from django.template import Library, Node
from django.db.models import get_model
from django.db.models import Q
from datetime import datetime

register = Library()

class ArchiveDatesNode(Node):
    def __init__(self, model, fieldnames, kind, varname):
        self.kind, self.varname = kind, varname
        self.fieldnames = fieldnames.split('|')
        self.model = get_model(*model.split('.'))

    def render(self, context):
        now = datetime.now()
        fieldnames = self.fieldnames[:]
        # do an OR lookup with the given fieldnames
        query = Q(**{'%s__lte' % fieldnames.pop(0): now})
        for fieldname in fieldnames:
            query = query | Q(**{'%s__lte' % fieldname: now})
        try:
            context[self.varname] = self.model._default_manager.filter(query).dates(self.fieldnames[0], self.kind, order='DESC').distinct()
        except self.model.DoesNotExist:
            pass
        return''

def get_archive_dates(parser, token):
    """
    {% get_archive_dates app.Model fieldname as variablename %}
    {% get_archive_dates news.Entry pub_date as archive_dates %}
    {% get_archive_dates news.Entry pub_date year as archive_dates %}
    {% get_archive_dates events.Event start_date|end_date year as archive_dates %}
    """
    bits = token.contents.split()
    if len(bits) < 5:
        raise template.TemplateSyntaxError, "'%s' tag takes at least three arguments" % bits[0]
    elif len(bits) > 6:
        raise template.TemplateSyntaxError, "'%s' tag takes at most four arguments" % bits[0]
    if bits[3] == 'as':
        kind = 'month'
        varname = bits[4]
    elif bits[4] == 'as':
        kind = bits[3]
        varname = bits[5]
    else:
        raise TemplateSyntaxError, "Second last argument to '%s' tag must be 'as'" % bits[0]
    return ArchiveDatesNode(bits[1], bits[2], kind, varname)
get_archive_dates = register.tag(get_archive_dates)


def strftime(value, arg=None):
    "Formats a date according to the given format using datetime.strftime"
    from django.utils.dateformat import format
    if not value:
        return ''
    if arg is None:
        arg = settings.DATE_FORMAT
    return value.strftime(arg)
strftime = register.filter(strftime)