import warnings

from django.utils import six
from django.conf import global_settings
from django.core.exceptions import ImproperlyConfigured

from .utils import uppercase_attributes
from .values import Value, setup_value

__all__ = ['Configuration']


install_failure = ("django-configurations settings importer wasn't "
                   "correctly installed. Please use one of the starter "
                   "functions to install it as mentioned in the docs: "
                   "http://django-configurations.readthedocs.org/")


class ConfigurationBase(type):

    def __new__(cls, name, bases, attrs):
        # also check for "Configuration" here to handle the Settings class
        # below remove it when we deprecate the Settings class
        if (bases not in ((object,), ()) and
                bases[0].__name__ not in ('NewBase', 'Configuration')):
            # if this is actually a subclass in a settings module
            # we better check if the importer was correctly installed
            from . import importer
            if not importer.installed:
                raise ImproperlyConfigured(install_failure)
        settings_vars = uppercase_attributes(global_settings)
        parents = [base for base in bases if isinstance(base,
                                                        ConfigurationBase)]
        if parents:
            for base in bases[::-1]:
                settings_vars.update(uppercase_attributes(base))
        attrs = dict(settings_vars, **attrs)
        return super(ConfigurationBase, cls).__new__(cls, name, bases, attrs)

    def __repr__(self):
        return "<Configuration '{0}.{1}'>".format(self.__module__,
                                                  self.__name__)


class Configuration(six.with_metaclass(ConfigurationBase)):
    """
    The base configuration class to inherit from.

    ::

        class Develop(Configuration):
            EXTRA_AWESOME = True

            @property
            def SOMETHING(self):
                return completely.different()

            def OTHER(self):
                if whatever:
                    return (1, 2, 3)
                return (4, 5, 6)

    The module this configuration class is located in will
    automatically get the class and instance level attributes
    with upper characters if the ``DJANGO_CONFIGURATION`` is set
    to the name of the class.

    """
    @classmethod
    def pre_setup(cls):
        pass

    @classmethod
    def post_setup(cls):
        pass

    @classmethod
    def setup(cls):
        for name, value in uppercase_attributes(cls).items():
            if isinstance(value, Value):
                setup_value(cls, name, value)


class Settings(Configuration):

    @classmethod
    def pre_setup(cls):
        # make sure to remove the handling of the Settings class above when deprecating
        warnings.warn("configurations.Settings was renamed to "
                      "settings.Configuration and will be "
                      "removed in 1.0", PendingDeprecationWarning)