from django.conf import settings
from django.core.signals import setting_changed
from rest_framework.settings import perform_import

DEFAULTS = {
    "DEFAULT_PAGE_SIZE": 25,
    "DEFAULT_PERMISSION_CLASSES": ("djangochannelsrestframework.permissions.AllowAny",),
    "DEFAULT_PAGINATION_CLASS": None,
    "PAGE_SIZE": None,
}
IMPORT_STRINGS = ("DEFAULT_PERMISSION_CLASSES", "DEFAULT_PAGINATION_CLASS")


class APISettings:
    def __init__(self, user_settings=None, defaults=None, import_strings=None):
        if user_settings:
            self._user_settings = user_settings
        self.defaults = defaults or DEFAULTS
        self.import_strings = import_strings or IMPORT_STRINGS
        self._cached_attrs = set()

    @property
    def user_settings(self):
        if not hasattr(self, "_user_settings"):
            self._user_settings = getattr(settings, "DJANGO_CHANNELS_REST_API", {})
        return self._user_settings

    def __getattr__(self, attr):
        if attr not in self.defaults:
            raise AttributeError("Invalid API setting: '%s'" % attr)

        try:
            # Check if present in user settings
            val = self.user_settings[attr]
        except KeyError:
            # Fall back to defaults
            val = self.defaults[attr]

        # Coerce import strings into classes
        if attr in self.import_strings:
            val = perform_import(val, attr)

        # Cache the result
        self._cached_attrs.add(attr)
        setattr(self, attr, val)
        return val

    def reload(self):
        for attr in self._cached_attrs:
            delattr(self, attr)
        self._cached_attrs.clear()
        if hasattr(self, "_user_settings"):
            delattr(self, "_user_settings")


api_settings = APISettings(None, DEFAULTS, IMPORT_STRINGS)


def reload_api_settings(*args, **kwargs):
    setting = kwargs["setting"]
    if setting == "DJANGO_CHANNELS_REST_API":
        api_settings.reload()


setting_changed.connect(reload_api_settings)