from threading import local
from typing import Callable

_THREAD_LOCAL = local()
setattr(_THREAD_LOCAL, 'configuration', {})


class FakeMigrationModules:
    """Allows skipping migration applying process."""

    def __init__(self, module_name: str):
        self.module_name = module_name

    def __getitem__(self, item: str) -> str:
        return self.module_name

    def __contains__(self, item: str):
        return True


class Configuration:

    _prefix = 'DJANGOAPP_OPTIONS'
    _KEY_ADMIN = 'admin'
    KEY_APP = 'app_name'
    _KEY_EXTEND = 'extend'
    _KEY_HOOK = 'hook'
    _KEY_MIGRATE = 'migrate'

    DIR_TESTAPP = 'testapp'
    """Name of test application directory.
    
    Test application directory should be placed inside `tests` directory 
    and needs to be a Python package (contain __init__.py).
     
    Test application is useful to place there modules like `urls.py`,
    `models.py` (e.g. with custom models), etc.
    
    """

    @classmethod
    def get(cls) -> dict:
        return _THREAD_LOCAL.configuration

    @classmethod
    def set(
        cls,
        settings_dict: dict = None,
        *,
        app_name: str = None,
        admin_contrib: bool = False,
        settings_hook: Callable = None,
        migrate: bool = True,
        **kwargs
    ):
        """
        :param settings_dict:

        :param app_name:

        :param admin_contrib: Setup Django to test Admin contrib related parts.

        :param settings_hook: Allows setting a function to get resulting settings.

            Function must accept settings dictionary, and return resulting settings dictionary.

            .. code-block:: python

                def hook_func(settings):
                    return settings

        :param migrate: Allows applying or skipping migration applying process.
            Skipping could be useful for testing applications with many migrations.

        :param kwargs: Additional arguments.

            Use `extend_` prefix to extend default configuration.
            E.g.: extend_INSTALLED_APPS=['a']

        """
        settings_dict = settings_dict or {}

        extend = {}

        for key, val in kwargs.items():
            _, _, extend_key = key.partition('extend_')

            if extend_key and extend_key == extend_key.upper():
                extend[extend_key] = val

        base_settings = {
            cls._prefix: {
                cls.KEY_APP: app_name,
                cls._KEY_EXTEND: extend,
                cls._KEY_ADMIN: admin_contrib,
                cls._KEY_HOOK: settings_hook,
                cls._KEY_MIGRATE: migrate,
            }
        }

        base_settings.update(settings_dict)

        _THREAD_LOCAL.configuration = base_settings

    @classmethod
    def get_defaults(cls) -> dict:
        from django.conf import global_settings

        if hasattr(global_settings, 'MIDDLEWARE_CLASSES'):
            middleware = global_settings.MIDDLEWARE_CLASSES

        else:
            middleware = global_settings.MIDDLEWARE

        installed_apps = list(global_settings.INSTALLED_APPS[:])
        installed_apps.extend([
            'django.contrib.auth',
            'django.contrib.contenttypes',
        ])
        installed_apps = list(set(installed_apps))

        settings_dict = dict(

            SECRET_KEY='djangoapp',

            ALLOWED_HOSTS=(
                global_settings.ALLOWED_HOSTS +
                # Satisfy Django test client needed in Django < 2.0
                ['testserver']
            ),

            INSTALLED_APPS=installed_apps,
            STATIC_URL='/static/',

            DATABASES={
                'default': {
                    'ENGINE': 'django.db.backends.sqlite3',
                    'NAME': ':memory:',
                },
            },

            MIDDLEWARE=middleware,

            EMAIL_BACKEND='django.core.mail.backends.locmem.EmailBackend',

            TEMPLATES=[
                {
                    'BACKEND': 'django.template.backends.django.DjangoTemplates',
                    'APP_DIRS': True,
                    'OPTIONS': {'context_processors': ['django.contrib.messages.context_processors.messages']}
                },
            ],

        )

        return settings_dict.copy()

    @classmethod
    def get_combined(cls, pytest_config) -> dict:
        from django import VERSION

        settings = cls.get()

        defaults = cls.get_defaults()
        defaults.update(settings)

        djapp_options = defaults[cls._prefix]

        app_name = djapp_options[cls.KEY_APP]
        extensions = djapp_options[cls._KEY_EXTEND]
        admin = djapp_options[cls._KEY_ADMIN]
        hook = djapp_options.pop(cls._KEY_HOOK, None) or (lambda settings_dict: settings_dict)

        # djangoapp is considered testing a whole project (a set of apps)
        # if hook function is a `partial` for function with a certain name.
        project_mode = getattr(getattr(hook, 'func', None), '__name__', '') == 'update_settings_from_module'

        if not djapp_options[cls._KEY_MIGRATE]:
            module_name = None

            if VERSION <= (1, 10):
                module_name = 'dummy_migrations'
                defaults['MIGRATIONS_MODULE_NAME'] = module_name

            defaults['MIGRATION_MODULES'] = FakeMigrationModules(module_name)

        if admin:
            middleware = extensions.setdefault('MIDDLEWARE', [])
            middleware.extend([
                'django.contrib.sessions.middleware.SessionMiddleware',
                'django.contrib.auth.middleware.AuthenticationMiddleware',
            ])
            apps = extensions.setdefault('INSTALLED_APPS', [])
            apps.extend([
                'django.contrib.admin',
                'django.contrib.sessions',
            ])

        for key, value in extensions.items():
            default_value = defaults.get(key, [])

            if isinstance(default_value, (list, tuple)):
                extended = list(default_value)

                for item in value:
                    if item not in extended:
                        extended.append(item)

                defaults[key] = extended

                if key == 'MIDDLEWARE':
                    # Special case for renamed.
                    defaults['MIDDLEWARE_CLASSES'] = extended

            elif isinstance(default_value, dict):
                defaults[key].update(value)

            else:  # pragma: nocover
                raise ValueError(f'Unable to extend `{key}` option.')

        installed_apps = defaults['INSTALLED_APPS']

        if app_name:

            if app_name not in installed_apps:
                installed_apps.append(app_name)

        else:
            dir_current = pytest_config.invocation_dir
            dir_tests = None

            app_name = dir_current.basename

            if app_name == 'tests':
                # Support certain module or function invocation tests dir as base (e.g. PyCharm behaviour).
                app_name = dir_current.parts()[-2].basename
                dir_tests = dir_current

            try:
                dir_tests = dir_current.listdir('tests')[0]

            except IndexError:
                pass

            if not dir_tests:
                # No `tests` subdir found. Let's try to deduce.

                app_name = None

                from setuptools import find_packages
                import py

                candidate_latest = ''
                candidates = []

                for package in find_packages(f'{dir_current}'):
                    # Consider only top level packages.
                    if not candidate_latest or not package.startswith(candidate_latest):
                        candidates.append(package)
                        candidate_latest = package

                for candidate in candidates:
                    dirs = py.path.local(candidate).listdir('tests')

                    if dirs:
                        app_name = candidate
                        dir_tests = dirs[0]
                        break

            if not app_name and not project_mode:
                raise Exception(
                    'Unable to deduce application name. '
                    'Check application package and `tests` directory exists. '
                    f'Current dir: {dir_current}')

            if app_name:
                installed_apps.append(app_name)

            if dir_tests:
                # Try to find and add an additional test app.
                dir_testapp_name = cls.DIR_TESTAPP
                dir_testapp = dir_tests.listdir(dir_testapp_name)

                if dir_testapp:
                    dir_testapp = dir_testapp[0]

                    testapp_name = f'{app_name}.tests.{dir_testapp_name}'

                    installed_apps.append(testapp_name)

                    if dir_testapp.listdir('urls.py'):
                        # Set customized `urls.py`.
                        defaults['ROOT_URLCONF'] = f'{testapp_name}.urls'

        djapp_options[cls.KEY_APP] = app_name

        defaults = hook(defaults)

        return defaults

    @classmethod
    def get_dict(cls) -> dict:
        """Returns current configuration as a dict."""
        return cls.get()[cls._prefix]