Django template filters for getting various user-specific things off models

userhelpers.py

"""
Some simple filters
 * `user_can`, which filters an object taking a string
   parameter, returning True or False depending on whether the current
   user "can" do the action in the parameter. This is done by calling
   `user_can_<action>` on the object.

   Anonymous users always return `False`.

 * `user_has`, which pulls the result of the `user_has_<feature>()`;
   anonymous users get `False`.

 * `user_property` pulls the result of `user_<property>()`; anonymous
   users get `None`.

Relies on django-globals: https://github.com/svetlyak40wt/django-globals

Untested, based on internal code that didn't use django-globals.
"""

from django import template
from django_globals import globals

register = template.Library()

@register.filter
def user_can(value, arg):
    "Is the current user allowed to perform the `arg` action on the `value` object?"
    user = globals.user
    if user.is_authenticated() and hasattr(value, "user_can_%s" % arg):
        return getattr(value, "user_can_%s" % arg)(user)
    else:
        return False

@register.filter
def user_has(value, arg):
    "Has the current user done the `arg` action on the `value` object?"
    user = globals.user
    if user.is_authenticated() and hasattr(value, "user_has_%s" % arg):
        return getattr(value, "user_has_%s" % arg)(user)
    else:
        return False

@register.filter
def user_property(value, arg):
    "A property user_{arg} on the object {value}."
    user = globals.user
    if user.is_authenticated() and hasattr(value, "user_%s" % arg):
        return getattr(value, "user_%s" % arg)(user)
    else:
        return None