Ajax decorator for Django views

from django.http import HttpResponse, HttpResponseBadRequest, HttpResponseRedirect
from django.utils import simplejson as json
from django.conf import settings


class AjaxError(Exception):

    def __init__(self, message, status=200):
        super(AjaxError, self).__init__(message)
        self.status = status


def ajax_view(function_view):
    """
    Always return a valid ajax response with status code = 200.
    The decorated function just have to return a dictionary that will be
    converted to JSON and that JSON will be included in the HttpResponse.
    When the decorated function fails, the returned JSON will include just an
    'error' attr with the description of the error. This descriptin
    will be the exception message if the raised exception is an AjaxError
    instance or "Internal error" otherwise.
    """

    def _wrapped_view(request, *args, **kwargs):

        if not request.is_ajax():
            return HttpResponseBadRequest()

        status = 200
        try:
            response = function_view(request, *args, **kwargs)
            if type(response) == HttpResponseRedirect:
                raise AjaxError("Permission denied")
            error = None
        except AjaxError, e:
            response = {}
            error = unicode(e)
            status = e.status
        except Exception, e:
            response = {}
            error = "Internal Error"
            if settings.DEBUG:
                raise
        response.update({'error': error})

        return HttpResponse(
            json.dumps(response if status == 200 else response['error']),
            content_type='application/json; charset=utf8',
            status=status,
        )

    return _wrapped_view


def get_parameter_or_ajax_error(parameters, key):
    """
    Intended to avoid code repetition when checking if the ajax request includes
    the required parameters.
    The first argument should be request.POST or request.GET
    """
    if not key:
        raise AjaxError('"%s" is not a valid parameter name' % key)
    value = parameters.get(key, None)
    if value is None:
        raise AjaxError('Invalid input data (%s is null)' % key)

    return value


def get_boolean_parameter_or_ajax_error(parameters, key):
    """
    Same as get_parameter_or_ajax_error but for boolean values. The idea is to
    avoid some known gotchas related to boolean parameters.
    """
    if not key:
        raise AjaxError('"%s" is not a valid parameter name' % key)
    value = parameters.get(key, None)
    if value is None:
        raise AjaxError('Invalid input data (%s is null)' % key)

    if value == 'False' or value == 'false' or value == '0' or value == 0:
        value = False
    elif value:
        value = True
    else:
        value = False

    return value


def get_list_parameter_or_ajax_error(parameters, key):
    """
    Same as get_parameter_or_ajax_error but for lists. The idea is to
    avoid some known gotchas related to list parameters.
    """
    if not key:
        raise AjaxError('"%s" is not a valid parameter name' % key)
    value = parameters.getlist(key, None)
    if value is None:
        raise AjaxError('Invalid input data (%s is null)' % key)

    return value


# Usage:
# @ajax_view
# @user_passes_test(lambda u: u.is_staff)
# def cms_search_companies_ajax(request):
#
#     country_pk = get_parameter_or_ajax_error(request.GET, 'country_pk')
#     city_pk = get_parameter_or_ajax_error(request.GET, 'city_pk')
#     query = get_parameter_or_ajax_error(request.GET, 'query')
#
#     params = {}
#     if city_pk:
#         params['city__pk'] = city_pk
#     elif country_pk:
#         params['city__country__pk'] = country_pk
#     if query:
#         params['name__icontains'] = query

    return {
        'targets': [{
            'value': company.pk,
            'text': company.name
        } for company in Company.objects.filter(**params)]
    }