from django.conf import settings
from django.db.models.query import QuerySet
from django.utils.cache import cache
from django.utils.hashcompat import md5_constructor

def stringify_object(obj):
    if isinstance(obj, QuerySet):
        return obj.query.as_sql()
    return unicode(obj)

def key_from_args(*args, **kwargs):
    strings = []
    for arg in args:
        strings.append(stringify_object(arg))
    for k,v in kwargs.items():
        strings.append('%s=%s' % (k, stringify_object(v)))
    return md5_constructor(''.join(strings).hexdigest())

def cached_filter(func, timeout=300):
    def inner(*args, **kwargs):
        if settings.DEBUG:
            return func(*args, **kwargs)
        cache_key = key_from_args(*args, **kwargs)
        result = cache.get(cache_key)
        if not result:
            result = func(*args, **kwargs)
            cache.set(cache_key, result, timeout)
        return result
    inner._decorated_function = func
    return inner