"""
Settings for Graphene are all namespaced in the GRAPHENE setting.
For example your project's `settings.py` file might look like this:
GRAPHENE = {
    'SCHEMA': 'my_app.schema.schema'
    'MIDDLEWARE': (
        'graphene_django.debug.DjangoDebugMiddleware',
    )
}
This module provides the `graphene_settings` object, that is used to access
Graphene settings, checking for user settings first, then falling
back to the defaults.
"""
from __future__ import unicode_literals

from django.conf import settings
from django.test.signals import setting_changed
from django.utils import six

try:
    import importlib  # Available in Python 3.1+
except ImportError:
    from django.utils import importlib  # Will be removed in Django 1.9


# Copied shamelessly from Django REST Framework

DEFAULTS = {
    'SCHEMA': None,
    'SCHEMA_OUTPUT': 'schema.json',
    'MIDDLEWARE': (),
}

if settings.DEBUG:
    DEFAULTS['MIDDLEWARE'] += (
        'graphene_django.debug.DjangoDebugMiddleware',
    )

# List of settings that may be in string import notation.
IMPORT_STRINGS = (
    'MIDDLEWARE',
    'SCHEMA',
)


def perform_import(val, setting_name):
    """
    If the given setting is a string import notation,
    then perform the necessary import or imports.
    """
    if val is None:
        return None
    elif isinstance(val, six.string_types):
        return import_from_string(val, setting_name)
    elif isinstance(val, (list, tuple)):
        return [import_from_string(item, setting_name) for item in val]
    return val


def import_from_string(val, setting_name):
    """
    Attempt to import a class from a string representation.
    """
    try:
        # Nod to tastypie's use of importlib.
        parts = val.split('.')
        module_path, class_name = '.'.join(parts[:-1]), parts[-1]
        module = importlib.import_module(module_path)
        return getattr(module, class_name)
    except (ImportError, AttributeError) as e:
        msg = "Could not import '%s' for Graphene setting '%s'. %s: %s." % (val, setting_name, e.__class__.__name__, e)
        raise ImportError(msg)


class GrapheneSettings(object):
    """
    A settings object, that allows API settings to be accessed as properties.
    For example:
        from graphene_django.settings import settings
        print(settings.SCHEMA)
    Any setting with string import paths will be automatically resolved
    and return the class, rather than the string literal.
    """

    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

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

    def __getattr__(self, attr):
        if attr not in self.defaults:
            raise AttributeError("Invalid Graphene 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
        setattr(self, attr, val)
        return val


graphene_settings = GrapheneSettings(None, DEFAULTS, IMPORT_STRINGS)


def reload_graphene_settings(*args, **kwargs):
    global graphene_settings
    setting, value = kwargs['setting'], kwargs['value']
    if setting == 'GRAPHENE':
        graphene_settings = GrapheneSettings(value, DEFAULTS, IMPORT_STRINGS)


setting_changed.connect(reload_graphene_settings)