base.py

import os
import pathlib
import sys

import dj_database_url


class SettingsBase(type):
    """Class-based settings meta class"""

    def __new__(mcs, classname, bases, classdict):
        for key in list(classdict):
            fail_conditions = (
                type(key) != str or
                not key[0].isalnum() or
                '__call__' in dir(classdict[key]) or
                isinstance(classdict[key], classmethod)
            )

            if fail_conditions:
                continue

            classdict[key.upper()] = classdict[key]

        return type.__new__(mcs, classname, bases, classdict)


class Settings(metaclass=SettingsBase):

    # Django base settings
    site_id = 1
    root_urlconf = 'config.urls'
    base_dir = pathlib.Path(__file__).parents[2].resolve()
    atomic_requests = True
    debug = None
    wsgi_application = 'config.wsgi.application'

    @property
    def secret_key(self):
        return self.get_env_var('SECRET_KEY', 'totally-insecure')

    # Apps / middleware / templates
    @property
    def installed_apps(self):
        return [
            'django.contrib.admin',
            'django.contrib.auth',
            'django.contrib.contenttypes',
            'django.contrib.sessions',
            'django.contrib.messages',
            'django.contrib.staticfiles',

            'users.apps.UsersConfig',
        ]

    @property
    def middleware(self):
        return [
            'django.middleware.security.SecurityMiddleware',
            'django.contrib.sessions.middleware.SessionMiddleware',
            'django.middleware.common.CommonMiddleware',
            'django.middleware.csrf.CsrfViewMiddleware',
            'django.contrib.auth.middleware.AuthenticationMiddleware',
            'django.contrib.messages.middleware.MessageMiddleware',
            'django.middleware.clickjacking.XFrameOptionsMiddleware',
        ]

    @property
    def templates(self):
        return [
            {
                'BACKEND': 'django.template.backends.django.DjangoTemplates',
                'DIRS': [str(self.base_dir / 'templates')],
                'APP_DIRS': True,
                'OPTIONS': {
                    'context_processors': [
                        'django.template.context_processors.debug',
                        'django.template.context_processors.request',
                        'django.contrib.auth.context_processors.auth',
                        'django.contrib.messages.context_processors.messages',
                    ],
                },
            },
        ]

    # Databases / caches
    @property
    def databases(self):
        return {
            'default': dj_database_url.config(
                default='postgres://user:pass@localhost:5432/db',
                conn_max_age=600
            )
        }

    # Project config
    auth_user_model = 'users.User'
    auth_password_validators = [
        {
            'NAME': ('django.contrib.auth.password_validation.'
                     'UserAttributeSimilarityValidator'),
        },
        {
            'NAME': ('django.contrib.auth.password_validation.'
                     'MinimumLengthValidator'),
        },
        {
            'NAME': ('django.contrib.auth.password_validation.'
                     'CommonPasswordValidator'),
        },
        {
            'NAME': ('django.contrib.auth.password_validation.'
                     'NumericPasswordValidator'),
        },
    ]

    language_code = 'en-us'
    time_zone = 'UTC'
    use_i18n = True
    use_l10n = True
    use_tz = True

    # static files
    static_url = '/static/'

    # helper classes
    @classmethod
    def get_env_var(cls, key, default=None):
        try:
            return os.environ[key]
        except KeyError:
            if default is not None:
                return default
            else:
                raise ValueError(
                    'Undefined value for `{}` environment variable at {}'
                    ' settings class.'.format(key, cls)
                )

    @classmethod
    def load_settings(cls, module_name):
        self = cls()
        module = sys.modules[module_name]

        for key in dir(self):
            if key.upper() and not key.startswith('_'):
                setattr(module, key, getattr(self, key))