Naked CSS Day

from django import template
from datetime import datetime, timedelta

register = template.Library()

class NakedDayNode(template.Node):

    def __init__(self, params, varname):
        self.params = params
        self.varname = varname

    def render(self, context):
        naked_date = datetime(year=self.params['year'],
            month=self.params['month'], day=self.params['day'])
        start = naked_date - timedelta(hours=12)
        end = naked_date + timedelta(hours=36)
        now = datetime.utcnow()
        is_naked = now > start and now < end

        if self.varname:
            context[self.varname] = is_naked

        return is_naked


def do_naked_day(parser, token):
    """
    Returns True or False if today is Naked CSS Day (2009-04-09ish) and spans
    ~48 hours. Optionally accepts ``year``, ``month``, and ``day`` values in
    case Naked CSS Day changes in the future. Optionally takes a template
    context with a variable containing that value, whose name is defined by
    the ``as`` clause.

    Usage::

        {% is_naked_day [year:integer] [month:integer] [day:integer] as [varname] %}

    Example::

        {% if is_naked_day %}
        <!-- naked day has no styles -->
        {% else %}
        <link rel="stylesheet" type="text/css" href="/media/example.css" />
        {% endif %}

    Example with parameters::

        {% is_naked_day month:4 day:9 as is_naked %}
        {% if is_naked %}
        <!-- naked day has no styles -->
        {% else %}
        <link rel="stylesheet" type="text/css" href="/media/example.css" />
        {% endif %}

    Additional information:

    For more information on Naked CSS Day and to add your site to the list:
    http://naked.dustindiaz.com/

    """
    params = {
        'year': datetime.utcnow().year,
        'month': 4,
        'day': 9,
    }
    varname = None
    items = token.split_contents()

    for index, item in enumerate(items):
        if item == 'as':
            varname = items[index + 1]
        elif ':' in item:
            param, value = item.split(':')
            param, value = param.strip(), value.strip()
            if param in params:
                if value[0] == '"':
                    value = value[1:-1]
                try:
                    params[param] = int(value)
                except ValueError:
                    raise template.TemplateSyntaxError(
                        'Parameter "%s" can only be an integer field.' % (param))

    return NakedDayNode(params, varname)

register.tag('is_naked_day', do_naked_day)