# Source code for staticconf.proxy

    """
    Proxy a configuration value. Defers the lookup until the value is used, so that
    values can be read statically at import time.
    """
    import functools
    import operator
    from typing import Any
    from typing import Callable
    from typing import cast
    from typing import Type
    from typing import TypeVar
    from typing import TYPE_CHECKING

    from staticconf import errors
    from staticconf.validation import Validator

    if TYPE_CHECKING:
        from staticconf.config import ConfigNamespace

    class UndefTokenType:
        """A token to represent an undefined value, so that None can be used
        as a default value.
        """
        def __repr__(self) -> str:
            return "<Undefined>"

    UndefToken = UndefTokenType()

    _special_names = [
        '__abs__', '__add__', '__and__', '__bool__', '__call__', '__cmp__',
        '__coerce__',
        '__contains__', '__delitem__', '__delslice__', '__div__', '__divmod__',
        '__eq__', '__float__', '__floordiv__', '__ge__', '__getitem__',
        '__getslice__', '__gt__', '__hash__', '__hex__', '__iadd__', '__iand__',
        '__idiv__', '__idivmod__', '__ifloordiv__', '__ilshift__', '__imod__',
        '__imul__', '__int__', '__invert__', '__ior__', '__ipow__', '__irshift__',
        '__isub__', '__iter__', '__itruediv__', '__ixor__', '__le__', '__len__',
        '__long__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__',
        '__neg__', '__oct__', '__or__', '__pos__', '__pow__', '__radd__',
        '__rand__', '__rdiv__', '__rdivmod__',
        '__repr__', '__reversed__', '__rfloorfiv__', '__rlshift__', '__rmod__',
        '__rmul__', '__ror__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__',
        '__rtruediv__', '__rxor__', '__setitem__', '__setslice__', '__sub__',
        '__truediv__', '__xor__', 'next', '__nonzero__', '__str__', '__unicode__',
        '__index__', '__fspath__',
    ]

    def identity(x: Any) -> Any:
        return x

    unary_funcs = {
        '__unicode__':  cast(Callable[[Any], Any], str),
        '__str__':      cast(Callable[[Any], Any], str),
        '__fspath__':   identity,  # python3.6+ os.PathLike interface
        '__repr__':     cast(Callable[[Any], Any], repr),
        '__nonzero__':  cast(Callable[[Any], Any], bool),  # Python2 bool
        '__bool__':     cast(Callable[[Any], Any], bool),  # Python3 bool
        '__hash__':     cast(Callable[[Any], Any], hash),
    }

    def build_class_def(cls: Type["ValueProxy"]) -> type:
        def build_method(name: str) -> Callable[["ValueProxy", Any, Any], Any]:
            def method(self: "ValueProxy", *args: Any, **kwargs: Any) -> Any:
                if name in unary_funcs:
                    return unary_funcs[name](self.value)

                if hasattr(operator, name):
                    return getattr(operator, name)(self.value, *args)

                return getattr(self.value, name)(*args, **kwargs)
            return method

        namespace = {name: build_method(name) for name in _special_names}
        return type(cls.__name__, (cls,), namespace)

    F = TypeVar("F", bound=Callable[..., Any])

    def cache_as_field(cache_name: str) -> Callable[[F], F]:
        """Cache a functions return value as the field 'cache_name'."""
        def cache_wrapper(func: F) -> F:
            @functools.wraps(func)
            def inner_wrapper(self: object, *args: Any, **kwargs: Any) -> Any:
                value = getattr(self, cache_name, UndefToken)
                if value != UndefToken:
                    return value

                ret = func(self, *args, **kwargs)
                setattr(self, cache_name, ret)
                return ret
            return cast(F, inner_wrapper)
        return cache_wrapper

    def extract_value(proxy: "ValueProxy") -> Any:
        """Given a value proxy type, Retrieve a value from a namespace, raising
        exception if no value is found, or the value does not validate.
        """
        value = proxy.namespace.get(proxy.config_key, proxy.default)
        if value is UndefToken:
            raise errors.ConfigurationError("%s is missing value for: %s" %
                (proxy.namespace, proxy.config_key))

        try:
            return proxy.validator(value)
        except errors.ValidationError as e:
            raise errors.ConfigurationError("%s failed to validate %s: %s" %
                (proxy.namespace, proxy.config_key, e))

    class ValueProxy:
        """Proxy a configuration value so it can be loaded after import time."""
        __slots__ = [
            'validator',
            'config_key',
            'default',
            '_value',
            'namespace',
            '__weakref__'
        ]

        @classmethod
        @cache_as_field('_class_def')
        def get_class_def(cls) -> type:
            return build_class_def(cls)

        def __new__(cls, *args: Any, **kwargs: Any) -> "ValueProxy":
            """Create instances of this class with proxied special names."""
            klass = cast(Type["ValueProxy"], cls.get_class_def())
            instance = cast("ValueProxy", object.__new__(klass))
            klass.__init__(instance, *args, **kwargs)
            return instance

        def __init__(
            self,
            validator: Validator,
            namespace: "ConfigNamespace",
            key: str,
            default: Any = UndefToken,
        ) -> None:
            self.validator      = validator
            self.config_key     = key
            self.default        = default
            self.namespace      = namespace
            self._value         = UndefToken

        @cache_as_field('_value')
        def get_value(self) -> Any:
            return extract_value(self)

        value = property(get_value)

        def __getattr__(self, item: str) -> Any:
            return getattr(self.value, item)

        def reset(self) -> None:
            """Clear the cached value so that configuration can be reloaded."""
            self._value = UndefToken