from importlib import import_module
from django.conf import settings


class PermissionProviders(object):
    def __init__(self):
        self._initialized = False
        self._providers = []
        self._providers_dict = {}

    def initialize_providers(self):
        if not self._initialized:
            self.import_providers()
            self._initialized = True

    def import_providers(self):
        for namespace in settings.MISAGO_PERMISSION_PROVIDERS:
            self._providers.append((namespace, import_module(namespace)))
            self._providers_dict[namespace] = import_module(namespace)

    def get_change_permissions_forms(self, role):
        self.initialize_providers()

        forms = []
        for provider, module in self._providers:
            try:
                module.change_permissions_form
            except AttributeError:
                message = "'%s' object has no attribute '%s'"
                raise AttributeError(
                    message % (provider, 'change_permissions_form'))
            forms.append(module.change_permissions_form(role))

        return [f for f in forms if f]

    def build_acl_cache(self, roles):
        self.initialize_providers()

    def hydrate_acl_cache(self, acl):
        self.initialize_providers()

    def get_acl_by_token(self, token):
        pass

    def get_acl_by_roles(self, roles):
        pass


providers = PermissionProviders()