from django.conf import settings
from django.conf.urls.defaults import patterns, include
from django.core.management import call_command
from django.db.models import loading
from django.test import TestCase
from django.utils import importlib

NO_SETTING = ('!', None)

class TestSettingsManager(object):
    """
    A class which can modify some Django settings temporarily for a
    test and then revert them to their original values later.

    Automatically handles resyncing the DB if INSTALLED_APPS is
    modified.
    """
    def __init__(self):
        self._original_settings = {}

    def set(self, **kwargs):
        for k,v in kwargs.iteritems():
            self._original_settings.setdefault(k, getattr(settings, k,
                                                          NO_SETTING))
            setattr(settings, k, v)
        if 'INSTALLED_APPS' in kwargs:
            self.syncdb()

    def syncdb(self):
        loading.cache.loaded = False
        call_command('syncdb', verbosity=0)

    def revert(self):
        for k,v in self._original_settings.iteritems():
            if v == NO_SETTING:
                delattr(settings, k)
            else:
                setattr(settings, k, v)
        if 'INSTALLED_APPS' in self._original_settings:
            self.syncdb()
        self._original_settings = {}


class BaseTestCase(TestCase):
    """
    A subclass of the Django TestCase with a settings_manager
    attribute which is an instance of TestSettingsManager.

    Comes with a tearDown() method that calls
    self.settings_manager.revert().

    """
    def __init__(self, *args, **kwargs):
        super(BaseTestCase, self).__init__(*args, **kwargs)
        self.settings_manager = TestSettingsManager()

    def addTestApps(self, apps):
        installed_apps = settings.INSTALLED_APPS
        installed_apps = list(installed_apps) + list(apps)
        urlpatterns = importlib.import_module(settings.ROOT_URLCONF).urlpatterns

        for app in apps:
            try:
                app_url = importlib.import_module("%s.urls" % app)
                app_name = app.split(".")[-1]
                urlpatterns += patterns('',(r'%s/' % app_name,include(app_url)))
            except ImportError:
                pass

        self.settings_manager.set(**{
                'INSTALLED_APPS': installed_apps,
                'DEBUG' : True,
                })

    def tearDown(self):
        self.settings_manager.revert()
