"""
Export Django settings to templates

https://github.com/jakubroztocil/django-settings-export

"""
from django.conf import settings as django_settings
from django.core.exceptions import ImproperlyConfigured


__version__ = '1.2.1'


VARIABLE_NAME = getattr(django_settings,
                        'SETTINGS_EXPORT_VARIABLE_NAME',
                        'settings')


class SettingsExportError(ImproperlyConfigured):
    """Base error indicating misconfiguration."""


class UndefinedSettingError(SettingsExportError):
    """An undefined setting name included in SETTINGS_EXPORT."""


class UnexportedSettingError(SettingsExportError):
    """An unexported setting has been accessed from a template."""


def settings_export(request):
    """
    The template context processor that adds settings defined in
    `SETTINGS_EXPORT` to the context. If SETTINGS_EXPORT_VARIABLE_NAME is not
    set, the context variable will be `settings`.

    """
    variable_name = getattr(django_settings,
                            'SETTINGS_EXPORT_VARIABLE_NAME',
                            'settings')
    return {
        variable_name: _get_exported_settings()
    }


class ExportedSettings(dict):

    def __getitem__(self, item):
        """Fail loudly if accessing a setting that is not exported."""
        try:
            return super(ExportedSettings, self).__getitem__(item)
        except KeyError:
            if hasattr(self, item):
                # Let the KeyError propagate so that Django templates
                # can access the existing attribute (e.g. `items()`).
                raise
            raise UnexportedSettingError(
                'The `{key}` setting key is not accessible'
                ' from templates: add "{key}" to'
                ' `settings.SETTINGS_EXPORT` to change that.'
                .format(key=item)
            )


def _get_exported_settings():
    exported_settings = ExportedSettings()
    for key in getattr(django_settings, 'SETTINGS_EXPORT', []):
        try:
            value = getattr(django_settings, key)
        except AttributeError:
            raise UndefinedSettingError(
                '"settings.%s" is included in settings.SETTINGS_EXPORT '
                'but it does not exist. '
                % key
            )
        exported_settings[key] = value
    return exported_settings