model_name': model_cls._meta.model_name
            }
        else:
            kwargs = {
                'prefix': model_cls._meta.app_label+".",
                'model_name': model_cls._meta.model_name
            }

        if method not in self.perms_map:
            raise MethodNotAllowed(method)

        return [perm % kwargs for perm in self.perms_map[method]]

    def has_permission(self, request, view):

        if hasattr(view, 'get_queryset'):
            queryset = view.get_queryset()
        else:
            queryset = getattr(view, 'queryset', None)

        perms = self.get_required_permissions(request.method, view,
                                              queryset.model)

        return (
            request.user and
            is_authenticated(request.user) and
            request.user.has_perms(perms, view.event)
        )